title: mSharp-1/DEC2, a basic helix-loop-helix protein functions as a transcriptional repressor of E box activity and Stra13 expression.
abstract: Transcription factors belonging to the basic helix-loop-helix (bHLH) family play critical roles in the regulation of cellular differentiation of distinct cell types. In this study, we have characterized the DNA-binding and transcriptional properties of the bHLH factor mSharp-1/DEC2. mSharp-1 belongs to the Hairy/Enhancer of Split subfamily of bHLH factors and exhibits the highest structural and sequence identity with Stra13. We show that mSharp-1 specifically binds to the E box motif (CANNTG) as a homodimer and acts as a potent transcriptional repressor of MyoD- and E12-induced E box activity and differentiation. The inhibitory activity of mSharp-1 occurs through several mechanisms including occupancy of E box sites by mSharp-1 homodimers and by direct physical interaction with MyoD and E proteins. Furthermore, by using gel mobility shift assays and chromatin immunoprecipitation experiments, we have identified Stra13 as a target for mSharp-1-mediated repression. We demonstrate that transcriptional repression of Stra13 depends, in part, on binding of mSharp-1 to three conserved E box motifs in the Stra13 proximal promoter. Moreover, mSharp-1 directly interacts with the transcriptional activator Sp1 and impairs Sp1 induction of Stra13 promoter. Our results suggest that mSharp-1 functions as a transcriptional repressor by DNA binding dependent and independent mechanisms.
authors.affiliation: Brookdale Department of Molecular, Cell and Developmental Biology, Mount Sinai School of Medicine, New York, New York 10029-6574, USA.
authors.forename: Sameena
authors.initials: S
authors.lastname: Azmi
authors.forename: Hong
authors.initials: H
authors.lastname: Sun
authors.forename: Anne
authors.initials: A
authors.lastname: Ozog
authors.forename: Reshma
authors.initials: R
authors.lastname: Taneja
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D024202:Electrophoretic Mobility Shift Assay; D018257:Helix-Loop-Helix Motifs; D018398:Homeodomain Proteins / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012097:Repressor Proteins / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D018398:Homeodomain Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C470968:Bhlhb3 protein, mouse; C491539:Bhlhe40 protein, mouse