ATXN1L

ATXN1L (BOAT1) functions as a stabilizing partner of the transcriptional repressor CIC, and through this complex governs developmental, immune, and oncogenic gene-expression programs (PMID:22014525, PMID:33115448). It binds CIC and prevents its polyubiquitination and TRIM25-mediated proteasomal degradation independently of ERK activity, so loss of ATXN1L destabilizes CIC and derepresses CIC target genes including the ETS factors ETV1/4/5 (PMID:33115448, PMID:28178529). ETV4 derepression in turn drives downstream programs: MMP gene induction and extracellular matrix remodeling during lung alveolarization (PMID:22014525), and suppression of Notch1/Notch2 transcription that disrupts marginal zone B cell development and humoral immunity (PMID:39632849). The CIC-ATXN1L complex also binds an 8-nucleotide motif near interferon and ISG promoters to repress them under homeostasis, with MAPK-driven complex degradation during respiratory viral infection relieving this repression to permit robust IFN/ISG induction (PMID:40132591). ATXN1L competes with its paralog ATXN1 for incorporation into the CIC complex, and CIC isoforms partition between them, the CIC-S isoform preferentially binding ATXN1L; elevated ATXN1L displaces polyglutamine-expanded ATXN1 and suppresses SCA1 neuropathology (PMID:17322884, PMID:41279815). Through the CIC-ETS axis, ATXN1L also modulates cancer-cell sensitivity to MAPK pathway inhibitors (PMID:28178529) and maintains hematopoietic stem cell quiescence (PMID:23555280).

1. 2007 High

   Established that ATXN1L is a native component of the ATXN1-CIC complex and that it competes with ATXN1, reframing it from a paralog of unknown role into a dose-dependent modifier of an established complex.

   Evidence Targeted Atxn1l duplication and genetic epistasis in a knock-in SCA1 mouse model

   PMID:17322884

   Open questions at the time

   • Did not define the biochemical determinants of competition with ATXN1
   • Did not establish CIC target genes regulated by ATXN1L
2. 2011 High

   Defined ATXN1L's core mechanism as a CIC stabilizer whose loss derepresses ETV4 and downstream MMPs, linking the complex to a concrete developmental output (lung alveolarization).

   Evidence Atxn1l and Atxn1/Atxn1l double-knockout mice, CIC protein stability assays, and genetic epistasis with Cic-deficient mice

   PMID:22014525

   Open questions at the time

   • Mechanism of CIC destabilization not yet identified
   • E3 ligase mediating CIC turnover unknown
3. 2011 Medium

   Tested whether ATXN1L acts beyond CIC by probing Notch output, showing ATXN1L and ATXN1 bind the Hey1 promoter and interact with CBF1 to inhibit Notch transcription.

   Evidence Drosophila genetics plus mammalian promoter-binding and CBF1 interaction assays

   PMID:21475249

   Open questions at the time

   • Single-lab data
   • Relationship between CBF1-dependent Notch repression and the CIC-dependent mechanism not reconciled
4. 2013 Medium

   Extended ATXN1L function to adult stem cell biology, showing it maintains hematopoietic stem cell quiescence.

   Evidence Atxn1l knockout mice with in vitro and in vivo HSC assays and expression profiling

   PMID:23555280

   Open questions at the time

   • Did not establish whether the quiescence phenotype is CIC-dependent
   • Downstream transcriptional effectors not defined
5. 2017 High

   Connected the ATXN1L-CIC-ETS axis to therapy response, showing ATXN1L loss reduces CIC and modulates MEK inhibitor sensitivity, with ETS overexpression phenocopying the loss.

   Evidence Genome-scale CRISPR screens in KRAS-mutant pancreatic cancer lines plus ectopic ETS factor expression and MAPKi sensitivity assays

   PMID:28178529

   Open questions at the time

   • Did not resolve the molecular step linking ATXN1L to CIC stability
   • Clinical generalizability across tumor types not established
6. 2018 Medium

   Demonstrated convergent CIC and ATXN1L function at the transcriptome level, implicating the axis in mitotic cell cycle and division control.

   Evidence ATXN1LKO and CICKO human cell lines with transcriptomic profiling

   PMID:30093628

   Open questions at the time

   • Correlative transcriptomics without direct cell-cycle mechanistic dissection
   • Single lab
7. 2020 High

   Resolved the biochemical mechanism of CIC stabilization, identifying TRIM25 as the E3 ligase whose ATXN1L-blocked polyubiquitination targets CIC for proteasomal degradation, independent of ERK.

   Evidence ATXN1LKO cell lines, polyubiquitination and proteasome-inhibition assays, TRIM25 functional assays, validated in glioma lines

   PMID:33115448

   Open questions at the time

   • How ATXN1L binding sterically or allosterically blocks TRIM25 not defined
   • Whether other ligases contribute under ERK-active conditions unknown
8. 2022 Medium

   Implicated ATXN1L in cardiomyocyte cell death regulation, both via CIC-dependent suppression of PYDC1 (controlled by miR-136-5p) and via HDAC3-mediated histone deacetylation repressing NOL3.

   Evidence Luciferase reporter and co-IP for the miR-136-5p/ATXN1L/CIC axis, plus ChIP and HDAC3 inhibition for the NOL3 mechanism in cardiomyocytes and rats

   PMID:35084609 PMID:35414011

   Open questions at the time

   • Co-IP without reciprocal validation for the ATXN1L-CIC pyroptosis link
   • Whether HDAC3 recruitment is CIC-dependent not established
   • Single disease-model context
9. 2024 High

   Showed the CIC-ATXN1L complex is required for marginal zone B cell development and humoral immunity, with ETV4 derepression repressing Notch1/Notch2 as the operative mechanism.

   Evidence B cell-specific conditional Atxn1l knockout mice with Etv4 deletion epistasis rescue and an LPS sepsis model

   PMID:39632849

   Open questions at the time

   • How ETV4 represses Notch receptor transcription mechanistically not detailed
   • Generalizability to other B cell subsets unclear
10. 2025 High

    Defined an antiviral function: the CIC-ATXN1L complex represses IFN/ISG promoters via an 8-nt motif at homeostasis, and MAPK-triggered complex degradation during viral infection unleashes interferon responses.

    Evidence DNA-binding motif identification, complex degradation assays during infection, and loss-of-function studies in human and mouse cells

    PMID:40132591

    Open questions at the time

    • Whether TRIM25 mediates the infection-triggered complex degradation not established
    • Kinetics relative to other IFN-regulatory layers unresolved
11. 2025 Medium

    Resolved paralog/isoform specificity, showing CIC-S preferentially binds ATXN1L and CIC-L binds ATXN1, with isoform-specific knockouts phenocopying the respective paralog knockouts.

    Evidence CIC isoform-specific knockout mice and co-immunoprecipitation binding-preference assays (preprint)

    PMID:41279815

    Open questions at the time

    • Preprint not yet peer-reviewed
    • Structural basis of isoform-paralog selectivity not defined

• How ATXN1L binding mechanistically blocks TRIM25-mediated CIC ubiquitination, and how this is reversed during MAPK-driven signaling, remains undefined at the structural level.
• No structural model of the ATXN1L-CIC interface
• Signal that triggers complex degradation during infection vs homeostasis not biochemically mapped