UBAP2L

UBAP2L is a multifunctional ubiquitin- and RNA-binding protein that serves as a master nucleator of cytoplasmic stress granules (SGs), acting upstream of and independently from G3BP1/2 (PMID:31956030). It assembles distinct granule cores spatially separate from G3BP1 cores and drives both SG assembly and disassembly, recruiting mRNPs, RNA-binding proteins, and ribosomal subunits through its RGG motif while engaging G3BP1/2 through its DUF domain; overexpression of UBAP2L alone nucleates SGs without stress (PMID:31956030, PMID:31114027). The RGG-dependent SG-component interactions are governed by PRMT1-catalyzed asymmetric dimethylation, which dampens recruitment and SG assembly when increased (PMID:31114027), and the UBAP2L–G3BP1 association is further bridged by snoRNAs (PMID:37059803). Beyond SGs, UBAP2L localizes to processing bodies (PBs), contributes to PB biogenesis, and mediates SG–PB interactions and hybrid granule formation through binding both G3BP and DDX6 (PMID:39007803). Outside of RNA granules, UBAP2L scaffolds nuclear pore complex assembly at the intact nuclear envelope by promoting Y-complex formation and its interactions with POM121 and Nup153 (PMID:38652117), controls PLK1 protein stability and mitotic localization via its C-terminal domain through ubiquitin-mediated turnover (PMID:37039032), and functions as the human orthologue of yeast Def1 to drive UV-induced ubiquitylation and degradation of RNA polymerase II by recruiting the Elongin-Cul5 ligase (PMID:35633597). UBAP2L also physically interacts with BMI1 within a Polycomb subcomplex to sustain hematopoietic stem cell activity (PMID:25185265) and associates with mTOR/Raptor to maintain basal mTORC1 activity (PMID:34171383). In cancer contexts, UBAP2L stability and activity are tuned by O-GlcNAcylation antagonizing TRIM37-mediated ubiquitination (PMID:41029457) and by PCK1-modulated Ser454 phosphorylation (PMID:37062825).

1. 2014 High

   Established the first physical and functional partner of UBAP2L by showing it joins a BMI1-containing Polycomb subcomplex required for stem cell maintenance, defining a chromatin/regulatory role distinct from BMI1's canonical Ink4a/Arf axis.

   Evidence Affinity purification/MS of BMI1 complexes, co-IP, shRNA knockdown, and in vivo transplantation rescue in hematopoietic stem cells

   PMID:25185265

   Open questions at the time

   • Molecular role of UBAP2L within the PcG subcomplex undefined
   • No structural basis for the BMI1 interaction
   • Does not connect this Polycomb role to UBAP2L's cytoplasmic functions
2. 2017 Medium

   Linked UBAP2L to EMT regulation, showing it supports SNAIL1-driven E-cadherin repression via SMAD2 signaling in hepatocellular carcinoma.

   Evidence siRNA knockdown, ChIP for SNAIL1 at the E-cadherin promoter, and invasion assays

   PMID:28334716

   Open questions at the time

   • Direct molecular link between UBAP2L and SMAD2/SNAIL1 not biochemically defined
   • Single cell-line context
   • Connection to UBAP2L's RNA-granule or scaffolding functions unclear
3. 2019 High

   Defined UBAP2L's domain logic in stress granule biology, showing the RGG motif recruits SG components and the DUF domain engages G3BP1/2, and that PRMT1-mediated arginine methylation of the RGG motif tunes assembly.

   Evidence Domain deletion mutants, co-IP, fluorescence microscopy, in vitro methylation assay with site mutants and SG assembly readout

   PMID:31114027

   Open questions at the time

   • Demethylase / methylation-reversal mechanism unidentified
   • How DUF deletion drives nuclear translocation mechanistically unresolved
   • Stress-signal that triggers methylation changes unknown
4. 2020 High

   Resolved the hierarchy of SG nucleation by demonstrating UBAP2L forms cores spatially and functionally distinct from G3BP1 and acts upstream of G3BP1 core assembly, repositioning UBAP2L as a master SG nucleator rather than a G3BP1 accessory.

   Evidence Super-resolution and expansion microscopy with reverse-genetic knockdown across multiple stress conditions

   PMID:31956030

   Open questions at the time

   • Biophysical driver of UBAP2L core condensation undefined
   • Relationship between UBAP2L cores and G3BP1 cores during maturation incompletely mapped
5. 2021 Medium

   Placed UBAP2L (NICE-4) in mTOR signaling by identifying it as a specific mTORC1 (Raptor) interactor required for basal mTORC1 activity, extending its functional repertoire beyond RNA granules.

   Evidence SILAC mTOR interactome screen, co-IP confirmation, and phospho-S6K mTORC1 activity assays with siRNA knockdown

   PMID:34171383

   Open questions at the time

   • Mechanism by which UBAP2L sustains mTORC1 activity unknown
   • Direct vs indirect Raptor binding not resolved
   • Single-lab finding without reciprocal in-pathway validation
6. 2022 High

   Identified UBAP2L as the human Def1 orthologue mediating the 'last resort' pathway for stalled RNA polymerase II, recruiting Elongin-Cul5 to ubiquitylate and degrade RPB1 after UV damage.

   Evidence UV irradiation, knockdown/knockout, ubiquitylation and RNAPII degradation assays, co-IP with Elongin-Cul5

   PMID:35633597

   Open questions at the time

   • Domain of UBAP2L responsible for Elongin-Cul5 recruitment not mapped
   • Interplay with redundant RNAPII degradation pathways unresolved
7. 2023 Medium

   Extended the G3BP1-interaction mechanism by showing snoRNAs bridge UBAP2L to G3BP1, making the interaction RNA-dependent.

   Evidence Proteomics, RNA-seq, in vitro binding reconstitution, snoRNA knockdown, and co-IP

   PMID:37059803

   Open questions at the time

   • Which specific snoRNAs and binding sites mediate bridging undefined
   • Single-lab finding
   • Relationship to RGG/DUF-mediated interactions not integrated
8. 2023 High

   Uncovered a mitotic function distinct from stress response, showing UBAP2L's C-terminal domain controls PLK1 protein stability and localization via ubiquitin-mediated turnover.

   Evidence siRNA depletion, immunofluorescence, domain mutants, PLK1 inhibitor rescue, and Western blot for PLK1 levels

   PMID:37039032

   Open questions at the time

   • Direct E3 ligase coupling UBAP2L to PLK1 turnover not identified
   • Whether UBAP2L acts as adaptor or substrate-receptor unresolved
9. 2024 High

   Defined a nuclear-envelope function, showing UBAP2L scaffolds nuclear pore complex assembly by promoting Y-complex formation and its contacts with POM121 and Nup153.

   Evidence siRNA depletion, super-resolution microscopy, co-IP, fractionation, and nuclear transport assays

   PMID:38652117

   Open questions at the time

   • Structural basis of Y-complex scaffolding by UBAP2L unknown
   • Whether NPC role shares determinants with its SG/granule activities unclear
10. 2024 High

    Broadened UBAP2L's granule role to processing bodies, showing it binds DDX6, promotes PB biogenesis, and nucleates hybrid SG-PB granules.

    Evidence siRNA depletion, live imaging, fluorescence microscopy, co-IP, and granule quantification

    PMID:39007803

    Open questions at the time

    • Determinants that partition UBAP2L between SGs and PBs undefined
    • Functional consequence of hybrid granules unclear
11. 2024 High

    Mapped a defined UBAP2L peptide-FMRP binding interface that SARS-CoV-2 NSP3 hijacks, blocking FMRP incorporation into stress granules and revealing a viral antagonism mechanism.

    Evidence Co-IP, direct peptide competition binding assay, NSP3 mutant viruses, and SG incorporation assays

    PMID:38177924

    Open questions at the time

    • Functional role of FMRP recruitment within UBAP2L-nucleated SGs incompletely defined
    • Generality of the shared interface across other RGG proteins untested
12. 2025 Medium

    Identified post-translational and pathway controls on UBAP2L in cancer: O-GlcNAcylation stabilizes UBAP2L against TRIM37 ubiquitination to drive SG-dependent mRNA stabilization and PI3K signaling, and UBAP2L-nucleated SGs sequester RACK1 to confer chemoresistance.

    Evidence Modification proteomics, RIP-seq, ubiquitination assays, SG/RACK1 colocalization, AKT-HSF1 phosphorylation analysis, and xenograft experiments

    PMID:40804300 PMID:41029457

    Open questions at the time

    • TRIM37 vs O-GlcNAc balance regulation in vivo unresolved
    • Direct causality between SG sequestration and apoptosis suppression incompletely defined
    • Single-lab findings

• How UBAP2L's many roles—SG/PB nucleation, NPC assembly, PLK1 and RNAPII turnover, mTORC1 and Polycomb function—are coordinated or share structural determinants remains unresolved.
• No unifying structural model linking the RGG/DUF/C-terminal domains to distinct functions
• Regulatory hierarchy among modifications (methylation, O-GlcNAcylation, phosphorylation) undefined
• Tissue-specific deployment of each function uncharacterized