Comparison of the Deacylase and Deacetylase Activity of Zinc-Dependent HDACs.

The acetylation status of lysine residues on histone proteins has long been attributed to a balance struck between the catalytic activity of histone acetyl transferases and histone deacetylases (HDAC). HDACs were identified as the sole removers of acetyl post-translational modifications (PTM) of histone lysine residues. Studies into the biological role of HDACs have also elucidated their role as removers of acetyl PTMs from lysine residues of nonhistone proteins. These findings, coupled with high-resolution mass spectrometry studies that revealed the presence of acyl-group PTMs on lysine residues of nonhistone proteins, brought forth the possibility of HDACs acting as removers of both acyl- and acetyl-based PTMs. We posited that HDACs fulfill this dual role and sought to investigate their specificity. Utilizing a fluorescence-based assay and biologically relevant acyl-substrates, the selectivities of zinc-dependent HDACs toward these acyl-based PTMs were identified. These findings were further validated using cellular models and molecular biology techniques. As a proof of principal, an HDAC3 selective inhibitor was designed using HDAC3's substrate preference. This resulting inhibitor demonstrates nanomolar activity and >30 fold selectivity toward HDAC3 compared to the other class I HDACs. This inhibitor is capable of increasing p65 acetylation, attenuating NF-κB activation, and thereby preventing downstream nitric oxide signaling. Additionally, this selective HDAC3 inhibition allows for control of HMGB-1 secretion from activated macrophages without altering the acetylation status of histones or tubulin.