ARL8A encodes ADP-ribosylation factor-like protein 8A, an ARF-family small GTPase that associates with lysosomal and late-endosomal membranes in its active GTP-bound state. Together with ARL8B, it organizes endolysosome positioning and microtubule-based motility by engaging BORC-dependent recruitment and effectors such as SKIP/PLEKHM2, PLEKHM1/HOPS, and RUFY3/RUFY4. These interactions support peripheral and juxtanuclear redistribution of lysosomes/endolysosomes, cargo delivery to lysosomes, and specialized neuronal axonal transport of lysosome-related vesicles. ARL8A also has reported tubulin/spindle-midzone associations and chromosome-segregation phenotypes from early GIE studies, but those mitotic observations are secondary to its endolysosomal transport role.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005765 lysosomal membrane | IBA GO_REF:0000033 | ACCEPT | Summary: ARL8A lysosomal membrane localization is a core, well-supported location. Reason: Multiple evidence streams converge on ARL8A/ARL8 proteins as lysosome-associated small GTPases. The original ARL8 study directly showed ARL8A/ARL8B lysosome localization and lysosome motility effects, BORC work places ARL8 recruitment at lysosomal membranes, and lysosomal membrane proteomics is consistent with this localization. Supporting Evidence: PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells PMID:25898167 two paralogs of Arl8 (Arl8a and Arl8b) are the only ones known to associate specifically with lysosomes PMID:35314674 ARL8A and ARL8B paralogs ... are unique in their ability to associate with endolysosomes |
| GO:0008089 anterograde axonal transport | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Anterograde axonal transport is plausible for ARL8-family endolysosomal transport but is a neuron-specific manifestation of the broader lysosome/endolysosome motility role. Reason: ARL8-dependent endolysosome movement has strong support, including kinesin-linked anterograde movement and neuronal axonal contexts. For human ARL8A in the PN review, however, the core function is lysosome/endolysosome localization and motility; axonal anterograde transport should be retained as a specialized neuronal context rather than the central function. Supporting Evidence: PMID:25898167 This initiates a chain of interactions that promotes the kinesin-dependent movement of lysosomes toward the plus ends of microtubules PMID:35314674 ARL8 can thus regulate both anterograde and retrograde endolysosome transport through interactions with kinesin and dynein-dynactin motors PMID:35314674 toward the distal axon in neurons |
| GO:0003924 GTPase activity | IEA GO_REF:0000002 | ACCEPT | Summary: GTPase activity is consistent with ARL8A being an ARF-family small GTPase. Reason: ARL8A is a small GTPase that cycles between GDP-bound and GTP-bound states, and structural/biochemical literature supports nucleotide-bound ARL8 family function. The NAS/IEA evidence is broad but biologically correct for this protein family. Supporting Evidence: PMID:15331635 Here, we identify novel GTPases (human Gie1 and Gie2) that form a distinct subfamily of the small GTPases PMID:35314674 Like other small GTPases, ARL8 cycles between GDP-bound, inactive, and GTP-bound, active forms |
| GO:0005525 GTP binding | IEA GO_REF:0000002 | ACCEPT | Summary: GTP binding is consistent with ARL8A being an ARF-family small GTPase. Reason: ARL8A is a small GTPase that cycles between GDP-bound and GTP-bound states, and structural/biochemical literature supports nucleotide-bound ARL8 family function. The NAS/IEA evidence is broad but biologically correct for this protein family. Supporting Evidence: PMID:15331635 Here, we identify novel GTPases (human Gie1 and Gie2) that form a distinct subfamily of the small GTPases PMID:35314674 Like other small GTPases, ARL8 cycles between GDP-bound, inactive, and GTP-bound, active forms |
| GO:0005765 lysosomal membrane | IEA GO_REF:0000044 | ACCEPT | Summary: ARL8A lysosomal membrane localization is a core, well-supported location. Reason: Multiple evidence streams converge on ARL8A/ARL8 proteins as lysosome-associated small GTPases. The original ARL8 study directly showed ARL8A/ARL8B lysosome localization and lysosome motility effects, BORC work places ARL8 recruitment at lysosomal membranes, and lysosomal membrane proteomics is consistent with this localization. Supporting Evidence: PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells PMID:25898167 two paralogs of Arl8 (Arl8a and Arl8b) are the only ones known to associate specifically with lysosomes PMID:35314674 ARL8A and ARL8B paralogs ... are unique in their ability to associate with endolysosomes |
| GO:0005819 spindle | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: spindle reflects the older GIE/ARL8 mitotic localization study and is not the proteostasis-centered ARL8A role. Reason: The 2004 GIE study supports spindle-midzone/microtubule-associated mitotic localization and chromosome-segregation phenotypes. This appears biologically plausible but is peripheral to the current ARL8A synthesis, where the best-supported function is lysosome/endolysosome localization and motility. Supporting Evidence: PMID:15331635 Gie protein has ability to bind to tubulin and localizes with microtubules on the spindle mid-zone in late mitosis PMID:15331635 Expression of dominant-negative Gie mutants in mammalian cells or knockdown of Gie transcripts using RNA interference in Drosophila S2 cells induced abnormal morphology in the chromosome segregation |
| GO:0015031 protein transport | IEA GO_REF:0000002 | MODIFY | Summary: Generic protein transport is too broad for the ARL8A evidence. Reason: ARL8A regulates lysosome/endolysosome positioning and movement along microtubules rather than protein transport as a generic cargo class. The better process-level assertion is lysosome localization, which captures the positioning/motility role without implying direct protein-cargo transport. Proposed replacements: lysosome localization Supporting Evidence: PMID:16537643 Live cell imaging shows that lysosomes move more frequently both toward and away from the cell periphery PMID:25898167 This initiates a chain of interactions that promotes the kinesin-dependent movement of lysosomes toward the plus ends of microtubules PMID:35314674 ARL8 can thus regulate both anterograde and retrograde endolysosome transport through interactions with kinesin and dynein-dynactin motors |
| GO:0030424 axon | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: axon is a plausible neuronal context for ARL8-family endolysosomal transport but not the core PN function. Reason: ARL8 family studies support neuronal/axonal endolysosome transport contexts, but ARL8A is principally a lysosomal/late-endosomal small GTPase. These neuron-associated locations should not replace the core lysosomal membrane and late endosome membrane locations. Supporting Evidence: PMID:35314674 toward the distal axon in neurons PMID:35314674 RUFY3 and RUFY4 promote retrograde transport of ARL8-positive endolysosomal vesicles from the axon to the soma |
| GO:0031902 late endosome membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Late endosome membrane is a reasonable endolysosomal ARL8A location. Reason: ARL8A/ARL8B are described as endolysosomal GTPases, with the endolysosome term covering lysosomes, late endosomes, and related organelles. This location is consistent with ARL8 effector studies and UniProt-derived late endosome membrane placement. Supporting Evidence: PMID:35314674 endolysosomes broadly to denote various types of lysosomes, late endosomes, and related endolysosomal organelles PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells |
| GO:0045202 synapse | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: synapse is a plausible neuronal context for ARL8-family endolysosomal transport but not the core PN function. Reason: ARL8 family studies support neuronal/axonal endolysosome transport contexts, but ARL8A is principally a lysosomal/late-endosomal small GTPase. These neuron-associated locations should not replace the core lysosomal membrane and late endosome membrane locations. Supporting Evidence: PMID:35314674 toward the distal axon in neurons PMID:35314674 RUFY3 and RUFY4 promote retrograde transport of ARL8-positive endolysosomal vesicles from the axon to the soma |
| GO:0051233 spindle midzone | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: spindle midzone reflects the older GIE/ARL8 mitotic localization study and is not the proteostasis-centered ARL8A role. Reason: The 2004 GIE study supports spindle-midzone/microtubule-associated mitotic localization and chromosome-segregation phenotypes. This appears biologically plausible but is peripheral to the current ARL8A synthesis, where the best-supported function is lysosome/endolysosome localization and motility. Supporting Evidence: PMID:15331635 Gie protein has ability to bind to tubulin and localizes with microtubules on the spindle mid-zone in late mitosis PMID:15331635 Expression of dominant-negative Gie mutants in mammalian cells or knockdown of Gie transcripts using RNA interference in Drosophila S2 cells induced abnormal morphology in the chromosome segregation |
| GO:1904115 axon cytoplasm | IEA GO_REF:0000108 | KEEP AS NON CORE | Summary: axon cytoplasm is a plausible neuronal context for ARL8-family endolysosomal transport but not the core PN function. Reason: ARL8 family studies support neuronal/axonal endolysosome transport contexts, but ARL8A is principally a lysosomal/late-endosomal small GTPase. These neuron-associated locations should not replace the core lysosomal membrane and late endosome membrane locations. Supporting Evidence: PMID:35314674 toward the distal axon in neurons PMID:35314674 RUFY3 and RUFY4 promote retrograde transport of ARL8-positive endolysosomal vesicles from the axon to the soma |
| GO:0005515 protein binding | IPI PMID:24955142 Exploration of panviral proteome: high-throughput cloning an... | REMOVE | Summary: Protein binding is an uninformative representation of ARL8A interaction data. Reason: GO:0005515 does not describe the specific ARL8A molecular function. Where the interaction is biologically meaningful, it is better captured in the synthesis as GTPase-dependent effector recruitment for lysosome/endolysosome positioning, transport, or HOPS-linked cargo delivery; where the evidence is high-throughput interactomics, it is not sufficient for a functional GO term. Supporting Evidence: PMID:24955142 Exploration of panviral proteome: high-throughput cloning and functional implications in virus-host interactions. |
| GO:0005515 protein binding | IPI PMID:25416956 A proteome-scale map of the human interactome network. | REMOVE | Summary: Protein binding is an uninformative representation of ARL8A interaction data. Reason: GO:0005515 does not describe the specific ARL8A molecular function. Where the interaction is biologically meaningful, it is better captured in the synthesis as GTPase-dependent effector recruitment for lysosome/endolysosome positioning, transport, or HOPS-linked cargo delivery; where the evidence is high-throughput interactomics, it is not sufficient for a functional GO term. Supporting Evidence: PMID:25416956 A proteome-scale map of the human interactome network. |
| GO:0005515 protein binding | IPI PMID:28325809 The Rab7 effector PLEKHM1 binds Arl8b to promote cargo traff... | REMOVE | Summary: Protein binding is an uninformative representation of ARL8A interaction data. Reason: GO:0005515 does not describe the specific ARL8A molecular function. Where the interaction is biologically meaningful, it is better captured in the synthesis as GTPase-dependent effector recruitment for lysosome/endolysosome positioning, transport, or HOPS-linked cargo delivery; where the evidence is high-throughput interactomics, it is not sufficient for a functional GO term. Supporting Evidence: PMID:28325809 PLEKHM1 directly binds to Arl8b via its N-terminal RUN domain-containing region |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | REMOVE | Summary: Protein binding is an uninformative representation of ARL8A interaction data. Reason: GO:0005515 does not describe the specific ARL8A molecular function. Where the interaction is biologically meaningful, it is better captured in the synthesis as GTPase-dependent effector recruitment for lysosome/endolysosome positioning, transport, or HOPS-linked cargo delivery; where the evidence is high-throughput interactomics, it is not sufficient for a functional GO term. Supporting Evidence: PMID:32296183 A reference map of the human binary protein interactome. |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | REMOVE | Summary: Protein binding is an uninformative representation of ARL8A interaction data. Reason: GO:0005515 does not describe the specific ARL8A molecular function. Where the interaction is biologically meaningful, it is better captured in the synthesis as GTPase-dependent effector recruitment for lysosome/endolysosome positioning, transport, or HOPS-linked cargo delivery; where the evidence is high-throughput interactomics, it is not sufficient for a functional GO term. Supporting Evidence: PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. |
| GO:0005515 protein binding | IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func... | REMOVE | Summary: Protein binding is an uninformative representation of ARL8A interaction data. Reason: GO:0005515 does not describe the specific ARL8A molecular function. Where the interaction is biologically meaningful, it is better captured in the synthesis as GTPase-dependent effector recruitment for lysosome/endolysosome positioning, transport, or HOPS-linked cargo delivery; where the evidence is high-throughput interactomics, it is not sufficient for a functional GO term. Supporting Evidence: PMID:40205054 Multimodal cell maps as a foundation for structural and functional genomics. |
| GO:0008089 anterograde axonal transport | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Anterograde axonal transport is plausible for ARL8-family endolysosomal transport but is a neuron-specific manifestation of the broader lysosome/endolysosome motility role. Reason: ARL8-dependent endolysosome movement has strong support, including kinesin-linked anterograde movement and neuronal axonal contexts. For human ARL8A in the PN review, however, the core function is lysosome/endolysosome localization and motility; axonal anterograde transport should be retained as a specialized neuronal context rather than the central function. Supporting Evidence: PMID:25898167 This initiates a chain of interactions that promotes the kinesin-dependent movement of lysosomes toward the plus ends of microtubules PMID:35314674 ARL8 can thus regulate both anterograde and retrograde endolysosome transport through interactions with kinesin and dynein-dynactin motors PMID:35314674 toward the distal axon in neurons |
| GO:0005765 lysosomal membrane | ISS GO_REF:0000024 | ACCEPT | Summary: ARL8A lysosomal membrane localization is a core, well-supported location. Reason: Multiple evidence streams converge on ARL8A/ARL8 proteins as lysosome-associated small GTPases. The original ARL8 study directly showed ARL8A/ARL8B lysosome localization and lysosome motility effects, BORC work places ARL8 recruitment at lysosomal membranes, and lysosomal membrane proteomics is consistent with this localization. Supporting Evidence: PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells PMID:25898167 two paralogs of Arl8 (Arl8a and Arl8b) are the only ones known to associate specifically with lysosomes PMID:35314674 ARL8A and ARL8B paralogs ... are unique in their ability to associate with endolysosomes |
| GO:0031902 late endosome membrane | ISS GO_REF:0000024 | ACCEPT | Summary: Late endosome membrane is a reasonable endolysosomal ARL8A location. Reason: ARL8A/ARL8B are described as endolysosomal GTPases, with the endolysosome term covering lysosomes, late endosomes, and related organelles. This location is consistent with ARL8 effector studies and UniProt-derived late endosome membrane placement. Supporting Evidence: PMID:35314674 endolysosomes broadly to denote various types of lysosomes, late endosomes, and related endolysosomal organelles PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells |
| GO:0045202 synapse | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: synapse is a plausible neuronal context for ARL8-family endolysosomal transport but not the core PN function. Reason: ARL8 family studies support neuronal/axonal endolysosome transport contexts, but ARL8A is principally a lysosomal/late-endosomal small GTPase. These neuron-associated locations should not replace the core lysosomal membrane and late endosome membrane locations. Supporting Evidence: PMID:35314674 toward the distal axon in neurons PMID:35314674 RUFY3 and RUFY4 promote retrograde transport of ARL8-positive endolysosomal vesicles from the axon to the soma |
| GO:0005515 protein binding | IPI PMID:35314674 RUFY3 and RUFY4 are ARL8 effectors that promote coupling of ... | REMOVE | Summary: Protein binding is an uninformative representation of ARL8A interaction data. Reason: GO:0005515 does not describe the specific ARL8A molecular function. Where the interaction is biologically meaningful, it is better captured in the synthesis as GTPase-dependent effector recruitment for lysosome/endolysosome positioning, transport, or HOPS-linked cargo delivery; where the evidence is high-throughput interactomics, it is not sufficient for a functional GO term. Supporting Evidence: PMID:35314674 both RUFY3.1 and RUFY4 have the ability to interact with GTP-bound, but not GDP-bound, ARL8 |
| GO:0005515 protein binding | IPI PMID:25898167 BORC, a multisubunit complex that regulates lysosome positio... | REMOVE | Summary: Protein binding is an uninformative representation of ARL8A interaction data. Reason: GO:0005515 does not describe the specific ARL8A molecular function. Where the interaction is biologically meaningful, it is better captured in the synthesis as GTPase-dependent effector recruitment for lysosome/endolysosome positioning, transport, or HOPS-linked cargo delivery; where the evidence is high-throughput interactomics, it is not sufficient for a functional GO term. Supporting Evidence: PMID:25898167 BORC functions to recruit Arl8 to lysosomes |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-6798739 | MARK AS OVER ANNOTATED | Summary: plasma membrane is a Reactome granule-exocytosis context and is not supported as an ARL8A steady-state location. Reason: The row comes from Reactome's neutrophil degranulation model, in which azurophil granule membrane proteins reach the plasma membrane on exocytosis; the cached entry describes the granules in general and gives no gene-level evidence for ARL8A. ARL8A is a lysosomal and late-endosomal membrane GTPase, and neutrophil granules are lysosome-related compartments, so its presence on granule membranes and transient delivery to the plasma membrane is plausible but not shown. The plasma membrane term therefore goes beyond the evidence without being contradicted by it. Supporting Evidence: Reactome:R-HSA-6798739 Azurophil granules undergo limited exocytosis in response to stimulation PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells PMID:25898167 two paralogs of Arl8 (Arl8a and Arl8b) are the only ones known to associate specifically with lysosomes |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-6800426 | MARK AS OVER ANNOTATED | Summary: plasma membrane is a Reactome granule-exocytosis context and is not supported as an ARL8A steady-state location. Reason: The row comes from Reactome's neutrophil degranulation model, in which ficolin-1-rich granule membrane proteins reach the plasma membrane on exocytosis; the cached entry gives no gene-level evidence for ARL8A. ARL8A is a lysosomal and late-endosomal membrane GTPase, and neutrophil granules are lysosome-related compartments, so its presence on granule membranes and transient delivery to the plasma membrane is plausible but not shown. The plasma membrane term therefore goes beyond the evidence without being contradicted by it. Supporting Evidence: Reactome:R-HSA-6800426 Ficolin-1 rich granules can be differentiated by having low levels of gelatinases and an elevated exocytosis propensity PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells PMID:25898167 two paralogs of Arl8 (Arl8a and Arl8b) are the only ones known to associate specifically with lysosomes |
| GO:0035577 azurophil granule membrane | TAS Reactome:R-HSA-6798739 | MARK AS OVER ANNOTATED | Summary: azurophil granule membrane is a Reactome granule-exocytosis context and is not supported as an ARL8A steady-state location. Reason: The row comes from Reactome's neutrophil degranulation model, which lists ARL8A among azurophil granule membrane proteins; the cached entry describes the granules in general and gives no gene-level evidence. ARL8A is a lysosomal and late-endosomal membrane GTPase and azurophil granules are lysosome-related compartments, so the location is plausible, but it is not demonstrated for ARL8A and is peripheral to its established lysosomal role. The term therefore goes beyond the evidence without being contradicted by it. Supporting Evidence: Reactome:R-HSA-6798739 Azurophil granules undergo limited exocytosis in response to stimulation PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells PMID:25898167 two paralogs of Arl8 (Arl8a and Arl8b) are the only ones known to associate specifically with lysosomes |
| GO:0101003 ficolin-1-rich granule membrane | TAS Reactome:R-HSA-6800426 | MARK AS OVER ANNOTATED | Summary: ficolin-1-rich granule membrane is a Reactome granule-exocytosis context and is not supported as an ARL8A steady-state location. Reason: The row comes from Reactome's neutrophil degranulation model, which lists ARL8A among ficolin-1-rich granule membrane proteins; the cached entry gives no gene-level evidence. ARL8A is a lysosomal and late-endosomal membrane GTPase and neutrophil granules are lysosome-related compartments, so the location is plausible, but it is not demonstrated for ARL8A and is peripheral to its established lysosomal role. The term therefore goes beyond the evidence without being contradicted by it. Supporting Evidence: Reactome:R-HSA-6800426 Ficolin-1 rich granules can be differentiated by having low levels of gelatinases and an elevated exocytosis propensity PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells PMID:25898167 two paralogs of Arl8 (Arl8a and Arl8b) are the only ones known to associate specifically with lysosomes |
| GO:0016020 membrane | HDA PMID:19946888 Defining the membrane proteome of NK cells. | KEEP AS NON CORE | Summary: Membrane is a broad high-throughput location that should be kept only as non-core context. Reason: ARL8A is membrane-associated when active, but the generic membrane term is much less informative than lysosomal membrane and late endosome membrane. The high-throughput NK-cell membrane-proteome result is compatible with membrane association but not a core location term. Supporting Evidence: PMID:19946888 Defining the membrane proteome of NK cells. PMID:35314674 the GTP-bound form associates with endolysosomes |
| GO:0070062 extracellular exosome | HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos... | KEEP AS NON CORE | Summary: Detected in an extracellular-vesicle proteome. The protein is plausible EV content, but this is not where it functions. Reason: Peripheral late-endosome/lysosome GTPase. Cytosolic protein with lipid or membrane-protein binding ability; MISEV2018 (PMID:30637094) category 2a lists such proteins (ESCRT components, ALIX, annexins, HSPA8 and others) as expected EV contents. True, but not its core location. (Manual re-review for OMICS_EVIDENCE, 2026-10-10; previous action: MARK_AS_OVER_ANNOTATED.) Supporting Evidence: PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exosomes. PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells PMID:25898167 two paralogs of Arl8 (Arl8a and Arl8b) are the only ones known to associate specifically with lysosomes |
| GO:0005765 lysosomal membrane | HDA PMID:17897319 Integral and associated lysosomal membrane proteins. | ACCEPT | Summary: Lysosomal membrane is supported by lysosomal membrane proteomics and by direct ARL8 lysosome-localization studies. Reason: The high-throughput lysosomal membrane proteomics call is consistent with independent direct evidence that ARL8A/ARL8B localize to lysosomes and regulate lysosome motility, so this location should be retained as core. Supporting Evidence: PMID:17897319 We searched for novel proteins in lysosomal membranes PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells PMID:25898167 two paralogs of Arl8 (Arl8a and Arl8b) are the only ones known to associate specifically with lysosomes |
| GO:0003924 GTPase activity | NAS PMID:15331635 Novel small GTPase subfamily capable of associating with tub... | ACCEPT | Summary: GTPase activity is consistent with ARL8A being an ARF-family small GTPase. Reason: ARL8A is a small GTPase that cycles between GDP-bound and GTP-bound states, and structural/biochemical literature supports nucleotide-bound ARL8 family function. The NAS/IEA evidence is broad but biologically correct for this protein family. Supporting Evidence: PMID:15331635 Here, we identify novel GTPases (human Gie1 and Gie2) that form a distinct subfamily of the small GTPases PMID:35314674 Like other small GTPases, ARL8 cycles between GDP-bound, inactive, and GTP-bound, active forms |
| GO:0005525 GTP binding | IDA PMID:15331635 Novel small GTPase subfamily capable of associating with tub... | ACCEPT | Summary: GTP binding is consistent with ARL8A being an ARF-family small GTPase. Reason: ARL8A is a small GTPase that cycles between GDP-bound and GTP-bound states, and structural/biochemical literature supports nucleotide-bound ARL8 family function. The NAS/IEA evidence is broad but biologically correct for this protein family. Supporting Evidence: PMID:15331635 Here, we identify novel GTPases (human Gie1 and Gie2) that form a distinct subfamily of the small GTPases PMID:35314674 Like other small GTPases, ARL8 cycles between GDP-bound, inactive, and GTP-bound, active forms |
| GO:0005737 cytoplasm | IDA PMID:15331635 Novel small GTPase subfamily capable of associating with tub... | KEEP AS NON CORE | Summary: Cytoplasm is a broad localization from the original GIE study and is non-core relative to lysosomal/endolysosomal membranes. Reason: ARL8A can have cytosolic and membrane-associated nucleotide states, but cytoplasm is too broad to represent the principal location when lysosomal and late-endosomal membrane terms are available. Supporting Evidence: PMID:35314674 Whereas the GDP-bound form is cytosolic, the GTP-bound form associates with endolysosomes PMID:16537643 Arl8a and Arl8b ... localise to lysosomes in mammalian cells |
| GO:0007059 chromosome segregation | ISS PMID:14871887 Drosophila Topors is a RING finger-containing protein that f... | KEEP AS NON CORE | Summary: Chromosome segregation is a plausible but non-core mitotic ARL8/GIE role; the original GOA PMID is not the relevant ARL8 paper. Reason: The cited original reference in GOA is a Drosophila Topors paper and does not support ARL8A directly. However, PMID:15331635 does report GIE/ARL8 perturbation effects on chromosome segregation, so the biological idea is not rejected. It should remain non-core for the PN review because lysosome/endolysosome motility is the dominant ARL8A function. Supporting Evidence: PMID:14871887 Drosophila Topors is a RING finger-containing protein PMID:15331635 Gie protein has ability to bind to tubulin and localizes with microtubules on the spindle mid-zone in late mitosis PMID:15331635 Expression of dominant-negative Gie mutants in mammalian cells or knockdown of Gie transcripts using RNA interference in Drosophila S2 cells induced abnormal morphology in the chromosome segregation |
| GO:0030496 midbody | IDA PMID:15331635 Novel small GTPase subfamily capable of associating with tub... | KEEP AS NON CORE | Summary: midbody reflects the older GIE/ARL8 mitotic localization study and is not the proteostasis-centered ARL8A role. Reason: The 2004 GIE study supports spindle-midzone/microtubule-associated mitotic localization and chromosome-segregation phenotypes. This appears biologically plausible but is peripheral to the current ARL8A synthesis, where the best-supported function is lysosome/endolysosome localization and motility. Supporting Evidence: PMID:15331635 Gie protein has ability to bind to tubulin and localizes with microtubules on the spindle mid-zone in late mitosis PMID:15331635 Expression of dominant-negative Gie mutants in mammalian cells or knockdown of Gie transcripts using RNA interference in Drosophila S2 cells induced abnormal morphology in the chromosome segregation |
| GO:0043014 alpha-tubulin binding | ISS PMID:15331635 Novel small GTPase subfamily capable of associating with tub... | KEEP AS NON CORE | Summary: alpha-tubulin binding is supported by the GIE/ARL8 tubulin-association study but is non-core. Reason: The original ARL8/GIE study reports tubulin binding and spindle-midzone localization. This is a real experimental context, but it does not capture the main ARL8A role in lysosome/endolysosome membrane localization and transport. Supporting Evidence: PMID:15331635 Gie protein has ability to bind to tubulin and localizes with microtubules on the spindle mid-zone in late mitosis PMID:15331635 Expression of dominant-negative Gie mutants in mammalian cells or knockdown of Gie transcripts using RNA interference in Drosophila S2 cells induced abnormal morphology in the chromosome segregation |
| GO:0048487 beta-tubulin binding | ISS PMID:15331635 Novel small GTPase subfamily capable of associating with tub... | KEEP AS NON CORE | Summary: beta-tubulin binding is supported by the GIE/ARL8 tubulin-association study but is non-core. Reason: The original ARL8/GIE study reports tubulin binding and spindle-midzone localization. This is a real experimental context, but it does not capture the main ARL8A role in lysosome/endolysosome membrane localization and transport. Supporting Evidence: PMID:15331635 Gie protein has ability to bind to tubulin and localizes with microtubules on the spindle mid-zone in late mitosis PMID:15331635 Expression of dominant-negative Gie mutants in mammalian cells or knockdown of Gie transcripts using RNA interference in Drosophila S2 cells induced abnormal morphology in the chromosome segregation |
| GO:0051233 spindle midzone | IDA PMID:15331635 Novel small GTPase subfamily capable of associating with tub... | KEEP AS NON CORE | Summary: spindle midzone reflects the older GIE/ARL8 mitotic localization study and is not the proteostasis-centered ARL8A role. Reason: The 2004 GIE study supports spindle-midzone/microtubule-associated mitotic localization and chromosome-segregation phenotypes. This appears biologically plausible but is peripheral to the current ARL8A synthesis, where the best-supported function is lysosome/endolysosome localization and motility. Supporting Evidence: PMID:15331635 Gie protein has ability to bind to tubulin and localizes with microtubules on the spindle mid-zone in late mitosis PMID:15331635 Expression of dominant-negative Gie mutants in mammalian cells or knockdown of Gie transcripts using RNA interference in Drosophila S2 cells induced abnormal morphology in the chromosome segregation |
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Download this section (compressed HTML)Q: Should ARL8A receive a direct GO:0061906 autophagosome localization annotation, or should the PN projection remain limited to lysosome/endolysosome positioning until ARL8A-dependent autophagosome movement is shown directly?
Suggested experts: GO autophagy editors, GO proteostasis PN curators
Q: Should broad ARL8A protein binding annotations be replaced by a more specific curator model of small-GTPase effector recruitment for lysosome/endolysosome transport?
Suggested experts: GO molecular function editors, UniProt curators
Q: Does ARL8A contribute non-redundantly to BORC-ARL8-HOPS-dependent lysosomal cholesterol egress (NPC2 trafficking) and to endolysosome fusion that limits exosome secretion, or are these roles fully covered by ARL8B in cells expressing both paralogs?
Suggested experts: GO lysosome/membrane trafficking curators, lysosomal lipid trafficking experts
Experiment: Use ARL8A knockout, ARL8B knockout, double knockout, and matched rescue cells expressing endogenous-level ARL8A to image LC3-positive autophagosomes and LAMP1-positive lysosomes during basal and induced autophagy. Quantify autophagosome movement, lysosome movement, autophagosome-lysosome contacts, and cargo degradation to separate direct autophagosome localization from lysosome positioning effects.
Hypothesis: ARL8A regulates lysosome/endolysosome positioning but does not directly position autophagosomes independently of ARL8B or lysosome movement.
Type: ARL8A-specific autophagosome positioning assay
Experiment: Compare wild-type ARL8A and effector-binding-defective mutants in ARL8A/ARL8B-deficient cells, measuring BORC-dependent lysosome recruitment, RUFY3/RUFY4-dependent dynein-dynactin coupling, SKIP/kinesin-dependent peripheral movement, and PLEKHM1/HOPS-dependent delivery of endocytic and autophagic cargo to lysosomes.
Hypothesis: ARL8A effector binding to PLEKHM1/HOPS, SKIP, and RUFY3/RUFY4 separates lysosome localization, anterograde movement, retrograde movement, and autophagic cargo-delivery phenotypes.
Type: Effector-binding separation of function
Experiment: Using ARL8A single-knockout, ARL8B single-knockout, double-knockout, and matched rescue HeLa cells, quantify lysosomal free-cholesterol accumulation (filipin), NPC2 lysosomal association versus secretion, and exosome output (CD63/CD9 nanoparticle tracking and immunoblot), to determine the non-redundant contribution of ARL8A to the BORC-ARL8-HOPS cholesterol-egress and endolysosome-fusion programs.
Hypothesis: ARL8A contributes to BORC-ARL8-HOPS-dependent lysosomal cholesterol egress and to endolysosome fusion that restrains exosome secretion, with partial redundancy with ARL8B.
Type: ARL8A-specific cholesterol egress and exosome secretion assay
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