HDAC7-Induced Epigenetic Repression Modulates ATF3 Functional Plasticity in Colorectal Cancer Pathogenesis

Class IIa histone deacetylase 7 (HDAC7) regulates transcription primarily through scaffolding functions, but its molecular mechanisms in cancer pathogenesis remain incompletely understood. Here, we establish HDAC7 as a key epigenetic regulator in colorectal cancer (CRC). HDAC7 is overexpressed in CRC tumors and correlates with advanced disease stages, lymph node metastasis, and poor patient survival. Mechanistically, HDAC7 scaffolds a repressive complex with HDAC3 and the stress-responsive transcription factor ATF3. This reduces H3K27ac/H3K18ac occupancy and blocks BRD4/RNA polymerase II (Pol II) recruitment at ATF3 regulatory regions to epigenetically silence its transcription. Consequently, this repression inactivates ATF3's tumor-suppressive functions, activating oncogenic PI3K-Akt signaling while suppressing the Hippo pathway. Genetic depletion or pharmacological inhibition of HDAC7 disrupts this repressive complex, triggering a functional switch in ATF3. This promotes BRD4/Pol II recruitment and H3K27ac enrichment at the ATF3 locus, enabling ATF3 to undergo transcriptional self-activation. Reactivated ATF3 suppresses CRC proliferation and survival by downregulating Bcl-2, upregulating p21 (CDKN1A) to induce cell cycle arrest, promoting caspase-3-mediated apoptosis, and inhibiting PI3K-Akt signaling. Xenograft studies confirm that HDAC7 depletion suppresses tumorigenicity in vivo. Our work identifies HDAC7 as a molecular mediator that governs ATF3's functional plasticity through competitive cofactor recruitment, positioning HDAC7 inhibition as a therapeutic strategy to reactivate ATF3-mediated tumor suppression in CRC.