Hepatic tyrosine-phosphorylated proteins identified and localized following in vivo inhibition of protein tyrosine phosphatases: effects of H₂O₂ and vanadate administration into rat livers

Injection of a combination of H₂O₂ and vanadate (H/V) into the portal vein of rat livers resulted in inhibition of protein tyrosine phosphatase activity and led to a dramatic enhanced in vivo protein tyrosine phosphorylation. Some of the phosphorylated proteins were identified as the β-subunit of the insulin receptor, the insulin receptor substrate 1 (ppl85), PLC-γ (pp145), and a 100 kDa PLC-γ-associated protein. Immunofluorescense and immune electron microscopy of frozen liver sections with anti-P-Tyr antibodies revealed that most of the tyrosine-phosphorylated proteins are localized in close proximity to the plasma membrane in intercellular adherence junctions and tight junction regions. This close in vivo association between membranal protein tyrosine kinases, their target proteins, and cytoskeletal elements could enable formation of 'signaling complexes' which may play a role in transmembrane signal transduction. By affinity chromatography over immobilized anti-P-Tyr antibodies, a large number of these tyrosine-phosphorylated proteins were partially purified.