Abstract
NIH3T3 cells were transfected with activated Ha-ras and the corresponding proto-oncogene was subjected to transcriptional control by recombination in vitro with MMTV-LTR. Induction of p21 ras expression in quiescent cells by dexamethasone causes an increased turnover of phosphatidylinositol 4,5-bisphosphate with a concomitant rise in inositol phosphates, and an activation of the Na +/H +-antiporter. Addition of serum growth factors to dexamethasone treated cells does not result in an additional stimulation of phosphatidylinositol metabolism or Na +/H +-exchange. There is also a desensitization to exogenous growth factors of the intracellular Ca 2+-mobilizing system, leading to a depression of the transitory increase in cytosolic Ca 2+ after addition of serum growth factors. None of these effects are seen after expression of the Ha-ras proto-oncogene. Results are discussed as indicating a constitutive growth factor independent activation of growth factor signal transduction by the activated Ha-ras.
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