Involvement of Ca 2+-calmodulin in platelet-derived growth factor-, fibroblast growth factor-, and insulin-induced ornithine decarboxylase in NIH-3T3 cells

Abstract

Ornithine decarboxylase (ODC) was induced by platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), and insulin at doses ranging from 0.125 to 0.5 U/mL, 25 to 500 ng/mL, and 10 −8 to 10 −7 mol/L, respectively, in NIH-3T3 cells. The induction of ODC reached a plateau approximately 4 to 6 hours after addition of each mitogen. PDGF exerted a synergistic action with 10 −7 mol/L insulin until the concentration of PDGF reached 0.5 U/mL and exerted an additive action at concentrations greater than 0.5 U/mL. FGF also accelerated ODC induction by insulin (10 −7 mol/L) synergistically when it was added at doses up to 500 ng/mL. PDGF added to the intact monolayer cells caused a spike-and-plateau increase in cytosolic Ca 2+ concentration ([Ca 2+] i); the spike was independent of extracellular Ca 2+, whereas the plateau formation was dependent on extracellular Ca 2+. On the other hand, FGF caused a plateau-like increase in [Ca 2+] i, exclusively dependent on extracellular Ca 2+. Insulin did not affect [Ca 2+] i in NIH-3T3 cells. Trifluoperazine (15 to 30 μmol/L) inhibited the induction of ODC by PDGF and FGF, but did not inhibit the effect of insulin to induce ODC. N-(6-aminohexyl)-5-chloro-1-Naphthalenesulfonamide ([W-7] 30 to 40 μmol/L) showed a more profound suppressive effect on ODC induced by PDGF and FGF than N-(6-aminohexyl)-naphthalenesulfonamide (W-5) did. There was no difference between the effects of W-7 and W-5 on ODC induction by insulin. In addition, 20 μmol/L trifluoperazine inhibited the synergistic effect of ODC by insulin and PDGF or FGF. W-7 (40 μmol/L) also inhibited this effect more significantly than W-5 (40 μmol/L). These data suggest that ODC in NIH-3T3 cells is induced in response to PDGF or FGF by the activation of a pathway involving the Ca 2+-calmodulin system, whereas ODC induction by insulin involves a pathway independent of the Ca 2+-calmodulin system. The simultaneous activation of distinct signal transduction pathways of ODC induction by PDGF or FGF and insulin generates synergism. It is also suggested that the synergistic effect of the ODC induction in NIH-3T3 cells by insulin and PDGF or FGF is regulated by a calmodulin-dependent function.