Phosphatidylinositol 3-kinase activity regulates alpha -thrombin-stimulated G1 progression by its effect on cyclin D1 expression and cyclin-dependent kinase 4 activity.
In this study, we present evidence that PI 3-kinase is required for alpha-thrombin-stimulated DNA synthesis in Chinese hamster embryonic fibroblasts (IIC9 cells). Previous results from our laboratory demonstrate that the mitogen-activated protein kinase (extracellular signal-regulated kinase (ERK)) pathway controls transit through G(1) phase of the cell cycle by regulating the induction of cyclin D1 mRNA levels and cyclin dependent kinase 4 (CDK4)-cyclin D1 activity. In IIC9 cells, PI 3-kinase activation also is an important controller of the expression of cyclin D1 protein and CDK4-cyclin D1 activity. Pretreatment of IIC9 cells with the selective PI 3-kinase inhibitor, LY294002 blocks the alpha-thrombin-stimulated increase in cyclin D1 protein and CDK4 activity. However, LY294002 does not affect alpha-thrombin-induced cyclin D1 steady state message levels, indicating that PI 3-kinase acts independent of the ERK pathway. Interestingly, expression of a dominant-negative Ras significantly decreased both alpha-thrombin-stimulated ERK and PI 3-kinase activities. These data clearly demonstrate that the alpha-thrombin-induced Ras activation coordinately regulates ERK and PI 3-kinase activities, both of which are required for expression of cyclin D1 protein and progression through G(1).
Phillips-Mason
P J
PJ
Departments of Cell and Molecular Biology and Pharmacological and Physiological Sciences, St. Louis University School of Medicine, St. Louis, Missouri 63104, USA.
Raben
D M
DM
Baldassare
J J
JJ
D000818:Animals; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D019938:Cyclin D1 / Q000096:biosynthesis*; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D004261:DNA Replication; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016193:G1 Phase; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D013917:Thrombin / Q000378:metabolism*
D002867:Chromones; D019938:Cyclin D1; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D004791:Enzyme Inhibitors; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D013917:Thrombin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one