title: The N-terminal 24 amino acids of the p55 gamma regulatory subunit of phosphoinositide 3-kinase binds Rb and induces cell cycle arrest.
abstract: Although phosphoinositide 3-kinase (PI 3-kinase) is essential for cell cycle progression, the molecular mechanisms that regulate its diverse biological effects are poorly understood. We demonstrate here that Rb, a key regulator of cell cycle progression, associates with p55 kDa (p55alpha and p55gamma) regulatory subunits of PI 3-kinase in vivo and in vitro. Both confocal microscopy and biochemical analysis demonstrated the presence of p55gamma in the nucleus. The 24-amino-acid N-terminal end of p55gamma, which is unique among PI 3-kinase regulatory subunits, was sufficient to bind Rb. Addition of serum or growth factors to quiescent cells triggered the dissociation of Rb from p55. Ectopic expression of the 24-amino-acid N-terminal end of p55gamma inhibited cell cycle progression, as evidenced by induction of cell growth arrest at the G0/G1 phase, inhibition of DNA synthesis, inhibition of cyclin D and cyclin E promoter activity, and changes in the expression of cell cycle-related proteins. The inhibitory effects of the N-terminal end of p55gamma on cell cycle progression depended on the presence of functional Rb. These data demonstrate for the first time an association of p55gamma with Rb and show that modification of this association can lead to cell cycle arrest.
authors.affiliation: Greenebaum Cancer Center, University of Maryland, Baltimore, Maryland 21201, USA.
authors.forename: Xianmin
authors.initials: X
authors.lastname: Xia
authors.forename: Aiwu
authors.initials: A
authors.lastname: Cheng
authors.forename: Damilola
authors.initials: D
authors.lastname: Akinmade
authors.forename: Anne W
authors.initials: AW
authors.lastname: Hamburger
mesh_terms: D016475:3T3 Cells; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D015153:Blotting, Western; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002453:Cell Cycle; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D056741:Cyclin D; D019927:Cyclin E / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D005434:Flow Cytometry; D016193:G1 Phase; D005982:Glutathione Transferase / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry* / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016192:Resting Phase, Cell Cycle; D016160:Retinoblastoma Protein / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000963:Antimetabolites; D056741:Cyclin D; D019927:Cyclin E; D016213:Cyclins; D018076:DNA, Complementary; D008164:Luminescent Proteins; D016160:Retinoblastoma Protein; D049452:Green Fluorescent Proteins; D008156:Luciferases; D005982:Glutathione Transferase; D019869:Phosphatidylinositol 3-Kinases; D001973:Bromodeoxyuridine