title: Inhibition of cortical astrocyte differentiation by Hes6 requires amino- and carboxy-terminal motifs important for dimerization and phosphorylation.
abstract: Hairy/Enhancer of split (Hes) 6 is a basic helix-loop-helix protein that interacts with the transcriptional co-repressor, Groucho, and antagonizes the neural functions of the Notch pathway. More specifically, mouse Hes6 regulates cerebral corticogenesis by promoting neurogenesis and suppressing astrocyte differentiation. The molecular mechanisms underlying the anti-astrogenic function of Hes6 are poorly defined. Here we describe studies aimed at testing whether Hes6 inhibits astrocyte differentiation by antagonizing the transcription repression activity of Notch-activated Hes family members like Hes1. It is reported that Hes6 preferentially forms homodimers. Heterodimerization with Hes1 is antagonized in part by a conserved N-terminal patch of negatively charged residues. Mutation of this motif enhances heterodimerization with Hes1 and increases Hes6 ability to antagonize Hes1-mediated transcriptional repression. However, this mutation does not increase, but instead decreases, the anti-astrogenic activity of Hes6. It is shown further that Hes6 harbors a second conserved sequence, a C-terminal SPXXSP motif. This sequence is phosphorylated by the mitogen activated protein kinase pathway and its mutation disrupts the anti-astrogenic activity of Hes6 without affecting its ability to suppress Hes1. Together, these observations suggest that Hes6 homodimers regulate astrocyte differentiation through mechanisms that depend on the phosphorylation of Hes6 C-terminal domain but are independent of its ability to suppress Hes1-mediated transcriptional repression.
authors.affiliation: Center for Neuronal Survival, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Belanger-Jasmin
authors.forename: Estelle
authors.initials: E
authors.lastname: Llamosas
authors.forename: Yeman
authors.initials: Y
authors.lastname: Tang
authors.forename: Kerline
authors.initials: K
authors.lastname: Joachim
authors.forename: Ana-Maria
authors.initials: AM
authors.lastname: Osiceanu
authors.forename: Sumit
authors.initials: S
authors.lastname: Jhas
authors.forename: Stefano
authors.initials: S
authors.lastname: Stifani
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000502:physiology; D051792:Basic Helix-Loop-Helix Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D002454:Cell Differentiation / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured; D019281:Dimerization; D004622:Embryo, Mammalian; D005786:Gene Expression Regulation / Q000235:genetics; D006801:Humans; D051379:Mice; D009154:Mutation / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D010766:Phosphorylation / Q000187:drug effects; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D013234:Stem Cells / Q000187:drug effects / Q000502:physiology; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D012097:Repressor Proteins; C486570:Hes6 protein, mouse