Inhibition of FGF-induced alpha A-crystallin promoter activity in lens epithelial explants by TGF beta

PURPOSE. Fibroblast growth factor (FGF) plays a key role in normal lens bio logy, and recent studies suggest that transforming growth factor (TGE)-beta is involved in the origin of certain forms of cataract. In the current stu dy, the effects of FGF and TGF beta on alpha A-crystallin promoter activity were investigated. METHODS. Rat lens epithelial explants were cultured with or without growth factors after transfecting with the firefly luciferase reporter gene driven by either the mouse alpha A-crystallin promoter region or a control simian virus (SV)40 promoter. RESULTS. FGF-2, at a concentration that induced lens fiber differentiation, strongly stimulated alpha A-crystallin promoter activity in explants at 3 to 4 days of culture, whereas SV40 promoter control specimens showed no com parable increase. At lower concentrations of FGF, sufficient to induce cell proliferation but not differentiation, there was only a slight increase in alpha A-crystallin promoter activity. Stimulation of alpha A-crystallin pr omoter activity induced by the fiber-differentiating concentration of FGF w as virtually abolished by as little as 25 pg/ml TGF beta 2, but the onset o f fiber-specific beta-crystallin accumulation was not prevented at this con centration. Phase-contrast microscopy revealed overt cataractous changes on ly at concentrations of TGF beta more than 25 pg/ml. CONCLUSIONS, The stimulation of alpha A-crystallin promoter activity by FGF is consistent with its role in inducing accumulation of crystallins in exp lants. The blocking effect of TGF beta on this process, even at a concentra tion too low to induce obvious pathologic changes, indicates the potential for TGF beta to disturb alpha A-crystallin gene expression during early fib er differentiation.