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

Class I and II Histone Deacetylases (HDACs) represent a critical family of zinc-dependent enzymes that modulate the epigenetic landscape by removing acetyl groups from lysine residues on histones and various non-histone proteins (UniProt, 2023). Class I HDACs (1, 2, 3, and 8) are ubiquitously expressed and primarily nuclear, playing a central role in cell proliferation and survival, whereas Class II HDACs (4, 5, 6, 7, 9, and 10) show tissue-specific expression and shuttle between the nucleus and cytoplasm to regulate diverse cellular processes (StatPearls, 2023). By maintaining histones in a deacetylated state, these enzymes facilitate a condensed chromatin conformation that typically represses gene transcription (NIH, 2024). In oncology, the dysregulation or overexpression of HDACs is a well-documented mechanism for the silencing of tumor suppressor genes, making them high-priority therapeutic targets (PubMed: Li et al., 2020). Small molecule HDAC inhibitors (HDACis) function by chelating the zinc ion in the active site, leading to hyperacetylation and the subsequent reactivation of genes that trigger cell cycle arrest and apoptosis in malignant cells (PubChem, 2024). While several HDACis are currently FDA-approved for hematological malignancies like T-cell lymphoma and multiple myeloma, the field is evolving toward more selective inhibitors to mitigate the systemic toxicities associated with pan-HDAC inhibition (FDA, 2023).

Other names

Histone deacetylasesKDACsLysine deacetylasesZinc-dependent HDACsHDAC family

The primary mechanism of action involves the competitive inhibition of the zinc-dependent catalytic domain of Class I and II HDACs, which prevents the removal of acetyl groups from lysine residues (PubMed: Seto & Yoshida, 2014). This inhibition results in the hyperacetylation of histone tails, promoting an open chromatin structure (euchromatin) that facilitates the transcription of genes involved in growth regulation and apoptosis, such as p21 (NIH, 2024). Beyond histones, these enzymes also regulate the acetylation of non-histone substrates including p53, alpha-tubulin, and Hsp90, thereby influencing protein stability, intracellular transport, and DNA repair pathways (StatPearls, 2023).