Regulation of phosphoinositide phosphorylation in Swiss 3T3 cells stimulated by platelet-derived growth factor.
The regulation of phosphoinositide phosphorylation was studied in Swiss 3T3 cells that were stimulated by platelet-derived growth factor (PDGF). Studies with intact cells showed that the mitogen increased the incorporation of 32P into phosphatidylinositol (PtdIns), phosphatidylinositol 4-phosphate (PtdIns-P), and phosphatidylinositol 4,5-bisphosphate (PtdIns-P2) during the cell cycle, with distinct peaks of incorporation for all three phosphoinositides after 1 h, and for PtdIns and PtdIns-P2 after 20 h. Direct measurements of the activities of PtdIns kinase and PtdIns-P kinase in freeze-thawed cells revealed that the activity of PtdIns kinase was rate-limiting for the synthesis of PtdIns-P2. Maximal activities of PtdIns kinase and PtdIns-P kinase, with exogenous substrates, were unchanged during the 1st h of PDGF treatment, but doubled during the next 24 h. The increase in PtdIns kinase activity began within 2-4 h, exceeded the increase in cell protein, and was abolished by cycloheximide, which suggests that the enzyme was induced specifically in response to PDGF. The increase in activity of PtdIns-P kinase paralleled the increase in cell protein. Dose-response curves for PDGF showed that the activities of PtdIns kinase and PtdIns-P kinase at 24 h increased in proportion to the extent of mitogenic stimulation of the cells. Our results support the conclusion that the activities of PtdIns kinase and PtdIns-P kinase increase in response to PDGF, but only after several hours of cell cycle traverse.
D019870:1-Phosphatidylinositol 4-Kinase; D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D007700:Kinetics; D051379:Mice; D010712:Phosphatidic Acids / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor); D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*
D010712:Phosphatidic Acids; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010982:Platelet-Derived Growth Factor; C037178:phosphatidylinositol 4-phosphate; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); D019870:1-Phosphatidylinositol 4-Kinase; C020077:1-phosphatidylinositol-4-phosphate 5-kinase