Phosphoinositide hydrolysis in Ki- ras-transformed fibroblasts stimulated by platelet-derived growth factor and bradykinin

Abstract

1. 1. Signal transduction in response to platelet-derived growth factor (PDGF)-BB and bradykinin (BK) have been examined by measuring inositol polyphosphate formation in NIH3T3 fibrobalst and v-Ki- ras -transformed NIH3T3 fibroblast (DT). 2. 2. The PDGF-induced inositol polyphosphate formation in NIH3T3 was greater than that in DT cells, in which autophosphorylation of PDGF receptor and tyrosine phosphorylation of phospholipase C (PLC)-γ 1 were suppressed when examined by immunoblotting with anti-phosphotyrosine antibody. 3. 3. On the other hand, BK-stimulation produced a much higher level of inositol polyphosphate in DT cells which have a greater number of BK receptors. 4. 4. These results indicate that in Ki- ras transformed cells the decrease (caused by PDGF) and the increase (caused by BK) in phosphoinositide hydrolysis are due to the defective autophosphorylation of PDGF receptors leading to a reduction in PLC-γ 1 tyrosine phosphorylation and the overexpression of BK receptors, respectively.