Effect of GTP gamma S on insulin binding and tyrosine phosphorylation in liver membranes and L6 muscle cells
Burdett, E.; Mills, G.B.; Klip, A.
American Journal of Physiology 258(1 Pt 1): C99-108
1990
ISSN/ISBN: 0002-9513 PMID: 2105654 Document Number: 364751
Guanosine 5'O-(3-thiotriphosphate) (GTP.gamma.S), a specific activator of G proteins, did not change the Kd nor total binding of [125I]insulin in plasma membranes from rat liver. Insulin did not alter GTP.gamma.35S binding nor polypeptide ADP ribosylation in crude and plasma membranes catalyzed either intrinsically or by cholera toxin. In L6 muscle cells, insulin caused tyrosine phosphorylation of a polypeptide of Mr 160,000. Cell electroporation enabled testing of G protein action in this cellular system. Phosphorylation of the Mr 160,000 polypeptide in these permeabilized cells was insulin and ATP dependent but other small molecules or ionic gradients were not essential. the reaction could not be mimicked by the G protein agonist GTP-.gamma.S nor inhibited by the G protein antagonist guanosine 5'-O-(2-thiodiphosphate) (GDP.beta.S). However, GTP.gamma.S effectively decreased insulin-mediated phosphorylation of this polypeptide. This suggests that the tyrosine kinase activity of the insulin receptor can be modulated by G protein agonists. It is concluded that cross talk between the insulin receptor and G protein could not be demonstrated in isolated membrane by strategies that detected interactions between .beta.-adrenergic receptors and G proteins. In contrast, in permeabilized cells, G protein-mediated regulation of the insulin receptor kinase activity could be detected.