ATP6V0C: V-type Proton ATPase 16 kDa Proteolipid Subunit c

Introduction

ATP6V0C (also known as ATP6C, ATP6L, ATPL) encodes the 16 kDa proteolipid subunit c of the vacuolar H+-ATPase (V-ATPase), one of the most fundamental proton-translocating enzymes in eukaryotic cells. The human ATP6V0C gene is located on chromosome 16p13.3 and produces a small, highly hydrophobic integral membrane protein that is essential for the proton-pumping function of V-ATPases [mucha-2018-microdeletion-abstract]. As a core component of the V0 membrane sector, ATP6V0C forms the proteolipid ring that constitutes the proton channel through which protons are translocated across membranes. V-ATPases are responsible for acidifying numerous intracellular compartments including lysosomes, endosomes, the Golgi apparatus, and synaptic vesicles, and are also present at the plasma membrane of specialized cell types [cotter-2015-insights-abstract].

The V-ATPase is among the most ancient and conserved enzyme complexes, with clear evolutionary relationships to the F-type ATP synthases of mitochondria and bacteria [forgac-1992-structure-function-abstract]. The c-subunit proteolipid belongs to the ATPase proteolipid subunit family characterized by the highly conserved Pfam domain PF00137. Understanding the precise molecular function of ATP6V0C is essential not only for comprehending fundamental cellular physiology but also for addressing its emerging roles in disease, particularly neurological disorders [colacurcio-2016-lysosomal-acidification-abstract].

Structure of the V-ATPase Complex and the c-Subunit

The V-ATPase holoenzyme is a large multisubunit complex of approximately 900 kDa, organized into two distinct functional domains: the peripheral V1 sector and the membrane-integral V0 sector [cipriano-2008-structure-regulation-abstract]. The V1 sector contains eight different subunits (A-H) and is responsible for ATP hydrolysis. The V0 sector contains six different subunits in yeast (a, c, c', c'', d, and e) or five in mammals (where c' and c'' are replaced by additional copies of c), and is responsible for proton translocation across the membrane [vasanthakumar-2020-structure-roles-abstract].

ATP6V0C is a small, extremely hydrophobic protein of 155 amino acids in humans that spans the membrane four times with both termini facing the cytoplasm. The protein contains two hairpin structures, each consisting of two transmembrane helices connected by short loops [roh-2018-cryoem-abstract]. This four-helix bundle topology is characteristic of V-ATPase c-subunits and represents a duplication compared to the two-helix c-subunits found in F-type ATPases, where approximately 10-15 copies form the c-ring. Consequently, V-ATPases require fewer c-subunit copies to form a complete proteolipid ring [powell-2000-proton-pore-abstract].

Cryo-electron microscopy studies of the yeast V-ATPase have revealed that the proteolipid ring contains ten c-subunits arranged in a ring structure [zhao-2015-cryoem-rotational-abstract]. This stoichiometry sets the ATP:H+ ratio for proton pumping at 3:10, meaning that for every three ATP molecules hydrolyzed, ten protons are translocated across the membrane. The 3.5 Å resolution structure of the yeast V0 sector has provided detailed atomic information about the proton pathway at the interface between the proteolipid ring and subunit a [roh-2018-cryoem-abstract]. Importantly, this structure revealed that a helix from the assembly factor Voa1 remains bound inside the proteolipid ring in the mature complex, contributing to its stability.

Molecular Function: Proton Translocation Mechanism

The primary molecular function of ATP6V0C is to provide the proton-binding sites and form the rotary conduit for proton translocation in V-ATPases. The mechanism operates through a rotary catalysis process analogous to F-type ATP synthases but functioning in the ATP-hydrolysis direction to pump protons rather than synthesize ATP [oot-2017-breaking-up-abstract].

Central to the proton translocation function is a highly conserved glutamate residue located in the fourth transmembrane helix of ATP6V0C. In human ATP6V0C, this is Glu137, which corresponds to the essential acidic residue found in all c-subunit homologs. This glutamate residue serves as the proton-binding site that transiently binds and releases protons during the rotary cycle [wang-2004-TM-interaction-abstract]. Protonation and deprotonation of this glutamate is coupled to the rotation of the c-ring relative to subunit a.

The proton translocation mechanism involves protons entering from the cytoplasmic side through a hemichannel in subunit a, binding to the glutamate residue on a c-subunit, rotating almost a full turn with the c-ring, and then being released into the luminal (or extracellular) hemichannel in subunit a [roh-2018-cryoem-abstract]. A critical arginine residue (Arg735 in yeast subunit a) is positioned at the interface between the two hemichannels and is essential for preventing proton leakage and maintaining unidirectional transport. Cross-linking studies have demonstrated direct interaction between the helical face of transmembrane helix 7 of subunit a containing this arginine and the helical face of the c-subunit containing the essential glutamate [wang-2004-TM-interaction-abstract].

The c-subunit is also the binding target for the potent V-ATPase inhibitors bafilomycin A1 and concanamycin A. Photoaffinity labeling studies demonstrated that these plecomacrolide antibiotics bind specifically and exclusively to the c-subunit proteolipid, inhibiting proton transport by preventing rotation of the c-ring [huss-2002-concanamycin-binding-abstract]. This pharmacological targeting has made bafilomycin A1 an invaluable tool for studying V-ATPase function in cells.

Subcellular Localization

ATP6V0C functions as part of V-ATPase complexes localized to multiple cellular membranes. The primary sites of V-ATPase activity and thus ATP6V0C localization include the membranes of lysosomes, endosomes, the trans-Golgi network, secretory granules, synaptic vesicles, and clathrin-coated vesicles [cipriano-2008-structure-regulation-abstract]. In certain specialized cell types, V-ATPases are also present at the plasma membrane.

In lysosomes, V-ATPases maintain the acidic pH (approximately 4.5-5.0) required for the activity of lysosomal hydrolases that degrade proteins, lipids, carbohydrates, and nucleic acids [colacurcio-2016-lysosomal-acidification-abstract]. In endosomes, progressive acidification along the endocytic pathway is essential for ligand-receptor dissociation and receptor recycling [forgac-1992-structure-function-abstract]. The trans-Golgi network requires moderate acidification for proper protein sorting and processing.

In synaptic vesicles, V-ATPases generate the electrochemical gradient that drives neurotransmitter uptake via vesicular neurotransmitter transporters [elfar-2011-synaptic-vesicle-abstract]. The acidification establishes both a pH gradient and a membrane potential across the synaptic vesicle membrane. In the zebrafish nervous system, expression studies of a neuron-specific ATP6V0C isoform (atp6v0c2) revealed co-localization with the presynaptic marker SV2, consistent with its role in neurotransmitter storage and release [chung-2010-zebrafish-abstract].

At the plasma membrane of specialized cells such as osteoclasts, renal intercalated cells, and certain tumor cells, V-ATPases pump protons out of the cell [cotter-2015-insights-abstract]. In osteoclasts, plasma membrane V-ATPases are essential for creating the acidic resorption lacuna that dissolves bone mineral. In renal intercalated cells, they contribute to urinary acidification and systemic pH homeostasis.

Role in Cellular Processes and Signaling Pathways

Beyond its fundamental role in acidification, ATP6V0C participates in several critical cellular pathways.

Lysosomal Function and Autophagy

V-ATPase activity is essential for lysosomal degradative function and thus for autophagy. Proper lysosomal acidification is required for the activity of cathepsins and other acid hydrolases [colacurcio-2016-lysosomal-acidification-abstract]. When V-ATPase function is impaired, autophagosomes accumulate because fusion with lysosomes is compromised and lysosomal degradation fails. Interestingly, studies using the V-ATPase inhibitor bafilomycin A1 have revealed that it blocks autophagy through two distinct mechanisms: V-ATPase-dependent inhibition of acidification and Ca-P60A/SERCA-dependent inhibition of autophagosome-lysosome fusion [mauvezin-2015-bafilomycin-abstract].

A groundbreaking discovery revealed that the V-ATPase, and specifically ATP6V0C, plays a direct role in initiating xenophagy (antibacterial autophagy). Upon vacuolar damage caused by intracellular bacteria, the V-ATPase recruits ATG16L1 to the damaged compartment, initiating autophagosomal engulfment [xu-2019-bacterial-effector-abstract]. The Salmonella effector protein SopF was found to ADP-ribosylate Gln124 of ATP6V0C, blocking this xenophagy-initiating function. This represents a non-canonical function of ATP6V0C that is independent of proton pumping.

mTORC1 Signaling

V-ATPases function as a key platform for mTORC1 signaling at the lysosomal membrane. The V-ATPase directly interacts with the Ragulator complex, and this interaction is required for amino acid-dependent activation of mTORC1 [abu-remaileh-2017-lysosomal-metabolomics-abstract]. Lysosomal metabolomics studies have shown that mTOR inhibition strongly reduces lysosomal amino acid efflux, converting the lysosome into a cellular depot for essential amino acids [abu-remaileh-2017-lysosomal-metabolomics-abstract]. The E2F1 transcription factor was shown to regulate V-ATPase activity and lysosomal positioning, thereby influencing mTORC1 activation [meo-evoli-2015-e2f1-abstract].

Neurotransmitter Release

Beyond its established role in synaptic vesicle acidification for neurotransmitter loading, accumulating evidence indicates that the V0 sector, including ATP6V0C, may have a direct role in the membrane fusion event underlying neurotransmitter release [elfar-2011-synaptic-vesicle-abstract]. The c-subunit has been shown to directly interact with the v-SNARE VAMP2 (synaptobrevin), and this interaction appears to function at a late step in transmitter release.

Chromophore-assisted light inactivation (CALI) experiments demonstrated that specific inactivation of ATP6V0C rapidly inhibited neurotransmission in hippocampal neurons, and this effect occurred downstream of synaptic vesicle acidification [rama-2018-neurotransmitter-abstract]. Studies using gene transfer of ATP6V0C into striatal cells of parkinsonian mice showed that ATP6V0C could mediate dopamine release, and this improved motor performance, supporting a functional role in neurotransmitter release beyond acidification [jin-2012-dopamine-abstract].

Regulation

V-ATPase activity is regulated at multiple levels, with reversible dissociation of the V1 and V0 sectors being a particularly important mechanism [cipriano-2008-structure-regulation-abstract]. In yeast, glucose deprivation triggers rapid dissociation of V1 from V0, which silences ATP hydrolysis while preventing proton leakage through V0. Reassembly occurs upon glucose restoration and requires the RAVE complex (Regulator of the ATPase of Vacuolar and Endosomal membranes) [kane-2003-assembly-regulation-abstract].

Assembly of the V0 sector occurs in the endoplasmic reticulum and requires dedicated assembly factors including Vma21p, Vma12p, Vma22p, Pkr1p, and Voa1p in yeast [ryan-2008-voa1-assembly-abstract; davis-kaplan-2006-pkr1-abstract]. These factors assist in the proper folding and assembly of the c-subunit proteolipid ring. The Voa1 factor was found to remain associated with the C-terminus bound inside the assembled proteolipid ring even in the mature complex [roh-2018-cryoem-abstract].

ATP6V0C protein levels are also regulated by ubiquitin-mediated degradation. The brain-enriched E3 ubiquitin ligase RNF182, which is upregulated in Alzheimer's disease brains, was shown to directly interact with ATP6V0C and target it for proteasomal degradation [liu-2008-rnf182-abstract]. This provides a potential mechanism linking V-ATPase dysfunction to neurodegeneration.

Disease Associations

Mutations affecting V-ATPase subunits are associated with multiple human diseases, and emerging evidence implicates ATP6V0C specifically in neurological disorders.

Epilepsy and Developmental Delay

De novo mutations in ATP6V0C have been identified as causative for epilepsy with intellectual disability. Whole-exome sequencing identified a novel heterozygous stop-loss mutation (c.467A>T, p.156Leuext35) in ATP6V0C in a patient with epilepsy and intellectual disability [ittiwut-2020-epilepsy-abstract]. The finding that the mutant RNA level was approximately half that of controls suggested haploinsufficiency as the pathogenic mechanism. More recently, two unrelated patients with Dravet-like syndrome were identified with heterozygous de novo missense variants in ATP6V0C (c.319G>C, p.Gly107Arg and c.284C>T, p.Ala95Val), placing ATP6V0C variants at the severe end of the epileptic encephalopathy spectrum [rong-2025-dravet-abstract].

16p13.3 Microdeletion Syndrome

A contiguous gene deletion syndrome involving ATP6V0C along with TBC1D24 and PDPK1 on chromosome 16p13.3 causes microcephaly, developmental delay, intellectual disability, and epilepsy [mucha-2018-microdeletion-abstract]. All eight individuals identified with overlapping 205-504 kb deletions displayed developmental delay, intellectual disability, and seizures, with six being microcephalic. This syndrome illustrates that ATP6V0C haploinsufficiency contributes to neurodevelopmental pathology.

Neurodegenerative Disease

Alterations in V-ATPase function and lysosomal acidification have been implicated in Alzheimer's disease and Parkinson's disease [colacurcio-2016-lysosomal-acidification-abstract]. The discovery that RNF182, an E3 ligase upregulated in AD brains, targets ATP6V0C for degradation provides a potential molecular link [liu-2008-rnf182-abstract]. Impaired lysosomal acidification leads to defective autophagy and accumulation of protein aggregates characteristic of these diseases.

Open Questions

Several important questions about ATP6V0C function remain to be resolved:

1. Stoichiometry in humans: While the yeast V-ATPase has been shown to contain 10 c-subunits in its proteolipid ring, the precise stoichiometry in human V-ATPases has not been directly determined structurally. Does the human complex have the same 10-subunit ring, and is the ATP:H+ coupling ratio identical?

2. Non-canonical fusion function: The evidence for a direct role of ATP6V0C in membrane fusion events independent of its proton-pumping function is intriguing but mechanistically incomplete. What is the precise structural basis for the interaction between ATP6V0C and VAMP2, and how does this interaction facilitate fusion?

3. Tissue-specific functions: Unlike some other V-ATPase subunits that have tissue-specific isoforms (e.g., the a-subunit), humans have only one ATP6V0C gene. How is tissue-specific V-ATPase function regulated in the absence of c-subunit isoforms? Are there post-translational modifications that confer tissue-specific properties?

4. Disease mechanisms: While haploinsufficiency appears to be the mechanism for ATP6V0C-associated epilepsy, the precise cellular defects leading to seizures are unclear. Is the phenotype primarily due to impaired synaptic vesicle acidification, defective autophagy, or the proposed fusion function?

5. Therapeutic targeting: Given the essential role of V-ATPases in multiple cell types, can ATP6V0C or V-ATPase function be therapeutically modulated in specific tissues without systemic toxicity? What is the therapeutic window for V-ATPase inhibitors in cancer or osteoporosis treatment?

6. Xenophagy signaling: The ADP-ribosylation of Gln124 by bacterial effectors reveals a specific signaling function, but does this residue have a physiological role in normal cellular autophagy regulation?

References

• cotter-2015-insights-abstract - Cotter K, Stransky L, McGuire C, Forgac M. Recent Insights into the Structure, Regulation, and Function of the V-ATPases. Trends Biochem Sci. 2015 Oct;40(10):611-622. PMID: 26410601. DOI: https://doi.org/10.1016/j.tibs.2015.08.005

• roh-2018-cryoem-abstract - Roh SH, Stam NJ, Hryc CF, Couoh-Cardel S, Pintilie G, Chiu W, Wilkens S. The 3.5-Å CryoEM Structure of Nanodisc-Reconstituted Yeast Vacuolar ATPase V0 Proton Channel. Mol Cell. 2018;69(6):993-1004.e3. PMID: 29526695. DOI: https://doi.org/10.1016/j.molcel.2018.02.006

• zhao-2015-cryoem-rotational-abstract - Zhao J, Benlekbir S, Rubinstein JL. Electron cryomicroscopy observation of rotational states in a eukaryotic V-ATPase. Nature. 2015;521(7551):241-5. PMID: 25971514. DOI: https://doi.org/10.1038/nature14365

• cipriano-2008-structure-regulation-abstract - Cipriano DJ, Wang Y, Bond S, Hinton A, Jefferies KC, Qi J, Forgac M. Structure and regulation of the vacuolar ATPases. Biochim Biophys Acta. 2008;1777(7-8):599-604. PMID: 18423392. DOI: https://doi.org/10.1016/j.bbabio.2008.03.013

• vasanthakumar-2020-structure-roles-abstract - Vasanthakumar T, Rubinstein JL. Structure and Roles of V-type ATPases. Trends Biochem Sci. 2020;45(4):295-307. PMID: 32001091. DOI: https://doi.org/10.1016/j.tibs.2019.12.007

• forgac-1992-structure-function-abstract - Forgac M. Structure, function and regulation of the coated vesicle V-ATPase. J Exp Biol. 1992;172:155-69. PMID: 1491223. DOI: https://doi.org/10.1242/jeb.172.1.155

• oot-2017-breaking-up-abstract - Oot RA, Couoh-Cardel S, Sharma S, Stam NJ, Wilkens S. Breaking up and making up: The secret life of the vacuolar H+-ATPase. Protein Sci. 2017;26(5):896-909. PMID: 28247968. DOI: https://doi.org/10.1002/pro.3147

• colacurcio-2016-lysosomal-acidification-abstract - Colacurcio DJ, Nixon RA. Disorders of lysosomal acidification-The emerging role of v-ATPase in aging and neurodegenerative disease. Ageing Res Rev. 2016;32:75-88. PMID: 27197071. DOI: https://doi.org/10.1016/j.arr.2016.05.004

• xu-2019-bacterial-effector-abstract - Xu Y, Zhou P, Cheng S, et al. A Bacterial Effector Reveals the V-ATPase-ATG16L1 Axis that Initiates Xenophagy. Cell. 2019;178(3):552-566.e20. PMID: 31327526. DOI: https://doi.org/10.1016/j.cell.2019.06.007

• elfar-2011-synaptic-vesicle-abstract - El Far O, Seagar M. A role for V-ATPase subunits in synaptic vesicle fusion? J Neurochem. 2011;117(4):603-12. PMID: 21375531. DOI: https://doi.org/10.1111/j.1471-4159.2011.07234.x

• rama-2018-neurotransmitter-abstract - Rama S, Boumedine-Guignon N, Sangiardi M, et al. Chromophore-Assisted Light Inactivation of the V-ATPase V0c Subunit Inhibits Neurotransmitter Release Downstream of Synaptic Vesicle Acidification. Mol Neurobiol. 2018;56(5):3591-3602. PMID: 30155790. DOI: https://doi.org/10.1007/s12035-018-1324-1

• huss-2002-concanamycin-binding-abstract - Huss M, Ingenhorst G, König S, et al. Concanamycin A, the specific inhibitor of V-ATPases, binds to the V(o) subunit c. J Biol Chem. 2002;277(43):40544-8. PMID: 12186879. DOI: https://doi.org/10.1074/jbc.M207345200

• wang-2004-TM-interaction-abstract - Wang Y, Inoue T, Forgac M. TM2 but not TM4 of subunit c'' interacts with TM7 of subunit a of the yeast V-ATPase as defined by disulfide-mediated cross-linking. J Biol Chem. 2004;279(43):44628-38. PMID: 15322078. DOI: https://doi.org/10.1074/jbc.M407345200

• mucha-2018-microdeletion-abstract - Mucha BE, Banka S, Ajeawung NF, et al. A new microdeletion syndrome involving TBC1D24, ATP6V0C, and PDPK1 causes epilepsy, microcephaly, and developmental delay. Genet Med. 2018;21(5):1058-1064. PMID: 30245510. DOI: https://doi.org/10.1038/s41436-018-0290-3

• ittiwut-2020-epilepsy-abstract - Ittiwut C, Poonmaksatit S, Boonsimma P, et al. Novel de novo mutation substantiates ATP6V0C as a gene causing epilepsy with intellectual disability. Brain Dev. 2020;43(3):490-494. PMID: 33190975. DOI: https://doi.org/10.1016/j.braindev.2020.10.016

• rong-2025-dravet-abstract - Rong M, Marques PT, Ali QZ, et al. Variants in ATP6V0C are associated with Dravet-like developmental and epileptic encephalopathy. Epilepsia. 2025;66(6):2046-2052. PMID: 40085430. DOI: https://doi.org/10.1111/epi.18346

• liu-2008-rnf182-abstract - Liu QY, Lei JX, Sikorska M, Liu R. A novel brain-enriched E3 ubiquitin ligase RNF182 is up regulated in the brains of Alzheimer's patients and targets ATP6V0C for degradation. Mol Neurodegener. 2008;3:4. PMID: 18298843. DOI: https://doi.org/10.1186/1750-1326-3-4

• mauvezin-2015-bafilomycin-abstract - Mauvezin C, Neufeld TP. Bafilomycin A1 disrupts autophagic flux by inhibiting both V-ATPase-dependent acidification and Ca-P60A/SERCA-dependent autophagosome-lysosome fusion. Autophagy. 2015;11(8):1437-8. PMID: 26156798. DOI: https://doi.org/10.1080/15548627.2015.1066957

• abu-remaileh-2017-lysosomal-metabolomics-abstract - Abu-Remaileh M, Wyant GA, Kim C, et al. Lysosomal metabolomics reveals V-ATPase- and mTOR-dependent regulation of amino acid efflux from lysosomes. Science. 2017;358(6364):807-813. PMID: 29074583. DOI: https://doi.org/10.1126/science.aan6298

• meo-evoli-2015-e2f1-abstract - Meo-Evoli N, Almacellas E, Massucci FA, et al. V-ATPase: a master effector of E2F1-mediated lysosomal trafficking, mTORC1 activation and autophagy. Oncotarget. 2015;6(29):28057-70. PMID: 26356814. DOI: https://doi.org/10.18632/oncotarget.4812

• jin-2012-dopamine-abstract - Jin D, Muramatsu S, Shimizu N, et al. Dopamine release via the vacuolar ATPase V0 sector c-subunit, confirmed in N18 neuroblastoma cells, results in behavioral recovery in hemiparkinsonian mice. Neurochem Int. 2012;61(6):907-12. PMID: 22265874. DOI: https://doi.org/10.1016/j.neuint.2011.12.021

• kane-2003-assembly-regulation-abstract - Kane PM, Smardon AM. Assembly and regulation of the yeast vacuolar H+-ATPase. J Bioenerg Biomembr. 2003;35(4):313-21. PMID: 14635777. DOI: https://doi.org/10.1023/a:1025724814656

• ryan-2008-voa1-assembly-abstract - Ryan M, Graham LA, Stevens TH. Voa1p functions in V-ATPase assembly in the yeast endoplasmic reticulum. Mol Biol Cell. 2008;19(12):5131-42. PMID: 18799613. DOI: https://doi.org/10.1091/mbc.e08-06-0629

• davis-kaplan-2006-pkr1-abstract - Davis-Kaplan SR, Compton MA, Flannery AR, et al. PKR1 encodes an assembly factor for the yeast V-type ATPase. J Biol Chem. 2006;281(42):32025-35. PMID: 16926153. DOI: https://doi.org/10.1074/jbc.M606451200

• chung-2010-zebrafish-abstract - Chung AY, Kim MJ, Kim D, et al. Neuron-specific expression of atp6v0c2 in zebrafish CNS. Dev Dyn. 2010;239(9):2501-8. PMID: 20839327. DOI: https://doi.org/10.1002/dvdy.22383

• powell-2000-proton-pore-abstract - Powell B, Graham LA, Stevens TH. Molecular characterization of the yeast vacuolar H+-ATPase proton pore. J Biol Chem. 2000;275(31):23654-60. PMID: 10825180. DOI: https://doi.org/10.1074/jbc.M004440200

Citations

1. abu-remaileh-2017-lysosomal-metabolomics-abstract.md
2. chung-2010-zebrafish-abstract.md
3. cipriano-2008-structure-regulation-abstract.md
4. colacurcio-2016-lysosomal-acidification-abstract.md
5. cotter-2015-insights-abstract.md
6. davis-kaplan-2006-pkr1-abstract.md
7. elfar-2011-synaptic-vesicle-abstract.md
8. elfar-2011-synaptic-vesicle-summary.md
9. forgac-1992-structure-function-abstract.md
10. huss-2002-concanamycin-binding-abstract.md
11. ittiwut-2020-epilepsy-abstract.md
12. jin-2012-dopamine-abstract.md
13. kane-2003-assembly-regulation-abstract.md
14. liu-2008-rnf182-abstract.md
15. mauvezin-2015-bafilomycin-abstract.md
16. meo-evoli-2015-e2f1-abstract.md
17. mucha-2018-microdeletion-abstract.md
18. oot-2017-breaking-up-abstract.md
19. powell-2000-proton-pore-abstract.md
20. rama-2018-neurotransmitter-abstract.md
21. roh-2018-cryoem-abstract.md
22. rong-2025-dravet-abstract.md
23. ryan-2008-voa1-assembly-abstract.md
24. vasanthakumar-2020-structure-roles-abstract.md
25. wang-2004-TM-interaction-abstract.md
26. xu-2019-bacterial-effector-abstract.md
27. xu-2019-bacterial-effector-summary.md
28. zhao-2015-cryoem-rotational-abstract.md
29. zhao-2015-cryoem-rotational-summary.md

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Plan and approach
We verified the gene/protein identity and then synthesized recent, authoritative evidence on ATP6V0C’s biochemical role in V‑ATPase, with emphasis on 2023–2024 literature, supported by foundational reviews for core mechanism and localization. Where detailed, quantitative or site‑specific claims were not directly supported by the retrieved sources, we constrained statements accordingly and cited only available context.

Comprehensive research report: ATP6V0C (UniProt P27449) in human

1) Key concepts and definitions
- Identity and family. ATP6V0C encodes the c proteolipid subunit of the membrane Vo sector of the V‑type H+‑ATPase (V‑ATPase) in Homo sapiens. The c subunit is an essential component of the proteolipid c‑ring that constitutes the rotary proton‑translocating element of the pump; it belongs to the V‑ATPase proteolipid subunit family and is highly hydrophobic with multiple transmembrane helices (four in subunit c; a c″ variant has five) (review and structural context) (eaton2021theh+atpase(vatpase) pages 1-5, indrawinata2023structuralandfunctional pages 5-6, indrawinata2023structuralandfunctional pages 4-5). URL (Eaton 2021): https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021). URL (Indrawinata 2023): https://doi.org/10.3389/fnmol.2023.1135015 (Jul 2023).
- Structural role in the V‑ATPase. The c and c″ proteolipids assemble into a multi‑subunit c‑ring (often ~10 proteolipids with a ~9:1 c:c″ ratio) that rotates against subunit a during catalysis; essential glutamate on c (e.g., E139 in human c) cycles protonation/deprotonation to enable ion translocation (mechanistic summaries from recent structural analyses) (indrawinata2023structuralandfunctional pages 5-6, indrawinata2023structuralandfunctional pages 4-5). URL: https://doi.org/10.3389/fnmol.2023.1135015 (Jul 2023).

2) Biochemical function and current mechanistic understanding
- Core reaction and coupling. The V‑ATPase hydrolyzes ATP in its V1 domain to drive rotary torque transmitted to the Vo sector, moving protons across the membrane via the c‑ring and the paired hemichannels in subunit a; typical coupling is approximately 10 H+ translocated per 3 ATP hydrolyzed (mechanistic review and structural mapping of the Vo interface and catalytic coupling) (indrawinata2023structuralandfunctional pages 4-5, indrawinata2023structuralandfunctional pages 5-6). URL: https://doi.org/10.3389/fnmol.2023.1135015 (Jul 2023).
- Proton binding sites and pathway. In human c, a conserved glutamate (E139) binds and releases H+ as the ring rotates past subunit a’s hemichannels; proton release involves conserved arginine in subunit a and a luminal network at the a7–a8 helices, consistent with rotary proton pump models (indrawinata2023structuralandfunctional pages 5-6). URL: https://doi.org/10.3389/fnmol.2023.1135015 (Jul 2023).
- Inhibitors. Classic small‑molecule V‑ATPase inhibitors (e.g., bafilomycin, concanamycin) inhibit V‑ATPase activity in cells and are widely used as pharmacologic probes; the reviews establish their use but without site‑specific binding details in the retrieved excerpts (eaton2021theh+atpase(vatpase) pages 1-5). URL: https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021).
- Recent structural insights. Contemporary cryo‑EM work has further resolved the Vo interface and hemichannels, supporting the c‑ring mechanistic model and the a–c interactions underlying proton translocation; these 2023 analyses summarize human/yeast structural principles applicable to the human enzyme (indrawinata2023structuralandfunctional pages 4-5, indrawinata2023structuralandfunctional pages 5-6). URL: https://doi.org/10.3389/fnmol.2023.1135015 (Jul 2023).

3) Cellular localization and complex assembly
- Organellar distribution. V‑ATPases are broadly present on intracellular organelles (endosomes, lysosomes, secretory vesicles, Golgi/ER intermediates), where they acidify lumens; in specialized cell types, V‑ATPase can localize to the plasma membrane to acidify the extracellular milieu (e.g., kidney intercalated cells, osteoclast ruffled border) (eaton2021theh+atpase(vatpase) pages 1-5). URL: https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021).
- Assembly. V‑ATPase comprises V1 (ATP‑hydrolytic) and Vo (proton channel) sectors that associate reversibly; the Vo c‑ring (containing ATP6V0C) forms the rotary element contacting subunit a and the central rotor stalk from V1, while peripheral EG stalks act as stators (indrawinata2023structuralandfunctional pages 4-5, eaton2021theh+atpase(vatpase) pages 1-5). URL: https://doi.org/10.3389/fnmol.2023.1135015 (Jul 2023); https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021).

4) Pathway roles and regulatory axes
- Lysosomal acidification and degradative flux. V‑ATPase‑driven acidification is essential for lysosomal hydrolase activity and endocytic/autophagic cargo degradation; compromised c‑ring function impairs these pathways (eaton2021theh+atpase(vatpase) pages 1-5). URL: https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021).
- Nutrient sensing and mTORC1. V‑ATPase is a central hub at lysosomes linking acidification to mTORC1 nutrient sensing/signaling; the review positions the complex as a signaling scaffold beyond its pump activity (eaton2021theh+atpase(vatpase) pages 1-5). URL: https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021).
- Autophagy-related regulation via V0c. Recent work implicates V0c in single‑membrane LC3 lipidation (CASM) through interactions with ATG16L1–ATG5‑12 and highlights Rabconnectin‑3 (Rogdi/RAV2‑like) as a V‑ATPase regulatory factor in metazoans; this places the c subunit in broader vesicle/autophagy control networks (winkley2025abstract2474rogdi pages 17-21). URL: https://doi.org/10.1016/j.jbc.2025.110002 (May 2025).

5) Disease associations and perturbations (human evidence)
- Neurodevelopmental phenotypes from ATP6V0C variation. A 2024 review collating clinical genetics reports links heterozygous missense ATP6V0C variants and structural deletions with a syndromic neurodevelopmental spectrum including developmental delay, epilepsy (mean onset ~25 months), and brain MRI anomalies (corpus callosum/cerebellar vermis hypoplasia, delayed myelination). Cross‑species functional modeling (yeast, C. elegans, Drosophila) supports pathogenicity and implicates impaired Vo a–c interactions during catalysis (falace2024vatpasedysfunctionin pages 6-8). URL: https://doi.org/10.3390/cells13171441 (Aug 2024).
- Essentiality and organismal physiology. Disrupting the proteolipid c‑ring is embryonic lethal in animal models, underscoring indispensability for organelle acidification and specialized plasma membrane acidification roles (kidney, bone, sensory tissues) (eaton2021theh+atpase(vatpase) pages 1-5). URL: https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021).

6) Applications and real‑world implementations
- Pharmacological tools. Bafilomycin and concanamycin are widely used cellular probes to acutely inhibit V‑ATPase and interrogate acidification‑dependent trafficking, lysosomal degradation, and signaling; they remain standard tools across cell biology and disease models (eaton2021theh+atpase(vatpase) pages 1-5). URL: https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021).
- Translational angles. The V‑ATPase is positioned as a therapeutic target in cancer, bone disease and viral entry/trafficking due to its roles in acidification and signaling; the c‑ring is the pump’s core rotor targeted by such pharmacology (high‑level review perspective) (eaton2021theh+atpase(vatpase) pages 1-5). URL: https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021).

7) Quantitative/statistical details extracted
- Coupling stoichiometry. Approximate functional coupling reported as ~10 protons translocated per 3 ATP hydrolyzed in human V‑ATPase assemblies (mechanistic summary) (indrawinata2023structuralandfunctional pages 5-6). URL: https://doi.org/10.3389/fnmol.2023.1135015 (Jul 2023).
- Genetic cohort features. In the collated ATP6V0C patient cohort, seizures were frequent with mean onset 24.6 ± 8.0 months; neuroimaging abnormalities included corpus callosum/cerebellar vermis hypoplasia and delayed myelination (falace2024vatpasedysfunctionin pages 6-8). URL: https://doi.org/10.3390/cells13171441 (Aug 2024).

Expert analysis and synthesis
- The human ATP6V0C product is the rotary proteolipid of the V‑ATPase Vo sector, forming the c‑ring that underlies proton transport. Structural work converges on a conserved glutamate‑based binding/release cycle at the c‑ring that interfaces with subunit a hemichannels to mediate vectorial H+ movement. This explains why ATP6V0C variation perturbs acidification‑dependent biology in neurons and across organ systems. The evidence base strongly supports lysosomal/endosomal roles and broader signaling functions (e.g., mTORC1), while recent reports expand regulatory interactions to autophagy machinery (ATG16L1) and assembly factors (Rabconnectin‑3), highlighting how the c‑ring can be a nexus for both transport and scaffolding depending on context (indrawinata2023structuralandfunctional pages 4-5, indrawinata2023structuralandfunctional pages 5-6, eaton2021theh+atpase(vatpase) pages 1-5, falace2024vatpasedysfunctionin pages 6-8, winkley2025abstract2474rogdi pages 17-21). URLs: https://doi.org/10.3389/fnmol.2023.1135015 (Jul 2023); https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021); https://doi.org/10.3390/cells13171441 (Aug 2024); https://doi.org/10.1016/j.jbc.2025.110002 (May 2025).

Mandatory verification of identity
- The gene symbol ATP6V0C (human; UniProt P27449) matches the proteolipid subunit c of the V‑ATPase Vo domain described in the cited sources, confirming organism and family/domain alignment. The mechanistic/structural descriptions of the c‑ring proteolipid are consistent with V‑ATPase proteolipid family membership and Vo localization (eaton2021theh+atpase(vatpase) pages 1-5, indrawinata2023structuralandfunctional pages 5-6, indrawinata2023structuralandfunctional pages 4-5). URL: https://doi.org/10.1152/ajpcell.00442.2020 (Mar 2021); https://doi.org/10.3389/fnmol.2023.1135015 (Jul 2023).

Limitations and open questions
- The retrieved excerpts do not provide direct, human cryo‑EM copy numbers for synaptic vesicles or inhibitor binding site maps specific to ATP6V0C; site‑specific pharmacology and 2024 synaptic vesicle structural quantitation therefore could not be cited here. Nonetheless, the cited 2023–2024 reviews and structural summaries establish the c‑ring mechanism, coupling stoichiometry, and disease links. Future integration of high‑resolution human cryo‑EM maps will further refine ATP6V0C’s stoichiometry across organelles and drug‑binding determinants (indrawinata2023structuralandfunctional pages 5-6, indrawinata2023structuralandfunctional pages 4-5, falace2024vatpasedysfunctionin pages 6-8, eaton2021theh+atpase(vatpase) pages 1-5).

References

1. (eaton2021theh+atpase(vatpase) pages 1-5): Amity F. Eaton, Maria Merkulova, and Dennis Brown. The h⁺-atpase (v-atpase): from proton pump to signaling complex in health and disease. American Journal of Physiology-Cell Physiology, 320:C392-C414, Mar 2021. URL: https://doi.org/10.1152/ajpcell.00442.2020, doi:10.1152/ajpcell.00442.2020. This article has 164 citations.

2. (indrawinata2023structuralandfunctional pages 5-6): Karen Indrawinata, Peter Argiropoulos, and Shuzo Sugita. Structural and functional understanding of disease-associated mutations in v-atpase subunit a1 and other isoforms. Frontiers in Molecular Neuroscience, Jul 2023. URL: https://doi.org/10.3389/fnmol.2023.1135015, doi:10.3389/fnmol.2023.1135015. This article has 14 citations and is from a poor quality or predatory journal.

3. (indrawinata2023structuralandfunctional pages 4-5): Karen Indrawinata, Peter Argiropoulos, and Shuzo Sugita. Structural and functional understanding of disease-associated mutations in v-atpase subunit a1 and other isoforms. Frontiers in Molecular Neuroscience, Jul 2023. URL: https://doi.org/10.3389/fnmol.2023.1135015, doi:10.3389/fnmol.2023.1135015. This article has 14 citations and is from a poor quality or predatory journal.

4. (winkley2025abstract2474rogdi pages 17-21): Samuel Winkley and Patricia Kane. Abstract 2474 rogdi is the homolog of yeast rav2 and a novel rabconnectin-3 subunit. Journal of Biological Chemistry, 301:110002, May 2025. URL: https://doi.org/10.1016/j.jbc.2025.110002, doi:10.1016/j.jbc.2025.110002. This article has 0 citations and is from a domain leading peer-reviewed journal.

5. (falace2024vatpasedysfunctionin pages 6-8): Antonio Falace, Greta Volpedo, Marcello Scala, Federico Zara, Pasquale Striano, and Anna Fassio. V-atpase dysfunction in the brain: genetic insights and therapeutic opportunities. Cells, 13:1441, Aug 2024. URL: https://doi.org/10.3390/cells13171441, doi:10.3390/cells13171441. This article has 16 citations and is from a poor quality or predatory journal.

Citations

1. indrawinata2023structuralandfunctional pages 5-6
2. falace2024vatpasedysfunctionin pages 6-8
3. indrawinata2023structuralandfunctional pages 4-5
4. https://doi.org/10.1152/ajpcell.00442.2020
5. https://doi.org/10.3389/fnmol.2023.1135015
6. https://doi.org/10.1016/j.jbc.2025.110002
7. https://doi.org/10.3390/cells13171441
8. https://doi.org/10.1152/ajpcell.00442.2020,
9. https://doi.org/10.3389/fnmol.2023.1135015,
10. https://doi.org/10.1016/j.jbc.2025.110002,
11. https://doi.org/10.3390/cells13171441,

Overview of ATP6V0C and the V-ATPase Complex

ATP6V0C (also known as V-ATPase 16 kDa proteolipid subunit c, UniProt P27449) encodes the c subunit of the vacuolar H^+-ATPase (V-ATPase) in humans (pmc.ncbi.nlm.nih.gov) (go.drugbank.com). V-ATPase is a large multi-subunit enzyme complex that uses the energy from ATP hydrolysis to pump protons (H^+) across intracellular membranes, thereby acidifying organelles such as lysosomes, endosomes, and the Golgi apparatus (pmc.ncbi.nlm.nih.gov) (go.drugbank.com). This proton transport activity of V-ATPase is essential for maintaining pH homeostasis in cells and for creating the proton gradients required by many cellular processes (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). In certain specialized cells, V-ATPases are also targeted to the plasma membrane, where they actively acidify the extracellular environment (for example, in osteoclast-mediated bone resorption or renal acid secretion) (go.drugbank.com) (pmc.ncbi.nlm.nih.gov).

Key Functional Role: ATP6V0C’s gene product is a proton-conducting, pore-forming subunit of the V-ATPase V0 domain (go.drugbank.com). Within the V-ATPase complex, the V0 domain is the membrane-embedded sector that translocates protons, while the V1 domain is the peripheral sector that hydrolyzes ATP to power proton transport (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). The ATP6V0C-encoded subunit c forms part of the rotary proton pump mechanism: ATP hydrolysis in V1 drives rotation of a ring of c subunits in V0, which shuttles protons from the cytosol into the organelle lumen against the electrochemical gradient (pmc.ncbi.nlm.nih.gov) (go.drugbank.com). In biochemical terms, V-ATPase activity can be viewed as ATP hydrolysis coupled to H^+ transport – i.e. ATP6V0C is not an enzyme on its own, but an integral component of the transmembrane proton channel that is driven by the enzyme’s catalytic subunits. The substrate of this transporter is the proton (H^+), and the pumping cycle typically translocates multiple H^+ per ATP hydrolyzed via a rotary mechanism (pmc.ncbi.nlm.nih.gov).

Structure and Mechanism of the V0 c Subunit

Protein Features: The human V0 c subunit is a small 155-amino-acid protein with four transmembrane helices, characteristic of a hydrophobic proteolipid (pmc.ncbi.nlm.nih.gov). It is highly conserved evolutionarily – for instance, the human c subunit shares ~72% amino acid identity with its yeast ortholog, underscoring the conserved structure and function of this protein across species (pmc.ncbi.nlm.nih.gov). The subunit is encoded by a gene on chromosome 16p13.3 consisting of three exons (pmc.ncbi.nlm.nih.gov) (two other loci on chromosomes 6 and 17 encode non-functional pseudogene copies (www.genecards.org)). Alternative splicing of ATP6V0C can produce transcript variants, but all encode the same core protein product (www.genecards.org).

Assembly in V-ATPase: Multiple c subunits assemble together with related proteolipids to form the c-ring rotor within the V0 membrane domain. High-resolution structural studies indicate that in the human V-ATPase, the c-ring is composed of 10 proteolipid subunits in total: nine copies of the ATP6V0C-encoded subunit c and one copy of the related “cʺ” subunit (encoded by ATP6V0B) (pmc.ncbi.nlm.nih.gov). These subunits arrange in a ring within the lipid bilayer, and each c subunit contributes a proton-binding site. A key conserved residue in subunit c is glutamate 139 (E139), which plays a critical role in binding and releasing protons during the transport cycle (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). The rotary mechanism can be summarized as follows: the V1 domain hydrolyzes ATP and drives rotation of the c-ring; as the ring turns, each subunit c carries a proton from the cytosolic side to the luminal side of the membrane. The c subunits interact with the V0 subunit a (product of ATP6V0A genes), which provides two half-channels for proton entry and exit and contains a crucial arginine residue (R735). Proton translocation relies on a charge shuttle between E139 in subunit c and R735 in subunit a: a proton binds to E139 in a c subunit on the cytosolic side, the ring rotates and delivers that proton to the luminal half-channel where R735 in subunit a helps facilitate proton release (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). This coordinated hand-off mechanism is analogous to that of the F-ATP synthase in mitochondria, reflecting the conserved rotary ATPase design (pmc.ncbi.nlm.nih.gov).

Bafilomycin Binding: Notably, ATP6V0C is identified as the binding target of bafilomycin A1, a well-known macrolide inhibitor of V-ATPases (pmc.ncbi.nlm.nih.gov). Bafilomycin and related inhibitors (like concanamycin) bind the c-ring proteolipid subunits and block proton translocation, causing a collapse of organelle pH gradients. This reveals that the c subunit’s proton channel region is the pharmacological point of inhibition for these compounds (pmc.ncbi.nlm.nih.gov). Experimentally, treating cells with bafilomycin or knocking down ATP6V0C produces similar phenotypes of organelle de-acidification – for example, loss of lysosomal acidity, impaired protein degradation, and stalled autophagic flux (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). These observations underscore the c subunit’s central role in V-ATPase activity and its potential as a drug target in diseases where modulation of vesicular pH is therapeutic.

Biological Processes and Pathways Involving ATP6V0C

Organelle Acidification and Trafficking: The primary role of ATP6V0C (as part of V-ATPase) is to acidify intracellular organelles, and this acidification is absolutely critical for a host of cellular processes. V-ATPase–dependent luminal acidification is required for endocytic trafficking and protein sorting (e.g. dissociating ligands from receptors in endosomes), for zymogen activation in secretory granules (e.g. activation of pro-enzymes in endocrine and digestive cells), and for the generation of proton gradients in secretory vesicles (www.genecards.org) (pmc.ncbi.nlm.nih.gov). For instance, the low pH in Golgi and secretory granules facilitates proper protein processing (such as glycosylation steps and precursor cleavage), and late endosomes/lysosomes must be acidified for protease activation and substrate degradation by hydrolases (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Receptor-mediated endocytosis also requires V-ATPase function: as early endosomes mature and acidify, the pH drop triggers conformational changes that cause receptors to release their cargo (e.g. LDL from its receptor) and primes cargo for sorting or degradation (www.genecards.org). In yeast and other model systems, loss of V-ATPase activity leads to defects in sorting of vacuolar enzymes and accumulation of cargo in aberrant compartments, highlighting its fundamental role in vesicle trafficking (pmc.ncbi.nlm.nih.gov).

Autophagy and Lysosomal Function: Macroautophagy (the self-degradative pathway for recycling cellular components) is strongly dependent on ATP6V0C and V-ATPase function. The lysosome is the terminal organelle where autophagic cargo is degraded, and a highly acidic lumen (pH ~4.5–5) is required for lysosomal enzymes to function. Catabolic processes such as autophagic degradation strictly rely on V-ATPase-driven acidification (pmc.ncbi.nlm.nih.gov). If ATP6V0C function is lost or inhibited, lysosomal pH rises and autophagic flux is blocked, meaning cells accumulate autophagosomes and undegraded substrates (pmc.ncbi.nlm.nih.gov). Experimental knockdown of ATP6V0C in human neuroblastoma cells, for example, caused increased LC3-II levels and build-up of proteins like α-synuclein and amyloid precursor fragments, indicating impaired autophagosome-lysosome clearance (pmc.ncbi.nlm.nih.gov). These cells also showed reduced viability and neurite degeneration, especially under stress, consistent with failure of the autophagy-lysosome system (pmc.ncbi.nlm.nih.gov). Thus, through its role in V-ATPase, ATP6V0C is intimately tied to cellular clearance pathways; this has implications for neurodegenerative conditions where defective lysosomal acidification can lead to toxic protein accumulation.

Synaptic Vesicle Loading: In neurons, V-ATPases (containing ATP6V0C subunits) are crucial for neurotransmission. They acidify synaptic vesicles, creating an electrochemical proton gradient that is harnessed by neurotransmitter transporters to fill the vesicles with neurotransmitters. The human brain expresses high levels of V-ATPase, and synaptic vesicle acidification by V-ATPase is required to load various neurotransmitters into vesicles (pmc.ncbi.nlm.nih.gov). For example, vesicular glutamate transporters use the proton gradient (exchanging lumenal H^+ for cytosolic glutamate) to concentrate glutamate inside synaptic vesicles. If the V0 c subunit or other V-ATPase components are dysfunctional, synaptic vesicles cannot accumulate neurotransmitters properly, leading to synaptic transmission defects. This dependency links ATP6V0C to neurophysiological processes like synaptic plasticity and neural circuit function. Indeed, genetic and pharmacological disruptions of V-ATPase in neurons cause seizures and neurodevelopmental anomalies (discussed further below), underlining the importance of ATP6V0C for normal nervous system activity (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

Specialized Roles (Bone Resorption and pH Homeostasis): In certain cell types, V-ATPases perform “specialized” physiological roles beyond routine vesicle acidification. Osteoclasts (bone-resorbing cells) use plasma-membrane V-ATPases to pump protons into the sealed resorption lacuna between the cell and bone surface, thereby acidifying the extracellular compartment to dissolve bone mineral (pmc.ncbi.nlm.nih.gov). The c subunit is a part of these osteoclast V-ATPases, and mutations in other V-ATPase subunits (like ATP6V0A3, the osteoclast-specific a3 subunit) cause osteopetrosis due to failure of bone acidification, implying that ATP6V0C is also essential in this process as a core component of the proton pump (pmc.ncbi.nlm.nih.gov). In the kidneys, intercalated cells of the distal nephron have V-ATPases on their apical membrane to secrete protons into the urine, regulating systemic acid–base balance (pmc.ncbi.nlm.nih.gov). ATP6V0C contributes to these pumps, meaning it indirectly supports systemic pH homeostasis. In immune cells like neutrophils and macrophages, V-ATPases help acidify phagosomes and granules (e.g. azurophil granules) for microbial killing – consistent with GO annotations localizing subunit c to phagolysosomal and granule membranes (go.drugbank.com). These examples illustrate that ATP6V0C-containing V-ATPase complexes are not only housekeeping proton pumps but also facilitators of specialized physiological processes that require controlled acidification.

Cell Signaling and Metabolic Pathways: Beyond its direct role in proton transport, emerging evidence links V-ATPase (and by extension ATP6V0C) to cellular signaling pathways. One prominent example is the mTORC1 nutrient-sensing pathway: the lysosomal V-ATPase works in concert with the Ragulator complex to signal amino acid availability to mTORC1. The V-ATPase–Ragulator complex is essential for mTORC1 activation on the lysosome; in response to amino acids, this complex helps recruit and activate mTORC1, promoting anabolic growth signaling (pmc.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov). Although ATP6V0C is a structural subunit, the intact proton pump seems necessary for this signaling function – in fact, some studies suggest that the proton gradient or V-ATPase conformational state may act as a cue for mTORC1 activation (pmc.ncbi.nlm.nih.gov). Additionally, V-ATPase activity can impact Wnt/β-catenin signaling and other pathways indirectly by modulating the trafficking of receptors and the pH of endo-lysosomal compartments where signaling components are processed (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). There are also links to cellular metabolism: for example, cancer cells often upregulate V-ATPase subunits to maintain an acidic microenvironment and promote glycolysis. A 2019 study showed that silencing ATP6V0C in highly metastatic esophageal cancer cells attenuated their aerobic glycolysis (Warburg effect) and invasive growth – likely by disrupting cytosolic pH and enzyme activities – and reduced tumor cell proliferation (pmc.ncbi.nlm.nih.gov). Thus, while ATP6V0C’s primary role is structural (enabling proton transport), this function intersects with numerous signaling and metabolic pathways that depend on proper organelle acidification and pH dynamics.

Subcellular Localization

Membrane Localization: The ATP6V0C protein is an integral membrane protein that localizes to the membranes of acidic organelles and certain specialized membranes, consistent with the distribution of V-ATPase complexes. UniProt annotations and cell imaging studies indicate that subunit c is found in lysosomal and endosomal membranes, trans-Golgi network membranes, and in the membranes of secretory vesicles (e.g. synaptic vesicles, endocrine secretory granules) (www.genecards.org) (go.drugbank.com). For example, the Human Protein Atlas detects ATP6V0C in cytoplasmic vesicle structures, reflecting its presence in vesicle membranes. V-ATPase containing ATP6V0C is also present on clathrin-coated vesicles that bud from the plasma membrane or Golgi, suggesting it is poised to acidify endocytic vesicles soon after they form (www.genecards.org).

Within these membranes, ATP6V0C’s 4-pass transmembrane topology means it spans the lipid bilayer multiple times, likely arranging such that both the N- and C-termini face the cytosolic side (as shown for homologous proteolipid subunits) (pmc.ncbi.nlm.nih.gov). The crucial proton-binding residue (E139) lies in the transmembrane segment and faces the lipid/rotor interface where proton transfer occurs (pmc.ncbi.nlm.nih.gov).

Plasma Membrane Occurrence: Under typical conditions, most V-ATPases reside on intracellular organelles, but in specific cell types or stimuli, ATP6V0C-containing V-ATPases are targeted to the plasma membrane. This occurs in osteoclasts and kidney intercalated cells as discussed, and also in certain tumor cells and specialized epithelia. Compartments.jensenlab computational localization scores give high confidence for ATP6V0C at the lysosome (score 5) and plasma membrane (score 5), with slightly lower scores for Golgi and endosomes (www.genecards.org). Indeed, immunolabeling in osteoclasts shows a ruffled-border plasma membrane localization of V0 subunits during active bone resorption (pmc.ncbi.nlm.nih.gov). In cancer cell lines, V-ATPase subunits (including c) have been detected at the cell surface, where their activity correlates with an acidic pericellular milieu that facilitates invasion (pmc.ncbi.nlm.nih.gov). It’s worth noting that reversible relocalization of V-ATPase is a known regulatory mechanism: for instance, in response to cellular cues, V-ATPases can be trafficked to or from the plasma membrane. An example is in macrophages, where V-ATPases are stored on vesicles and deployed to the phagosome membrane upon ingestion of pathogens, acidifying the phagosome to kill microbes. Thus, ATP6V0C’s localization is dynamic, but always associated with membranes where proton pumping is needed. Consistent with this, gene ontology annotations list ATP6V0C as an integral component of membranes like lysosomal, endosomal, phagosomal, secretory granule, and synaptic vesicle** membranes (go.drugbank.com). No evidence suggests ATP6V0C ever exists in a soluble form; it is invariably membrane-bound and usually found as part of the assembled V0 complex.

Clinical Significance and Recent Research Developments

Disease Associations: Given its fundamental role in organelle acidification, it is not surprising that defects in ATP6V0C can have serious consequences. For many years, direct mutations in ATP6V0C were not widely reported in human disease (possibly because complete loss of such an essential subunit might be embryonically lethal). However, recent genetic studies (2020–2023) have uncovered multiple cases linking de novo ATP6V0C mutations to a pediatric neurodevelopmental syndrome. In 2023, Mattison et al. reported 27 patients from unrelated families harboring heterozygous missense variants in ATP6V0C, presenting with a syndromic neurodevelopmental disorder characterized by early-onset epilepsy, developmental delay, intellectual disability, and often corpus callosum hypoplasia (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Notably, many of these mutations clustered in the fourth transmembrane region of the protein (which includes the critical Glu-139), suggesting that they disrupt proton translocation. The researchers demonstrated in yeast and C. elegans models that patient-derived ATP6V0C variants impair V-ATPase function, leading to reduced lysosomal acidification and cellular growth defects (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). In a Drosophila knockdown model, loss of the ATP6V0C ortholog caused seizure-like activity that could be suppressed by existing anti-epileptic drugs, consistent with a hyperexcitability phenotype due to lysosomal dysfunction (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). These findings firmly establish ATP6V0C as a disease gene (OMIM #620465): even a partial loss of function (haploinsufficiency) in humans can lead to neurological disorders. Intriguingly, earlier studies of chromosomal microdeletions involving ATP6V0C (e.g. 16p13.3 deletions) also pointed to haploinsufficiency of ATP6V0C as the likely driver of epilepsy, microcephaly, and developmental delay in those patients (pmc.ncbi.nlm.nih.gov). A subsequent case in 2020 identified a de novo stop-loss mutation in ATP6V0C in an individual with epilepsy and intellectual disability, further implicating this gene in epilepsy pathogenesis (pmc.ncbi.nlm.nih.gov). Now, with dozens of cases reported, ATP6V0C joins other V-ATPase subunit genes (such as ATP6V1A, ATP6V0A1, ATP6V1B2) that are linked to neurological disorders, underscoring the unique vulnerability of neurons to endo-lysosomal dysfunction (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

Beyond the nervous system, ATP6V0C might play roles in other diseases, though these are less well characterized. There is evidence that aberrant regulation of V-ATPase subunits is involved in cancer invasiveness, as mentioned. High ATP6V0C expression has been observed in some tumors and is correlated with aggressive behavior, presumably because it helps tumor cells survive in acidic, low-nutrient environments. Functional studies in esophageal cancer cells (KYSE lines) showed that silencing ATP6V0C suppressed glycolytic flux and cell invasiveness, hinting that targeting V0 subunits could be a strategy to impair cancer metabolism (pmc.ncbi.nlm.nih.gov). In the context of kidney disease, a 2022 study suggested ATP6V0C downregulation may contribute to defective autophagy and fibrosis in renal tubular cells, via interaction with SNARE proteins required for autophagosome–lysosome fusion (pmc.ncbi.nlm.nih.gov). These are areas of ongoing research.

Expert Insights and Therapeutic Potentials: As a central component of V-ATPase, ATP6V0C is considered a potential therapeutic target in certain conditions. Pharmacologically, general V-ATPase inhibitors like bafilomycin are too toxic for systemic use, but researchers are exploring ways to target specific V-ATPase isoforms or accessory interactions. For example, one approach has been to disrupt the interaction of V-ATPase with the actin cytoskeleton in osteoclasts to treat osteoporosis. Small molecules such as enoxacin were found to selectively inhibit the V-ATPases in osteoclasts by blocking the binding of the V1 sector to microfilaments, thereby reducing bone resorption without globally inhibiting all V-ATPases (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). This specificity arises because the osteoclast V-ATPase uses a particular isoform composition (including ATP6V0C plus the a3 subunit and others) that associates with actin. Enoxacin and related compounds showed efficacy in animal models of osteoporosis and bone metastasis, hinting that selective V-ATPase modulators could have clinical benefit (pmc.ncbi.nlm.nih.gov). Another emerging strategy is exploiting the dependence of cancer cells on V-ATPase: some tumors rely on plasma-membrane V-ATPase to acidify the tumor microenvironment, so inhibiting V-ATPase can reduce metastasis and make the environment less favorable for invasion (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). While no ATP6V0C-specific inhibitor exists, the subunit is part of the drug-binding c-ring, so any V0-directed inhibitor would act on it. Researchers are also interested in ATP6V0C as a biomarker: for instance, elevated expression of V0 subunits might predict tumors that would respond to pH-disrupting therapies, or mutations in ATP6V0C could be diagnostic for certain neurodevelopmental disorders.

Current and Future Directions: The latest research (2022–2024) continues to deepen our understanding of ATP6V0C. Structural biologists achieved near-atomic resolution structures of the human V-ATPase in 2020, revealing how subunit c and its partners assemble and indicating conformational changes during rotary catalysis (pmc.ncbi.nlm.nih.gov). These structures confirm the 1:1:10 stoichiometry of a:a2:c-ring subunits (consistent with 9 c and 1 cʺ in the ring) and provide templates for modeling disease mutations. On the clinical side, ongoing genotype-phenotype mapping of ATP6V0C variants (including studies in 2022 and 2023) is defining the spectrum of neurological disease and may uncover milder phenotypes or tissue-specific effects of partial V-ATPase dysfunction (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). There is also growing interest in how modulating V-ATPase activity can influence age-related diseases: for example, activating V-ATPase (to boost lysosomal degradation) is being explored in neurodegenerative disease models, whereas inhibiting V-ATPase in certain contexts (like tumor microenvironments or bone turnover) is desired in oncology and orthopedics (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

In summary, ATP6V0C is a vital component of the proton pump that acidifies cellular organelles, enabling diverse physiological processes from nutrient processing to synaptic signaling. Its protein product is a multi-pass membrane subunit that forms the proton-conducting rotor of V-ATPase, working in concert with other subunits to pump H^+ ions using ATP energy. This action underlies critical pathways such as lysosomal degradation, autophagy, and neurotransmitter storage. ATP6V0C predominantly localizes to endo-lysosomal membranes (and specialized plasma membranes), reflecting the sites of acidification in the cell. Disruption of ATP6V0C can derail these processes, as evidenced by recent discoveries linking ATP6V0C mutations to human disease. Ongoing research and expert analyses emphasize that proper regulation of V-ATPase (and thus ATP6V0C) is central to cellular homeostasis, and manipulating this proton pump – whether by genetic means or targeted drugs – holds potential for treating diseases ranging from epilepsy to cancer (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

References: (Publication dates and sources are included in citations for verification.)

Citations

1. AnnotationURLCitation(end_index=395, start_index=206, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=thereby%20creating%20the%20proton%2FpH%20gradient,conducted%20in%20Saccharomyces%20cerevisiae%20revealed')
2. AnnotationURLCitation(end_index=516, start_index=396, title='V-type proton ATPase 16 kDa proteolipid subunit c | DrugBank Online', type='url_citation', url='https://go.drugbank.com/polypeptides/P27449#:~:text=Proton,By%20similarity%29%20Specific%20Function')
3. AnnotationURLCitation(end_index=881, start_index=746, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=V,resorption%20compartment%20to%20solubilize%20bone')
4. AnnotationURLCitation(end_index=1002, start_index=882, title='V-type proton ATPase 16 kDa proteolipid subunit c | DrugBank Online', type='url_citation', url='https://go.drugbank.com/polypeptides/P27449#:~:text=Proton,By%20similarity%29%20Specific%20Function')
5. AnnotationURLCitation(end_index=1337, start_index=1178, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=The%20vacuolar%20H%5E%7B%2B%7D,silico%20modelling%20suggested%20that%20the')
6. AnnotationURLCitation(end_index=1477, start_index=1338, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=Vacuolar,impair%20brain%20development%20and%20synaptic')
7. AnnotationURLCitation(end_index=1821, start_index=1697, title='V-type proton ATPase 16 kDa proteolipid subunit c | DrugBank Online', type='url_citation', url='https://go.drugbank.com/polypeptides/P27449#:~:text=complex%20,By%20similarity%29%20Specific%20Function')
8. AnnotationURLCitation(end_index=1962, start_index=1822, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=include%20acidifying%20an%20extracellular%20resorption,9')
9. AnnotationURLCitation(end_index=2212, start_index=2092, title='V-type proton ATPase 16 kDa proteolipid subunit c | DrugBank Online', type='url_citation', url='https://go.drugbank.com/polypeptides/P27449#:~:text=Proton,By%20similarity%29%20Specific%20Function')
10. AnnotationURLCitation(end_index=2534, start_index=2407, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=The%20vacuolar%20H%5E%7B%2B%7D,1%20%2C%205')
11. AnnotationURLCitation(end_index=2731, start_index=2535, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=conservation%2C%20transmembrane%20transport%2C%20acidification%20of,subunits%2C%20forms%20the%20hydrogen%20pore')
12. AnnotationURLCitation(end_index=3116, start_index=2989, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=The%20vacuolar%20H%5E%7B%2B%7D,1%20%2C%205')
13. AnnotationURLCitation(end_index=3237, start_index=3117, title='V-type proton ATPase 16 kDa proteolipid subunit c | DrugBank Online', type='url_citation', url='https://go.drugbank.com/polypeptides/P27449#:~:text=Proton,By%20similarity%29%20Specific%20Function')
14. AnnotationURLCitation(end_index=3744, start_index=3656, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=V,1')
15. AnnotationURLCitation(end_index=4103, start_index=3962, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=shares%2072,affected%20residues%20that%20are%20conserved')
16. AnnotationURLCitation(end_index=4460, start_index=4319, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=shares%2072,affected%20residues%20that%20are%20conserved')
17. AnnotationURLCitation(end_index=4652, start_index=4543, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=ATP6V0C%2C%20a%20three,4')
18. AnnotationURLCitation(end_index=4904, start_index=4733, title='ATP6V0C Gene - GeneCards | VATL Protein | VATL Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=ATP6V0C#:~:text=of%20five%20different%20subunits%3A%20a%2C,provided%20by%20RefSeq%2C%20Nov%202010')
19. AnnotationURLCitation(end_index=5188, start_index=5017, title='ATP6V0C Gene - GeneCards | VATL Protein | VATL Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=ATP6V0C#:~:text=of%20five%20different%20subunits%3A%20a%2C,provided%20by%20RefSeq%2C%20Nov%202010')
20. AnnotationURLCitation(end_index=5682, start_index=5594, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=V,1')
21. AnnotationURLCitation(end_index=6059, start_index=5953, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=c%E2%80%B2%E2%80%B2,1')
22. AnnotationURLCitation(end_index=6169, start_index=6060, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=ATP6V0C%2C%20a%20three,4')
23. AnnotationURLCitation(end_index=6967, start_index=6879, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=V,1')
24. AnnotationURLCitation(end_index=7093, start_index=6968, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=the%20movement%20of%20protons%20across,1')
25. AnnotationURLCitation(end_index=7364, start_index=7237, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=The%20vacuolar%20H%5E%7B%2B%7D,1%20%2C%205')
26. AnnotationURLCitation(end_index=7672, start_index=7514, title='ATP6V0C Knockdown in Neuroblastoma Cells Alters Autophagy-Lysosome Pathway Function and Metabolism of Proteins that Accumulate in Neurodegenerative Disease - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3973706/#:~:text=ATP6V0C%20is%20the%20bafilomycin%20A1,by%20a%20significant%20decrease%20in')
27. AnnotationURLCitation(end_index=8123, start_index=7965, title='ATP6V0C Knockdown in Neuroblastoma Cells Alters Autophagy-Lysosome Pathway Function and Metabolism of Proteins that Accumulate in Neurodegenerative Disease - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3973706/#:~:text=ATP6V0C%20is%20the%20bafilomycin%20A1,by%20a%20significant%20decrease%20in')
28. AnnotationURLCitation(end_index=8526, start_index=8356, title='ATP6V0C Knockdown in Neuroblastoma Cells Alters Autophagy-Lysosome Pathway Function and Metabolism of Proteins that Accumulate in Neurodegenerative Disease - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3973706/#:~:text=shown%20previously%20that%20bafilomycin%20A1,terminal%20fragments%2C%20and%20inhibited')
29. AnnotationURLCitation(end_index=8697, start_index=8527, title='ATP6V0C Knockdown in Neuroblastoma Cells Alters Autophagy-Lysosome Pathway Function and Metabolism of Proteins that Accumulate in Neurodegenerative Disease - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3973706/#:~:text=knockdown%20was%20validated%20by%20quantitative,A1%2C%20a%20concentration%20that%20did')
30. AnnotationURLCitation(end_index=9616, start_index=9493, title='ATP6V0C Gene - GeneCards | VATL Protein | VATL Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=ATP6V0C#:~:text=,This%20gene%20encodes%20the%20V0')
31. AnnotationURLCitation(end_index=9786, start_index=9617, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=essential%20housekeeping%20enzymes%20in%20eukaryotic,and%20pumping%20protons%20across')
32. AnnotationURLCitation(end_index=10187, start_index=10052, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=V,resorption%20compartment%20to%20solubilize%20bone')
33. AnnotationURLCitation(end_index=10357, start_index=10188, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=essential%20housekeeping%20enzymes%20in%20eukaryotic,and%20pumping%20protons%20across')
34. AnnotationURLCitation(end_index=10749, start_index=10626, title='ATP6V0C Gene - GeneCards | VATL Protein | VATL Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=ATP6V0C#:~:text=,This%20gene%20encodes%20the%20V0')
35. AnnotationURLCitation(end_index=11096, start_index=10970, title='Role of vacuolar acidification in protein sorting and zymogen activation: a genetic analysis of the yeast vacuolar proton-translocating ATPase - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC360825/#:~:text=Role%20of%20vacuolar%20acidification%20in,1')
36. AnnotationURLCitation(end_index=11682, start_index=11543, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=Vacuolar,impair%20brain%20development%20and%20synaptic')
37. AnnotationURLCitation(end_index=12017, start_index=11847, title='ATP6V0C Knockdown in Neuroblastoma Cells Alters Autophagy-Lysosome Pathway Function and Metabolism of Proteins that Accumulate in Neurodegenerative Disease - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3973706/#:~:text=knockdown%20was%20validated%20by%20quantitative,A1%2C%20a%20concentration%20that%20did')
38. AnnotationURLCitation(end_index=12429, start_index=12259, title='ATP6V0C Knockdown in Neuroblastoma Cells Alters Autophagy-Lysosome Pathway Function and Metabolism of Proteins that Accumulate in Neurodegenerative Disease - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3973706/#:~:text=knockdown%20was%20validated%20by%20quantitative,A1%2C%20a%20concentration%20that%20did')
39. AnnotationURLCitation(end_index=12751, start_index=12581, title='ATP6V0C Knockdown in Neuroblastoma Cells Alters Autophagy-Lysosome Pathway Function and Metabolism of Proteins that Accumulate in Neurodegenerative Disease - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3973706/#:~:text=knockdown%20was%20validated%20by%20quantitative,A1%2C%20a%20concentration%20that%20did')
40. AnnotationURLCitation(end_index=13606, start_index=13439, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=%28Supplementary%20Table%201%20%29,presentations%20when%20compared%20to%20patients')
41. AnnotationURLCitation(end_index=14411, start_index=14293, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=,with%20a%20novel%20syndrome%20of')
42. AnnotationURLCitation(end_index=14555, start_index=14412, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=Dmel,hypothesis%20that%20haploinsufficiency%20of%20ATP6V0C')
43. AnnotationURLCitation(end_index=15090, start_index=14959, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=to%20the%20housekeeping%20functions%2C%20some,9')
44. AnnotationURLCitation(end_index=15530, start_index=15399, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=to%20the%20housekeeping%20functions%2C%20some,9')
45. AnnotationURLCitation(end_index=15884, start_index=15706, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=include%20acidifying%20an%20extracellular%20resorption,cells%20also%20have%20plasma%20membrane')
46. AnnotationURLCitation(end_index=16392, start_index=16225, title='V-type proton ATPase 16 kDa proteolipid subunit c | DrugBank Online', type='url_citation', url='https://go.drugbank.com/polypeptides/P27449#:~:text=azurophil%20granule%20membrane%20%2F%20endosome,membrane%20%2F%20tertiary%20granule%20membrane')
47. AnnotationURLCitation(end_index=17311, start_index=17159, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=%2832%20%2C%2031%29%2C%20NHE,The%20papillomavirus%20E5%20oncoprotein')
48. AnnotationURLCitation(end_index=17463, start_index=17312, title='The lysosomal v-ATPase-Ragulator complex is a common activator for AMPK and mTORC1, acting as a switch between catabolism and anabolism - PubMed', type='url_citation', url='https://pubmed.ncbi.nlm.nih.gov/25002183/#:~:text=AMPK%20and%20mTOR%20play%20principal,also%20uncovered%20that%20AMPK%20is')
49. AnnotationURLCitation(end_index=17855, start_index=17703, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=%2832%20%2C%2031%29%2C%20NHE,The%20papillomavirus%20E5%20oncoprotein')
50. AnnotationURLCitation(end_index=18209, start_index=18084, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=There%20are%20now%20strong%20evidences,17')
51. AnnotationURLCitation(end_index=18371, start_index=18210, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=proteins%2C%20a%20number%20of%20other,The%20papillomavirus%20E5%20oncoprotein')
52. AnnotationURLCitation(end_index=18959, start_index=18804, title='Vacuolar H+-ATPase Subunit V0C Regulates Aerobic Glycolysis of Esophageal Cancer Cells via PKM2 Signaling - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6830105/#:~:text=The%20vacuolar%20H%5E%7B%2B%7D,uptake%20and%20decreased%20lactate%20and')
53. AnnotationURLCitation(end_index=19875, start_index=19687, title='ATP6V0C Gene - GeneCards | VATL Protein | VATL Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=ATP6V0C#:~:text=%2A%20Cytoplasmic%20vesicle%2C%20clathrin,ECO%3A0000250%20UniProtKB%3AP63081%20%7C%20ECO%3A0000255')
54. AnnotationURLCitation(end_index=20043, start_index=19876, title='V-type proton ATPase 16 kDa proteolipid subunit c | DrugBank Online', type='url_citation', url='https://go.drugbank.com/polypeptides/P27449#:~:text=azurophil%20granule%20membrane%20%2F%20endosome,membrane%20%2F%20tertiary%20granule%20membrane')
55. AnnotationURLCitation(end_index=20562, start_index=20374, title='ATP6V0C Gene - GeneCards | VATL Protein | VATL Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=ATP6V0C#:~:text=%2A%20Cytoplasmic%20vesicle%2C%20clathrin,ECO%3A0000250%20UniProtKB%3AP63081%20%7C%20ECO%3A0000255')
56. AnnotationURLCitation(end_index=20944, start_index=20803, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=shares%2072,affected%20residues%20that%20are%20conserved')
57. AnnotationURLCitation(end_index=21212, start_index=21087, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=the%20movement%20of%20protons%20across,1')
58. AnnotationURLCitation(end_index=21897, start_index=21769, title='ATP6V0C Gene - GeneCards | VATL Protein | VATL Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=ATP6V0C#:~:text=Compartment%20%20%7C%20Confidence%20,2')
59. AnnotationURLCitation(end_index=22165, start_index=22034, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=to%20the%20housekeeping%20functions%2C%20some,9')
60. AnnotationURLCitation(end_index=22488, start_index=22354, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=for%20loading%20neurotransmitters%20in%20neurons,6')
61. AnnotationURLCitation(end_index=23345, start_index=23178, title='V-type proton ATPase 16 kDa proteolipid subunit c | DrugBank Online', type='url_citation', url='https://go.drugbank.com/polypeptides/P27449#:~:text=azurophil%20granule%20membrane%20%2F%20endosome,membrane%20%2F%20tertiary%20granule%20membrane')
62. AnnotationURLCitation(end_index=24547, start_index=24358, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=thereby%20creating%20the%20proton%2FpH%20gradient,conducted%20in%20Saccharomyces%20cerevisiae%20revealed')
63. AnnotationURLCitation(end_index=24721, start_index=24548, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=ATP6V0C%20%28NM_001694.4%29%20%20,gait%20ataxia%2C%20nonspecific%20dysmorphic%20features')
64. AnnotationURLCitation(end_index=25279, start_index=25107, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=patient%20variants%20interfere%20with%20the,clinical%20features%20of%20the%20associated')
65. AnnotationURLCitation(end_index=25398, start_index=25280, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=,with%20a%20novel%20syndrome%20of')
66. AnnotationURLCitation(end_index=25804, start_index=25627, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=interfered%20with%20the%20interactions%20between,Caenorhabditis%20elegans%20led%20to%20motor')
67. AnnotationURLCitation(end_index=25948, start_index=25805, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=Dmel,hypothesis%20that%20haploinsufficiency%20of%20ATP6V0C')
68. AnnotationURLCitation(end_index=26526, start_index=26370, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=match%20at%20L410%20of%20TBC1D24%2C,was%20proposed%20as%20the%20primary')
69. AnnotationURLCitation(end_index=26858, start_index=26720, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=match%20at%20L415%20,with%20a%20novel%20syndrome%20of')
70. AnnotationURLCitation(end_index=27280, start_index=27099, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=Catabolic%20processes%2C%20such%20as%20endocytic,genetic%20and%20functional%20evidence%20linking')
71. AnnotationURLCitation(end_index=27439, start_index=27281, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=%28Supplementary%20Table%201%20%29,variants%20in%20ATP6V1B2%20can%20cause')
72. AnnotationURLCitation(end_index=28237, start_index=28082, title='Vacuolar H+-ATPase Subunit V0C Regulates Aerobic Glycolysis of Esophageal Cancer Cells via PKM2 Signaling - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6830105/#:~:text=The%20vacuolar%20H%5E%7B%2B%7D,uptake%20and%20decreased%20lactate%20and')
73. AnnotationURLCitation(end_index=28580, start_index=28473, title='Impaired TFEB-mediated autophagy-lysosome fusion promotes tubular cell cycle G2/M arrest and renal fibrosis by suppressing ATP6V0C expression and interacting with SNAREs - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10929200/#:~:text=Impaired%20TFEB,Google')
74. AnnotationURLCitation(end_index=29502, start_index=29352, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=identified%20unexpected%20roles%20for%20V,enoxacin%20have%20proven')
75. AnnotationURLCitation(end_index=29660, start_index=29503, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=are%20two%20molecules%20that%20emerged,prove%20useful%20in%20the%20clinic')
76. AnnotationURLCitation(end_index=30149, start_index=30009, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=efforts%20to%20identify%20small%20molecule,ATPases%20may')
77. AnnotationURLCitation(end_index=30557, start_index=30417, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=include%20acidifying%20an%20extracellular%20resorption,9')
78. AnnotationURLCitation(end_index=30692, start_index=30558, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=for%20loading%20neurotransmitters%20in%20neurons,6')
79. AnnotationURLCitation(end_index=31528, start_index=31426, title='ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/#:~:text=,Google%20Scholar')
80. AnnotationURLCitation(end_index=32089, start_index=31957, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=match%20at%20L1164%20Zhang%20Y,Google%20Scholar')
81. AnnotationURLCitation(end_index=32257, start_index=32090, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=match%20at%20L1169%20Liang%20M,1.%20%5BDOI%5D%20%5BPubMed%5D%20%5BGoogle%20Scholar')
82. AnnotationURLCitation(end_index=32773, start_index=32622, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=Vacuolar%20H%5E%7B%2B%7D,nutrient%20and%20energy%20sensing%2C%20and')
83. AnnotationURLCitation(end_index=32940, start_index=32774, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=identified%20unexpected%20roles%20for%20V,which%20relates%20to%20the%20specialized')
84. AnnotationURLCitation(end_index=34175, start_index=33994, title='V-ATPase Dysfunction in the Brain: Genetic Insights and Therapeutic Opportunities - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC11393946/#:~:text=Catabolic%20processes%2C%20such%20as%20endocytic,genetic%20and%20functional%20evidence%20linking')
85. AnnotationURLCitation(end_index=34327, start_index=34176, title='Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6448788/#:~:text=Vacuolar%20H%5E%7B%2B%7D,nutrient%20and%20energy%20sensing%2C%20and')

ATP6V0C: The Essential Proteolipid Subunit of Vacuolar H+-ATPase and Its Role in Cellular Acidification and Homeostasis

Summary

ATP6V0C, encoding the 16 kilodalton proteolipid subunit c of the vacuolar H+-ATPase (V-ATPase) complex, represents a critical component of the cellular proton pumping machinery with profound implications for organellar acidification, membrane trafficking, metabolic regulation, and neurological function[2][7]. Located on human chromosome 16p13.3, this three-exon gene encodes a 155 amino acid transmembrane protein that forms the essential catalytic core of the V-ATPase's integral V0 domain, serving as the primary proton-conducting pore through which H+ ions traverse cellular membranes[2][7]. The ATP6V0C subunit functions as a critical element of the c-ring structure within the V0 domain, a rotary mechanism that converts ATP hydrolysis energy into an electrochemical gradient for proton translocation across lysosomal, endosomal, and synaptic vesicle membranes[2][3]. Beyond its canonical role in organelle acidification, ATP6V0C participates in diverse cellular processes including autophagy regulation, metabolic sensing through mTORC1 signaling, cancer cell invasiveness and metastasis, and neurotransmitter loading in synaptic vesicles[5][12][15]. Recent discoveries linking ATP6V0C variants to neurodevelopmental disorders characterized by early-onset epilepsy, developmental delay, and intellectual disability have firmly established this gene as an important human disease locus[2][31][34], while emerging evidence reveals its unexpected roles in metabolic adaptation, viral pathogenesis, and tumor microenvironment acidification[5][28][45]. This comprehensive report explores the structure, function, regulation, and disease relevance of ATP6V0C, integrating biochemical, cellular, and genetic evidence to illuminate this essential component of the cellular proton pump.

Structural Architecture and Positioning Within the V-ATPase Complex

The vacuolar H+-ATPase represents one of the most complex and highly conserved molecular machines in eukaryotic biology, comprising two functionally and structurally distinct domains: the peripheral V1 domain responsible for ATP hydrolysis and catalysis, and the integral V0 domain accountable for proton translocation across biological membranes[2][6][41]. The ATP6V0C subunit occupies a uniquely critical position within this complex architecture as a core component of the proteolipid ring structure of the V0 domain, which forms the rotary axis essential for the enzyme's function[3][8][20]. The human V-ATPase comprises thirteen distinct subunits in total, encoded by twenty-three different genes, with this genetic redundancy permitting the assembly of tissue-specific V-ATPase isoforms adapted to particular cellular compartments and physiological requirements[2][7]. The V0 domain itself consists of six different subunits designated a, c, c', c'', d, and e, with ATP6V0C encoding the major c-subunit, which polymerizes with ATP6V0B (encoding the c'' subunit) to form the functional proteolipid ring[2][3][41].

The molecular architecture of the c-ring demonstrates remarkable structural organization, with the archetypal composition consisting of nine copies of the ATP6V0C c-subunit together with a single copy of the ATP6V0B c'' subunit, forming a ten-membered ring structure embedded within the lipid bilayer[3][8][20]. This particular stoichiometry appears to be conserved across mammalian systems, though some variation exists among different organisms and cellular contexts[3][20][32]. Each ATP6V0C subunit possesses four transmembrane helical domains and contains a buried glutamic acid residue at position 139 (p.E139) that proves absolutely critical for the proton translocation mechanism[2][7][8][20]. This conserved glutamic acid undergoes sequential protonation and deprotonation cycles during proton transport, accepting protons from the cytoplasmic hemichannel and releasing them into the luminal hemichannel through conformational coupling with the subunit a protein of the V0 domain[8][20][41]. The critical importance of this residue becomes evident from the observation that point mutations such as p.E139A completely abolish V-ATPase activity[10]. The transmembrane topology of ATP6V0C places its N and C termini on the luminal side of the membrane, with the four transmembrane domains arranged to orient the proton-translocating glutamic acid in an optimal position for interacting with the arginine residue (p.R735) in the ATP6V0A subunit that serves as the essential counterpart in the proton translocation mechanism[2][7][8].

Recent structural studies employing high-resolution cryo-electron microscopy have begun to illuminate the precise three-dimensional organization and conformational dynamics of the ATP6V0C-containing V-ATPase complex[47][56]. The c-ring structure, including ATP6V0C, sits immediately adjacent to the subunit a protein, with which it forms the actual proton-conducting pathway through its rotation during catalytic turnover[8][41]. The arrangement of the proteolipid subunits around the ring appears to be highly organized and functionally optimized, with the placement of ATP6V0C relative to ATP6V0B (c'') and other c subunits critically determining proper assembly and function[3][8]. Structural modeling suggests that transmembrane domain 4 of ATP6V0C maintains critical spatial proximity to transmembrane domain 2 of ATP6V0B, suggesting that the interaction between these adjacent subunits plays an important role in stabilizing the ring structure and positioning the proton-translocating residues appropriately[8][10][20]. Furthermore, the proteolipid ring exists in dynamic rotational states during catalytic turnover, with recent cryo-EM studies revealing that ATP6V0C and its ring partners adopt distinct conformational states depending on whether the complex is actively translocating protons or in a resting state[38][47][56].

Molecular Mechanism of Proton Translocation and Rotary Catalysis

The ATP6V0C-containing V-ATPase operates through an elegant rotary mechanism fundamentally distinct from other proton pumps, in which ATP hydrolysis in the V1 domain drives mechanical rotation of the c-ring composed of ATP6V0C and other proteolipid subunits relative to the stationary subunit a within the V0 domain[2][13][41][45]. This rotary mechanism represents one of the most remarkable examples of biological energy transduction, directly coupling chemical energy from ATP hydrolysis to mechanical work and ultimately to electrochemical gradient establishment[13][41][47]. The mechanistic details of this process have been elucidated through a combination of biochemical characterization, single-molecule rotation experiments in both yeast and mammalian systems, and increasingly high-resolution structural determination by cryo-EM approaches[13][47][56]. Understanding the precise role of ATP6V0C within this mechanical framework requires careful consideration of how its structural features enable and facilitate proton movement during rotary catalysis.

The proton translocation pathway itself comprises two critical hemichannels, one facing the cytoplasmic side of the membrane and one facing the luminal side, both formed through interactions between the subunit a protein and the rotating c-ring containing ATP6V0C[8][17][41]. As the c-ring rotates, the buried glutamic acid residues of ATP6V0C and its partner proteolipid subunits sequentially come into alignment with these hemichannels, enabling stepwise proton binding, movement, and release[8][17][20][41]. The process begins when a proton enters the cytoplasmic hemichannel and binds to the glutamic acid of an ATP6V0C molecule as it passes through the channel; the protonated carboxyl group remains attached to the subunit as the ring rotates because of the hydrophobic environment of the lipid bilayer, which prevents deprotonation[8][41]. As continued rotation brings the protonated ATP6V0C molecule toward the luminal hemichannel, it encounters a critical conserved arginine residue (p.R735) within subunit a that stabilizes the glutamic acid in its charged form, promoting deprotonation and release of the proton into the luminal hemichannel[8][17][41]. The continued rotation then positions the now-deprotonated ATP6V0C glutamic acid back toward the cytoplasmic hemichannel, where it becomes available for rebinding another proton[8][17][41].

The stoichiometry of proton translocation relative to ATP hydrolysis represents a fundamental parameter determining the energetic efficiency of the pump and the magnitude of the electrochemical gradient it can establish[13][32][47]. Studies of V-ATPase and its F-ATPase relatives have demonstrated that the number of ATP molecules hydrolyzed per complete rotation of the c-ring correlates with the stoichiometry of the ring structure itself[32][47]. For the ten-membered c-ring typical of mammalian V-ATPases (containing nine ATP6V0C subunits plus one ATP6V0B subunit), the enzyme typically translocates approximately ten protons per three ATP molecules hydrolyzed, which corresponds to one complete rotation of the c-ring per three ATP hydrolysis events in the V1 domain[13][47]. This represents a remarkably efficient energy conversion, with each ATP hydrolysis event driving a 120-degree rotation of the rotor complex and translocating multiple protons across the membrane[13][47].

The ATP6V0C subunit also plays a crucial role in determining the mechanical properties of the c-ring rotation, as the glutamic acid residue and the overall hydrophobic environment of the transmembrane domains influence both the proton binding affinity and the mechanical torque generated during rotation[8][20]. The four transmembrane helical domains of ATP6V0C create a steric and electrostatic environment essential for properly orienting the proton-translocating glutamic acid and positioning it for optimal interaction with the subunit a arginine residue[8][20]. Moreover, the relative arrangement of ATP6V0C within the ring structure places certain spacing constraints on how the protonatable residues are distributed around the ring circumference, which appears to coordinate the timing of proton binding and release with mechanical rotation[3][8][20].

Cellular Localization, Tissue Distribution, and Organellar Targeting

The ATP6V0C subunit, as an integral component of the V0 domain, participates in the targeting and localization of the entire V-ATPase complex to specific cellular compartments, and its expression patterns vary across tissues reflecting the distinct acidification requirements of different cell types and organelles[2][5][15][22]. In most mammalian cells, V-ATPases containing ATP6V0C localize predominantly to intracellular compartments including lysosomes, endosomes, secretory vesicles, and Golgi-derived transport vesicles, where they perform the essential function of maintaining an acidic microenvironment necessary for proper organellar function[5][15][18]. Within neurons, ATP6V0C becomes particularly enriched in synaptic vesicles, where V-ATPases create the proton electrochemical gradient essential for the antiporter-mediated loading of neurotransmitters into these compartments[2][18][44]. The targeting of ATP6V0C-containing V-ATPases to these specific organelles occurs through a complex process involving tissue-specific isoforms of the subunit a protein (ATP6V0A1, ATP6V0A2, ATP6V0A4) that determine subcellular localization[15][17].

Beyond its canonical intracellular localization, ATP6V0C can localize to the plasma membrane in certain cell types under specific physiological conditions, where it participates in extracellular acidification and other plasma membrane-related functions[15][28][37][46]. In osteoclasts, plasma membrane V-ATPases containing ATP6V0C contribute to the acidification of the resorption lacunae beneath bone-resorbing cells, enabling the demineralization of bone matrix[15]. Similarly, in renal intercalated cells and epididymal clear cells, ATP6V0C-containing V-ATPases traffick to the apical plasma membrane in response to physiological signals regulating acid-base balance and sperm maturation[15][17]. The regulation of plasma membrane trafficking of ATP6V0C-containing complexes involves intricate signaling mechanisms including PKA-mediated phosphorylation, AMPK-dependent modulation, and bicarbonate-sensing pathways, allowing these specialized cells to rapidly adjust V-ATPase localization in response to changing metabolic and acid-base conditions[17][48].

Recent evidence indicates that ATP6V0C expression levels and localization also respond to nutrient availability and metabolic status, suggesting an adaptive mechanism whereby cells modulate proton pumping capacity in response to changing energetic demands[24][45][54]. In cancer cells, increased ATP6V0C expression and enhanced targeting to both intracellular acidic compartments and the plasma membrane support the elevated metabolic demands and invasive phenotype characteristic of malignant transformation[5][25][37][45][51]. The availability of tissue-specific isoforms of interacting subunits, along with post-translational modifications of ATP6V0C itself, provides multiple levels of regulation enabling cells to adjust V-ATPase function and localization to match specific cellular contexts and physiological demands.

Functional Roles in Lysosomal Acidification and Autophagy Regulation

The primary function of ATP6V0C within the context of cellular physiology centers on its absolutely essential role in maintaining the highly acidic pH of lysosomes, typically maintained at pH 4.5-5.0, which proves critical for the activity of the entire complement of lysosomal hydrolytic enzymes including proteases, nucleases, and lipases[5][12][15][43]. The broad majority of lysosomal enzymes exhibit optimal catalytic activity in this acidic pH range, with many requiring pH below 5.0 for efficient substrate hydrolysis[43]. ATP6V0C, as the core proton-conducting component of the lysosomal V-ATPase, directly enables this acidification through its role in the rotary proton pump mechanism[5][12][15][43]. The functional importance of this activity becomes starkly evident in cells in which ATP6V0C function has been disrupted, where impaired lysosomal acidification results in dramatic accumulation of undigested autophagic substrates, reduced hydrolytic enzyme activity, and compromised cellular homeostasis[5][12][21].

Beyond simple acidification, ATP6V0C participates critically in the broader process of autophagy, one of the most important cellular catabolic pathways for recycling damaged organelles and proteins[5][12][15]. During macroautophagy, cellular components become enclosed within double-membraned autophagosomes, which subsequently fuse with lysosomes to form autolysosomes where the enclosed contents are degraded[5][15][21]. The ATP6V0C-dependent acidification of autolysosomes proves essential not only for providing the optimal pH for hydrolase activity but also for proper regulation of the autophagic process itself[5][12][21][24]. Recent research has revealed that ATP6V0C participates in more nuanced roles within the autophagy-lysosome pathway beyond simple pH maintenance, including direct scaffolding functions that facilitate autophagosome-lysosome fusion[54]. In a striking demonstration of these scaffolding functions, ATP6V0C was shown to bridge key SNARE proteins (STX17 and VAMP8) essential for membrane fusion between autophagosomes and lysosomes, with this function appearing separable from the acidification-dependent aspects of ATP6V0C activity[54].

The regulation of autophagy itself appears intimately connected to ATP6V0C function and V-ATPase assembly status, with the enzyme serving as a key nexus point for nutrient sensing and metabolic regulation[15][24][43]. Under conditions of nutrient abundance, particularly high amino acid availability, the V-ATPase complex (including ATP6V0C) experiences a regulatory dissociation whereby the V1 and V0 domains separate, reducing proton pumping activity and in turn modulating autophagy[15][24][43]. This dissociation mechanism allows cells to fine-tune autophagy flux in response to nutrient availability, conserving energy during periods of metabolic sufficiency while maintaining active degradative capacity during nutrient scarcity[15][24][43]. The precise molecular mechanisms coordinating ATP6V0C-dependent lysosomal acidification with these regulatory dissociation events remain incompletely understood but clearly represent a critical nexus for metabolic homeostasis.

Regulation of mTORC1 Signaling and Metabolic Sensing

Beyond its direct role in lysosmal acidification, ATP6V0C functions as a critical component of the cellular nutrient-sensing machinery, particularly through its involvement in amino acid-dependent activation of the mechanistic target of rapamycin complex 1 (mTORC1), a master regulator of anabolic metabolism and autophagy[15][17][24]. The V-ATPase, including its ATP6V0C component, localizes to the lysosomal membrane where it assembles into a signaling complex with mTORC1 and its upstream regulators, collectively termed the "lysosomal signaling hub"[15][24]. In this context, V-ATPase-dependent lysosomal acidification and perhaps more importantly the assembly status of the V-ATPase complex itself, contributes to the regulation of mTORC1 localization and activity in response to amino acid availability[15][24]. When amino acids become available intracellularly, through either exogenous uptake or from lysosomal degradation products, mTORC1 becomes activated and phosphorylates downstream targets including ULK1, suppressing autophagy initiation[15][24].

The relationship between ATP6V0C function and mTORC1 regulation appears more complex than previously recognized, as disruption of V-ATPase function can paradoxically activate certain aspects of mTORC1 signaling despite impairing amino acid uptake[24]. Studies employing genetic approaches to selectively disrupt V-ATPase assembly have demonstrated that loss of functional V-ATPase, including ATP6V0C, does not simply suppress mTORC1 activity as would be predicted from a simple nutrient starvation response[24]. Instead, the loss of V-ATPase leads to altered patterns of mTORC1 phosphorylation at different substrate sites, suggesting that V-ATPase regulates multiple upstream nodes of mTORC1 signaling[24]. This complexity likely reflects the fact that V-ATPase participates in both direct amino acid sensing through the KICSTOR and other protein complexes and indirect effects on amino acid availability through lysosomal degradation and nutrient absorption[15][24].

ATP6V0C also participates in the regulation of AMPK (AMP-activated protein kinase), another critical metabolic sensor that responds to energy depletion, through mechanisms that remain not fully characterized but that likely involve pH-dependent effects and the assembly status of the V-ATPase complex[15][46][57]. AMPK antagonizes mTORC1 signaling and promotes catabolic processes including autophagy, making the interplay between V-ATPase-dependent mTORC1 and AMPK signaling central to metabolic adaptation[15][24][46]. The ability of cells to sense nutrient availability and energy status through ATP6V0C-dependent mechanisms represents one of the critical homeostatic functions of this subunit beyond simple proton pumping.

Post-Translational Regulation and V-ATPase Assembly

ATP6V0C, as an integral membrane protein component of the V-ATPase, undergoes multiple layers of post-translational regulation affecting its synthesis, assembly, trafficking, and stability, all of which modulate V-ATPase function in response to cellular demands[38][56][57]. The assembly of the V0 domain containing ATP6V0C occurs in the endoplasmic reticulum and requires specialized chaperone proteins including Vma12p, Vma21p, and Vma22p in yeast systems, with mammalian homologs playing analogous roles[38][56][59]. These dedicated assembly factors facilitate the proper folding of ATP6V0C, ensure its correct integration into the growing c-ring structure, and importantly mediate quality control mechanisms to prevent misfolded or partially assembled V-ATPases from reaching cellular acidic compartments where inappropriate proton pumping could prove detrimental[38][56]. The interaction between ATP6V0C and these assembly factors appears highly regulated, with the chaperones dissociating from assembled V0 only after productive complex formation and perhaps following subsequent assembly with the V1 domain[38][56][59].

The reversible association and dissociation of the V1 and V0 domains, with ATP6V0C remaining as a component of the membrane-bound V0, represents a critical regulatory mechanism whereby cells rapidly modulate V-ATPase activity in response to nutrient availability and metabolic status[15][43][57]. During glucose deprivation in yeast, approximately 70% of V-ATPase complexes rapidly dissociate into their component domains, reducing proton pumping and conserving ATP[15][43][57]. In mammalian systems, glucose starvation paradoxically appears to enhance V-ATPase assembly through AMPK and PI3K/Akt signaling mechanisms, suggesting distinct regulatory logic in different cell types and metabolic contexts[15][57]. The dissociation and reassembly of V1/V0 complexes occurs through mechanisms involving the release and reuptake of the regulatory V1C subunit, which plays a central coordinating role in mediating the V1-V0 interaction[15][43][57].

Beyond gross assembly and disassembly, ATP6V0C undergoes site-specific post-translational modifications including phosphorylation, ubiquitination, and glycosylation, all of which appear to modulate its function and stability[57]. The glycosylation of ATP6V0C and associated subunits affects both the assembly of the V-ATPase and its trafficking to appropriate cellular destinations, with disruptions in glycosylation impairing V-ATPase localization to lysosomes[57]. Ubiquitination of ATP6V0C, mediated by specific E3 ubiquitin ligases including RNF182, targets the protein for proteasomal degradation, providing a mechanism for adjusting V-ATPase abundance in response to cellular signals[19]. The identification of RNF182 as an ATP6V0C-targeting E3 ligase has suggested a role for dynamic regulation of V-ATPase levels in neuronal physiology, as RNF182 itself shows upregulation in Alzheimer's disease brain tissue[19]. Phosphorylation of ATP6V0C and associated V-ATPase subunits by PKA modulates the trafficking of V-ATPase-containing vesicles and the recruitment of the complex to the plasma membrane in specialized cells such as renal intercalated cells[15][17][48].

Pathogenic ATP6V0C Variants and Neurodevelopmental Disease

The discovery that heterozygous point mutations in ATP6V0C cause a previously unrecognized neurodevelopmental syndrome represents one of the most significant recent contributions to understanding this gene's importance in human health and disease[2][31][34]. In 2023, Mattison and colleagues published a landmark study describing twenty-seven patients carrying heterozygous missense variants in ATP6V0C who presented with a remarkably consistent clinical phenotype characterized by developmental delay, early-onset epilepsy, and intellectual disability[2][31][34]. The clinical presentation of this novel ATP6V0C-associated neurodevelopmental disorder demonstrates striking consistency across multiple unrelated families and populations, with developmental delay evident from infancy or early childhood, seizures typically manifesting within the first two years of life, and intellectual disability ranging from mild to severe[2][31][34]. Additional neurological features reported in the ATP6V0C variant cohort include corpus callosum hypoplasia and cardiac abnormalities in some affected individuals, suggesting broader developmental consequences of impaired V-ATPase function[2][31].

The genetic variants identified in affected patients predominantly clustered within transmembrane domains, with a remarkable enrichment observed within the fourth transmembrane domain of ATP6V0C[2][10]. This specific enrichment within TM4, which participates in interactions with the ATP6V0A subunit during proton translocation, suggested that the patient variants specifically disrupt the critical interaction between ATP6V0C and ATP6V0A necessary for proper proton pumping[2][10]. In silico modeling studies examining the structural consequences of patient variants predicted that these mutations would significantly impair the precise geometric relationship between the glutamic acid of ATP6V0C (p.E139) and the arginine of ATP6V0A (p.R735) that mediates proton release during the rotation cycle[2][10]. These computational predictions proved highly consistent with subsequent functional studies.

The functional consequences of patient variants were validated through multiple experimental approaches employing yeast, fly, and worm models, demonstrating the convergent evidence for pathogenicity and mechanism[2][31]. In Saccharomyces cerevisiae, patient variants were tested using complementation of yeast vma3Δ mutants (vma3 being the yeast ortholog of ATP6V0C), with the assays measuring both proton pumping capacity through LysoSensor fluorescence and indirect growth assessments on high-osmolarity media requiring functional V-ATPase[2][10]. The majority of patient variants exhibited substantially reduced LysoSensor fluorescence signal, indicating impaired proton translocation, and many showed reduced growth in high salt media, confirming that these variants produce dysfunctional V-ATPases[2][10]. In Drosophila melanogaster, pan-neuronal knockdown of the ATP6V0C ortholog (Vha16-3) resulted in increased duration of seizure-like behavior evoked by neural stimulation, directly demonstrating a link between ATP6V0C loss of function and seizure predisposition[2][31][42]. In Caenorhabditis elegans, expression of selected patient variants led to observable motor dysfunction, reduced growth, and shortened lifespan, indicating organism-level consequences of impaired ATP6V0C function[2][31].

The molecular mechanism underlying the neurodevelopmental phenotype in patients with ATP6V0C variants likely centers on the critical importance of V-ATPase function in synaptic vesicle acidification and neurotransmitter loading[2][18][31]. Synaptic vesicles depend absolutely on V-ATPase-generated proton gradients to load classical neurotransmitters including acetylcholine, glutamate, GABA, and monoamines through vesicular monoamine transporters and other H+-coupled antiporters[2][18][44]. Any impairment in ATP6V0C function would predictably reduce synaptic vesicle acidification, compromise neurotransmitter loading, and ultimately impair synaptic transmission, providing a plausible mechanistic basis for both the seizure phenotype and broader neurological dysfunction[2][18][31][44]. The seizure susceptibility may additionally relate to potential effects on GABAergic inhibitory neurotransmission, which depends critically on proper GABA loading into synaptic vesicles[2][31]. Furthermore, the broader intellectual disability phenotype might reflect more widespread effects of impaired V-ATPase function on dendritic spine development, synaptic plasticity, and circuit formation, processes all dependent on proper vesicular trafficking and acidification[2][31][34].

ATP6V0C in Cancer and the Tumor Microenvironment

ATP6V0C has emerged as an important mediator of cancer cell biology, with elevated expression and altered regulation of this subunit contributing to multiple hallmarks of malignant transformation including enhanced invasiveness, increased metastatic potential, metabolic reprogramming, and chemoresistance[5][25][37][45][46][51]. The role of ATP6V0C in cancer appears multifaceted, reflecting both the intrinsic metabolic requirements of rapidly proliferating tumor cells and their specific adaptations to hostile microenvironments characterized by hypoxia, nutrient limitation, and immune surveillance[5][25][28][45][46]. In numerous cancer types, elevated ATP6V0C expression correlates directly with invasiveness and metastatic potential, with particularly striking evidence emerging from prostate cancer studies demonstrating that highly metastatic prostate cancer cell lines express substantially higher levels of ATP6V0C protein compared to non-metastatic counterparts[37]. This expression correlation suggests a specific selective pressure favoring ATP6V0C upregulation during the process of malignant progression and metastatic dissemination.

The enhanced invasiveness imparted by elevated ATP6V0C expression operates through multiple interconnected mechanisms, with one particularly important pathway involving extracellular acidification and the degradation of extracellular matrix[5][25][37][46][51]. Tumor cells depend critically on maintaining relatively alkaline intracellular pH despite high rates of glycolytic metabolism that generates substantial intracellular acid; they achieve this through enhanced ATP6V0C-dependent proton extrusion to the extracellular space[5][25][46][51]. This extracellular acidification activates matrix metalloproteinases and other proteolytic enzymes that degrade and remodel the extracellular matrix, facilitating tumor cell invasion and dissemination[5][25][37]. Knockdown or inhibition of ATP6V0C in highly invasive cancer cell lines substantially reduces both the activity of secreted matrix metalloproteinases (particularly MMP-2 and MMP-9) and the invasive and migratory capacity of these cells, establishing a functional link between ATP6V0C expression and the invasive phenotype[37][46][51]. Moreover, the interaction between ATP6V0C and tumor metastasis suppressor proteins such as LASS2/TMSG1 appears to regulate V-ATPase activity with direct consequences for tumor cell behavior[5][37]. Silencing of ATP6V0C specifically inhibits prostate cancer cell invasion through mechanisms that appear to operate at least partially through LASS2/TMSG1-independent pathways, suggesting that ATP6V0C controls invasion through multiple regulatory nodes[37].

Beyond its effects on matrix degradation and invasion, ATP6V0C participates in cancer cell metabolic reprogramming, particularly in the context of aerobic glycolysis and the Warburg effect[45][46][51]. In esophageal cancer cells, ATP6V0C directly interacts with pyruvate kinase isoform M2 (PKM2), a key glycolytic enzyme and known regulator of cancer metabolism[45][51]. The ATP6V0C-PKM2 interaction promotes PKM2 phosphorylation at tyrosine 105, an important post-translational modification that enhances PKM2 dimer formation and nuclear translocation[45][51]. Nuclear PKM2 functions as a transcriptional coactivator, enhancing the expression of hypoxia-inducible factor 1 (HIF-1) target genes involved in glycolytic enzyme expression and metabolism[45][51]. This ATP6V0C-PKM2-HIF-1 axis directly enhances the expression of critical glycolytic enzymes including hexokinase 2 (HK2), phosphofructokinase-1 (PFK1), enolase 1 (ENO1), and lactate dehydrogenase A (LDHA), with depletion of ATP6V0C reducing the expression of this entire cohort of glycolytic genes and substantially impairing glucose metabolism[45][51]. These metabolic effects of ATP6V0C depletion directly impact cancer cell proliferation and survival, as the reduction in glucose metabolism and ATP production creates a state of bioenergetic insufficiency that triggers multiple pro-apoptotic pathways[45][51].

ATP6V0C also participates in chemoresistance of cancer cells through its role in intracellular pH homeostasis and the sequestration of chemotherapeutic agents into acidic compartments[5][25]. Many chemotherapeutic drugs, particularly weak base compounds, become preferentially accumulated in acidic intracellular vesicles such as lysosomes and endosomes through pH-dependent trapping mechanisms[5][25]. Tumor cells with enhanced ATP6V0C expression and elevated V-ATPase activity maintain more acidic intracellular vesicles, promoting sequestration of weak base chemotherapeutic agents away from their nuclear and cytoplasmic targets, thereby conferring chemoresistance[5][25]. Moreover, elevated V-ATPase activity supports the high energy demands required for active drug efflux through multidrug resistance transporters, further contributing to chemoresistance[5][25].

The role of ATP6V0C in the acidic tumor microenvironment has become increasingly recognized as a critical component of immune evasion and therapeutic resistance[28][46]. Extracellular acidification, driven substantially by ATP6V0C-dependent V-ATPase activity at the plasma membrane of tumor cells and supporting cells within the tumor stroma, profoundly inhibits anti-tumor immune responses[28]. Acidic pH in the tumor microenvironment directly impairs the function of infiltrating T cells, suppressing their proliferation, cytokine production, and cytotoxic activity[28]. Additionally, the acidic tumor microenvironment favors differentiation of tumor-associated macrophages toward the pro-tumorigenic M2 phenotype, which promotes tumor growth and inhibits immune responses[28]. Remarkably, pharmacological strategies to increase tumor microenvironment pH, including treatment with sodium bicarbonate, have shown promise in enhancing T cell infiltration and improving immune checkpoint inhibitor efficacy in preclinical models[28]. These observations raise the possibility that ATP6V0C inhibition or modulation might represent a strategy to normalize tumor microenvironment pH and enhance immunotherapy efficacy.

Interactions with Bacterial and Viral Pathogens

ATP6V0C has emerged as an unexpected target of multiple pathogenic microorganisms that have evolved mechanisms to manipulate or exploit V-ATPase function to facilitate their pathogenic strategies[5][9][26][27][29]. The bacterial pathogen Vibrio parahaemolyticus, a causative agent of acute gastroenteritis and septicemia, produces a type III secretion effector protein designated VepA that directly targets ATP6V0C to trigger lysosomal membrane permeabilization and host cell death[5][26][29]. Mechanistic studies have demonstrated that VepA specifically binds to ATP6V0C and through this interaction induces rupture of lysosomal membranes, releasing lysosomal contents including proteolytic enzymes into the cytoplasm and triggering caspase-independent cell death[26][29]. This mechanism appears to represent a virulence strategy whereby the pathogen directly triggers host cell death, potentially facilitating bacterial escape and dissemination from infected cells[26][29]. The identification of ATP6V0C as the specific cellular target of VepA reveals an unexpected vulnerability of the host cell to bacterial manipulation of V-ATPase function and suggests that variations in ATP6V0C expression or function might influence individual susceptibility to Vibrio parahaemolyticus infection[26][29].

The human immunodeficiency virus (HIV-1) has also been shown to manipulate ATP6V0C-dependent V-ATPase function through multiple mechanisms, particularly through the viral accessory protein Vpu[5][9][27]. Vpu promotes the degradation of tetherin (also known as BST-2), a cellular restriction factor that inhibits the release of HIV-1 virions from infected cells by tethering nascent virions to the cell surface[5][9][27]. The mechanism by which Vpu-mediated tetherin degradation depends on ATP6V0C involves the sequestration of tetherin in acidic endosomal and lysosomal compartments, where it becomes inaccessible for interaction with viral particles[9][27]. ATP6V0C overexpression has been shown to enhance the sequestration of tetherin in CD63-positive late endosomal and LAMP-1-positive lysosomal compartments, demonstrating a direct role for ATP6V0C in this process[9][27]. Notably, the stabilization of tetherin by ATP6V0C overexpression occurs without inducing general tetherin degradation, suggesting that ATP6V0C facilitates sequestration of tetherin rather than promoting its proteasomal or lysosomal catabolism[9][27]. This requirement for ATP6V0C in HIV-1 replication and Vpu function may represent an exploitable vulnerability of the virus to ATP6V0C inhibition, potentially offering therapeutic strategies to restrict viral replication[9][27].

Beyond direct targeting by pathogenic factors, ATP6V0C and V-ATPase function more broadly participate in critical aspects of host antiviral immunity including autophagy, endosomal acidification, and presentation of pathogen-associated antigens through major histocompatibility complex pathways[5]. Many viruses have evolved sophisticated mechanisms to antagonize V-ATPase function to evade host immune responses, suggesting that ATP6V0C represents a critical nexus point where host and viral pathogenic strategies intersect[5][9]. The targeting of ATP6V0C by multiple unrelated pathogens strongly suggests evolutionary conservation of this vulnerability and highlights ATP6V0C as an important emerging therapeutic target for infectious disease.

Conclusion and Future Perspectives

ATP6V0C, the 16 kilodalton proteolipid subunit of the vacuolar H+-ATPase V0 domain, emerges from contemporary research as an essential component of cellular homeostasis with ramifications extending far beyond its canonical role in organellar acidification. The fundamental function of ATP6V0C—serving as the proton-translocating core of the V-ATPase rotary mechanism—depends critically on its specific structural features, particularly the conserved glutamic acid at position 139 that undergoes reversible protonation and deprotonation during the mechanical rotation of the c-ring. Yet this basic bioenergetic function serves as the foundation for extraordinarily diverse cellular processes including autophagy regulation, metabolic sensing through mTORC1 and AMPK signaling, synaptic vesicle neurotransmitter loading, and intracellular pH homeostasis[2][5][12][15][18][21][45]. The discovery that heterozygous ATP6V0C variants cause a neurodevelopmental syndrome characterized by early-onset epilepsy and intellectual disability has firmly established this gene as an important human disease locus and revealed the critical importance of V-ATPase function in neurological development and function[2][31][34].

The emerging roles of ATP6V0C in cancer biology present both a challenge and an opportunity, as the heightened expression and activity of ATP6V0C in malignant cells contributes to invasiveness, metastatic potential, and therapeutic resistance through multiple mechanisms including extracellular acidification, metabolic reprogramming, and creation of an immunosuppressive tumor microenvironment[5][25][28][37][45][46]. The manipulation of ATP6V0C and V-ATPase function by pathogenic bacteria and viruses, including the deadly pathogen Vibrio parahaemolyticus and the pandemic pathogen HIV-1, underscores the critical vulnerabilities created by dependence on ATP6V0C function for essential cellular processes[5][9][26][27][29]. These diverse roles of ATP6V0C across physiological and pathological contexts position this protein as a particularly promising target for therapeutic intervention in multiple disease states, from neurodevelopmental disorders and epilepsy to cancer, infectious disease, and age-related neurodegeneration.

Future research directions should prioritize deeper mechanistic understanding of how ATP6V0C variants impair V-ATPase function at the molecular level and how such impaired function translates into the observed neurodevelopmental phenotypes. The emerging understanding of ATP6V0C's role in metabolic signaling through mTORC1 and AMPK presents opportunities to understand how altered V-ATPase function might perturb metabolic homeostasis with consequences for neurodevelopment and cancer progression. The identification of ATP6V0C as a target of pathogenic factors merits continued investigation into the molecular details of these interactions and the potential for targeting ATP6V0C or its interactions as anti-infective strategies. Finally, the possibility that selective modulation of ATP6V0C function or ATP6V0C-interacting partner proteins might enable therapeutic enhancement of immune responses against cancer or infectious pathogens represents an intriguing therapeutic avenue warranting clinical investigation.

References Cited

[2] Mattison et al. Brain, 2023; ATP6V0C variants impair V-ATPase function causing a neurodevelopmental disorder often associated with epilepsy

[3] Arrangement of subunits in the proteolipid ring of the V-ATPase, PMC2394185

[5] ATP6V0C Gene - Ma'ayan Lab, Computational Systems Biology

[7] ATP6V0C variants impair V-ATPase function, PMC10319782

[8] Arrangement of subunits in the proteolipid ring, PMC2394185

[9] The viral protein U (Vpu)-interacting host protein ATP6V0C, PMC7247306

[10] ATP6V0C variants functional studies, PDF document

[12] ATP6V0C Gene - Ma'ayan Lab summary

[13] Rotary mechanism of V/A-ATPases, PMC10166205

[15] Regulation and function of V-ATPases, PMC7508768

[17] Vacuolar ATPase as therapeutic target, PMC6089187

[18] The vesicular ATPase: A missing link, Rupress JCB

[19] A novel brain-enriched E3 ubiquitin ligase RNF182, PMC2279130

[21] ATP6V0C Gene - summary

[24] Disruption of vacuolar H+-ATPase complex in liver, PMC5388235

[25] ATP6V0C Gene - Ma'ayan Lab

[26] A Cytotoxic Type III Secretion Effector, PLOS Pathogens

[27] The viral protein U (Vpu)-interacting host protein, PubMed

[28] Emerging Role of Extracellular pH in Tumor Microenvironment, PMC11592846

[29] A cytotoxic type III secretion effector, PubMed

[31] ATP6V0C variants impair V-ATPase function, Brain 2023

[32] V-ATPase - Wikipedia

[34] ATP6V0C variants impair V-ATPase function, PubMed

[37] Silencing of vacuolar ATPase c subunit ATP6V0C, Spandidos Publications

[38] Structural basis of V-ATPase VO region assembly, PNAS

[41] Structure and Regulation of Vacuolar ATPases, PMC2467516

[42] ATP6V0C variants, Drosophila knockdown studies

[43] Disorders of lysosomal acidification, PMC5112157

[44] Monitoring of vacuolar-type H+ ATPase-mediated proton influx, PubMed

[45] Vacuolar H+-ATPase Subunit V0C Regulates Aerobic Glycolysis, PMC6830105

[46] Vacuolar ATPase as potential therapeutic target, PMC6089187

[47] Structure of V-ATPase from mammalian brain, Science

[48] Role of bicarbonate-responsive soluble adenylyl cyclase, PMC3918592

[51] Vacuolar H+-ATPase Subunit V0C Regulates Aerobic Glycolysis, PMC6830105

[54] Impaired TFEB-mediated autophagy-lysosome fusion, PMC10929200

[56] Structural basis of V-ATPase VO region assembly, PMC9963935

[57] The Emerging Roles of Vacuolar-Type ATPase-Dependent, PMC12024769

Citations

1. https://www.ncbi.nlm.nih.gov/gene/527
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC10319782/
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC2394185/
4. https://www.uniprot.org/uniprotkb/P27449/entry
5. https://maayanlab.cloud/Harmonizome/gene/ATP6V0C
6. https://journals.physiology.org/doi/full/10.1152/physiol.00017.2006?doi=10.1152%2Fphysiol.00017.2006
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC7247306/
8. https://pure.manchester.ac.uk/ws/files/239469826/Mattison_ATP6V0C_AAV.pdf
9. https://en.wikipedia.org/wiki/ATP_synthase_subunit_C
10. https://pmc.ncbi.nlm.nih.gov/articles/PMC10166205/
11. https://pmc.ncbi.nlm.nih.gov/articles/PMC7508768/
12. https://elifesciences.org/articles/56862
13. https://pmc.ncbi.nlm.nih.gov/articles/PMC6089187/
14. https://rupress.org/jcb/article/203/2/171/37551/The-vesicular-ATPase-A-missing-link-between
15. https://pmc.ncbi.nlm.nih.gov/articles/PMC2279130/
16. https://www.proteinatlas.org/ENSG00000185883-ATP6V0C/tissue
17. https://pmc.ncbi.nlm.nih.gov/articles/PMC5388235/
18. https://journals.plos.org/plospathogens/article?id=10.1371%2Fjournal.ppat.1002803
19. https://pubmed.ncbi.nlm.nih.gov/32291285/
20. https://pmc.ncbi.nlm.nih.gov/articles/PMC11592846/
21. https://pubmed.ncbi.nlm.nih.gov/22829766/
22. https://journals.plos.org/plospathogens/article?id=10.1371%2Fjournal.ppat.1000856
23. https://en.wikipedia.org/wiki/V-ATPase
24. https://www.science.org/doi/10.1126/sciadv.adt3778
25. https://pubmed.ncbi.nlm.nih.gov/36074901/
26. https://pmc.ncbi.nlm.nih.gov/articles/PMC2467516/
27. https://www.spandidos-publications.com/10.3892/or.2017.6092
28. https://www.pnas.org/doi/10.1073/pnas.2217181120
29. http://medicalgenomics.md.chula.ac.th/genomics/Publications/203%20Epilepsy%20ATP6V0C%20brainDev%202020.pdf
30. https://pmc.ncbi.nlm.nih.gov/articles/PMC11589881/
31. https://pmc.ncbi.nlm.nih.gov/articles/PMC5112157/
32. https://pubmed.ncbi.nlm.nih.gov/25716867/
33. https://pmc.ncbi.nlm.nih.gov/articles/PMC6830105/
34. https://www.science.org/doi/10.1126/science.aaz2924
35. https://pmc.ncbi.nlm.nih.gov/articles/PMC3918592/
36. https://pmc.ncbi.nlm.nih.gov/articles/PMC3543021/
37. https://lirias.kuleuven.be/retrieve/c156bd35-ff8b-40f1-9e1f-a8a219e73886
38. https://pmc.ncbi.nlm.nih.gov/articles/PMC3973706/
39. https://pmc.ncbi.nlm.nih.gov/articles/PMC10929200/
40. https://journals.plos.org/plospathogens/article/file?id=10.1371%2Fjournal.ppat.1002803&type=printable
41. https://pmc.ncbi.nlm.nih.gov/articles/PMC9963935/
42. https://pmc.ncbi.nlm.nih.gov/articles/PMC12024769/
43. https://pmc.ncbi.nlm.nih.gov/articles/PMC6609633/
44. https://www.molbiolcell.org/doi/10.1091/mbc.e04-06-0514
45. https://pmc.ncbi.nlm.nih.gov/articles/PMC9424811/