Histone deacetylase 1 or Histone deacetylase 2 (HDAC1 or HDAC2)

Histone deacetylase 1 and 2 are highly homologous, nuclear-localized enzymes that remove acetyl groups from lysine residues on the N-terminal tails of core histones (H2A, H2B, H3, and H4), leading to chromatin condensation and transcriptional repression. They act as the principal catalytic components of several large multi-protein corepressor complexes, including Sin3, NuRD, and CoREST. While they have distinct biologic roles (e.g., HDAC1 is essential for embryonic development, whereas HDAC2 is critical for memory formation), they are generally functionally redundant and compensate for each other in many contexts. HDAC1/2 regulate essential cellular processes, including the cell cycle, differentiation, DNA repair, and apoptosis, and improper regulation or mutation has been linked to cancer, neurodegeneration, and other diseases. HDAC inhibitors targeting HDAC1/2 are established therapeutics, especially in oncology, but can be limited by off-target toxicity, reflecting the broad essential functions of these enzymes. HDAC1/2 are widely considered prototypical targets in epigenetic drug development, with ongoing research into their specific biological roles, complexes, and therapeutic modulation.

Other names

HDAC1: Histone deacetylase 1HDAC2: Histone deacetylase 2May also be referred to as class I histone deacetylases or HDAC1/2 complex (when discussed together)

Most drugs act as competitive inhibitors, chelating the catalytic Zn²⁺ ion in the active site of the enzyme and blocking deacetylation of lysine residues on histones and other proteins. This results in increased histone acetylation, chromatin relaxation, and reactivation of silenced genes (such as tumor suppressors).