Molecular basis for control of antibiotic production by a bacterial hormone.

Actinobacteria produce numerous antibiotics and other specialized metabolites that have important applications in medicine and agriculture1. Diffusible hormones frequently control the production of such metabolites by binding TetR family transcriptional repressors (TFTRs), but the molecular basis for this remains unclear2. The production of methylenomycin antibiotics in Streptomyces coelicolor A3(2) is initiated by the binding of 2-alkyl-4-hydroxymethylfuran-3-carboxylic acid (AHFCA) hormones to the TFTR MmfR3. Here we report the X-ray crystal structure of an MmfR-AHFCA complex, establishing the structural basis for hormone recognition. We also elucidate the mechanism for DNA release upon hormone binding through the single-particle cryo-electron microscopy structure of an MmfR-operator complex. DNA binding and release assays with MmfR mutants and synthetic AHFCA analogues define the role of individual amino acid residues and hormone functional groups in ligand recognition and DNA release. These findings will facilitate the exploitation of actinobacterial hormones and their associated TFTRs in synthetic biology and in the discovery of new antibiotics.

Overexpression of iASPP is required for autophagy in response to oxidative stress in choriocarcinoma.

BACKGROUND: Gestational trophoblastic disease (GTD) is a heterogeneous group of diseases developed from trophoblasts. ASPP (Ankyrin-repeat, SH3-domain and proline-rich region containing protein) family proteins, ASPP1 and ASPP2, have been reported to be dysregulated in GTD. They modulate p53 activities and are responsible for multiple cellular processes. Nevertheless, the functional role of the ASPP family inhibitory member, iASPP, is not well characterized in GTD. METHODS: To study the functional role of iASPP in GTD, trophoblastic tissues from normal placentas, hydatidiform mole (HM) and choriocarcinoma were used for immunohistochemistry, whereas siRNAs were used to manipulate iASPP expression in choriocarcinoma cell lines and study the subsequent molecular changes. RESULTS: We demonstrated that iASPP was overexpressed in both HM and choriocarcinoma when compared to normal placenta. Progressive increase in iASPP expression from HM to choriocarcinoma suggests that iASPP may be related to the development of trophoblastic malignancy. High iASPP expression in HM was also significantly associated with a high expression of autophagy-related protein LC3. Interestingly, iASPP silencing retarded the growth of choriocarcinoma through senescence instead of induction of apoptosis. LC3 expression decreased once iASPP was knocked down, suggesting a downregulation on autophagy. This may be due to iASPP downregulation rendered decrease in Atg5 expression and concomitantly hindered autophagy in choriocarcinoma cells. Autophagy inhibition per se had no effect on the growth of choriocarcinoma cells but increased the susceptibility of choriocarcinoma cells to oxidative stress, implying a protective role of iASPP against oxidative stress through autophagy in choriocarcinoma. CONCLUSIONS: iASPP regulates growth and the cellular responses towards oxidative stress in choriocarcinoma cells. Its overexpression is advantageous to the pathogenesis of GTD. (266 words).

Porphyromonas gingivalis PgFur Is a Member of a Novel Fur Subfamily With Non-canonical Function.

Porphyromonas gingivalis, a keystone pathogen of chronic periodontitis, uses ferric uptake regulator homolog (PgFur) to regulate production of virulence factors. This study aimed to characterize PgFur protein in regard to its structure-function relationship. We experimentally identified the 5' mRNA sequence encoding the 171-amino-acid-long PgFur protein in the A7436 strain and examined this PgFur version as a full-length protein. PgFur protein did not bind to the canonical Escherichia coli Fur box, but the wild-type phenotype of the mutant Δpgfur strain was restored partially when expression of the ecfur gene was induced from the native pgfur promoter. The full-length PgFur protein contained one zinc atom per protein monomer, but did not bind iron, manganese, or heme. Single cysteine substitutions of CXXC motifs resulted in phenotypes similar to the mutant Δpgfur strain. The modified proteins were produced in E. coli at significantly lower levels, were highly unstable, and did not bind zinc. The pgfur gene was expressed at the highest levels in bacteria cultured for 24 h in the absence of iron and heme or at higher levels in bacteria cultured for 10 h in the presence of protoporphyrin IX source. No influence of high availability of Fe2+, Zn2+, or Mn2+ on pgfur gene expression was observed. Two chromosomal mutant strains producing protein lacking 4 (pgfurΔ4aa) or 13 (pgfurΔ13aa) C-terminal amino acid residues were examined in regard to importance of the C-terminal lysine-rich region. The pgfurΔ13aa strain showed a phenotype typical for the mutant Δpgfur strain, but both the wild-type PgFur protein and its truncated version bound zinc with similar ability. The Δpgfur mutant strain produced higher amounts of HmuY protein compared with the wild-type strain, suggesting compromised regulation of its expression. Potential PgFur ligands, Fe2+, Mn2+, Zn2+, PPIX, or serum components, did not influence HmuY production in the Δpgfur mutant strain. The mutant pgfurΔ4aa and pgfurΔ13aa strains exhibited affected HmuY protein production. PgFur, regardless of the presence of the C-terminal lysine-rich region, bound to the hmu operon promoter. Our data suggest that cooperation of PgFur with partners/cofactors and/or protein/DNA modifications would be required to accomplish its role played in an in vivo multilayer regulatory network.

Functional and cancer genomics of ASXL family members.

Additional sex combs-like (ASXL)1, ASXL2 and ASXL3 are human homologues of the Drosophila Asx gene that are involved in the regulation or recruitment of the Polycomb-group repressor complex (PRC) and trithorax-group (trxG) activator complex. ASXL proteins consist of ASXN, ASXH, ASXM1, ASXM2 and PHD domains. ASXL1 directly interacts with BAP1, KDM1A (LSD1), NCOA1 and nuclear hormone receptors (NHRs), such as retinoic acid receptors, oestrogen receptor and androgen receptor. ASXL family members are epigenetic scaffolding proteins that assemble epigenetic regulators and transcription factors to specific genomic loci with histone modifications. ASXL1 is involved in transcriptional repression through an interaction with PRC2 and also contributes to transcriptional regulation through interactions with BAP1 and/or NHR complexes. Germ-line mutations of human ASXL1 and ASXL3 occur in Bohring-Opitz and related syndromes. Amplification and overexpression of ASXL1 occur in cervical cancer. Truncation mutations of ASXL1 occur in colorectal cancers with microsatellite instability (MSI), malignant myeloid diseases, chronic lymphocytic leukaemia, head and neck squamous cell carcinoma, and liver, prostate and breast cancers; those of ASXL2 occur in prostate cancer, pancreatic cancer and breast cancer and those of ASXL3 are observed in melanoma. EPC1-ASXL2 gene fusion occurs in adult T-cell leukaemia/lymphoma. The prognosis of myeloid malignancies with misregulating truncation mutations of ASXL1 is poor. ASXL family members are assumed to be tumour suppressive or oncogenic in a context-dependent manner.

E6 and E7 variants of human papillomavirus-16 and -52 in Japan, the Philippines, and Vietnam.

Human papillomavirus (HPV) has several intragenotypic variants with different geographical and ethnic distributions. This study aimed to elucidate the distribution patterns of E6 and E7 (E6/E7) intragenotypic variants of HPV type 16 (HPV-16), which is most common worldwide, and HPV-52, which is common in Asian countries such as Japan, the Philippines, and Vietnam. In previous studies, genomic DNA samples extracted from cervical swabs were collected from female sex workers in these three countries and found to be positive for HPV-16 or HPV-52. Samples were amplified further for their E6/E7 genes using type-specific primers and analyzed genetically. Seventy-nine HPV-16 E6/E7 genes were analyzed successfully and grouped into three lineages: European (Prototype), European (Asian), and African-2. The prevalences of HPV-16 European (Prototype)/European (Asian) lineages were 19.4%/80.6% (n = 31) in Japan, 75.0%/20.8% (n = 24) in the Philippines, and 0%/95.8% (n = 24) in Vietnam. The 109 HPV-52 E6/E7 genes analyzed successfully were grouped into four lineages, A-D; the prevalences of lineages A/B/C/D were, respectively, 5.1%/92.3%/0%/2.6% in Japan (n = 39), 34.4%/62.5%/0%/3.1% in the Philippines (n = 32), and 15.8%/73.7%/7.9%/2.6% in Vietnam (n = 38). The distribution patterns of HPV-16 and HPV-52 lineages in these countries differed significantly (P < 0.000001 and P = 0.0048, respectively). There was no significant relationship between abnormal cervical cytology and either HPV-16 E6/E7 lineages or specific amino acid mutations, such as E6 D25E, E6 L83V, and E7 N29S. Analysis of HPV-16 and HPV-52 E6/E7 genes can be a useful molecular-epidemiological tool to distinguish geographical diffusion routes of these HPV types in Asia.

The zebrafish genes encoding the Polycomb repressive complex (PRC) 1.

Polycomb repression controls regulation of hundreds of genes involved in development, signalling or cancer and is mediated by essentially two classes of chromatin-associated protein complexes, the Polycomb repressive complexes 1 and 2 (PRC1 and PRC2). PRC2 trimethylates histone H3 at Lysine 27 and this H3K27me3 epigenetic mark serves as a docking site for the PRC1 protein complex. Drosophila core PRC1 is composed of four subunits, Polycomb (Pc), Posterior sex combs (Psc), Polyhomeotic (Ph), and Sex combs extra (Sce). Each of these proteins has multiple orthologs in vertebrates. In particular, mammalian genomes encode five Pc family members (CBX2, 4, 6, 7 and 8), six Psc family members (BMI1, PCGF1, 2, 3, 5, and 6), three Ph family members (PHC1, 2 and 3) and two Sce family members (RING1 and RNF2) generating an enormous scope for potential combinatorial diversity. In order to identify the corresponding PRC1 genes in zebrafish, homology searches were undertaken and allowed the identification of a total of 19 genes. Using phylogenetic, gene organization and gene location analyses, these genes were classified. The zebrafish genes encoding the PRC1 protein complex include 8 Pc orthologs (cbx2, cbx4, cbx6a, cbx6b, cbx7a, cbx7b, cbx8a and cbx8b), 6 Psc orthologs (bmi1a, bmi1b, pcgf1, pcgf5a, pcgf5b and pcgf6), 4 Ph orthologs (phc1, phc2a, phc2b and phc3) and a single Sce ortholog (rnf2). Our results indicate that the potentially high number of distinct PRC1 protein complexes generated by the components combinatorial appeared early in the vertebrate evolution. In addition to conserved gene organization and syntenies, transcript analyses revealed that transcriptional regulation leading to various isoforms syntheses is also conserved at genes encoding the PRC1 components, highlighting a possible important biological role of these isoforms.

Family reunion--the ZIP/prion gene family.

Prion diseases are fatal neurodegenerative diseases of humans and animals which, in addition to sporadic and familial modes of manifestation, can be acquired via an infectious route of propagation. In disease, the prion protein (PrP(C)) undergoes a structural transition to its disease-causing form (PrP(Sc)) with profoundly different physicochemical properties. Surprisingly, despite intense interest in the prion protein, its function in the context of other cellular activities has largely remained elusive. We recently employed quantitative mass spectrometry to characterize the interactome of the prion protein in a murine neuroblastoma cell line (N2a), an established cell model for prion replication. Extensive bioinformatic analyses subsequently established an evolutionary link between the prion gene family and the family of ZIP (Zrt-, Irt-like protein) metal ion transporters. More specifically, sequence alignments, structural threading data and multiple additional pieces of evidence placed a ZIP5/ZIP6/ZIP10-like ancestor gene at the root of the PrP gene family. In this review we examine the biology of prion proteins and ZIP transporters from the viewpoint of a shared phylogenetic origin. We summarize and compare available data that shed light on genetics, function, expression, signaling, post-translational modifications and metal binding preferences of PrP and ZIP family members. Finally, we explore data indicative of retropositional origins of the prion gene founder and discuss a possible function for the prion-like (PL) domain within ZIP transporters. While throughout the article emphasis is placed on ZIP proteins, the intent is to highlight connections between PrP and ZIP transporters and uncover promising directions for future research.

Interpretation of developmental signaling at chromatin: the Polycomb perspective.

The Polycomb group (PcG) system represses the transcription of important developmental regulators and perpetuates this repression across multiple cell divisions. Inputs from outside the cell can influence PcG function by recruiting additional chromatin factors to PcG-regulated loci or by downregulating the PcG genes themselves. These types of PcG system modulation allow context-dependent induction of genes during development, in cancer, and in response to changes in the environment. In this review, we outline instances where molecular players in this process have been recently identified, comparing and contrasting different ways in which derepression is achieved, and projecting directions for future research.

[The study of gene variation and phylogenetic analysis of HPV16 E6 and E7 gene in Hubei, China].

To study the gene variation and the distribution of HPV16 variant in Hubei, China, DNA was extracted from cervical cancer tissue samples. The E6 and E7 genes of HPV16 were amplified and the PCR products were sequenced using E6- and E7-specific primers. Fortyseven cases were found mutations at nucleotide position 178 of HPV16 E6 gene in 80 cervical cancer samples. This mutation resulted in amino acid change from Asp to Glu. The rate of mutation at nucleotide position 178 of E6 gene was 58. 75%. Twenty two cases were found mutations at nucleotide position 647 of HPV16 E7 gene in 31 cervical cancer samples. This mutation resulted in amino acid change from Asn to Ser. The rate of mutation was 70.97%. These results showed that mutations at nucleotide position 178 of E6 gene, nucleotide position 647 of E7 gene of HPV16 in cerveical cancer samples were prevalent in Hubei, China. Phylogenetic analysis showed that Asian (As) variants of HPV16 are predominated in Hubei, China. European (Ep) varinats were also found in Samples in Hubei areas. None of Asian American (AA), African-1 (Af-1), African-2 (Af-2) variants of HPV16 was found in this region. Whether Asian (As) variants of HPV16 are more oncogenic and play a much more important role in the progress of cervical cancer than European (Ep) variants is not clear. More sequences of E6 and E7 gene in CIN and normal cervical tissue samples and study of the function of E6 and E7 protein of these HPV16 variants are needed to adress above question.

Structural basis for the specialization of Nur, a nickel-specific Fur homolog, in metal sensing and DNA recognition.

Nur, a member of the Fur family, is a nickel-responsive transcription factor that controls nickel homeostasis and anti-oxidative response in Streptomyces coelicolor. Here we report the 2.4-A resolution crystal structure of Nur. It contains a unique nickel-specific metal site in addition to a nonspecific common metal site. The identification of the 6-5-6 motif of the Nur recognition box and a Nur/DNA complex model reveals that Nur mainly interacts with terminal bases of the palindrome on complex formation. This contrasts with more distributed contacts between Fur and the n-1-n type of the Fur-binding motif. The disparity between Nur and Fur in the conformation of the S1-S2 sheet in the DNA-binding domain can explain their different DNA-recognition patterns. Furthermore, the fact that the specificity of Nur in metal sensing and DNA recognition is conferred by the specific metal site suggests that its introduction drives the evolution of Nur orthologs in the Fur family.

Atrophin proteins: an overview of a new class of nuclear receptor corepressors.

The normal development and physiological functions of multicellular organisms are regulated by complex gene transcriptional networks that include myriad transcription factors, their associating coregulators, and multiple chromatin-modifying factors. Aberrant gene transcriptional regulation resulting from mutations among these elements often leads to developmental defects and diseases. This review article concentrates on the Atrophin family proteins, including vertebrate Atrophin-1 (ATN1), vertebrate arginine-glutamic acid dipeptide repeats protein (RERE), and Drosophila Atrophin (Atro), which we recently identified as nuclear receptor corepressors. Disruption of Atrophin-mediated pathways causes multiple developmental defects in mouse, zebrafish, and Drosophila, while an aberrant form of ATN1 and altered expression levels of RERE are associated with neurodegenerative disease and cancer in humans, respectively. We here provide an overview of current knowledge about these Atrophin proteins. We hope that this information on Atrophin proteins may help stimulate fresh ideas about how this newly identified class of nuclear receptor corepressors aids specific nuclear receptors and other transcriptional factors in regulating gene transcription, manifesting physiological effects, and causing diseases.

The PMS2 subunit of human MutLalpha contains a metal ion binding domain of the iron-dependent repressor protein family.

DNA mismatch repair (MMR) is responsible for correcting replication errors. MutLalpha, one of the main players in MMR, has been recently shown to harbor an endonuclease/metal-binding activity, which is important for its function in vivo. This endonuclease activity has been confined to the C-terminal domain of the hPMS2 subunit of the MutLalpha heterodimer. In this work, we identify a striking sequence-structure similarity of hPMS2 to the metal-binding/dimerization domain of the iron-dependent repressor protein family and present a structural model of the metal-binding domain of MutLalpha. According to our model, this domain of MutLalpha comprises at least three highly conserved sequence motifs, which are also present in most MutL homologs from bacteria that do not rely on the endonuclease activity of MutH for strand discrimination. Furthermore, based on our structural model, we predict that MutLalpha is a zinc ion binding protein and confirm this prediction by way of biochemical analysis of zinc ion binding using the full-length and C-terminal domain of MutLalpha. Finally, we demonstrate that the conserved residues of the metal ion binding domain are crucial for MMR activity of MutLalpha in vitro.

The function and regulation of the JARID1 family of histone H3 lysine 4 demethylases: the Myc connection.

Epigenetic regulation of transcription refers to reversible, heritable changes in gene expression that occur in the absence of changes in DNA sequence. A major epigenetic mechanism involves the covalent modification of nucleosomal histones to create binding sites for transcriptional regulators and chromatin remodeling complexes that mediate activation or repression of transcription. While it has been known for a number of years that many histone modifications are reversible, it has only recently been shown that methyl groups are enzymatically removed from lysine residues. Here we discuss the recent characterization of a new class of demethylase enzyme, the JARID1 family, which catalyzes the removal of methyl groups from lysine 4 of histone H3. We summarize recent findings regarding the function of this family of proteins, focusing on our characterization of Little imaginal discs (Lid), the sole JARID1 family protein in Drosophila, which is rate-limiting for Myc-induced cell growth. Finally, we propose models to explain the role of Lid in Myc-mediated growth and discuss the relevance of these findings to human disease and tumor formation.

Splice variants of TLE family genes and up-regulation of a TLE3 isoform in prostate tumors.

The TLE genes constitute a family of important transcriptional co-repressors involved in many cellular processes. We found evidence of alternatively spliced mRNAs for human TLE1-4 containing premature stop codons, thus encoding putative shortened proteins. Microarray experiments and Real-time RT-PCR assays showed that alternatively spliced isoforms of TLE1, TLE2 an d TLE3 were preferentially expressed in prostate in comparison to liver and kidney tissues. We identified by orientation-specific R T-PCR an antisense partially intronic non-coding RNA that overlaps a novel exon of the TLE3 gene, raising the possibility of regulation of alternative splicing by this non-coding transcript. The alternatively spliced isoform of TLE3 was up-regulated (6- to 17-fo ld) in prostate tumors in comparison to matched non-tumor adjacent tissue from 7 out of 11 (64%) patients and in four prostate tumor cell lines in comparison to a normal prostate cell line. These results demonstrate that different isoforms of TLE genes are commonly transcribed in human tissues and suggest that TLE3 could be involved in prostate cancer development.

BMI-1 is highly expressed in M0-subtype acute myeloid leukemia.

Recent studies have suggested that one of the polycomb group genes, BMI-1, has an important role in the maintenance of normal and leukemic stem cells by repressing the INK4a/ARF locus. Here, we quantitatively examined BMI-1 expression level in samples from patients with acute myeloid leukemia (AML) and other hematologic malignancies. Moderate to high BMI-1 expression was detected in AML patients, and the BMI-1 expression levels in AML samples were significantly higher than in normal bone marrow controls (P = .0011). Specimens of French-American-British classification subtype M0 showed higher relative expression of the BMI-1 transcript (median, 390.2 3 10(-3)) than the other subtypes (median, 139.0 3 10(-3)) (P < .0001). Leukemia other than AML showed low to moderate expression. INK4a-ARF transcript expression tended to be inverse proportion to that of BMI-1. In an M0 patient with a high BMI-1 transcript level, the INK4a-ARF transcript level fell promptly and maintained a low value after the patient achieved complete remission. These results indicated that a subgroup of M0 patients has a high expression level of polycomb group gene BMI-1, which may contribute to leukemogenesis.

Histone deacetylase 3, a class I histone deacetylase, suppresses MAPK11-mediated activating transcription factor-2 activation and represses TNF gene expression.

During inflammatory events, the induction of immediate-early genes, such as TNF-alpha, is regulated by signaling cascades including the JAK/STAT, NF-kappaB, and the p38 MAPK pathways, which result in phosphorylation-dependent activation of transcription factors. We observed the direct interaction of histone deacetylase (HDAC) 3, a class I histone deacetylase, with MAPK11 (p38 beta isoform) by West-Western-based screening analysis, pull-down assay, and two-hybrid system analysis. Results further indicated that HDAC3 decreases the MAPK11 phosphorylation state and inhibits the activity of the MAPK11-dependent transcription factor, activating transcription factor-2 (ATF-2). LPS-mediated activation of ATF-2 was inhibited by HDAC3 in a time- and dose-dependent manner. Inhibition of HDAC3 expression by RNA interference resulted in increased ATF-2 activation in response to LPS stimulation. In agreement with decreased ATF-2 transcriptional activity by HDAC3, HDAC3-repressed TNF gene expression, and TNF protein production observed in response to LPS stimulation. Therefore, our results indicate that HDAC3 interacts directly and selectively with MAPK11, represses ATF-2 transcriptional activity, and acts as a regulator of TNF gene expression in LPS-stimulated cells, especially in mononuclear phagocytes.

Noncanonical Wnt signaling pathways in C. elegans converge on POP-1/TCF and control cell polarity.

In the nematode Caenorhabditis elegans, a canonical Wnt signaling pathway controls a cell migration whereas noncanonical Wnt pathways control the polarities of individual cells. Despite the differences in the identities and interactions among canonical and noncanonical Wnt pathway components, as well as the processes they regulate, almost all C. elegans Wnt pathways involve the sole Tcf homolog, POP-1. Intriguingly, POP-1 is asymmetrically distributed between the daughters of an asymmetric cell division, with the anterior sister cell usually having a higher level of nuclear POP-1 than its posterior sister. At some divisions, asymmetric distribution of POP-1 is controlled by noncanonical Wnt signaling, but at others the asymmetry is generated independently. Recent experiments suggest that despite this elaborate anterior-posterior POP-1 asymmetry, the quantity of POP-1 protein may have less to do with the subsequent determination of fate than does the quality of the POP-1 protein in the cell. In this review, we will embark on a quest to understand Quality (1), at least from the standpoint of the effect POP/Tcf quality has on the control of cell polarity in C. elegans.

Dissociation of mammalian Polycomb-group proteins, Ring1B and Rae28/Ph1, from the chromatin correlates with configuration changes of the chromatin in mitotic and meiotic prophase.

The Polycomb group (PcG) gene products form complexes that regulate chromatin configuration to mediate cellular memory to postmitotic somatic cells and postmeiotic oocytes in Drosophila melanogaster. Structural and functional similarities of PcG proteins between invertebrates and vertebrates suggest mammalian PcG proteins may be involved to imprint transcriptional status at various loci into postmitotic and postmeiotic daughter cells. To address molecular mechanisms underlying PcG-mediated cellular memory, it might be a prerequisite to understand subcellular localization of PcG proteins during mitosis and meiosis. In this study, we analyzed subcellular localization of Rae28/Ph1 and Ring1B by using newly generated monoclonal antibodies in mitotic somatic cells and meiotic mouse oocytes. Results suggest that Rae28/Ph1 and Ring1B dissociate from the chromatin upon its condensation in mitotic prophase in the U2-OS human osteosarcoma cell line. During maturation of oocytes, significant alterations of Rae28/Ph1 and Ring1B localization are concordant with configuration changes of the chromatin at the germinal vesicle stage of meiotic prophase. Importantly, dissociation of Rae28/Ph1 and Ring1B from the chromatin temporally correlates with transcriptional arrest both in mitosis and meiosis. Present and previous observations suggest molecular mechanisms required for mitotic regulation of RNA polymerase II could be involved in dissociation of PcG proteins.

CtBP, an unconventional transcriptional corepressor in development and oncogenesis.

CtBP family proteins are conserved among vertebrates and invertebrates and function as transcriptional corepressors. They repress transcription in a histone deacetylase-dependent or -independent manner. CtBPs play important roles during development and oncogenesis. In this review, their unusual properties, the mechanisms of transcriptional repression, regulation, and their biological functions are discussed.

Cloning and characterization of human histone deacetylase 8.

To date, seven different human histone deacetylases (HDACs) have been identified, which fall into two distinct classes. We have isolated and characterized a cDNA encoding a novel human HDAC, which we name HDAC8. HDAC8 shows a high degree of sequence similarity to HDAC1 and HDAC2 and thus belongs to the class I of HDACs. HDAC8 is expressed in a variety of tissues. Human cells overexpressing HDAC8 localize the protein in sub-nuclear compartments whereas HDAC1 shows an even nuclear distribution. 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.