Functional analysis of Hes-1 in preadipocytes.
Notch signaling blocks differentiation of 3T3-L1 preadipocytes, and this can be mimicked by constitutive expression of the Notch target gene Hes-1. Although considered initially to function only as a repressor, recent evidence indicates that Hes-1 can also activate transcription. We show here that the domains of Hes-1 needed to block adipogenesis coincide with those necessary for transcriptional repression. HRT1, another basic-helix-loop-helix protein and potential Hes-1 partner, was also induced by Notch in 3T3-L1 cells but did not block adipogenesis, suggesting that Hes-1 functions primarily as a homodimer or possibly as a heterodimer with an unknown partner. Purification of Hes-1 identified the Groucho/transducin-like enhancer of split family of corepressors as the only significant Hes-1 interacting proteins in vivo. An evaluation of global gene expression in preadipocytes identified approximately 200 Hes-1-responsive genes comprising roughly equal numbers of up-regulated and down-regulated genes. However, promoter analyses indicated that the down-regulated genes were significantly more likely to contain Hes-1 binding sites, indicating that Hes-1 is more likely to repress transcription of its direct targets. We conclude that Notch most likely blocks adipogenesis through the induction of Hes-1 homodimers, which repress transcription of key target genes.
Ross
David A
DA
Department of Genetics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Hannenhalli
Sridhar
S
Tobias
John W
JW
Cooch
Neil
N
Shiekhattar
Ramin
R
Kadesch
Tom
T
D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D056970:Co-Repressor Proteins; D019281:Dimerization; D020869:Gene Expression Profiling; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D041681:NIH 3T3 Cells / Q000378:metabolism; D011401:Promoter Regions, Genetic; D051880:Receptors, Notch / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013234:Stem Cells / Q000378:metabolism; D051780:Sterol Regulatory Element Binding Protein 1 / Q000235:genetics / Q000378:metabolism; D000072056:Transcription Factor HES-1
D051792:Basic Helix-Loop-Helix Proteins; D018797:Cell Cycle Proteins; D056970:Co-Repressor Proteins; D018398:Homeodomain Proteins; D051880:Receptors, Notch; D012097:Repressor Proteins; D051780:Sterol Regulatory Element Binding Protein 1; D000072056:Transcription Factor HES-1; C485631:HEY1 protein, human; C489734:Hes1 protein, mouse; C489735:Hes1 protein, rat; C434946:Tle1 protein, mouse