Disease relevance of HDAC8

• In addition, the HDAC8 gene is localized on the X chromosome at position q13, which is close to the XIST gene and chromosomal breakpoints associated with preleukemia [1].
• Furthermore, active recombinant HDAC8 was expressed and purified from Escherichia coli [2].
• HDAC8 immunohistochemical staining was performed in 15 leiomyomas (LMs), 9 highly cellular leiomyomas (HCLs), 8 epithelioid SMTs, 13 leiomyosarcomas (LMSs), and 17 ESTs, including 3 with sex-cord differentiation and 5 with smooth muscle differentiation [3].
• While anti-alpha-SMA staining was generally normal, immunoreactivity for SMMHC, HDAC8 and/or SM was either absent or focally lacking in Hirschsprung's disease (80%), idiopathic megacolon (75%) and slow-transit constipation (70%) [4].
• In mammalian cells the product of the human retinoblastoma tumour suppressor gene (pRb) can recruit Rpd3-like histone deacetylases to repress transcription [5].

High impact information on HDAC8

• RPD3 can deacetylate all histone H4 acetylation sites in cell extracts [6].
• Here, we describe four Rpd3 derivatives with mutations in evolutionarily invariant histidine residues in a putative deacetylation motif [7].
• In addition, structural and biochemical studies of these enzymes have focused on the histone lysine deacetylases HDAC8 and sirtuins, and on the arginine and lysine demethylases PAD and BHC110/LSD1, respectively [8].
• Crystal structure of a eukaryotic zinc-dependent histone deacetylase, human HDAC8, complexed with a hydroxamic acid inhibitor [9].
• However, significant differences are observed in the length and structure of the loops surrounding the active site, including the presence of two potassium ions in HDAC8 structure, one of which interacts with key catalytic residues [9].

Biological context of HDAC8

• In contrast, mutation of Ser(39) to Glu or induction of HDAC8 phosphorylation by forskolin, a potent activator of adenyl cyclase, decreases HDAC8's enzymatic activity [10].
• Mutation of two adjacent histidine residues within the predicted active site severely decreases activity, confirming these residues as important for HDAC8 enzyme activity [11].
• Here we present the complete nucleotide sequence of a cDNA clone, termed HDAC8, that encodes a protein product with similarity to the RPD3 class (I) of HDACs [11].
• Knockdown of HDAC8 by RNA interference inhibits growth of human lung, colon, and cervical cancer cell lines, highlighting the importance of this HDAC subtype for tumor cell proliferation [9].
• Co-transfection experiments demonstrated that expression of HDAC8 repressed a viral SV40 early promoter activity [2].

Anatomical context of HDAC8

• Unexpectedly, HDAC8, another class I HDAC, was not detected in epithelial cells but was uniquely expressed in the cytoplasm of stromal cells [12].
• These findings were confirmed in vitro by nucleo-cytoplasmic fractionation and immunoblot experiments performed on human primary smooth muscle cells, and by the cytosolic detection of epitope-tagged HDAC8 overexpressed in fibroblasts [13].
• Using immunohistochemistry, we unexpectedly found that, in normal human tissues, HDAC8 is exclusively expressed by cells showing smooth muscle differentiation, including visceral and vascular smooth muscle cells, myoepithelial cells, and myofibroblasts, and is mainly detected in their cytosol [13].
• In this study, we examined HDAC8 expression in SMTs and ESTs of the uterus to determine whether HDAC8 may be a useful diagnostic tool in the classification of problematic uterine mesenchymal tumors [3].
• Two such lines, HD6 and HD8, differentiate to 97 and 76% mucus-secreting goblet cells, respectively, in columnar monolayers in postconfluent culture [14].

Associations of HDAC8 with chemical compounds

• Here we report that HDAC8 is phosphorylated by cyclic AMP-dependent protein kinase A (PKA) in vitro and in vivo [10].
• After expression in two cell systems, immunopurified HDAC8 is shown to possess trichostatin A- and sodium butyrate-inhibitable HDAC activity on histone H4 peptide substrates as well as on core histones [11].
• Here we demonstrate that histone deacetylase 8 (HDAC8) is catalytically active with a number of divalent metal ions in a 1:1 stoichiometry with the following order of specific activity: Co(II) > Fe(II) > Zn(II) > Ni(II) [15].
• Analysis of the predicted amino acid sequence of HDAC-A revealed an open reading frame of 967 amino acids containing two domains: a NH2-terminal domain with no homology to known proteins and a COOH-terminal domain with homology to known histone deacetylases (42% similarity to RPD3, 60% similarity to HDA1) [16].

Regulatory relationships of HDAC8

• TGF alpha induced a 2-fold increase in growth of the HD8 subline but inhibited the growth of the more differentiated HD6 subline by 40% [17].
• Our findings reveal a novel mechanism by which HDAC8 contributes to tumorigenesis by regulating telomerase activity [18].

Other interactions of HDAC8

• Human cells overexpressing HDAC8 localize the protein in sub-nuclear compartments whereas HDAC1 shows an even nuclear distribution [1].
• This was specific, since HDAC1, HDAC2, and HDAC8 failed to do so [19].
• HDAC1 protein was more abundantly expressed in SW620 cells compared with that of HDAC3 and HDAC8 [20].
• Phosphorylated HDAC8 preferentially recruits Hsp70 to a complex that inhibits the CHIP (C-terminal heat shock protein interacting protein) E3 ligase-mediated degradation of hEST1B [18].
• In contrast, the more differentiated HD6 cells showed an increase in 105 kDa MBP kinase activity with EGF treatment, while HD8 cells displayed constitutively elevated levels of this kinase [17].

Analytical, diagnostic and therapeutic context of HDAC8

• Finally, linkage analysis after radiation hybrid mapping has localized HDAC8 to chromosomal position Xq21.2-Xq21 [11].
• HDAC8, a class I HDAC, is considered to be ubiquitously expressed, as suggested by results of Northern blots performed on tissue RNA extracts, and transfection experiments using various cell lines have indicated that this enzyme may display a prominent nuclear localization [13].
• Further double-immunofluorescence staining experiments coupled with confocal microscopy analysis showed that epitope-tagged HDAC8 overexpressed in murine fibroblasts formed cytoplasmic stress fiber-like structures that co-localized with the smooth muscle cytoskeleton protein smooth muscle alpha-actin [13].
• Thus, HDAC8 detection may be useful in helping the differential diagnosis of uterine mesenchymal tumors [3].
• SMMHC and the novel smooth muscle markers SM and HDAC8 often display striking abnormalities linked to the smooth muscle contractile apparatus unnoticed by both routine stainings and alpha-SMA, suggesting specific defects of smooth muscle cells involved in the pathogenesis of gastrointestinal motility disorders [4].

References