UBAP2L

UBAP2L is a ubiquitin-associated and RNA-binding scaffolding protein that functions as a master nucleator of cytoplasmic RNA granules, a regulator of mitotic progression, and a facilitator of nuclear pore complex assembly. In stress granule biology, UBAP2L acts upstream of G3BP1/2 to nucleate stress granules via its RGG motif (which recruits mRNPs and is regulated by PRMT1-mediated arginine methylation) and its DUF domain (which engages G3BP1/2 in a snoRNA-bridged complex); it also localizes to processing bodies through DDX6 binding and mediates SG–PB interactions (PMID:31956030, PMID:31114027, PMID:37059803, PMID:39007803). Beyond RNA granule biology, UBAP2L promotes UV-induced ubiquitylation and degradation of RNA polymerase II by recruiting the Elongin–Cul5 ubiquitin ligase as the human orthologue of yeast Def1, controls PLK1 localization and ubiquitin-mediated turnover during mitosis to ensure proper chromosome segregation, and scaffolds Y-complex assembly and sequential nucleoporin interactions (POM121, Nup153, FXR1) required for nuclear pore complex biogenesis (PMID:35633597, PMID:37039032, PMID:38652117). UBAP2L also resides in a BMI1-containing Polycomb subcomplex essential for long-term hematopoietic stem cell maintenance and interacts specifically with mTORC1 components mTOR and Raptor to sustain mTORC1 signaling (PMID:25185265, PMID:34171383).

1. 2014 High

   Establishing that UBAP2L functions within the Polycomb pathway: UBAP2L was identified as a physical partner of BMI1 in a distinct PcG subcomplex, and BMI1 overexpression rescued UBAP2L-depleted hematopoietic stem cell defects, placing UBAP2L in chromatin-associated gene regulation independent of the canonical Ink4a/Arf-targeting complex.

   Evidence Reciprocal co-IP with mass spectrometry, genetic epistasis via BMI1 rescue, in vivo transplantation assays in mouse hematopoietic system

   PMID:25185265

   Open questions at the time

   • Biochemical function of UBAP2L within the BMI1 complex (e.g., ubiquitin ligase adaptor vs. reader) not defined
   • Genomic targets of the UBAP2L–BMI1 subcomplex not identified
   • Whether this function extends beyond hematopoietic stem cells is unknown
2. 2019 High

   Defining the domain architecture and post-translational regulation of UBAP2L in stress granule nucleation: the RGG motif was shown to recruit mRNPs and SG components while the DUF domain mediated G3BP1/2 binding, and PRMT1-catalyzed asymmetric arginine dimethylation of the RGG motif was demonstrated to antagonize SG assembly by weakening UBAP2L–mRNP interactions.

   Evidence Domain deletions, co-IP, overexpression-driven SG assay, PRMT1 knockdown/overexpression, in vitro methylation assays

   PMID:31114027

   Open questions at the time

   • Whether PRMT1-mediated methylation is dynamically regulated during stress recovery is not resolved
   • Structure of the DUF–G3BP interface not determined
   • Specific RNA species bound by the RGG motif during SG formation not catalogued
3. 2020 High

   Resolving the epistatic hierarchy of stress granule nucleation: super-resolution imaging revealed that UBAP2L forms distinct granule cores separate from G3BP1 cores, and genetic experiments established that UBAP2L can nucleate granules independently of G3BP1/2, placing it as the most upstream known SG nucleator.

   Evidence Super-resolution and expansion microscopy, siRNA knockdown of UBAP2L and G3BP1/2, multiple stress conditions in human cells

   PMID:31956030

   Open questions at the time

   • What triggers UBAP2L condensation upon stress is unknown
   • Whether UBAP2L undergoes liquid-liquid phase separation or forms solid-like assemblies not established
   • Relationship between UBAP2L cores and downstream SG maturation not fully defined
4. 2021 Medium

   Linking UBAP2L to mTORC1 signaling: UBAP2L was identified as a specific interactor of mTOR and Raptor (but not Rictor), and its depletion reduced mTORC1 activity as measured by S6K phosphorylation.

   Evidence SILAC-based mTOR interactome, confirmatory co-IP, UBAP2L knockdown with mTORC1 readout

   PMID:34171383

   Open questions at the time

   • Single co-IP confirmation from one laboratory without reciprocal pull-down from UBAP2L side
   • Mechanism by which UBAP2L sustains mTORC1 activity (adaptor vs. localization vs. substrate presentation) unknown
   • Whether mTORC1 interaction is linked to or independent of SG biology not addressed
5. 2022 High

   Identifying UBAP2L as the human functional orthologue of yeast Def1 in transcription-coupled DNA damage response: UBAP2L (and UBAP2) were shown to recruit the Elongin–Cul5 E3 ubiquitin ligase to promote UV-induced ubiquitylation and proteasomal degradation of RNA Pol II subunit RPB1.

   Evidence UV-irradiation, UBAP2/UBAP2L knockdown, co-IP with Elongin–Cul5, RPB1 ubiquitylation and degradation assays in human cells

   PMID:35633597

   Open questions at the time

   • Whether UBAP2L acts as a direct substrate adaptor or an allosteric activator of the Elongin–Cul5 complex not determined
   • Structural basis for Elongin–Cul5 recruitment by UBAP2L not resolved
   • Redundancy between UBAP2 and UBAP2L in this pathway not fully dissected
6. 2023 High

   Revealing that snoRNAs bridge the UBAP2L–G3BP1 interaction: in vitro binding experiments demonstrated that snoRNAs are required for UBAP2L to associate with G3BP1, and snoRNA depletion suppressed SG formation, establishing an RNA-dependent mechanism for SG nucleation complex assembly.

   Evidence In vitro binding assays, RNA immunoprecipitation, snoRNA knockdown, proteomics and RNA-seq

   PMID:37059803

   Open questions at the time

   • Identity of the specific snoRNA species most critical for bridging not narrowed to individual candidates
   • Whether snoRNAs serve a structural vs. catalytic role in the complex is unknown
   • Whether snoRNA bridging is stress-regulated not tested
7. 2023 High

   Establishing UBAP2L as a mitotic regulator of PLK1: UBAP2L depletion caused PLK1 stabilization and mislocalization to kinetochores, centrosomes, and spindle, leading to chromosome segregation errors; chemical PLK1 inhibition rescued these defects, and the C-terminal domain of UBAP2L was mapped as necessary for PLK1 regulation.

   Evidence siRNA knockdown, live-cell imaging, immunofluorescence, PLK1 inhibitor rescue, C-terminal domain deletion

   PMID:37039032

   Open questions at the time

   • Whether UBAP2L directly binds PLK1 or acts through an intermediate E3 ligase not resolved
   • The E3 ubiquitin ligase responsible for UBAP2L-dependent PLK1 ubiquitylation not identified
   • Whether the mitotic and SG functions of UBAP2L are mutually exclusive in cycling cells not tested
8. 2024 High

   Defining UBAP2L as a scaffold for nuclear pore complex assembly: UBAP2L was shown to localize to nuclear pores, promote Y-complex formation and its recruitment to the nuclear envelope, and facilitate sequential interactions with POM121, Nup153, and FXR1, establishing it as a nucleoporin assembly factor at intact NEs.

   Evidence Co-IP, super-resolution microscopy, proximity ligation assay, siRNA knockdown, nuclear transport assays

   PMID:38652117

   Open questions at the time

   • Whether UBAP2L is a bona fide stoichiometric NPC component or a transient assembly factor not determined
   • Structural basis for UBAP2L interaction with the Y-complex not resolved
   • Interplay between NPC assembly and SG/PB functions of UBAP2L not examined
9. 2024 High

   Expanding UBAP2L's granule biology to processing bodies: UBAP2L was shown to localize to PBs, bind DDX6 (a core PB component), promote PB biogenesis, and mediate physical SG–PB interactions including formation of hybrid granules.

   Evidence Immunofluorescence, live-cell imaging, UBAP2L knockdown with quantitative PB/SG analysis, co-IP with DDX6 and G3BP

   PMID:39007803

   Open questions at the time

   • Mechanism by which UBAP2L simultaneously engages SG and PB components at molecular level not defined
   • Functional consequence of SG–PB hybrid granules for mRNA fate not established
   • Whether PB localization requires the same domains (RGG, DUF) as SG localization not mapped
10. 2024 High

    Revealing viral subversion of UBAP2L-dependent antiviral granule assembly: SARS-CoV-2 NSP3 was found to directly bind FMRP KH domains via a peptide motif that competes with a corresponding UBAP2L motif, disrupting FMRP–UBAP2L interaction and preventing FMRP incorporation into stress granules.

    Evidence In vitro binding/competition assay with synthetic peptides, mutant virus, domain mapping, infectivity assays

    PMID:38177924

    Open questions at the time

    • Whether other viral proteins similarly target the UBAP2L–FMRP axis not surveyed
    • Functional impact of FMRP exclusion from SGs on antiviral innate immunity not mechanistically dissected
    • Whether UBAP2L's NPC assembly role is also targeted during viral infection not examined
11. 2025 Medium

    Connecting UBAP2L post-translational regulation to its stability and oncogenic functions: O-GlcNAcylation of UBAP2L was shown to antagonize TRIM37-mediated ubiquitylation, stabilizing the protein and promoting SG-dependent mRNA stabilization of Melk to activate PI3K signaling; separately, UBAP2L-nucleated SGs mediate chemoresistance by sequestering pro-apoptotic RACK1.

    Evidence IP-mass spectrometry for O-GlcNAcylation sites, TRIM37 ubiquitylation assays, RIP-seq, RACK1 co-localization/co-IP, in vivo xenograft models

    PMID:40804300 PMID:41029457

    Open questions at the time

    • Whether O-GlcNAcylation and arginine methylation cross-regulate each other on UBAP2L not tested
    • Direct evidence that RACK1 sequestration is the primary mechanism of chemoresistance (vs. other SG-sequestered factors) not established
    • TRIM37 as the primary E3 for UBAP2L turnover confirmed in only one cancer context

• Key unresolved questions include: what upstream signal triggers UBAP2L condensation upon stress, the structural basis for its multi-domain scaffolding of diverse complexes (SGs, PBs, NPCs, Polycomb, mitotic spindle), whether its distinct cellular functions are temporally segregated across the cell cycle, and how its multiple post-translational modifications (methylation, O-GlcNAcylation, phosphorylation, ubiquitylation) are integrated to coordinate its pleiotropic roles.
• No structural model of UBAP2L exists
• How UBAP2L partitions between its nuclear (NPC, Polycomb) and cytoplasmic (SG, PB, mitotic) roles is unknown
• Whether UBAP2L's diverse functions reflect independent modules or an integrated signaling hub is unresolved