title: Mastermind-Like 1 Is Ubiquitinated: Functional Consequences for Notch Signaling.
abstract: Early studies demonstrated the involvement of ubiquitination of the Notch intracellular domain for rapid turnover of the transcriptional complex at Notch target genes. It was shown that this ubiquitination was promoted by the co-activator Mastermind like 1 (MAML1). MAML1 also contains numerous lysine residues that may also be ubiquitinated and necessary for protein regulation. In this study, we show that over-expressed MAML1 is ubiquitinated and identify eight conserved lysine residues which are required for ubiquitination. We also show that p300 stimulates ubiquitination and that Notch inhibits ubiquitination. Furthermore, we show that a mutant MAML1 that has decreased ubiquitination shows increased output from a HES1 reporter gene assay. Therefore, we speculate that ubiquitination of MAML1 might be a mechanism to maintain low levels of the protein until needed for transcriptional activation. In summary, this study identifies that MAML1 is ubiquitinated in the absence of Notch signaling to maintain low levels of MAML1 in the cell. Our data supports the notion that a precise and tight regulation of the Notch pathway is required for this signaling pathway.
authors.affiliation: From the Department of Biological Sciences, San José State University, San José, California, United States of America.
authors.forename: Mozhgan
authors.initials: M
authors.lastname: Farshbaf
authors.affiliation: From the Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Mikael J
authors.initials: MJ
authors.lastname: Lindberg
authors.affiliation: From the Department of Biological Sciences, San José State University, San José, California, United States of America.
authors.forename: Anh
authors.initials: A
authors.lastname: Truong
authors.affiliation: From the Department of Biological Sciences, San José State University, San José, California, United States of America.
authors.forename: Zachery
authors.initials: Z
authors.lastname: Bevens
authors.affiliation: From the Department of Biological Sciences, San José State University, San José, California, United States of America.
authors.forename: Elaina
authors.initials: E
authors.lastname: Chambers
authors.affiliation: From the Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Angeliki
authors.initials: A
authors.lastname: Pournara
authors.affiliation: From the Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Annika E
authors.initials: AE
authors.lastname: Wallberg
authors.affiliation: From the Department of Biological Sciences, San José State University, San José, California, United States of America.
authors.forename: J Brandon
authors.initials: JB
authors.lastname: White
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D017930:Genes, Reporter; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000235:genetics; D006801:Humans; D008239:Lysine / Q000378:metabolism; D051880:Receptors, Notch / Q000378:metabolism*; D015398:Signal Transduction; D000072056:Transcription Factor HES-1; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D054875:Ubiquitination; D050880:p300-CBP Transcription Factors / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D008239:Lysine; D051880:Receptors, Notch; D000072056:Transcription Factor HES-1; D014157:Transcription Factors; D050880:p300-CBP Transcription Factors; C430872:MAML1 protein, human; C078493:HES1 protein, human