A novel histone deacetylase, HDAC10, was isolated from a mixed tissue human cDNA library. HDAC10 was classified as a class II subfamily member based upon similarity to HDAC6. The genomic structure of HDAC10 was found to consist of 20 exons. HDAC10 has two sequence variants, HDAC10v1 and HDAC10v2, and two transcripts were detectable by Northern blot analysis. HDAC10v1 and HDAC10v2 were found to be identical through exon 17 but diverged after this exon. HDAC10v2 has an 82-bp alternate exon that generates a frameshift and shortens the sequence by 11 amino acids. In this study, the characterization of HDAC10v1 was performed. HDAC10v1 has an N-terminal catalytic domain, two putative C-terminal retinoblastoma protein binding domains, and a nuclear hormone receptor binding motif. The HDAC10v1 enzyme was found to be catalytically active based upon its ability to deacetylate a 3 H-acetylated histone H4 N-terminal peptide. Immunofluorescence detection of transfected HDAC10v1-FLAG indicated that the enzyme is a nuclear protein. Furthermore, coimmunoprecipitation experiments indicated that HDAC10v1 associated with HDAC2 and SMRT (silencing mediator for retinoid and thyroid hormone receptors). In addition, based upon the public data base, a single nucleotide polymorphism was found in the C terminus of HDAC10 which changes a Gly residue to Cys, suggesting that HDAC10 molecules containing these single nucleotide polymorphisms may be folded improperly. HDAC10 extends the HDAC superfamily and adds to a growing number of HDACs that have been found to have splice variants, suggesting that RNA processing may play a role in mediating the activity of HDACs.Chromatin remodeling plays a major regulatory role in transcription and DNA replication (1, 2). One model for how chromatin remodeling occurs involves ATP-dependent displacement of histones by nucleosome remodeling complexes (3, 4) and changes in the acetylation status of histones and transcription factors catalyzed by histone acetylases and histone deacetylases (HDACs) 1 (5-7).There are currently 16 reported human HDAC isoforms (8 -11) that are divided into three classes based upon sequence homology, intracellular localization, and association with proteins that form DNA-binding complexes. HDAC1, HDAC2, HDAC3, and HDAC8 were categorized as class I based upon their similarity to the yeast gene Rpd3 (8). HDAC 4/HDACA, HDAC5/HDACB, HDAC6, HDAC7, and HDAC9 were designated as class II, based upon their similarity to yeast gene Hda1 (9, 10). The third class of HDACs consists of seven human genes that are similar to yeast silent information regulator gene (Sir2) (13,14). A unique characteristic of class III HDACs is their NAD ϩ -dependent protein deacetylase and ADP-ribosylase activity (15-17).HDACs have been found in multiprotein complexes, implicating HDACs in transcription regulation, hormone signaling, cell cycle, differentiation, and DNA repair. Class I and class II HDACs were found to be components of different complexes (8 -10). HDAC1 and 2 formed a core complex with retinoblastom...

No abstract

The dynamic balance between histone acetylation and deacetylation plays a significant role in the regulation of gene transcription. Much of our current understanding of this transcriptional control comes from the use of HDAC inhibitors such as trapoxin A (TPX), which leads to hyperacetylated histone, alters local chromatin architecture and transcription and results in tumor cell death. In this study, we treated tumor cells with TPX and HDAC1 antisense oligonucleotides, and analysed the transcriptional consequences of HDAC inhibition. Among other genes, the small GTPase RhoB was found to be significantly upregulated by TPX and repressed by HDAC1. The induction of RhoB by HDAC inhibition was mediated by an inverted CCAAT box in the RhoB promoter. Interestingly, measurement of RhoB transcription in B130 tumor-derived cell lines revealed low expression in almost all of these samples, in contrast to RhoA and RhoC. Accumulating evidence indicates that the small GTPase Rho proteins are involved in a variety of important processes in cancer, including cell transformation, survival, invasion, metastasis and angiogenesis. This study for the first time demonstrates a link between HDAC inhibition and RhoB expression and provides an important insight into the mechanisms of HDACmediated transcriptional control and the potential therapeutic benefit of HDAC inhibition.

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HDAC inhibitors are promising antitumor drugs with several HDAC inhibitors already in clinical trials. LAQ824, a potent pan-HDAC inhibitor, has been shown to induce cell cycle arrest and cell death. However, the mechanism of its antitumor effects and specially its tumor selectivity are still poorly understood. The focus of this study is to elucidate LAQ824 mediated anti-proliferative effects in lung carcinoma cells and the mechanism underlying the different sensitivity of LAQ824 to cancer and normal cells. In this study, LAQ824 mediated apoptosis was found to occur mainly via activation of the mitochondrial death pathway by inducing Apaf1 and caspase 9 and promoting mitochondrial release of key proapoptotic factors in lung cancer cells, but not in normal fibroblast cells. Using chromatin immunoprecipitation assay, we found that RNA Pol II binding and histone H3 acetylation levels at Apaf1 promoter were increased following LAQ824 treatment, explaining LAQ824 induced expression of Apaf1 in lung cancer cells. Furthermore, we showed that LAQ824 only triggered the release of mitochondrial proapoptotic factors such as cytochrome C (Cyto C) and apoptosis inducing factor (AIF) in lung cancer cells but not in normal blast cells. In addition, LAQ824 was found to induce Bax translocation in lung cancer cell, which may play important role in the induction of the release of mitochondrial proapoptotic factors. These data provide insight into the mechanism underlying the selective induction of apoptosis by LAQ824 in cancer cells.