INSULIN-RECEPTOR SIGNALING IS AUGMENTED BY ANTISENSE INHIBITION OF THE PROTEIN-TYROSINE-PHOSPHATASE LAR

Considerable evidence has shown that most physiologic responses to ins ulin require activation of the intrinsic tyrosine kinase of the insuli n receptor, Biochemical studies have also supported the hypothesis tha t receptor kinase activity can be modulated by cellular protein tyrosi ne phosphatases (PTPases), which have not yet been identified, To test the hypothesis that the transmembrane PTPase LAR can modulate insulin receptor signaling in vivo, antisense RNA expression was used to spec ifically suppress LAR protein levels by 63% in the rat hepatoma cell l ine, McA-RH7777. Hormone-dependent autophosphorylation of the insulin receptor was increased by approximately 150% in the antisense-expressi ng cells at all insulin concentrations tested. This increase in autoph osphorylation was paralleled by a 35% increase in insulin receptor tyr osine kinase activity. Reduced LAR levels did not alter non-hormone-de pendent tyrosine phosphorylation nor basal insulin receptor tyrosine p hosphorylation and kinase activity. Most significantly, reduced LAR le vels resulted in a 350% increase in insulin-dependent phosphatidylinos itol 3-kinase activity. These studies provide unique in vivo evidence that LAR is involved In the modulation of insulin receptor signaling i n intact cells.