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

Area of Science:

• Molecular Biology
• Epigenetics
• Cancer Biology

Background:

• Histone deacetylase 7 (HDAC7) is a Class IIa histone deacetylase implicated in transcriptional regulation.
• The precise molecular mechanisms of HDAC7 in cancer, particularly colorectal cancer (CRC), are not fully understood.
• HDAC7's scaffolding functions suggest a role in assembling protein complexes that modify gene expression.

Purpose of the Study:

• To investigate the role of HDAC7 as an epigenetic regulator in colorectal cancer (CRC).
• To elucidate the molecular mechanisms by which HDAC7 influences CRC pathogenesis.
• To evaluate the therapeutic potential of targeting HDAC7 in CRC.

Main Methods:

• Analysis of HDAC7 expression in CRC tumors and correlation with clinical parameters.
• Mechanistic studies involving immunoprecipitation and Western blotting to identify protein complexes.
• Assessment of histone modifications (H3K27ac, H3K18ac) and recruitment of transcription factors (BRD4, RNA polymerase II).
• Functional assays including genetic depletion and pharmacological inhibition of HDAC7.
• Cellular assays to evaluate cell cycle arrest, apoptosis, and signaling pathways (PI3K-Akt, Hippo).
• In vivo studies using xenograft models to assess tumorigenicity.

Main Results:

• HDAC7 is overexpressed in CRC and associated with advanced stages, metastasis, and poor survival.
• HDAC7 forms a complex with HDAC3 and ATF3, epigenetically silencing ATF3 transcription by reducing H3K27ac/H3K18ac and blocking BRD4/Pol II recruitment.
• HDAC7-mediated silencing of ATF3 promotes oncogenic PI3K-Akt signaling and suppresses the Hippo pathway.
• HDAC7 inhibition or depletion disrupts the repressive complex, leading to ATF3 self-activation.
• Reactivated ATF3 suppresses CRC proliferation and survival by downregulating Bcl-2, upregulating p21, inducing apoptosis, and inhibiting PI3K-Akt signaling.
• HDAC7 depletion suppressed tumor growth in vivo xenograft models.

Conclusions:

• HDAC7 acts as a key epigenetic regulator in CRC by scaffolding a complex that silences the tumor suppressor ATF3.
• HDAC7 controls ATF3's functional plasticity through competitive cofactor recruitment, switching it from a tumor suppressor to a silenced state.
• Targeting HDAC7 reactivates ATF3-mediated tumor suppression, presenting a promising therapeutic strategy for CRC.