title: Cyclin D1 expression mediated by phosphatidylinositol 3-kinase through mTOR-p70(S6K)-independent signaling in growth factor-stimulated NIH 3T3 fibroblasts.
abstract: Phosphatidylinositol (PI) 3-kinase is required for G1 to S phase cell cycle progression stimulated by a variety of growth factors and is implicated in the activation of several downstream effectors, including p70(S6K). However, the molecular mechanisms by which PI 3-kinase is engaged in activation of the cell cycle machinery are not well understood. Here we report that the expression of a dominant negative (DN) form of either the p110alpha catalytic or the p85 regulatory subunit of heterodimeric PI 3-kinase strongly inhibited epidermal growth factor (EGF)-induced upregulation of cyclin D1 protein in NIH 3T3(M17) fibroblasts. The PI 3-kinase inhibitors LY294002 and wortmannin completely abrogated increases in both mRNA and protein levels of cyclin D1 and phosphorylation of pRb, inducing G1 arrest in EGF-stimulated cells. By contrast, rapamycin, which potently suppressed p70(S6K) activity throughout the G1 phase, had little inhibitory effect, if any, on either of these events. PI 3-kinase, but not rapamycin-sensitive pathways, was also indispensable for upregulation of cyclin D1 mRNA and protein by other mitogens in NIH 3T3 (M17) cells and in wild-type NIH 3T3 cells as well. We also found that an enforced expression of wild-type p110 was sufficient to induce cyclin D1 protein expression in growth factor-deprived NIH 3T3(M17) cells. The p110 induction of cyclin D1 in quiescent cells was strongly inhibited by coexpression of either of the PI 3-kinase DN forms, and by LY294002, but was independent of the Ras-MEK-ERK pathway. Unlike mitogen stimulation, the p110 induction of cyclin D1 was sensitive to rapamycin. These results indicate that the catalytic activity of PI 3-kinase is necessary, and could also be sufficient, for upregulation of cyclin D1, with mTOR signaling being differentially required depending upon cellular conditions.
authors.affiliation: Department of Molecular and Cellular Physiology, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan. ntakuwa@m.u-tokyo.ac.jp
authors.forename: N
authors.initials: N
authors.lastname: Takuwa
authors.forename: Y
authors.initials: Y
authors.lastname: Fukui
authors.forename: Y
authors.initials: Y
authors.lastname: Takuwa
mesh_terms: D016475:3T3 Cells; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002867:Chromones / Q000494:pharmacology; D019938:Cyclin D1 / Q000235:genetics* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D011494:Protein Kinases; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D016196:S Phase; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014162:Transfection; D015854:Up-Regulation / Q000187:drug effects; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002867:Chromones; D019938:Cyclin D1; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017853:Phosphotransferases (Alcohol Group Acceptor); D011494:Protein Kinases; D012333:RNA, Messenger; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D000077191:Wortmannin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546843:mTOR protein, mouse