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Larry D. Bozulic, William L. Dean, Nicholas A. Delamere; The Influence of SRC-Family Tyrosine Kinases on Na,K-ATPase Activity in Lens Epithelium. Invest. Ophthalmol. Vis. Sci. 2005;46(2):618-622. doi: https://doi.org/10.1167/iovs.04-0809.
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© ARVO (1962-2015); The Authors (2016-present)
purpose. Na,K-adenosine triphosphatase (ATPase) is essential for the regulation of cytoplasmic ion concentrations in lens cells. Earlier studies demonstrated that tyrosine phosphorylation by Lyn kinase, a Src-family member, inhibits Na,K-ATPase activity in porcine lens epithelium. In the present study, experiments were conducted to compare the ability of other Src-family kinases (Fyn, Src, and Lck) and Fes, a non-Src-family tyrosine kinase, to alter Na,K-ATPase activity.
methods. Membranes prepared from porcine lens epithelium were incubated with partially purified tyrosine kinases in buffer containing 1 mM adenosine triphosphate (ATP). ATP hydrolysis in the presence and absence of ouabain was used to measure Na,K-ATPase activity. Western blot analysis was used to examine phosphotyrosine-containing proteins and tyrosine kinase expression.
results. Fyn reduced Na,K-ATPase activity by ∼30%. In contrast, Src caused a ∼38% increase of Na,K-ATPase activity. Na,K-ATPase activity in membrane material treated with Lck or Fes was not significantly altered, even though Lck and Fes treatment induced robust tyrosine phosphorylation. Added exogenously, each tyrosine kinase induced a different pattern of membrane protein tyrosine phosphorylation. As judged by immunoprecipitation, Src, Fyn, Lyn, and Lck elicited tyrosine phosphorylation of the Na,K-ATPase α1 protein. Src, Fyn, Lyn, Lck, and Fes were each detectable in the epithelium by Western blot.
conclusions. The results indicate considerable variation in the Na,K-ATPase activity response of lens epithelium to different tyrosine kinases. This could perhaps explain why inhibition of Na,K-ATPase activity is reported to be caused by tyrosine phosphorylation in some tissues, whereas stimulation of Na,K-ATPase activity is observed in other tissues.
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