title: Role of Drosophila retinoblastoma protein instability element in cell growth and proliferation.
abstract: The RB tumor suppressor, a regulator of the cell cycle, apoptosis, senescence, and differentiation, is frequently mutated in human cancers. We recently described an evolutionarily conserved C-terminal "instability element" (IE) of the Drosophila Rbf1 retinoblastoma protein that regulates its turnover. Misexpression of wild-type or non-phosphorylatable forms of the Rbf1 protein leads to repression of cell cycle genes. In contrast, overexpression of a defective form of Rbf1 lacking the IE (ΔIE), a stabilized but transcriptionally less active form of the protein, induced ectopic S phase in cell culture. To determine how mutations in the Rbf1 IE may induce dominant effects in a developmental context, we assessed the impact of in vivo expression of mutant Rbf1 proteins on wing development. ΔIE expression resulted in overgrowth of larval wing imaginal discs and larger adult wings containing larger cells. In contrast, a point mutation in a conserved lysine of the IE (K774A) generated severely disrupted, reduced wings. These contrasting effects appear to correlate with control of apoptosis; expression of the pro-apoptotic reaper gene and DNA fragmentation measured by acridine orange stain increased in flies expressing the K774A isoform and was suppressed by expression of Rbf1ΔIE. Intriguingly, cancer associated mutations affecting RB homologs p130 and p107 may similarly induce dominant phenotypes.
authors.affiliation: a Department of Biochemistry and Molecular Biology ; Michigan State University ; East Lansing , MI USA.
authors.forename: Jared S
authors.initials: JS
authors.lastname: Elenbaas
authors.forename: Rima
authors.initials: R
authors.lastname: Mouawad
authors.forename: R William
authors.initials: RW
authors.lastname: Henry
authors.forename: David N
authors.initials: DN
authors.lastname: Arnosti
authors.forename: Sandhya
authors.initials: S
authors.lastname: Payankaulam
mesh_terms: D000165:Acridine Orange; D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics*; D049109:Cell Proliferation / Q000235:genetics / Q000502:physiology*; D017931:DNA Primers / Q000235:genetics; D004330:Drosophila / Q000235:genetics / Q000502:physiology*; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000235:genetics*; D017354:Point Mutation / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D016160:Retinoblastoma Protein / Q000235:genetics*; D014921:Wings, Animal / Q000254:growth & development*
chemical_list: D018797:Cell Cycle Proteins; D017931:DNA Primers; D016160:Retinoblastoma Protein; D000165:Acridine Orange
keywords: Apaf-1, Apoptotic protease activating factor 1; Ark, Apaf-1 related killer; CDK, Cyclin-dependent kinase; COP9, Constitutive photomorphogenic 9; Dpp, Decapentaplegic; Drosophila; E2F, E2 promoter binding factor; Hid, Head involution defective; IE, Instability element; PCNA, Proliferating cell nuclear antigen; Polα, DNA polymerase α; Rb, Retinoblastoma; Wnt, Wingless; apoptosis; cell size; retinoblastoma; transcriptional regulation; tumor suppressor; wing size