HDAC4

HDAC4 is a class IIa histone deacetylase that acts as a signal-dependent transcriptional regulator linking extracellular cues to chromatin remodeling, gene expression, and cell differentiation^[1][2]. Mechanistically, class IIa HDACs, including HDAC4, shuttle between nuclear and cytoplasmic compartments through post-translational modification, and this localization controls their transcriptional functions^[3]. In liver, HDAC4, HDAC5, and HDAC7 respond to glucagon by entering the nucleus, associating with gluconeogenic promoters, recruiting HDAC3, activating FOXO transcription factors, and increasing blood-glucose-related gene expression^[4]. In skeletal muscle, class II HDAC proteins repress MEF2 activity and suppress slow-twitch oxidative myofiber formation, while MEF2 activation promotes endurance-associated fiber programs^[5]. In pancreatic endocrine models, HDAC4, HDAC5, and HDAC9 regulate β-cell and δ-cell lineage control, and class IIa HDAC inhibition with MC1568 amplifies endocrine β- and δ-cells^[6]. Compared with related isoforms, HDAC4 belongs to the HDAC4/5/7/9 class IIa subgroup, which shares MEF2-related transcriptional partners but shows distinct disease-linked regulatory roles^[7]. For experimental applications, LBH589 confined HDAC4 to the cytoplasm, prolonged γ-H2AX foci after irradiation, and sensitized non-small cell lung cancer models to radiation-induced DNA double-strand breaks^[8]. Selective inhibitor design also identified LMK235 as showing nanomolar inhibition of HDAC4 and HDAC5, unlike vorinostat and TSA, which inhibited these isoforms in the higher micromolar range^[9].