Regulation of protein phosphorylation by insulin and an insulinomimetic oligosaccharide in 3T3-L1 adipocytes and Fao hepatoma cells.

The ability of insulin and an insulinomimetic oligosaccharide (IOS) isolated from conditioned medium of Reuber hepatoma cells to regulate protein phosphorylation in 3T3-L1 adipocytes and Fao hepatoma cells has been examined in extracts prepared from 32P-labeled cells and by immunoblotting of unlabeled extracts with an anti-phosphotyrosine antibody. In 32P-labeled 3T3-L1 cells, both insulin and IOS stimulate the dephosphorylation of a 55K membrane-associated protein, yet only insulin stimulates the phosphorylation of the ribosomal S6 protein and a 22K heat-stable soluble protein. In 32P-labeled Fao cells, both insulin and IOS stimulate the phosphorylation of a 16K protein, but only insulin stimulates S6 phosphorylation. As judged by immunoblotting, IOS does not stimulate the tyrosine phosphorylation of the beta subunit of the insulin receptor and a 180K soluble protein in a manner similar to insulin. These data indicate that the insulinomimetic effects of IOS are selective for certain insulin-regulated pathways and that the effects of IOS are unlikely to be operating through stimulation of the insulin receptor tyrosine kinase.