HNRNPUL1

HNRNPUL1 (E1B-AP5) is a nuclear RNA-binding protein that couples RNA metabolism to the DNA damage response and transcriptional control (PMID:26020839, PMID:18480432). Structurally it is built around a central folded region of tightly juxtaposed SPRY and catalytically dead polynucleotide kinase (dPNK) domains flanked by intrinsically disordered regions; the dPNK domain binds both nucleotides and RNA, and nucleotide binding governs full-length RNA-binding behavior, protein stability, and a switch between homotypic and heterotypic (IDR-driven) protein interactions (PMID:41971996). Its intrinsically disordered RGG/RG motifs are asymmetrically arginine-methylated by PRMT1 at defined arginine residues, and this methylation is required for interaction with the DNA damage sensor NBS1 and for recruitment of HNRNPUL1 to damage sites (PMID:26020839); recruitment to double-strand breaks proceeds through association with PARP1 in a poly(ADP-ribosyl)ation-dependent manner, and HNRNPUL1 in turn restrains PARP1 accumulation and regulates PARP1 gene transcription (PMID:23577092). HNRNPUL1 directly binds the ATR-pathway components ATRIP, RPA70, and RPA32, localizing to replication centers and supporting ATR-dependent phosphorylation of RPA32, Smc1, and H2AX (PMID:18480432). In parallel it acts as a transcriptional regulator: it represses basal transcription through its N-terminal domain, forms a complex with the bromodomain protein BRD7 and core histones that modulates repression and hormone-dependent activation (PMID:12489984), and directly binds p53 to inhibit p53-dependent transactivation (PMID:15907477). In vivo loss of Hnrnpul1 in zebrafish disrupts alternative splicing and transcription of translation-, ubiquitination-, and DNA damage-related genes and causes skeletal and limb developmental defects (PMID:35325113). Rare ALS-associated coding variants alter its nucleotide binding, RNA binding, and interaction with FUS (PMID:41971996).

1. 2001 Medium

   Established that HNRNPUL1 is post-translationally modified by arginine methylation within its RGG-box and engages arginine methyltransferase machinery, framing it as a regulated RNA-binding protein.

   Evidence In vivo and in vitro methylation assays on the recombinant RGG-box, yeast two-hybrid screening, and co-IP/immunofluorescence identifying HRMT1L1/PRMT2 as an SH3-dependent interactor

   PMID:11513728

   Open questions at the time

   • Endogenous methyltransferase responsible in vivo was not definitively resolved (PRMT1 negative on endogenous substrate, PRMT2 assignment partly indirect)
   • Functional consequence of methylation not addressed at this stage
2. 2003 Medium

   Defined HNRNPUL1 as a context-dependent transcriptional regulator acting through a BRD7-containing chromatin complex, answering what nuclear function it serves beyond RNA binding.

   Evidence Reporter transcription assays, yeast two-hybrid, reciprocal co-IP and GST pull-down, and demonstration of a triple complex with BRD7 and core histones, plus domain mapping

   PMID:12489984

   Open questions at the time

   • Target promoters and physiological gene sets unknown
   • Mechanism converting it between activator and repressor not resolved at the molecular level
3. 2005 Medium

   Showed HNRNPUL1 directly inhibits p53 transcriptional output, linking it to tumor-suppressor signaling and stress responses.

   Evidence GST pull-down and co-IP mapping the p53 C-terminal interaction, reporter assays, and UV-induced target-gene readouts in tumor cells

   PMID:15907477

   Open questions at the time

   • Whether endogenous HNRNPUL1 levels regulate p53 targets under physiological stress unclear
   • Structural basis of the multi-region p53 contact not defined
4. 2008 High

   Placed HNRNPUL1 within the ATR-RPA branch of the DNA damage/replication response through direct binding to ATRIP and RPA, addressing how it participates in damage signaling.

   Evidence Co-IP, direct in vitro GST pull-down with RPA70/RPA32, immunofluorescence co-localization at replication centers, and siRNA knockdown with phosphorylation readouts (RPA32, Smc1, H2AX) during adenovirus infection

   PMID:18480432

   Open questions at the time

   • Most data obtained in the adenovirus-infection context; extent of role in cellular DSB signaling not fully established here
   • How HNRNPUL1 promotes RPA32 phosphorylation mechanistically unknown
5. 2013 Medium

   Identified the recruitment mechanism to double-strand breaks via PARP1 and PAR, and a reciprocal regulatory loop on PARP1 itself.

   Evidence Co-IP, laser micro-irradiation recruitment assays, siRNA knockdown, and transcription/expression assays on the PARP1 gene

   PMID:23577092

   Open questions at the time

   • Direct PAR-binding module on HNRNPUL1 not mapped
   • Functional outcome at the break (repair pathway choice) not resolved
6. 2015 High

   Resolved that PRMT1-mediated asymmetric arginine methylation of the RGG/RG motifs is the molecular switch enabling NBS1 interaction and damage-site recruitment, unifying the methylation and DDR findings.

   Evidence Mass-spectrometry site mapping in U2OS cells, in vitro/in vivo methylation assays, RGG-to-RK mutagenesis, co-IP with NBS1, and laser-induced damage recruitment assays

   PMID:26020839

   Open questions at the time

   • Whether methylation is dynamically regulated by damage signaling not established
   • Relative contributions of individual methylated arginines not dissected
7. 2022 Medium

   Demonstrated the in vivo physiological requirement for Hnrnpul1 in alternative splicing/transcription and in skeletal and limb development.

   Evidence Zebrafish knockout with morphological phenotyping, RNA-sequencing of splicing and transcriptome changes, and human whole-exome sequencing

   PMID:35325113

   Open questions at the time

   • Direct RNA targets and splicing regulatory mechanism not defined
   • Human disease causality from exome data not firmly established
8. 2022 Medium

   Characterized how the HNRNPUL1 C-terminal moiety contributes trans-regulatory activity and dimerization within the MEF2D-HNRNPUL1 leukemic fusion, a disease-specific context.

   Evidence Knock-in mouse model, RNA-seq, ChIP-seq, X-ray crystallography of the MEF2D-MRE complex, and DNA-interface mutagenesis

   PMID:35544603

   Open questions at the time

   • Findings pertain to the fusion oncoprotein, not wild-type HNRNPUL1 function
   • Role of HNRNPUL1 IDRs in cofactor recruitment not separated from MEF2D activity
9. 2023 Medium

   Positioned HNRNPUL1 as a NAT10/ac4C-regulated effector promoting cervical cancer cell proliferation and invasion.

   Evidence acRIP-seq ac4C mapping, mRNA stability assays, siRNA knockdown, overexpression rescue, and xenograft models

   PMID:37484809

   Open questions at the time

   • Downstream effectors of HNRNPUL1 in this oncogenic axis not identified
   • Generality beyond cervical cancer untested
10. 2026 High

    Provided the structural-biochemical framework: a folded SPRY-dPNK core whose nucleotide binding governs RNA binding, protein stability, and a homotypic-to-heterotypic interaction switch, and linked patient ALS variants to these activities.

    Evidence AlphaFold modeling with experimental validation, nucleotide- and RNA-binding assays, kinase-reactivating and binding-disrupting mutagenesis, stability assays, protein-interaction assays (including FUS), and patient variant analysis

    PMID:41971996

    Open questions at the time

    • Physiological RNA ligands of the dPNK domain unknown
    • Whether ALS variants cause neurodegeneration in vivo not established

• How HNRNPUL1's RNA-binding/structural activities are mechanistically coupled to its splicing, DDR, and transcriptional roles, and the identity of its physiological RNA targets, remain unresolved.
• No defined endogenous RNA target set linking the dPNK/RNA-binding activity to splicing or DDR outcomes
• Mechanism integrating transcriptional repression (p53/BRD7) with damage signaling not unified
• No structure of full-length protein in complex with NBS1, RPA, or PARP1