Design and evaluation of 'Linkerless' hydroxamic acids as selective HDAC8 inhibitors.

In this report, we describe new HDAC inhibitors designed to exploit a unique sub-pocket in the HDAC8 active site. These compounds were based on inspection of the available HDAC8 crystal structures bound to various inhibitors, which collectively show that the HDAC8 active site is unusually malleable and can accommodate inhibitor structures that are distinct from the canonical 'zinc binding group-linker-cap group' structures of SAHA, TSA, and similar HDAC inhibitors. Some inhibitors based on this new scaffold are >100-fold selective for HDAC8 over other class I and class II HDACs with IC(50) values <1microM against HDAC8.

The flavoring agent dihydrocoumarin reverses epigenetic silencing and inhibits sirtuin deacetylases.

Sirtuins are a family of phylogenetically conserved nicotinamide adenine dinucleotide-dependent deacetylases that have a firmly established role in aging. Using a simple Saccharomyces cerevisiae yeast heterochromatic derepression assay, we tested a number of environmental chemicals to address the possibility that humans are exposed to sirtuin inhibitors. Here we show that dihydrocoumarin (DHC), a compound found in Melilotus officinalis (sweet clover) that is commonly added to food and cosmetics, disrupted heterochromatic silencing and inhibited yeast Sir2p as well as human SIRT1 deacetylase activity.

SIRT1 regulates HIV transcription via Tat deacetylation.

The human immunodeficiency virus (HIV) Tat protein is acetylated by the transcriptional coactivator p300, a necessary step in Tat-mediated transactivation. We report here that Tat is deacetylated by human sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide-dependent class III protein deacetylase in vitro and in vivo. Tat and SIRT1 coimmunoprecipitate and synergistically activate the HIV promoter.

Subtype selective substrates for histone deacetylases.

To probe the steric requirements for deacylation, we synthesized lysine-derived small molecule substrates and examined structure-reactivity relationships with various histone deacetylases. Rat liver, human HeLa, and human recombinant class I and II histone deacetylases (HDACs) as well as human recombinant NAD(+)-dependent SIRT1 (class III enzyme) were used in these studies. A benzyloxycarbonyl substituent on the alpha-amino group yielded the highest conversion rates.

The human Sir2 ortholog, SIRT2, is an NAD+-dependent tubulin deacetylase.

The silent information regulator 2 protein (Sir2p) of Saccharomyces cerevisiae is an NAD-dependent histone deacetylase that plays a critical role in transcriptional silencing. Here, we report that a human ortholog of Sir2p, sirtuin type 2 (SIRT2), is a predominantly cytoplasmic protein that colocalizes with microtubules. SIRT2 deacetylates lysine-40 of alpha-tubulin both in vitro and in vivo.