Class IIa HDACs Are Important Signal Transducers with Unclear Enzymatic Activities

Class IIa histone deacetylases (HDACs) are pleiotropic regulators of various differentiation pathways and adaptive responses. They form complexes with other co-repressors and can bind to DNA by interacting with selected transcription factors, with members of the Myocyte Enhancer Factor-2 (MEF2) family being the best characterized. A notable feature of class IIa HDACs is the substitution of tyrosine for histidine in the catalytic site, which has occurred over the course of evolution and has a profound effect on the efficiency of catalysis against acetyl-lysine. Another distinctive feature of this family of “pseudoenzymes” is the regulated nucleus–cytoplasm shuttling associated with several non-histone proteins that have been identified as potential substrates, including proteins localized in the cytosol. Within the complexity of class IIa HDACs, several aspects deserve further investigation. In the following, I will discuss some of the recent advances in our knowledge of class IIa HDACs.