We have previously demonstrated phospholipase C (PLC) independent activation of phospholipase A2(PLA2) by epidermal growth factor (EGF) in glomerular mesangial cells in culture. In the current study using glass beads to permeabilize [3H]- or [14C]-arachidonate labelled mesangial cells we demonstrate that guanine nucleotides modulate the EGF-mediated stimulation of arachidonic acid release (75% inhibition with 100 μM GDPβS and 108% augmentation with 100 μM GTPγS). GTPγS alone stimulated both the release of free arachidonic acid and production of diacylglycerol (DAG), while EGF itself neither stimulated DAG nor augmented the DAG response to GTPγS. These findings suggest the intermediacy of a G-protein in PLC-independent stimulation of PLA2 by a growth factor, and provide a model system for determining the relationship between G-protein intermediacy and the intrinsic tyrosine kinase activity of the growth factor receptor.
Abbreviations EGF, Epidermal Growth Factor; PLC, phospholipase C; PLA2, phospholipase A2; DAG, Diacylglycerol; NEFA, non-esterified fatty acid; GTPγS, guanosine-5′-0-[3-thio]triphosphate; GDPβS, guanosine-5′-0-[2-thio]diphosphate