@article {38269, title = {Functional Analysis of Hes-1 in Preadipocytes}, journal = {Molecular EndocrinologyMolecular EndocrinologyMolecular EndocrinologyMolecular Endocrinology}, volume = {20}, year = {2006}, type = {10.1210/me.2005-0325}, abstract = {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.}, isbn = {0888-8809, 1944-9917}, author = {Ross, David A. and Sridhar Hannenhalli and Tobias, John W. and Cooch, Neil and Shiekhattar, Ramin and Kadesch, Tom} }