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this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.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.
Identity is verified. The requested protein is human RBX1—RING-box protein 1, also called ROC1, regulator of cullins 1, RNF75, or protein ZYP—not the related protein RBX2/SAG/ROC2/RNF7. The literature describes RBX1 as a highly conserved 108-amino-acid, approximately 14-kDa protein whose C-terminal RING-H2 domain coordinates two Zn²⁺ ions in a cross-brace configuration. This agrees with the supplied RING-box/RING-H2 InterPro and Pfam annotations and with UniProt accession P62877. RBX2-only findings were excluded from this report. (wei2010smallringfinger pages 1-2, wei2010smallringfinger pages 7-8, wei2010smallringfinger pages 2-3)
RBX1 is best understood as the small catalytic RING subunit of numerous cullin–RING ligases (CRLs). Its N-terminal region binds the C terminus of a cullin scaffold, whereas its RING domain recruits a modifier-loaded E2 enzyme. RBX1 does not usually recognize protein substrates itself and does not form a covalent ubiquitin–RBX1 intermediate. Instead, it stabilizes a transfer-competent E2~ubiquitin complex so ubiquitin passes directly to a substrate nucleophile. RBX1 also works with UBE2M~NEDD8 to neddylate cullins and activate CRLs. Thus, RBX1 has experimentally supported E3 functions in both ubiquitylation and neddylation. (baek2021nedd8andubiquitin pages 1-2, mamun2023discoveryofneddylation pages 4-5, zhang2024proteinneddylationand pages 5-7)
Its physiological reach is broad because different cullins, adaptors, and receptors place the same RBX1 catalytic module into complexes controlling cell-cycle progression, DNA replication licensing, genome integrity, oxidative-stress signaling, DNA repair, and mTOR/autophagy. RBX1 is present in both nucleus and cytoplasm, with functional localization largely dictated by its assembled CRL. Genetic evidence establishes that it is essential: mouse disruption causes hypoproliferation and early embryonic lethality, only partly delayed by deleting the accumulated substrate p27. (wei2010smallringfinger pages 2-3, jia2009rbx1roc1scfe3ubiquitin pages 2-4, wei2010smallringfinger pages 3-5)
Recent work has refined rather than overturned this model. A 2023 study linked the RBX1–p27 axis to multiple-myeloma growth and context-dependent chemotherapy responses. In 2024, cryo-EM revealed an unusual 1.8-MDa CUL9–RBX1 complex in which cullin–RING and RBR E3 mechanisms cooperate. No cited evidence establishes an approved or clinically validated RBX1-selective drug; pharmacological applications remain indirect or preclinical. (hornghetko2024noncanonicalassemblyneddylation pages 1-2, bao2023ringboxprotein1(rbx1) pages 6-9, bao2023ringboxprotein1(rbx1) pages 2-5, zhang2024proteinneddylationand pages 5-7)
| Topic | Current conclusion | Key evidence/quantitative result | Evidence type and date |
|---|---|---|---|
| Identity and paralog distinction | Target is human RBX1 (UniProt P62877), also called ROC1/RNF75; it is distinct from RBX2/SAG/ROC2/RNF7, which preferentially supports CUL5 complexes. | RBX1 is reported as a 108-aa, approximately 14-kDa cullin-associated RING protein; RBX1 and RBX2 are genetically and biochemically nonredundant. (wei2010smallringfinger pages 1-2, wei2010smallringfinger pages 2-3, wei2010smallringfinger pages 3-5) | Protein characterization and review; 2010 |
| Structure and domain | RBX1 is a small RING-H2/RING-box protein. Its N-terminal region binds a cullin C-terminal cleft, whereas its C-terminal cross-braced RING domain coordinates two Zn²⁺ ions and recruits E2–modifier conjugates. | The RING domain and two-zinc architecture agree with the supplied InterPro/Pfam annotations; flexible tethering permits the E2-loaded RING domain to sample substrate positions. (wei2010smallringfinger pages 1-2, lin2024diversityofstructure pages 3-5, mamun2023discoveryofneddylation pages 4-5) | Structural and mechanistic reviews; 2010–2024 |
| Ubiquitin E3 mechanism | RBX1 is the catalytic RING subunit of many cullin–RING ubiquitin ligases, but it does not form a catalytic ubiquitin–RBX1 thioester. It binds E2~ubiquitin and stabilizes the transfer-competent closed conformation, enabling direct ubiquitin transfer to a substrate nucleophile. | RING “linchpin” contacts and multivalent E2~ubiquitin interactions orient ubiquitin for transfer; RBX1-containing complexes can support substrate priming and chain elongation. (baek2021nedd8andubiquitin pages 1-2, baek2021nedd8andubiquitin pages 9-9) | Structural synthesis; 2021 |
| NEDD8 E3 mechanism | RBX1 is also a cullin-directed NEDD8 E3 ligase, principally partnering with UBE2M to neddylate CUL1–CUL4 and activate their CRLs. | RBX1 binds and stabilizes UBE2M~NEDD8 for transfer to a cullin lysine. By contrast, RBX2 generally partners with UBE2F for CUL5. (mamun2023discoveryofneddylation pages 4-5, zhang2024proteinneddylationand pages 5-7) | Mechanistic review; 2023–2024 |
| NEDD8-dependent activation | Cullin neddylation releases inhibitory cullin–RING arrangements and promotes dynamic ubiquitin-transfer assemblies; the exact activation mechanism varies among CRLs. | In a UBE2D–CRL1–β-TrCP system, NEDD8 increased reaction rate approximately 2,000-fold; initial substrate ubiquitylation was about 10-fold faster than chain elongation. These are complex-level values, not intrinsic RBX1 turnover constants. (lin2024diversityofstructure pages 3-5) | Quantitative structural review; October 2024 |
| Substrate-specificity logic | RBX1 supplies catalytic E2 recruitment but ordinarily does not select protein substrates by itself. Specificity is primarily conferred by interchangeable CRL substrate receptors and adaptors, with phosphorylation or other degrons controlling receptor binding. | In SCF complexes, an F-box receptor recruits the substrate through SKP1–CUL1, while CUL1–RBX1 positions E2~ubiquitin for transfer. E2 identity and geometry further influence priming and ubiquitin-chain architecture. (wei2010smallringfinger pages 2-3, baek2021nedd8andubiquitin pages 1-2) | Biochemical and structural reviews; 2010–2021 |
| Cellular localization | RBX1 is found in both nucleus and cytoplasm, consistent with assembly into CRLs acting on substrates in both compartments. Localization is often determined by the associated cullin, adaptor, receptor, and substrate rather than by a single fixed RBX1 organelle address. | Constitutive expression and nuclear/cytoplasmic distribution were reported; no strong evidence supports classification as a secreted or integral-membrane protein. (wei2010smallringfinger pages 2-3, bungsy2019determiningtheimpact pages 33-39) | Cellular characterization and supporting synthesis; 2010–2019 |
| Representative pathways and substrates | RBX1-containing CRLs regulate cell-cycle progression, replication licensing, genome integrity, redox signaling, DNA repair, and mTOR/autophagy. Representative axes include SCF–SKP2–p27, CRL4–CDT1, CRL1–ORC1, CUL3–KEAP1–NRF2, and CRL-dependent DEPTOR turnover. | RBX1 depletion can accumulate p27, CDT1 and ORC1, trigger DNA-damage signaling, and stabilize DEPTOR to inhibit mTORC1; CUL3–KEAP1–RBX1 targets NRF2 under basal redox conditions. (jia2009rbx1roc1scfe3ubiquitin pages 2-4, wei2010smallringfinger pages 5-6, zhao2013cullinringligasesas pages 6-8, mamun2023discoveryofneddylation pages 4-5) | Genetic, knockdown, and biochemical evidence; 2009–2023 |
| Essentiality | RBX1 is required for early mammalian development and normal proliferative control; this broad essentiality also predicts toxicity risks for systemic direct inhibition. | Mouse Rbx1 disruption caused early embryonic lethality with p27 accumulation and hypoproliferation. Removing p27 extended survival from approximately E6.5 to E9.5 but did not fully rescue development, indicating additional essential substrates. (jia2009rbx1roc1scfe3ubiquitin pages 2-4, wei2010smallringfinger pages 3-5) | Mouse knockout and genetic rescue; 2009–2010 |
| Cancer-cell dependency | Many experimental cancer models depend on RBX1-containing CRLs, but RBX1 effects are context-dependent because its complexes degrade both oncogenic and tumor-suppressive proteins. | RBX1 silencing produced G2/M arrest, apoptosis and senescence in several cancer-cell lines; associated changes included 14-3-3σ and PUMA accumulation and reduced cyclin B1, CDC2, BCL-2, MCL-1 and survivin. (jia2009roc1rbx1e3ubiquitin pages 1-1, wei2010smallringfinger pages 5-6) | Human cell knockdown studies; 2009–2010 |
| Multiple myeloma development | A 2023 study implicated the RBX1–p27 axis in myeloma proliferation and cell-adhesion-mediated drug responses. Interpretation is nuanced: RBX1 depletion inhibited growth but could also reduce sensitivity to selected cytotoxic drugs through p27-dependent cell-cycle arrest. | In myeloma xenografts, RBX1 knockdown yielded mean tumor volumes of 52 ± 25.9 mm³, versus 357.9 ± 50.7 mm³ in controls after six weeks. Cell studies used doxorubicin, mitoxantrone and melphalan and supported Thr187-dependent p27 degradation. (bao2023ringboxprotein1(rbx1) pages 6-9, bao2023ringboxprotein1(rbx1) pages 2-5) | Cell, biochemical, SCID-Hu and xenograft study; August 2023 |
| CUL9 structural advance | A 2024 study revealed that RBX1 participates in an atypical CUL9 complex combining cullin–RING and RBR catalysis rather than behaving as a conventional stand-alone CRL catalytic arm. | Cryo-EM and biochemical analysis resolved a 1.8-MDa hexameric CUL9–RBX1 assembly at approximately 4.4 Å. Neddylated CUL9–RBX1 activates an adjacent E2-bound RBR domain in trans, and CUL9 uniquely depends on UBE2F among characterized RBX1-bound cullins. (hornghetko2024noncanonicalassemblyneddylation pages 1-2) | Cryo-EM, biochemistry and cellular assays; online April 11, 2024 |
| Therapeutic status | RBX1 is a compelling research target, but the cited literature does not establish an approved or clinically validated RBX1-selective inhibitor. Current applications are chiefly target validation, disease modeling, CRL mechanistic studies, and indirect pharmacological suppression. | Proposed approaches include disrupting UBE2M–RBX1 or cullin–RBX1 interactions. Pevonedistat/MLN4924 targets NEDD8-activating E1, not RBX1, and therefore broadly and indirectly inhibits neddylation-dependent CRLs; it must not be described as RBX1-selective. (shafique2018structuralbasisfor pages 15-17, mamun2023discoveryofneddylation pages 4-5, zhang2024proteinneddylationand pages 5-7) | Drug-discovery and neddylation reviews; 2018–2024 |
Table: Evidence-based functional annotation of human RBX1/P62877, spanning identity, catalytic mechanisms, localization, pathways, essentiality, recent disease research, and therapeutic status. Complex-level findings and indirect neddylation inhibitors are explicitly distinguished from RBX1-specific evidence.
The evidence supports the following target assignment:
The principal ambiguity risk is confusion with RBX2, whose aliases include SAG, ROC2, and RNF7. RBX1 and RBX2 are related but nonredundant RING proteins. Current structural syntheses generally assign CUL1–CUL4 complexes to RBX1 and CUL5 preferentially to RBX2, although historical biochemical studies detected broader pairings under some conditions. Therefore, RBX2 mitochondrial, cardiovascular, or CUL5-specific results should not be transferred automatically to RBX1. (wei2010smallringfinger pages 7-8, lin2024diversityofstructure pages 3-5, wei2010smallringfinger pages 3-5)
RBX1 has two tightly integrated structural roles. Its N-terminal segment binds a cleft in the cullin C-terminal region, anchoring RBX1 to the CRL scaffold. Its C-terminal RING-H2 domain uses conserved cysteine and histidine ligands to coordinate two zinc ions. The metal-supported fold is a protein-interaction and catalytic-positioning module rather than a zinc-dependent catalytic center in the conventional sense. Flexible tethering between cullin and RING allows the E2-bound catalytic arm to sample alternative geometries and reach substrates recruited at the opposite end of the CRL. (wei2010smallringfinger pages 1-2, lin2024diversityofstructure pages 3-5, mamun2023discoveryofneddylation pages 4-5)
The net reaction catalyzed by an RBX1-containing CRL can be written schematically as:
E2–S–ubiquitin + substrate–NH₂ → E2–SH + substrate–NH–CO–ubiquitin.
The E2 carries ubiquitin as a thioester. RBX1 binds E2~ubiquitin and stabilizes a closed, reactive conformation through the RING domain, a conserved RING “linchpin” residue, and—in some assemblies—additional CRL contacts. Ubiquitin is then transferred directly to a lysine ε-amino group or another suitable substrate nucleophile. Unlike HECT or RBR catalytic domains, canonical RBX1 does not receive ubiquitin onto an RBX1 catalytic cysteine. (baek2021nedd8andubiquitin pages 1-2)
A CRL may monoubiquitylate a target, initiate a chain, or extend a pre-existing ubiquitin chain, depending on the E2 and assembly. K48-linked chains commonly direct proteasomal degradation, while nondegradative topologies can regulate signaling. RBX1 is therefore not accurately described as having one invariant ubiquitin linkage specificity. E2 selection, receptor geometry, substrate lysines, and collaborating E3s determine the product. (wei2010smallringfinger pages 1-2, baek2021nedd8andubiquitin pages 1-2)
RBX1 also acts in the NEDD8 pathway. In its canonical partnership with UBE2M, the net reaction is:
UBE2M–S–NEDD8 + cullin–NH₂ → UBE2M–SH + cullin–NH–CO–NEDD8.
RBX1 binds the UBE2M~NEDD8 intermediate and promotes transfer of NEDD8 to a conserved cullin lysine. Current reviews assign RBX1–UBE2M principally to CUL1–CUL4, whereas RBX2–UBE2F principally supports CUL5. Cullin neddylation changes cullin/RING conformational dynamics, relieves inhibitory arrangements, and promotes productive ubiquitin-transfer assemblies. (mamun2023discoveryofneddylation pages 4-5, zhang2024proteinneddylationand pages 5-7)
NEDD8 can have a very large kinetic effect at the level of the assembled complex. In one UBE2D–CRL1–β-TrCP system summarized in a 2024 structural review, neddylation increased reaction rate approximately 2,000-fold, while initial substrate ubiquitylation was about 10-fold faster than chain elongation. These values characterize that particular CRL system, not a universal intrinsic turnover number for isolated RBX1. (lin2024diversityofstructure pages 3-5)
RBX1 has broad complex compatibility but little autonomous protein-substrate recognition. Specificity is chiefly imposed by modular receptors:
The cullin spans receptor and RBX1 catalytic modules. Consequently, it is more precise to say that an RBX1-containing CRL ubiquitylates a named substrate than that free RBX1 has direct specificity for that substrate. Degron phosphorylation, redox-induced receptor changes, cell-cycle phase, E2 identity, receptor exchange, neddylation, and CSN-mediated deneddylation provide additional specificity layers. (wei2010smallringfinger pages 2-3, baek2021nedd8andubiquitin pages 1-2, zhang2024proteinneddylationand pages 8-10)
Representative experimentally supported substrates or pathways include p27 through SCF–SKP2, CDT1 through CRL4, ORC1 through a CUL1 complex, NRF2 through CUL3–KEAP1, and DEPTOR through CRLs affecting mTOR signaling. These examples illustrate the diversity of receptor-defined RBX1 outputs rather than direct recognition by RBX1. (jia2009rbx1roc1scfe3ubiquitin pages 2-4, wei2010smallringfinger pages 5-6, zhao2013cullinringligasesas pages 6-8, mamun2023discoveryofneddylation pages 4-5)
RBX1 is reported in both the nucleus and cytoplasm, consistent with degradation of substrates in both compartments. It is neither a secreted protein nor an integral membrane transporter. Its operative localization should be viewed as complex-dependent: association with a particular cullin, adaptor, receptor, or substrate recruits the compact RBX1 catalytic subunit to the relevant cellular site. (wei2010smallringfinger pages 2-3, bungsy2019determiningtheimpact pages 33-39)
Nuclear RBX1-containing CRLs are especially important in cell-cycle control, replication licensing, chromatin-associated DNA-damage responses, and repair. Cytoplasmic CRLs control signaling proteins, redox responses, and mTOR/autophagy regulators. Some partner proteins shuttle, so the nucleus–cytoplasm distinction is dynamic rather than absolute. Evidence for a dedicated mitochondrial RBX1 role is substantially weaker than for RBX2–CUL5; mitochondrial RBX2 findings should not be reassigned to RBX1.
The SCF–SKP2–p27 axis is among the clearest mechanistic examples. RBX1-containing SCF promotes ubiquitin-dependent degradation of phosphorylated p27, permitting CDK activity and G1/S progression. Mouse Rbx1 disruption caused p27 accumulation, hypoproliferation, and early embryonic death. Simultaneous p27 deletion extended embryonic survival from approximately E6.5 to E9.5, but did not fully rescue development, demonstrating both the causal importance of p27 and the existence of other essential RBX1-controlled substrates. (jia2009rbx1roc1scfe3ubiquitin pages 2-4, wei2010smallringfinger pages 3-5)
This genetic result is stronger functional evidence than expression correlation alone. It establishes RBX1 as essential for proliferative control during early development, but also warns that systemic RBX1 inhibition may have a narrow therapeutic window.
RBX1-containing CRL1 and CRL4 complexes regulate replication-licensing proteins such as ORC1 and CDT1. RBX1 silencing causes their accumulation, DNA-damage signaling, and G2/M arrest; reported markers include phosphorylated H2AX, CHK1, and CHK2. The mechanistic interpretation is that failure to remove licensing proteins permits inappropriate rereplication or replication stress, producing DNA breaks and checkpoint activation. (jia2009rbx1roc1scfe3ubiquitin pages 2-4, wei2010smallringfinger pages 5-6)
RBX1 can also regulate pathway choice in double-strand-break repair. Cell-cycle-regulated RBX1/CUL1 activity has been linked to EXO1 degradation in G1, limiting end resection and thereby suppressing homologous recombination when no sister chromatid is available. This is biologically coherent with RBX1’s broader role in coordinating proteolysis with cell-cycle phase.
In the canonical KEAP1–CUL3–RBX1 ligase, KEAP1 recruits NRF2 for ubiquitylation under basal conditions. Proteasomal turnover keeps antioxidant-response transcription low. Oxidative or electrophilic stress modifies KEAP1 and weakens productive NRF2 ubiquitylation, allowing NRF2 to accumulate and enter the nucleus. Thus, RBX1 is the catalytic RING component of a redox-sensitive receptor system, but KEAP1—not RBX1—directly senses the relevant chemical stress. (jia2009rbx1roc1scfe3ubiquitin pages 2-4, mamun2023discoveryofneddylation pages 4-5)
This pathway illustrates RBX1’s context dependence in cancer: reducing CUL3–KEAP1–RBX1 activity can protect normal cells through NRF2, but persistent NRF2 stabilization in tumors may enhance survival, ferroptosis resistance, and therapy resistance.
RBX1 depletion or global CRL inactivation can stabilize DEPTOR, suppress mTORC1, and trigger autophagy. In cancer models, this autophagy may be protective rather than purely cytotoxic. RBX1 knockdown also causes senescence and apoptosis through accumulated CRL substrates and replication stress. Reported correlates include 14-3-3σ and PUMA accumulation and reduced cyclin B1, CDC2, BCL-2, MCL-1, and survivin. These are downstream consequences of disabling many RBX1-containing CRLs, not evidence that RBX1 directly binds every affected protein. (jia2009roc1rbx1e3ubiquitin pages 1-1, wei2010smallringfinger pages 5-6, zhao2013cullinringligasesas pages 6-8)
Conditional mouse studies have shown that the UBE2M–RBX1 neddylation/CRL axis is required for regulatory-T-cell homeostasis and suppressive fitness. This supports an immunological role but also reinforces the expected toxicity of indiscriminate systemic inhibition. The evidence is genetically compelling in mice, although it should not be interpreted as proof of a clinically actionable human RBX1 indication.
Bao and colleagues reported that RBX1 binds into the machinery promoting p27 ubiquitylation and degradation in multiple-myeloma models. RBX1 overexpression shortened p27 half-life, increased cyclin E, cyclin A, and phosphorylated CDK2, and promoted G1/S progression. The p27 Thr187 phosphodegron was important. RBX1 silencing elevated p27 and inhibited proliferation. (bao2023ringboxprotein1(rbx1) pages 6-9, bao2023ringboxprotein1(rbx1) pages 1-2)
The treatment phenotype was nuanced. RBX1 depletion reduced growth but, through p27-associated quiescence, could also reduce sensitivity to selected cytotoxic agents. Experiments included doxorubicin at 100 nM, mitoxantrone at 2 μM, and melphalan at 10 μM for 48 hours and were reported across five independent experiments. In vivo, mean xenograft volume after six weeks was 52 ± 25.9 mm³ with RBX1 knockdown versus 357.9 ± 50.7 mm³ in controls. The study therefore supports target validity for tumor growth, but also shows why RBX1 inhibition might antagonize cell-cycle-dependent chemotherapy in some contexts. Published August 2023; DOI: https://doi.org/10.1080/15384047.2023.2231670. (bao2023ringboxprotein1(rbx1) pages 6-9, bao2023ringboxprotein1(rbx1) pages 2-5)
A 2023 review of neddylation E2 inhibitors highlighted the UBE2M–RBX1 interface as a potential anticancer intervention point. Mechanistically, disrupting this interaction should reduce neddylation of RBX1-associated cullins and hence their ubiquitin-ligase activity. This remains a proposed, preclinical strategy, not evidence of an approved RBX1 drug. Published September 2023; DOI: https://doi.org/10.1038/s41389-023-00490-2. (mamun2023discoveryofneddylation pages 4-5)
A major 2024 review reaffirmed that RBX1 works predominantly with UBE2M to neddylate CUL1–CUL4, whereas RBX2 generally uses UBE2F for CUL5. The review catalogued structures containing NEDD8–CUL1–RBX1, DCN1, UBE2M, ARIH1, and receptor modules, emphasizing that CRL activation is conformationally and compositionally diverse. Published April 2024; DOI: https://doi.org/10.1038/s41392-024-01800-9. (zhang2024proteinneddylationand pages 5-7, zhang2024proteinneddylationand pages 8-10)
The same review cited 2023 evidence that RBX1 inactivation suppresses KRAS(G12D)-driven lung tumorigenesis, supporting oncogenic dependency in that model. However, the retrieved review excerpt did not provide the primary study’s numerical tumor outcomes, so no quantitative effect is asserted here. (zhang2024proteinneddylationand pages 32-32)
Horn-Ghetko and colleagues used cryo-EM, biochemistry, and cellular assays to resolve a 1.8-MDa, hexameric human CUL9–RBX1 assembly at approximately 4.4-Å resolution. CUL9 is unusual because it combines a cullin–RING module with an RBR catalytic domain. Neddylation activates an E2-bound RBR domain positioned by an adjacent CUL9–RBX1 protomer in trans; the RBR region also protects CUL9 from deneddylation. CUL9 was exceptional among characterized RBX1-bound cullins in depending on UBE2F. (hornghetko2024noncanonicalassemblyneddylation pages 1-2)
This work expands the functional annotation of RBX1 beyond a simple “E2 docking site.” RBX1 can participate in higher-order, chimeric E3 architectures that organize catalytic communication between distinct ligase classes. CUL9 can monoubiquitylate TP53 without necessarily causing degradation and has been linked to DNA-damage responses and tumor suppression. Published in Nature Structural & Molecular Biology, online April 11, 2024; DOI: https://doi.org/10.1038/s41594-024-01257-y. (hornghetko2024noncanonicalassemblyneddylation pages 1-2)
A 2024 review emphasized flexible RBX tethering, separation of substrate priming from chain elongation, and the lack of one universal NEDD8-activation mechanism across CRL families. The expert consensus is therefore shifting from a static “cullin scaffold” model to a dynamic ensemble in which neddylation, E2 choice, substrate receptor, and accessory E3s determine catalytic geometry. Published October 2024; DOI: https://doi.org/10.1016/j.sbi.2024.102879. (lin2024diversityofstructure pages 3-5)
RBX1 is frequently reported as overexpressed in lung, liver, breast, colon, ovarian, and gastric tumors and in cancer-derived cell lines. RNA interference studies across several models caused G2/M arrest, senescence, apoptosis, or autophagy. Nevertheless, expression correlations should not be equated with a universal oncogenic function because different RBX1-containing CRLs degrade both oncogenic and tumor-suppressive substrates. (jia2009rbx1roc1scfe3ubiquitin pages 2-4, jia2009roc1rbx1e3ubiquitin pages 1-1, wei2010smallringfinger pages 3-5)
A 2019 thesis-level analysis reported heterozygous RBX1 loss in approximately 83.2% of ovarian cancers and 25.5% of colorectal cancers, with low RBX1 mRNA associated with worse ovarian-cancer survival. Because this evidence came from a thesis excerpt rather than a retrieved peer-reviewed primary cohort paper, these figures should be treated as hypothesis-generating rather than definitive clinical statistics. (bungsy2019determiningtheimpact pages 33-39)
The strongest quantitative recent disease evidence retrieved here is the 2023 myeloma xenograft difference—52 ± 25.9 versus 357.9 ± 50.7 mm³ after six weeks—which supports a substantial growth dependency in that model but does not establish patient efficacy. (bao2023ringboxprotein1(rbx1) pages 6-9)
Current uses of RBX1 knowledge are principally:
No retrieved source establishes an approved, marketed, or clinically validated RBX1-selective inhibitor. Proposed strategies include disrupting RBX1–cullin or UBE2M–RBX1 interfaces, but these remain preclinical. (shafique2018structuralbasisfor pages 15-17, mamun2023discoveryofneddylation pages 4-5)
Pevonedistat/MLN4924 must not be described as an RBX1 inhibitor. It inhibits NEDD8-activating enzyme, blocks cullin neddylation, and thereby indirectly suppresses numerous CRLs. The 2024 review discusses clinical development of pathway inhibitors, but that does not constitute direct RBX1 pharmacology. Moreover, the retrieved excerpt’s statement concerning FDA approval should not be relied upon as proof of current regulatory status without independent regulatory verification. (wei2010smallringfinger pages 6-7, lan2016neddylationinhibitormln4924 pages 11-12, zhang2024proteinneddylationand pages 5-7)
The authoritative structural literature supports five conclusions.
First, RBX1 is an obligate catalytic organizer, not a conventional substrate-binding enzyme. Functional annotations that list numerous direct “RBX1 substrates” without naming the cullin/receptor complex are mechanistically incomplete. (baek2021nedd8andubiquitin pages 1-2, lin2024diversityofstructure pages 3-5)
Second, its two E3 roles are coupled: RBX1 helps neddylate cullins, and neddylated cullins then use RBX1 to promote ubiquitin transfer. This creates a feed-forward activation architecture but also complicates attribution when RBX1 is depleted. (mamun2023discoveryofneddylation pages 4-5, zhang2024proteinneddylationand pages 5-7)
Third, RBX1 function is complex- and context-dependent. The same catalytic component can promote degradation of p27, CDT1, NRF2, or other proteins with very different physiological consequences. A blanket designation as oncogene or tumor suppressor is therefore inadequate.
Fourth, broad essentiality presents the central translational challenge. Complete systemic inhibition is likely to disrupt development, proliferation, immune homeostasis, and genome maintenance. A viable therapeutic strategy may require tumor-selective delivery, partial inhibition, transient dosing, or targeting a particular RBX1–E2/cullin interface instead of all RBX1 activity. (jia2009rbx1roc1scfe3ubiquitin pages 2-4, wei2010smallringfinger pages 3-5, mamun2023discoveryofneddylation pages 4-5)
Fifth, newer structures show that RBX1 complexes are dynamic and sometimes noncanonical. Future annotation should specify the exact cullin, receptor, E2, modification state, and cooperating E3 rather than treating all RBX1-containing ligases as equivalent. The 2024 CUL9 structure is the clearest example. (hornghetko2024noncanonicalassemblyneddylation pages 1-2, lin2024diversityofstructure pages 3-5)
Human RBX1/P62877 is a compact, evolutionarily conserved RING-H2 protein that forms the catalytic cullin-bound arm of a large set of CRLs. Its primary molecular function is to position and activate E2~ubiquitin for direct modifier transfer to receptor-recruited substrates; it also promotes UBE2M-dependent cullin neddylation. Substrate specificity resides mainly in the associated CRL receptor, whereas RBX1 supplies catalytic competence and conformational flexibility. It acts in both nucleus and cytoplasm and is mechanistically central to cell-cycle control, DNA replication licensing, genome integrity, NRF2 redox regulation, DNA repair, and mTOR/autophagy.
Genetic and biochemical evidence is strong, including mouse knockout/rescue studies, substrate-accumulation phenotypes, reconstituted structural mechanisms, and recent xenograft and cryo-EM studies. The translational case is promising but immature: RBX1 dependencies occur in cancer, yet context-dependent substrate effects and organismal essentiality create substantial safety and combination-therapy risks. As of the cited 2023–2024 literature, RBX1 is best regarded as a validated biological node and emerging preclinical target, not a protein with an established selective clinical drug.
References
(wei2010smallringfinger pages 1-2): Dongping Wei and Yi Sun. Small ring finger proteins rbx1 and rbx2 of scf e3 ubiquitin ligases: the role in cancer and as cancer targets. Genes & cancer, 1 7:700-7, Jul 2010. URL: https://doi.org/10.1177/1947601910382776, doi:10.1177/1947601910382776. This article has 119 citations.
(wei2010smallringfinger pages 7-8): Dongping Wei and Yi Sun. Small ring finger proteins rbx1 and rbx2 of scf e3 ubiquitin ligases: the role in cancer and as cancer targets. Genes & cancer, 1 7:700-7, Jul 2010. URL: https://doi.org/10.1177/1947601910382776, doi:10.1177/1947601910382776. This article has 119 citations.
(wei2010smallringfinger pages 2-3): Dongping Wei and Yi Sun. Small ring finger proteins rbx1 and rbx2 of scf e3 ubiquitin ligases: the role in cancer and as cancer targets. Genes & cancer, 1 7:700-7, Jul 2010. URL: https://doi.org/10.1177/1947601910382776, doi:10.1177/1947601910382776. This article has 119 citations.
(baek2021nedd8andubiquitin pages 1-2): Kheewoong Baek, Daniel C Scott, and Brenda A Schulman. Nedd8 and ubiquitin ligation by cullin-ring e3 ligases. Current Opinion in Structural Biology, 67:101-109, Apr 2021. URL: https://doi.org/10.1016/j.sbi.2020.10.007, doi:10.1016/j.sbi.2020.10.007. This article has 166 citations and is from a peer-reviewed journal.
(mamun2023discoveryofneddylation pages 4-5): MAA Mamun, Ying Liu, Yin-Ping Geng, Yi-Chao Zheng, Ya Gao, Jian-Gang Sun, Long-Fei Zhao, Li-Juan Zhao, and Hong-Min Liu. Discovery of neddylation e2s inhibitors with therapeutic activity. Oncogenesis, Sep 2023. URL: https://doi.org/10.1038/s41389-023-00490-2, doi:10.1038/s41389-023-00490-2. This article has 16 citations and is from a domain leading peer-reviewed journal.
(zhang2024proteinneddylationand pages 5-7): Shizhen Zhang, Qing Yu, Zhijian Li, Yongchao Zhao, and Yi Sun. Protein neddylation and its role in health and diseases. Signal Transduction and Targeted Therapy, Apr 2024. URL: https://doi.org/10.1038/s41392-024-01800-9, doi:10.1038/s41392-024-01800-9. This article has 202 citations and is from a peer-reviewed journal.
(jia2009rbx1roc1scfe3ubiquitin pages 2-4): Lijun Jia and Yi Sun. Rbx1/roc1-scf e3 ubiquitin ligase is required for mouse embryogenesis and cancer cell survival. Cell Division, 4:16-16, Aug 2009. URL: https://doi.org/10.1186/1747-1028-4-16, doi:10.1186/1747-1028-4-16. This article has 48 citations and is from a peer-reviewed journal.
(wei2010smallringfinger pages 3-5): Dongping Wei and Yi Sun. Small ring finger proteins rbx1 and rbx2 of scf e3 ubiquitin ligases: the role in cancer and as cancer targets. Genes & cancer, 1 7:700-7, Jul 2010. URL: https://doi.org/10.1177/1947601910382776, doi:10.1177/1947601910382776. This article has 119 citations.
(hornghetko2024noncanonicalassemblyneddylation pages 1-2): Daniel Horn-Ghetko, Linus V. M. Hopf, Ishita Tripathi-Giesgen, Jiale Du, Sebastian Kostrhon, D. Tung Vu, Viola Beier, Barbara Steigenberger, J. Rajan Prabu, Luca Stier, Elias M. Bruss, Matthias Mann, Yue Xiong, and Brenda A. Schulman. Noncanonical assembly, neddylation and chimeric cullin–ring/rbr ubiquitylation by the 1.8 mda cul9 e3 ligase complex. Nature Structural & Molecular Biology, 31:1083-1094, Apr 2024. URL: https://doi.org/10.1038/s41594-024-01257-y, doi:10.1038/s41594-024-01257-y. This article has 18 citations and is from a highest quality peer-reviewed journal.
(bao2023ringboxprotein1(rbx1) pages 6-9): Enfang Bao, Yu Zhou, Song He, Jie Tang, Yunhua He, Mengyuan Zhu, Chun Cheng, and Yuchan Wang. Ring box protein-1(rbx1), a key component of scf e3 ligase, induced multiple myeloma cell drug-resistance though suppressing p27. Cancer Biology & Therapy, Aug 2023. URL: https://doi.org/10.1080/15384047.2023.2231670, doi:10.1080/15384047.2023.2231670. This article has 9 citations and is from a peer-reviewed journal.
(bao2023ringboxprotein1(rbx1) pages 2-5): Enfang Bao, Yu Zhou, Song He, Jie Tang, Yunhua He, Mengyuan Zhu, Chun Cheng, and Yuchan Wang. Ring box protein-1(rbx1), a key component of scf e3 ligase, induced multiple myeloma cell drug-resistance though suppressing p27. Cancer Biology & Therapy, Aug 2023. URL: https://doi.org/10.1080/15384047.2023.2231670, doi:10.1080/15384047.2023.2231670. This article has 9 citations and is from a peer-reviewed journal.
(lin2024diversityofstructure pages 3-5): Calvin P. Lin and Elizabeth A. Komives. Diversity of structure and function in cullin e3 ligases. Current Opinion in Structural Biology, 88:102879, Oct 2024. URL: https://doi.org/10.1016/j.sbi.2024.102879, doi:10.1016/j.sbi.2024.102879. This article has 17 citations and is from a peer-reviewed journal.
(baek2021nedd8andubiquitin pages 9-9): Kheewoong Baek, Daniel C Scott, and Brenda A Schulman. Nedd8 and ubiquitin ligation by cullin-ring e3 ligases. Current Opinion in Structural Biology, 67:101-109, Apr 2021. URL: https://doi.org/10.1016/j.sbi.2020.10.007, doi:10.1016/j.sbi.2020.10.007. This article has 166 citations and is from a peer-reviewed journal.
(bungsy2019determiningtheimpact pages 33-39): M Bungsy. Determining the impact diminished rbx1 expression has on chromosome stability in cancer. Unknown journal, 2019.
(wei2010smallringfinger pages 5-6): Dongping Wei and Yi Sun. Small ring finger proteins rbx1 and rbx2 of scf e3 ubiquitin ligases: the role in cancer and as cancer targets. Genes & cancer, 1 7:700-7, Jul 2010. URL: https://doi.org/10.1177/1947601910382776, doi:10.1177/1947601910382776. This article has 119 citations.
(zhao2013cullinringligasesas pages 6-8): Yongchao Zhao and Yi Sun. Cullin-ring ligases as attractive anti-cancer targets. Current pharmaceutical design, 19 18:3215-25, May 2013. URL: https://doi.org/10.2174/13816128113199990300, doi:10.2174/13816128113199990300. This article has 338 citations and is from a peer-reviewed journal.
(jia2009roc1rbx1e3ubiquitin pages 1-1): Lijun Jia, Maria S. Soengas, and Yi Sun. Roc1/rbx1 e3 ubiquitin ligase silencing suppresses tumor cell growth via sequential induction of g2-m arrest, apoptosis, and senescence. Cancer research, 69 12:4974-82, Jun 2009. URL: https://doi.org/10.1158/0008-5472.can-08-4671, doi:10.1158/0008-5472.can-08-4671. This article has 146 citations and is from a highest quality peer-reviewed journal.
(shafique2018structuralbasisfor pages 15-17): Shagufta Shafique, Waqar Ali, Sonia Kanwal, and Sajid Rashid. Structural basis for cullins and ring component inhibition: targeting e3 ubiquitin pathway conductors for cancer therapeutics. International journal of biological macromolecules, 106:532-543, Jan 2018. URL: https://doi.org/10.1016/j.ijbiomac.2017.08.047, doi:10.1016/j.ijbiomac.2017.08.047. This article has 21 citations and is from a peer-reviewed journal.
(zhang2024proteinneddylationand pages 8-10): Shizhen Zhang, Qing Yu, Zhijian Li, Yongchao Zhao, and Yi Sun. Protein neddylation and its role in health and diseases. Signal Transduction and Targeted Therapy, Apr 2024. URL: https://doi.org/10.1038/s41392-024-01800-9, doi:10.1038/s41392-024-01800-9. This article has 202 citations and is from a peer-reviewed journal.
(bao2023ringboxprotein1(rbx1) pages 1-2): Enfang Bao, Yu Zhou, Song He, Jie Tang, Yunhua He, Mengyuan Zhu, Chun Cheng, and Yuchan Wang. Ring box protein-1(rbx1), a key component of scf e3 ligase, induced multiple myeloma cell drug-resistance though suppressing p27. Cancer Biology & Therapy, Aug 2023. URL: https://doi.org/10.1080/15384047.2023.2231670, doi:10.1080/15384047.2023.2231670. This article has 9 citations and is from a peer-reviewed journal.
(zhang2024proteinneddylationand pages 32-32): Shizhen Zhang, Qing Yu, Zhijian Li, Yongchao Zhao, and Yi Sun. Protein neddylation and its role in health and diseases. Signal Transduction and Targeted Therapy, Apr 2024. URL: https://doi.org/10.1038/s41392-024-01800-9, doi:10.1038/s41392-024-01800-9. This article has 202 citations and is from a peer-reviewed journal.
(wei2010smallringfinger pages 6-7): Dongping Wei and Yi Sun. Small ring finger proteins rbx1 and rbx2 of scf e3 ubiquitin ligases: the role in cancer and as cancer targets. Genes & cancer, 1 7:700-7, Jul 2010. URL: https://doi.org/10.1177/1947601910382776, doi:10.1177/1947601910382776. This article has 119 citations.
(lan2016neddylationinhibitormln4924 pages 11-12): Huiyin Lan, Zaiming Tang, Hongchuan Jin, and Yi Sun. Neddylation inhibitor mln4924 suppresses growth and migration of human gastric cancer cells. Scientific Reports, Apr 2016. URL: https://doi.org/10.1038/srep24218, doi:10.1038/srep24218. This article has 130 citations and is from a peer-reviewed journal.