Expression and Regulation of GammaS-Crystallin in the Lens Epithelium: An Epithelial "Stress Crystallin"

Abstract

Abstract: : Purpose: To characterize the expression of γS- and the α-crystallins in lens epithelial cells and to measure changes in expression caused by injury or treatment with FGF2. Methods: RNA from P3 or adult rat lens epithelia cultured for 0 or 20 hours in defined medium or in medium supplemented with FGF2 (50 ng/ml) was used to synthesize probes for Affymetrix microarrays. Quantitative PCR confirmed the expression levels of selected mRNAs isolated from cultured rat and bovine lens epithelia. Immunostaining and Western blotting with an antibody specific for γS-crystallin were used to characterize protein expression and distribution. Results: γS-crystallin mRNA and protein were present in rat and bovine lens epithelia. In P3 rat lens epithelial cells, mRNA levels increased approximately 20-fold and 150-fold after culture for 20 and 96 hours in defined medium, reaching levels comparable to the α-crystallins. The mRNAs for αA- and αB-crystallin were high at the initiation of culture and remained high or declined slightly during culture. FGF treatment prevented the increase in γS mRNA and markedly reduced the levels of alphaA- and alphaB-crystallin mRNAs. In adult rat lens epithelial cells, γS protein was mainly in the cytoplasm, but rapidly moved to the nucleus after injury. Conclusions: γS crystallin is normally present in lens epithelial cells. Its synthesis and distribution suggest that it functions to protect these cells from stress. Although FGF2 can promote fiber cell differentiation, it prevents or reduces endogenous crystallin gene expression in short-term cultures. These studies reveal a new mode of regulation of crystallin genes in lens epithelial cells and identify γS as a putative "stress crystallin." Note: X.W. and C.M.G. contributed equally to this work.

Keywords: crystallins • gene microarray • stress response