title: Integrated stability and activity control of the Drosophila Rbf1 retinoblastoma protein.
abstract: The retinoblastoma (RB) family transcriptional corepressors regulate diverse cellular events including cell cycle, senescence, and differentiation. The activity and stability of these proteins are mediated by post-translational modifications; however, we lack a general understanding of how distinct modifications coordinately impact both of these properties. Previously, we showed that protein turnover and activity are tightly linked through an evolutionarily conserved C-terminal instability element (IE) in the Drosophila RB-related protein Rbf1; surprisingly, mutant proteins with enhanced stability were less, not more active. To better understand how activity and turnover are controlled in this model RB protein, we assessed the impact of Cyclin-Cdk kinase regulation on Rbf1. An evolutionarily conserved N-terminal threonine residue is required for Cyclin-Cdk response and showed a dominant impact on turnover and activity; however, specific residues in the C-terminal IE differentially impacted Rbf1 activity and turnover, indicating an additional level of regulation. Strikingly, specific IE mutations that impaired turnover but not activity induced dramatic developmental phenotypes in the Drosophila eye. Mutation of the highly conserved Lys-774 residue induced hypermorphic phenotypes that mimicked the loss of phosphorylation control; mutation of the corresponding codon of the human RBL2 gene has been reported in lung tumors. Our data support a model in which closely intermingled residues within the conserved IE govern protein turnover, presumably through interactions with E3 ligases, and protein activity via contacts with E2F transcription partners. Such functional relationships are likely to similarly impact mammalian RB family proteins, with important implications for development and disease.
authors: From the Cell and Molecular Biology Program and.
authors: Liang
authors: L
authors: Zhang
authors: the Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319 and.
authors: Yiliang
authors: Y
authors: Wei
authors: the Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319 and.
authors: Irina
authors: I
authors: Pushel
authors: the Biochemistry and Molecular Biology Program, Friedrich-Schiller University Jena, D-07743 Jena, Germany.
authors: Karolin
authors: K
authors: Heinze
authors: the Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319 and.
authors: Jared
authors: J
authors: Elenbaas
authors: From the Cell and Molecular Biology Program and the Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319 and henryrw@msu.edu.
authors: R William
authors: RW
authors: Henry
authors: From the Cell and Molecular Biology Program and the Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319 and arnosti@msu.edu.
authors: David N
authors: DN
authors: Arnosti
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002460:Cell Line; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D005123:Eye / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D008239:Lysine / Q000235:genetics / Q000378:metabolism*; D008854:Microscopy, Electron; D009154:Mutation; D010766:Phosphorylation; D055550:Protein Stability; D016160:Retinoblastoma Protein; D012694:Serine / Q000235:genetics / Q000378:metabolism*; D013912:Threonine / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014921:Wings, Animal / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D016213:Cyclins; D029721:Drosophila Proteins; C099965:Rbf protein, Drosophila; D016160:Retinoblastoma Protein; D014157:Transcription Factors; D013912:Threonine; D012694:Serine; D018844:Cyclin-Dependent Kinases; D008239:Lysine
keywords: Drosophila; Phosphorylation; Retinoblastoma Protein (pRb, RB); Transcription Repressor; Tumor Suppressor Gene