A new family of human histone deacetylases related to Saccharomyces cerevisiae HDA1p.
(9/3697)
Histone deacetylases are the catalytic subunits of multiprotein complexes that are targeted to specific promoters through their interaction with sequence-specific DNA-binding factors. We have cloned and characterized a new human cDNA, HDAC-A, with homology to the yeast HDA1 family of histone deacetylases. 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). Three additional human cDNAs with high homology to HDAC-A were identified in sequence data bases, indicating that HDAC-A itself is a member of a new family of human histone deacetylases. The mRNA encoding HDAC-A was differentially expressed in a variety of human tissues. The expressed protein, HDAC-Ap, exhibited histone deacetylase activity and this activity mapped to the COOH-terminal region (amino acids 495-967) with homology to HDA1p. In immunoprecipitation experiments, HDAC-A interacted specifically with several cellular proteins, indicating that it might be part of a larger multiprotein complex. (+info)
Retinoid X receptor (RXR) agonist-induced activation of dominant-negative RXR-retinoic acid receptor alpha403 heterodimers is developmentally regulated during myeloid differentiation.
(10/3697)
The multiple biologic activities of retinoic acid (RA) are mediated through RAR and retinoid X receptor (RXR) nuclear receptors that interact with specific DNA target sequences as heterodimers (RXR-RAR) or homodimers (RXR-RXR). RA receptor activation appears critical to regulating important aspects of hematopoiesis, since transducing a COOH-terminally truncated RARalpha exhibiting dominant-negative activity (RARalpha403) into normal mouse bone marrow generates hematopoietic growth factor-dependent cell lines frozen at the multipotent progenitor (EML) or committed promyelocyte (MPRO) stages. Nevertheless, relatively high, pharmacological concentrations of RA (1 to 10 microM) overcome these differentiation blocks and induce terminal granulocytic differentiation of the MPRO promyelocytes while potentiating interleukin-3 (IL-3)-induced commitment of EML cells to the granulocyte/monocyte lineage. In the present study, we utilized RXR- and RAR-specific agonists and antagonists to determine how RA overcomes the dominant-negative activity of the truncated RARalpha in these different myeloid developmental stages. Unexpectedly, we observed that an RXR-specific, rather than an RAR-specific, agonist induces terminal granulocytic differentiation of MPRO promyelocytes, and this differentiation is associated with activation of DNA response elements corresponding to RAR-RXR heterodimers rather than RXR-RXR homodimers. This RXR agonist activity is blocked by RAR-specific antagonists, suggesting extensive cross-talk between the partners of the RXR-RARalpha403 heterodimer. In contrast, in the more immature, multipotent EML cells we observed that this RXR-specific agonist is inactive either in potentiating IL-3-mediated commitment of EML cells to the granulocyte lineage or in transactivating RAR-RXR response elements. RA-triggered GALdbd-RARalpha hybrid activity in these cells indicates that the multipotent EML cells harbor substantial nuclear hormone receptor coactivator activity. However, the histone deacetylase (HDAC) inhibitor trichostatin A readily activates an RXR-RAR reporter construct in the multipotent EML cells but not in the committed MPRO promyelocytes, indicating that differences in HDAC-containing repressor complexes in these two closely related but distinct hematopoietic lineages might account for the differential activation of the RXR-RARalpha403 heterodimers that we observed at these different stages of myeloid development. (+info)
Net1, a Sir2-associated nucleolar protein required for rDNA silencing and nucleolar integrity.
(11/3697)
The Sir2 protein mediates gene silencing and repression of recombination at the rDNA repeats in budding yeast. Here we show that Sir2 executes these functions as a component of a nucleolar complex designated RENT (regulator of nucleolar silencing and telophase exit). Net1, a core subunit of this complex, preferentially cross-links to the rDNA repeats, but not to silent DNA regions near telomeres or to active genes, and tethers the RENT complex to rDNA. Net1 is furthermore required for rDNA silencing and nucleolar integrity. During interphase, Net1 and Sir2 colocalize to a subdomain within the nucleous, but at the end of mitosis a fraction of Sir2 leaves the nucleolus and disperses as foci throughout the nucleus, suggesting that the structure of rDNA silent chromatin changes during the cell cycle. Our findings suggest that a protein complex shown to regulate exit from mitosis is also involved in gene silencing. (+info)
Three proteins define a class of human histone deacetylases related to yeast Hda1p.
(12/3697)
Gene expression is in part controlled by chromatin remodeling factors and the acetylation state of nucleosomal histones. The latter process is regulated by histone acetyltransferases and histone deacetylases (HDACs). Previously, three human and five yeast HDAC enzymes had been identified. These can be categorized into two classes: the first class represented by yeast Rpd3-like proteins and the second by yeast Hda1-like proteins. Human HDAC1, HDAC2, and HDAC3 proteins are members of the first class, whereas no class II human HDAC proteins had been identified. The amino acid sequence of Hda1p was used to search the GenBank/expressed sequence tag databases to identify partial sequences from three putative class II human HDAC proteins. The corresponding full-length cDNAs were cloned and defined as HDAC4, HDAC5, and HDAC6. These proteins possess certain features present in the conserved catalytic domains of class I human HDACs, but also contain additional sequence domains. Interestingly, HDAC6 contains an internal duplication of two catalytic domains, which appear to function independently of each other. These class II HDAC proteins have differential mRNA expression in human tissues and possess in vitro HDAC activity that is inhibited by trichostatin A. Coimmunoprecipitation experiments indicate that these HDAC proteins are not components of the previously identified HDAC1 and HDAC2 NRD and mSin3A complexes. However, HDAC4 and HDAC5 associate with HDAC3 in vivo. This finding suggests that the human class II HDAC enzymes may function in cellular processes distinct from those of HDAC1 and HDAC2. (+info)
BRCA1 interacts with components of the histone deacetylase complex.
(13/3697)
Germ-line mutations in the BRCA1 tumor-suppressor gene are associated with an increased susceptibility to breast and ovarian cancer. BRCA1 contains a carboxyl-terminal domain (BRCT) that is shared with several other proteins involved in maintaining genome integrity. In an effort to understand the function of BRCA1, we sought to isolate proteins that interact with the BRCT domain. Purified BRCT polypeptide was used as a probe to screen a human placenta cDNA expression library by Far Western analysis. Here we report that BRCA1 interacts in vivo and in vitro with the Rb-binding proteins, RbAp46 and RbAp48, as well as with Rb. Moreover, the BRCT domain associates with the histone deacetylases HDAC1 and HDAC2. These results demonstrate that BRCA1 interacts with components of the histone deacetylase complex, and therefore may explain the involvement of BRCA1 in multiple processes such as transcription, DNA repair, and recombination. (+info)
The Caenorhabditis elegans genes egl-27 and egr-1 are similar to MTA1, a member of a chromatin regulatory complex, and are redundantly required for embryonic patterning.
(14/3697)
We show here that two functionally redundant Caenorhabditis elegans genes, egl-27 and egr-1, have a fundamental role in embryonic patterning. When both are inactivated, cells in essentially all regions of the embryo fail to be properly organised. Tissue determination and differentiation are unaffected and many zygotic patterning genes are expressed normally, including HOX genes. However, hlh-8, a target of the HOX gene mab-5, is not expressed. egl-27 and egr-1 are members of a gene family that includes MTA1, a human gene with elevated expression in metastatic carcinomas. MTA1 is a component of a protein complex with histone deacetylase and nucleosome remodelling activities. We propose that EGL-27 and EGR-1 function as part of a chromatin regulatory complex required for the function of regional patterning genes. (+info)
The E7 oncoprotein associates with Mi2 and histone deacetylase activity to promote cell growth.
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E7 is the main transforming protein of human papilloma virus type 16 (HPV16) which is implicated in the formation of cervical cancer. The transforming activity of E7 has been attributed to its interaction with the retinoblastoma (Rb) tumour suppressor. However, Rb binding is not sufficient for transformation by E7. Mutations within a zinc finger domain, which is dispensable for Rb binding, also abolish E7 transformation functions. Here we show that HPV16 E7 associates with histone deacetylase in vitro and in vivo, via its zinc finger domain. Using a genetic screen, we identify Mi2beta, a component of the recently identified NURD histone deacetylase complex, as a protein that binds directly to the E7 zinc finger. A zinc finger point mutant which is unable to bind Mi2beta and histone deacetylase but is still able to bind Rb fails to overcome cell cycle arrest in osteosarcoma cells. Our results suggest that the binding to a histone deacetylase complex is an important parameter for the growthpromoting activity of the human papilloma virus E7 protein. This provides the first indication that viral oncoproteins control cell proliferation by targeting deacetylation pathways. (+info)
Phenotypic switching in Candida albicans is controlled by a SIR2 gene.
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We report the cloning of a gene from the human fungal pathogen Candida albicans with sequence and functional similarity to the Saccharomyces cerevisiae SIR2 gene. Deletion of the gene in C. albicans produces a dramatic phenotype: variant colony morphologies arise at frequencies as high as 1 in 10. The morphologies resemble those described previously as part of a phenotypic switching system proposed to contribute to pathogenesis. Deletion of SIR2 also produces a high frequency of karyotypic changes. These and other results are consistent with a model whereby Sir2 controls phenotypic switching and chromosome stability in C.albicans by organizing chromatin structure. (+info)