Histone deacetylase 3 (HDAC3) activity is regulated by interaction with protein serine/threonine phosphatase 4

Abstract

Histone deacetylase 3 (HDAC3) is one of four members of the human class I HDACs that regulates gene expression by deacetylation of histones and nonhistone proteins. Early studies have suggested that HDAC3 activity is regulated by association with the corepressors N-CoR and SMRT. Here we demonstrate that, in addition to protein–protein interactions with NCoR/SMRT, the activity of HDAC3 is regulated by both phosphorylation and dephosphorylation. A protein kinase CK2 phosphoacceptor site in the HDAC3 protein was identified at position Ser⁴²⁴, which is a nonconserved residue among the class I HDACs. Mutation of this residue was found to reduce deacetylase activity. Interestingly, unlike other class I HDACs, HDAC3 uniquely copurifies with the catalytic and regulatory subunits of the protein serine/threonine phosphatase 4 complex (PP4_c/PP4_R1). Furthermore, HDAC3 complexes displayed protein phosphatase activity and a series of subsequent mutational analyses revealed that the N terminus of HDAC3 (residues 1–122) was both necessary and sufficient for HDAC3–PP4_c interactions. Significantly, both overexpression and siRNA knock-down approaches, and analysis of cells devoid of PP4_c, unequivocally show that HDAC3 activity is inversely proportional to the cellular abundance of PP4_c. These findings therefore further highlight the importance of protein–protein interactions and extend the significance of dephosphorylation in the regulation of HDAC activity, as well as present a novel alternative pathway by which HDAC3 activity is regulated.

Keywords

• HDAC3
• histone deacetylation
• protein phosphatase
• PP4