Histone acetylation plays an important role in regulating chromatin structure and thus gene expression. Here we describe the functional characterization of HDAC4, a human histone deacetylase whose C-terminal part displays significant sequence similarity to the deacetylase domain of yeast HDA1. HDAC4 is expressed in various adult human tissues, and its gene is located at chromosome band 2q37. HDAC4 possesses histone deacetylase activity intrinsic to its C-terminal domain. When tethered to a promoter, HDAC4 represses transcription through two independent repression domains, with repression domain 1 consisting of the N-terminal 208 residues and repression domain 2 containing the deacetylase domain. Through a small region located at its N-terminal domain, HDAC4 interacts with the MADS-box transcription factor MEF2C. Furthermore, HDAC4 and MEF2C individually upregulate but together downmodulate c-jun promoter activity. These results suggest that HDAC4 interacts with transcription factors such as MEF2C to negatively regulate gene expression.In eukaryotic cells, genetic information is packaged into chromatin, a highly organized DNA-protein complex which controls gene activities. A central question in studying eukaryotic gene regulation is how the generally repressive chromatin structure is regulated when necessary. In the past several years, three regulatory mechanisms have been recognized: DNA methylation, posttranslational modifications of histones, and ATP-dependent chromatin remodeling (53,55,57). The most extensively studied form of posttranslational modifications of histones is acetylation of ε-amino groups of lysine residues located at the flexible N-terminal tails of core histones (53, 55). The level of histone acetylation at a given region of chromatin correlates well with its transcriptional activity (39). Mechanistically, histone acetylation affects nucleosome stability and/or internucleosomal interaction (2, 29). The dynamic level of histone acetylation in vivo is maintained through opposing actions of histone acetyltransferases and deacetylases. Several known transcriptional coactivators possess intrinsic histone acetyltransferase activity (14,27,49,57).The first histone deacetylase, originally called HD1 (histone deacetylase 1) and later renamed HDAC1 (histone deacetylase 1), was cloned from mammalian cells (18, 50). HDAC1 was found to be highly homologous to the known yeast transcriptional coregulator RPD3 (50). Two HDAC1 homologs (HDAC2 and HDAC3) have been cloned from human cDNA libraries (10,58,59). Transcriptional repressors recruit RPD3 or HDAC1 to -3 to downregulate transcription (reviewed in references 41 and 56). The deacetylase activity of HDAC1 and RPD3 has been found to be important for transcriptional repression (18, 24), suggesting that histone deacetylation directly leads to transcriptional repression. Consistent with this contention, recruitment of RPD3 by the yeast repressor Ume6 leads to local histone deacetylation and formation of a highly localized domain of repressed chromatin in vivo...

Histone (de)acetylation is important for the regulation of fundamental biological processes such as gene expression and DNA recombination. Distinct classes of histone deacetylases (HDACs) have been identified, but how they are regulated in vivo remains largely unexplored. Here we describe results demonstrating that HDAC4, a member of class II human HDACs, is localized in the cytoplasm and/or the nucleus. Moreover, we have found that HDAC4 interacts with the 14-3-3 family of proteins that are known to bind specifically to conserved phosphoserine-containing motifs. Deletion analyses suggested that S246, S467, and S632 of HDAC4 mediate this interaction. Consistent with this, alanine substitutions of these serine residues abrogated 14-3-3 binding. Although these substitutions had minimal effects on the deacetylase activity of HDAC4, they stimulated its nuclear localization and thus led to enhanced transcriptional repression. These results indicate that 14-3-3 proteins negatively regulate HDAC4 by preventing its nuclear localization and thereby uncover a novel regulatory mechanism for HDACs.Specific lysine acetylation of histones and nonhistone proteins has been recently recognized as a major mechanism by which eukaryotic transcription is regulated (12,23,24,44,45,56,57). Such acetylation is reversible and dynamic in vivo, and its level is governed by the opposing actions of histone acetyltransferases and histone deacetylases (HDACs). Distinct classes of HDACs have been identified in mammals (21, 36). Class I HDACs (HDAC1, HDAC2, HDAC3, and HDAC8) are homologous to yeast Rpd3 (8,16,49,60,61). HDAC1 and HDAC2 interact with each other and form the catalytic core of Sin3 and NuRD complexes, both of which play important roles in transcriptional repression and gene silencing (26,51,53,54,58,(63)(64)(65). Various transcriptional repressors recruit these complexes to inhibit transcription (reviewed in references 15, 45, and 56). Class II HDACs (HDAC4, HDAC5, HDAC6, and HDAC7) contain domains significantly similar to the catalytic domain of yeast Hda1 (9,11,20,33,41,52,55). HDAC4, HDAC5, and HDAC7 are homologous, whereas HDAC6 has two Hda1-related catalytic domains and a unique Cys-and Hisrich C-terminal domain. HDAC4 and HDAC5 interact with the MEF2 transcription factors (28,33,55), and this interaction is regulated (30, 62). Related to this, MITR/HDRP, a protein related to the N-terminal part of HDAC4, HDAC5, and HDAC7, binds to MEF2s and represses transcription (43,66). Moreover, HDAC4, HDAC5, and HDAC7 were found to interact with the nuclear receptor corepressors 17,20). These new findings suggest that like class I HDACs, some class II HDACs are recruited to promoters to inhibit transcription. One interesting but unaddressed question is how the function of HDACs is regulated in vivo.While HDAC1, HDAC2, and HDAC3 are nuclear, the plant deacetylase HD2 is a nucleolar protein (8, 31). Miska et al. reported that the HDAC4 protein lacking the N-terminal 117 residues is cytoplasmic or nuclear in HeLa cells (33), whereas Fischl...

We describe here the identification and functional characterization of a novel human histone acetyltransferase, termed MORF (monocytic leukemia zinc finger protein-related factor). MORF is a 1781-residue protein displaying significant sequence similarity to MOZ (monocytic leukemia zinc finger protein). MORF is ubiquitously expressed in adult human tissues, and its gene is located at human chromosome band 10q22. MORF has intrinsic histone acetyltransferase activity. In addition to its histone acetyltransferase domain, MORF possesses a strong transcriptional repression domain at its N terminus and a highly potent activation domain at its C terminus. Therefore, MORF is a novel histone acetyltransferase that contains multiple functional domains and may be involved in both positive and negative regulation of transcription.

Nucleocytoplasmic trafficking of histone deacetylase 4 (HDAC4) plays an important role in regulating its function, and binding of 14-3-3 proteins is necessary for its cytoplasmic retention. Here, we report the identification of nuclear import and export sequences of HDAC4. While its N-terminal 118 residues modulate the nuclear localization, residues 244 to 279 constitute an authentic, strong nuclear localization signal. Mutational analysis of this signal revealed that three arginine-lysine clusters are necessary for its nuclear import activity. As for nuclear export, leucine-rich sequences located in the middle part of HDAC4 do not function as nuclear export signals. By contrast, a hydrophobic motif (MXXLXVXV) located at the C-terminal end serves as a nuclear export signal that is necessary for cytoplasmic retention of HDAC4. This motif is required for CRM1-mediated nuclear export of HDAC4. Furthermore, binding of 14-3-3 proteins promotes cytoplasmic localization of HDAC4 by both inhibiting its nuclear import and stimulating its nuclear export. Unlike wild-type HDAC4, a point mutant with abrogated MEF2-binding ability remains cytoplasmic upon exogenous expression of MEF2C, supporting the notion that direct MEF2 binding targets HDAC4 to the nucleus. Therefore, HDAC4 possesses intrinsic nuclear import and export signals for its dynamic nucleocytoplasmic shuttling, and association with 14-3-3 and MEF2 proteins affects such shuttling and thus directs HDAC4 to the cytoplasm and the nucleus, respectively.