CHRAC1

CHRAC1 is a histone-fold protein of the H2A/H2B sub-family that functions as an accessory subunit of ATP-dependent chromatin-remodeling machinery and, through context-specific partners, in DNA repair and transcriptional control (PMID:14759371, PMID:11000277). It heterodimerizes through its histone-fold domain with CHRAC17/POLE3 and directly contacts the ACF1 subunit of the ACF/CHRAC remodeling complex; this CHRAC15/17 dimer is specifically required for ACF1 binding, enhances ATP-dependent nucleosome sliding, and facilitates chromatin assembly by a mechanism distinct from sliding (PMID:14759371, PMID:16403426). Within this complex CHRAC1 contributes to DNA double-strand break repair: the ACF1-containing remodeler associates with KU70/80 after damage and is required for KU accumulation at breaks and for both NHEJ and HR (PMID:21172662), and the CHRAC1–POLE3 interaction supports homology-directed repair protein expression and KU80 recruitment, an activity attenuated by the colorectal-cancer-associated CHRAC1 D121Y mutation (PMID:37682991). Beyond chromatin remodeling, CHRAC1 binds the Hippo-pathway coactivator YAP and enhances transcription of YAP target oncogenes to drive proliferation and tumor growth in lung, breast, and cervical cancer models (PMID:34718437, PMID:38223760), and it transcriptionally activates IRF9 to engage a NOD-like-receptor/GSDMD/caspase-1 pyroptotic axis underlying doxorubicin-induced cardiomyocyte death (PMID:41325875).

1. 2000 Medium

   Establishing the biochemical identity of CHRAC1 answered whether it is a histone-fold protein capable of nucleosome-associated function rather than a sequence-specific DNA-binding factor.

   Evidence Nucleosome reconstitution and glycerol gradient sedimentation of YCL1 with core histones

   PMID:11000277

   Open questions at the time

   • No functional mutagenesis or cellular validation
   • Did not define the in vivo complex CHRAC1 acts within
   • Partner specificity for assembly into remodeling complexes untested
2. 2004 High

   In vitro reconstitution defined CHRAC1's mechanistic role, showing the CHRAC15/17 dimer bridges to ACF1 and is required to enhance ATP-dependent nucleosome sliding and chromatin assembly.

   Evidence In vitro nucleosome sliding and chromatin assembly assays with subunit-resolved dissection

   PMID:14759371

   Open questions at the time

   • Structural basis of the ACF1 contact not resolved
   • Mechanism distinguishing assembly enhancement from sliding undefined
   • In vivo consequences of CHRAC1 loss not tested
3. 2006 Medium

   Characterizing the histone-fold heterodimers clarified how CHRAC1 partitions between the remodeling complex and DNA polymerase epsilon machinery via shared POLE3 partnering.

   Evidence Protein interaction characterization, ChIP, and cell-cycle expression analysis

   PMID:16403426

   Open questions at the time

   • Functional consequence of POLE3/CHRAC15 association with ACF1/SNF2H not measured
   • CHRAC1-specific role versus POLE3 not separated
   • Single-lab interaction study
4. 2010 Medium

   Linking the CHRAC complex to damage signaling answered whether ACF-type remodeling participates in DSB repair, showing it is needed for KU recruitment and repair pathway execution.

   Evidence Co-IP, siRNA knockdown with NHEJ/HR assays, and live-cell imaging of accumulation at DSBs

   PMID:21172662

   Open questions at the time

   • CHRAC15-specific contribution inferred from complex membership, not directly tested
   • Direct CHRAC1–KU interaction not demonstrated
   • Mechanism of remodeler recruitment to breaks unresolved
5. 2023 Medium

   Disease-mutation analysis tied CHRAC1's repair role to a concrete molecular interface, showing the CHRAC1–POLE3 contact supports HDR protein expression and KU80 recruitment.

   Evidence Co-IP and cell-based DNA repair assays with the cancer-associated D121Y mutation

   PMID:37682991

   Open questions at the time

   • How the interaction regulates repair-protein expression mechanistically unclear
   • Single-lab validation
   • Structural effect of D121Y not determined
6. 2022 Medium

   Identifying a YAP partnership revealed a chromatin-independent oncogenic role, showing CHRAC1 binds YAP and amplifies Hippo-pathway target oncogene transcription to drive lung tumorigenesis.

   Evidence Co-IP, knockdown/overexpression proliferation and migration assays, KrasG12D and xenograft mouse models

   PMID:34718437

   Open questions at the time

   • Direct binding interface with YAP not mapped
   • Relationship between this role and chromatin remodeling function unclear
   • Single-lab study
7. 2024 Medium

   Extending the YAP connection to additional cancers tested its generality, confirming CHRAC1 co-localizes with YAP and drives target gene transcription and tumor growth in breast and cervical models.

   Evidence Bio-ID proximity labeling, immunofluorescence, colony/proliferation assays, xenograft, RNA-seq

   PMID:38223760

   Open questions at the time

   • Proximity labeling does not establish direct binding
   • Mechanism of YAP target selection unresolved
   • Single-lab corroboration
8. 2025 Medium

   Defining a CHRAC1-IRF9 transcriptional axis revealed a pyroptotic function, showing CHRAC1 activates IRF9 to engage GSDMD/caspase-1 cell death in cardiomyocytes during doxorubicin cardiotoxicity.

   Evidence RNA-seq, ATAC-seq, knockdown/overexpression, and IRF9-silencing epistasis in murine and cellular models

   PMID:41325875

   Open questions at the time

   • No direct biochemical binding assay for CHRAC1 at the IRF9 locus
   • How a histone-fold accessory protein achieves gene-specific transcriptional activation unclear
   • Single-lab study

• It remains unresolved how CHRAC1 mechanistically switches between its core chromatin-remodeling/DSB-repair role and its partner-specific transcriptional functions with YAP and IRF9.
• No structural model unifying histone-fold remodeling and transcriptional coactivation
• Direct DNA/chromatin binding at YAP and IRF9 targets not demonstrated
• Whether these roles are independent or share the CHRAC15/17 dimer unknown