The basic helix-loop-helix protein, sharp-1, represses transcription by a histone deacetylase-dependent and histone deacetylase-independent mechanism.
Many aspects of neurogenesis and neuronal differentiation are controlled by basic helix-loop-helix (bHLH) proteins. One such factor is SHARP-1, initially identified on the basis of its sequence similarity to hairy. Unlike hairy, and atypically for bHLHs, SHARP-1 is expressed late in development, suggestive of a role in terminal aspects of differentiation. Nevertheless, the role of SHARP-1 and the identity of its target genes remain unknown. During the course of a one-hybrid screen for transcription factors that bind to regulatory domains of the M1 muscarinic acetylcholine receptor gene, we isolated the bHLH transcription factor SHARP-1. In this study, we investigated the functional role of SHARP-1 in regulating transcription. Fusion proteins of SHARP-1 tethered to the gal4 DNA binding domain repress both basal and activated transcription when recruited to either a TATA-containing or a TATAless promoter. Furthermore, we identified two independent repression domains that operate via distinct mechanisms. Repression by a domain in the C terminus is sensitive to the histone deacetylase inhibitor trichostatin A, whereas repression by the bHLH domain is insensitive to TSA. Furthermore, overexpression of SHARP-1 represses transcription from the M(1) promoter. This study represents the first report to assign a function to, and to identify a target gene for, the bHLH transcription factor SHARP-1.
Schools of Biochemistry and Molecular Biology and Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom.
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M
Garriga-Canut
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Roopra
N J
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Buckley
D000595:Amino Acid Sequence; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D002460:Cell Line; D017931:DNA Primers; D018257:Helix-Loop-Helix Motifs; D006655:Histone Deacetylases / Q000378:metabolism*; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000737:chemistry / Q000502:physiology*; D012097:Repressor Proteins / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*
D051792:Basic Helix-Loop-Helix Proteins; D017931:DNA Primers; D006655:Histone Deacetylases; D009479:Neuropeptides; D012097:Repressor Proteins; D014157:Transcription Factors; C109509:Bhlhe41 protein, rat