The mitogenic signaling pathway of fibroblast growth factor is not mediated through polyphosphoinositide hydrolysis and protein kinase C activation in hamster fibroblasts.
Basic or acidic fibroblast growth factor (FGF), alone, was found to be as potent as alpha-thrombin to reinitiate DNA synthesis in G0-arrested Chinese hamster lung fibroblasts (CCL39). Basic FGF at 50 ng/ml or thrombin at 1 unit/ml rapidly initiated early events such as cytoplasmic alkalinization (0.2-0.3 pH units), rise in cytoplasmic Ca2+, phosphorylation of ribosomal protein S6 and increased c-myc expression, followed by a 30-40-fold increase in labeled nuclei. Whereas thrombin is a potent activator of phospholipase C as judged by the rapid release of inositol trisphosphate, inositol bisphosphate and by the massive accumulation of total inositol phosphate (IP) in the presence of 20 mM Li+, FGF failed to induce the breakdown of polyphosphoinositides in quiescent CCL39 cells. Indeed, no inositol trisphosphate nor inositol bisphosphate could be detected in response to FGF; in presence of Li+ the total IP release never exceeded 8% of the IP released by the action of thrombin. Two additional findings indicated that FGF and thrombin activate different signaling pathways. First, we found that, in contrast to thrombin, the FGF-induced rise in the cytoplasmic free Ca2+ concentration measured by quin-2 fluorescence, is strictly dependent upon the presence of Ca2+ in the external medium. Second, we found that FGF failed to activate protein kinase C as judged by the epidermal growth factor-receptor binding assay. Treatment of the cells with either thrombin or phorbol esters, rapidly inhibited 125I-labeled epidermal growth factor binding (50-60%). Basic or acidic FGF had no effect. We conclude that: the FGF-receptor signaling pathway is not coupled to phospholipase C activation, and early mitogenic events and reinitiation of DNA synthesis can be initiated independently of inositol lipid breakdown and protein kinase C activation.
D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004261:DNA Replication / Q000187:drug effects*; D004789:Enzyme Activation; D005346:Fibroblast Growth Factors / Q000494:pharmacology*; D006868:Hydrolysis; D007700:Kinetics; D008168:Lung; D008934:Mitogens; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology*
D008934:Mitogens; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D005346:Fibroblast Growth Factors; D011493:Protein Kinase C; D013917:Thrombin