The transcriptional repressor, REST, helps restrict neuronal traits to neurons by blocking their expression in nonneuronal cells. To examine the repercussions of REST expression in neurons, we generated a neuronal cell line that expresses REST conditionally. REST expression inhibited differentiation by nerve growth factor, suppressing both sodium current and neurite growth. A novel corepressor complex, CoREST/HDAC2, was shown to be required for REST repression. In the presence of REST, the CoREST/HDAC2 complex occupied the native Nav1.2 sodium channel gene in chromatin. In neuronal cells that lack REST and express sodium channels, the corepressor complex was not present on the gene. Collectively, these studies define a novel HDAC complex that is recruited by the C-terminal repressor domain of REST to actively repress genes essential to the neuronal phenotype.

Several genes encoding proteins critical to the neuronal phenotype, such as the brain type II sodium channel gene, are expressed to high levels only in neurons. This cell specificity is due, in part, to long-term repression in nonneural cells mediated by the repressor protein REST͞NRSF (RE1 silencing transcription factor͞neural-restrictive silencing factor). We show here that CoREST, a newly identified human protein, functions as a corepressor for REST. A single zinc finger motif in REST is required for A large number of genes encoding neuronal phenotypic traits, including ion channels, neurotransmitters, synaptic proteins, and cell-adhesion molecules, are expressed only in neurons. One mechanism important in establishing and maintaining this neural specificity involves the DNA-binding protein REST͞ NRSF (RE1 silencing transcription factor͞neural-restrictive silencing factor) (1-4), which serves to block expression of its target genes in nonneural tissues. Such maintained gene repression is in contrast to the more dynamic repression mechanism that regulates inducible gene expression in response to steroid hormone receptors, one of the best-studied mammalian repressor mechanisms (for review, see ref. 5).One REST target gene essential for neuronal physiology is that encoding the brain type II voltage-dependent sodium channel. This ion channel is required for the propagation of fast electrical signals in neurons, in the form of neuronal impulses, and is not expressed in nonneural tissues. As is true for other REST target genes, there is a reciprocal relationship between expression of the type II sodium channel gene and expression of REST. Additionally, when a REST expression plasmid is cotransfected into neuronal cells along with a type II sodium channel reporter, the expression of the reporter gene is reduced dramatically (1). This result indicates either that REST alone is sufficient to repress its target genes or that REST accessory factors are present in neuronal cells despite the absence of REST.Two distinct repressor domains have been identified and characterized in REST (6, 7). These domains are located in the amino and carboxyl termini of the protein. Both domains are required for full repression in the context of the intact molecule, but each domain is sufficient to repress type II sodium channel reporter genes when expressed as a Gal4 fusion protein (6). The C-terminal repressor domain contains a C 2 H 2 class zinc finger beginning approximately 40 aa upstream of the stop codon. Deleting this domain, or introducing a point mutation critical to the zinc finger motif, abolishes repressor activity (6). Because zinc finger motifs often mediate proteinprotein interactions, we proposed that REST might function in conjunction with other nuclear factors or corepressors.In this study, we find that repression of the type II sodium channel promoter by REST requires a newly identified protein, CoREST, which fulfills the criteria for a bona fide corepressor. CoREST is a repressor; mutations that disrupt CoREST...

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We have investigated the DNA-binding, oligomerization, and trans-activation functions of isolated segments of murine p53. We find that p53 has two autonomous DNA-binding regions. One domain, from amino acid 280 to 390, forms stable tetramers and binds DNA nonspecifically. The biological significance, ff any, of this DNA-binding activity is not known. A second domain, from amino acid 80 to 290, does not form stable tetramers under stringent conditions but binds DNA both specifically and nonspecifically. The specific DNA-binding function of p53, therefore, resides in the highly conserved central region of the protein and does not require stable tetramerization. Amino acids 1-290, which include both the specific DNA-binding domain and the amino-terminal acidic region, activate a p53-specific promoter in vivo. This finding strongly argues that the DNA-binding activity of p53 segment 80-290 is physiologically significant. The role of tetramerization in p53 function remains to be determined.

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A function of the transcription factor REST is to block the expression of neuronal phenotypic traits in nonneuronal cells. Previous studies have shown that RESTmediated repression requires histone deacetylase activity and that recruitment of deacetylases is mediated by two co-repressors, Sin3A and CoREST. In this study, we show that a repressor domain in CoREST interacts with BRG1-associated factor (BAF) 57, a component of the hSWI⅐SNF complex. In vivo, BAF57 occupies the neuronal sodium channel gene (Nav1.2) promoter, and targeting to this gene requires REST. In addition to BAF57, the ATPase BRG1 and BAF170, other members of the hSWI⅐SNF complex, are also present in the REST⅐CoREST repressor complex. Microinjection of specific antibodies against BRG1, BAF57, or BAF170 into Rat1 fibroblasts relieves repression of RE1 reporter genes. Together, our data suggest that ATP-dependent chromatin remodeling, as well as histone deacetylation, is needed for REST-mediated repression.

Hospitalists and PCPs encounter similar challenges in care coordination, yet have important experiential differences related to sending and receiving roles for hospital discharges. Efforts to improve coordination of care between hospitalists and PCPs should aim to understand perspectives of clinicians in each setting.

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