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R Rajala, ME McClellan, JD Ash, RE Anderson; In Vivo Light-Dependent Regulation of Phosphatidylinositol 3-Kinase in Retina Through Tyrosine Phosphorylation of the Insulin Receptor ß-Subunit . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1404.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Recently we have shown that phosphatidylinositol 3-kinase (PI3K) in bovine rod outer segment (ROS) is activated in vitro by tyrosine phosphorylation of the C-terminal tail of the insulin receptor [Rajala and Anderson, IOVS (2001) 42:3110-3117]. In this study we have investigated the in vivo mechanism of light-dependent activation of PI3K in the rodent retina. Methods:Rats and mice were dark-adapted overnight and half were subjected to normal room light for 30 min. Retinas were homogenized and immunoprecipitated with antibodies against phosphotyrosine (PY), insulin receptor ß-subunit (IRß), or the p85 regulatory subunit of PI3K, and PI3K activity was measured using PI-4,5-P2 as substrate. In some experiments, PI3K activity was measured in purified ROS. Results:Light stimulation resulted in elevated p85 immunoreactivity and PI3K activity in anti-PY and anti-IRß immunoprecipitates (IPs) of proteins from whole retinas from mice and rats. We have also observed elevated p85 and elevated PI3K activity in ROS prepared from light-adapted rat retinas. In FVB mice (RD25 mutation), which have lost their photoreceptors, there were no light-dark differences in PI3K activity. Conclusion:1) 1) Our results suggest that light induces the association of PI3K with tyrosine-phosphorylated proteins including IRß that are located in rod outer segments. 2) The insulin receptor in outer segments is involved in the light-dependent regulation of PI3K activity. 3) Photon capture via rhodopsin in the outer segments is necessary for light activation of PI3K.
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