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J. Zhou, S. Menko; Src Kinase Activation Induces Formation of Lens Opacities Through a Pathway Involving p38 . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3136.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Our previous studies have shown that suppression of Src Family Kinase (SFK) activity blocks the formation of lens opacities in an in vitro cataract model system. The goal of this study is to map the downstream signaling effectors of Src kinases in the formation of cataract. Methods: E10 chick lenses were cultured in Medium 199 containing 10% fetal bovine serum in the presence or absence of the SFK-specific inhibitor PP1. Lenses were extracted over a time course from 10 minutes to 24 hours and examined by immunoblot analysis for affects on activation of potential downstream signaling effectors of Src kinases. These included Focal Adhesion Kinase (FAK), a direct Src target, and the MAP kinases ERK, JNK and p38. To examine the role of activation of specific MAP kinases on lens opacification, lenses were grown for 10 days in the presence or absence of inhibitors of ERK (U0126), JNK (SP600125) and p38 (SB203580). Lenses were observed and photographed daily, and degree of opacification was quantified using image analysis software. Results: In lenses grown under culture conditions in which they form cataracts, phosphorylation of two distinct tyrosines of the FAK signaling protein, FAK Y861 and FAK Y925, were greatly increased. Both of these FAK sites are phosphorylated by Src kinases. In lens cultures in which cataract formation was suppressed by inhibition of SFK activity, phosphorylation of both FAK Y861 and FAK Y925 was inhibited. These results suggest a role for FAK signaling downstream of Src kinases in the formation of cataracts. Since both Src and FAK are known to mediate activation of MAP kinases, we investigated the activation state of MAP kinases in our lens cultures. We found transient activation of ERK, JNK and p38. This MAP kinase activation was blocked when the lenses were grown in the presence of the SFK inhibitor PP1. To analyze the potential role of ERK, JNK, and p38 in cataract formation lenses were cultured in the presence of specific MAP kinase inhibitors. While inhibitors to ERK and JNK did not interfere with the formation of cataract, growth of the lens in the presence of the p38 inhibitor blocked the formation of lens opacity with a similar efficacy to the Src kinase inhibitor PP1. Conclusions: Src kinase activation leads to the formation of cataract through a pathway involving the phosphorylation of FAK and the activation of the MAP kinase p38.
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