HDAC6 is a specific deacetylase of peroxiredoxins and is involved in redox regulation.

Eighteen histone deacetylases (HDACs) are present in humans, categorized into two groups: zinc-dependent enzymes (HDAC1-11) and NAD(+)-dependent enzymes (sirtuins 1-7). Among zinc-dependent HDACs, HDAC6 is unique. It has a cytoplasmic localization, two catalytic sites, a ubiquitin-binding site, and it selectively deacetylases alpha-tubulin and Hsp90. Here, we report the discovery that the redox regulatory proteins, peroxiredoxin (Prx) I and Prx II are specific targets of HDAC6. Prx are antioxidants enzymes whose main function is H(2)O(2) reduction. Prx are elevated in many cancers and neurodegenerative diseases. The acetylated form of Prx accumulates in the absence of an active HDAC6. Acetylation of Prx increases its reducing activity, its resistance to superoxidation, and its resistance to transition to high-molecular-mass complexes. Thus, HDAC6 and Prx are targets for modulating intracellular redox status in therapeutic strategies for disorders as disparate as cancers and neurodegenerative diseases.

Histone deacetylase inhibitors: molecular mechanisms of action.

This review focuses on the mechanisms of action of histone deacetylase (HDAC) inhibitors (HDACi), a group of recently discovered 'targeted' anticancer agents. There are 18 HDACs, which are generally divided into four classes, based on sequence homology to yeast counterparts. Classical HDACi such as the hydroxamic acid-based vorinostat (also known as SAHA and Zolinza) inhibits classes I, II and IV, but not the NAD+-dependent class III enzymes. In clinical trials, vorinostat has activity against hematologic and solid cancers at doses well tolerated by patients. In addition to histones, HDACs have many other protein substrates involved in regulation of gene expression, cell proliferation and cell death. Inhibition of HDACs causes accumulation of acetylated forms of these proteins, altering their function. Thus, HDACs are more properly called 'lysine deacetylases.' HDACi induces different phenotypes in various transformed cells, including growth arrest, activation of the extrinsic and/or intrinsic apoptotic pathways, autophagic cell death, reactive oxygen species (ROS)-induced cell death, mitotic cell death and senescence. In comparison, normal cells are relatively more resistant to HDACi-induced cell death. The plurality of mechanisms of HDACi-induced cell death reflects both the multiple substrates of HDACs and the heterogeneous patterns of molecular alterations present in different cancer cells.