RRC ID 39338
Author Takuwa N, Fukui Y, Takuwa Y.
Title Cyclin D1 expression mediated by phosphatidylinositol 3-kinase through mTOR-p70(S6K)-independent signaling in growth factor-stimulated NIH 3T3 fibroblasts.
Journal Mol Cell Biol
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.
Volume 19(2)
Pages 1346-58
Published 1999-2-1
DOI 10.1128/mcb.19.2.1346
PMID 9891068
PMC PMC116063
MeSH 3T3 Cells Androstadienes / pharmacology Animals Chromones / pharmacology Cyclin D1 / genetics* Cyclin D1 / metabolism Enzyme Inhibitors / pharmacology Epidermal Growth Factor / pharmacology Mice Morpholines / pharmacology Phosphatidylinositol 3-Kinases / genetics Phosphatidylinositol 3-Kinases / metabolism* Phosphoinositide-3 Kinase Inhibitors Phosphotransferases (Alcohol Group Acceptor) / metabolism Protein Kinases* RNA, Messenger / genetics RNA, Messenger / metabolism Ribosomal Protein S6 Kinases / metabolism S Phase Signal Transduction Sirolimus / pharmacology TOR Serine-Threonine Kinases Transfection Up-Regulation / drug effects Wortmannin
IF 3.735
Times Cited 150
Human and Animal Cells