The influence of Lyn kinase on Na,K-ATPase in porcine lens epithelium

Na, K-ATPase is essential for the regulation of cytoplasmic Na+ and K+ levels in lens cells. Studies on the intact lens suggest activation of tyrosine kinases may inhibit Na, K-ATPase function. Here, we tested the influence of Lyn kinase, a Src-family member, on tyrosine phosphorylation and Na, K-ATPase activity in membrane material isolated from porcine lens epithelium. Western blot studies indicated the expression of Lyn in lens cells. When membrane material was incubated in ATP-containing solution containing partially purified Lyn kinase, Na,K-ATPase activity was reduced by similar to38%. Lyn caused tyrosine phosphorylation of multiple protein bands. Immunoprecipitation and Western blot analysis showed Lyn treatment causes an increase in density of a 100-kDa phosphotyrosine band immunopositive for Na, K-ATPase alpha(1) polypeptide. Incubation with protein tyrosine phosphatase 1B (PTP-1B) reversed the Lyn-dependent tyrosine phosphorylation increase and the change of Na, K-ATPase activity. The results suggest that Lyn kinase treatment of a lens epithelium membrane preparation is able to bring about partial inhibition of Na, K-ATPase activity associated with tyrosine phosphorylation of multiple membrane proteins, including the Na, K-ATPase alpha(1) catalytic subunit.