Class I and Class II Histone Deacetylases (Class I and Class II HDACs)

Class I and Class II Histone Deacetylases (HDACs) are a group of zinc-dependent enzymes that play a critical role in epigenetic regulation by removing acetyl groups from lysine residues on histones and various non-histone proteins (Morris & Monteggia, 2013). Class I HDACs (HDAC1, 2, 3, and 8) are primarily nuclear and ubiquitously expressed, while Class II HDACs (HDAC4, 5, 6, 7, 9, and 10) shuttle between the nucleus and cytoplasm and exhibit tissue-specific expression (Haberland et al., 2009). By promoting chromatin compaction, these enzymes generally act as transcriptional co-repressors, influencing essential cellular processes such as the cell cycle, apoptosis, and differentiation (Rosato & Grant, 2005). Dysregulation of Class I and II HDACs is strongly linked to the pathogenesis of various cancers, neurodegenerative disorders, and inflammatory diseases (Grant & Dai, 2012). Therapeutic targeting with HDAC inhibitors (HDACis), such as vorinostat and panobinostat, aims to restore normal gene expression patterns and induce cell death in malignant cells (Bolden et al., 2006). These drugs typically bind to the zinc ion in the catalytic pocket, blocking substrate access and leading to the hyperacetylation of target proteins (Parmigiani et al., 2008). However, the clinical use of these agents is often limited by systemic toxicities, including myelosuppression and cardiotoxicity, necessitating the development of more isoform-selective inhibitors (Tse et al., 2009).

Other names

Lysine deacetylasesKDACsZinc-dependent histone deacetylasesClassical HDACs

HDAC inhibitors bind to the zinc-containing catalytic domain of the enzymes, preventing the removal of acetyl groups from lysine residues on histones and non-histone proteins. This results in hyperacetylation, which relaxes chromatin structure and promotes the re-expression of tumor suppressor genes, leading to cell cycle arrest and apoptosis.