Human alphaA– and alphaB–Crystallins Prevent UVA–Induced Apoptosis though Regulation of RAF/MEK/ERK and AKT Signaling Pathways

Abstract

Abstract: : Purpose: Alpha–Crystallins, members of the small heat shock protein family, are distinct antiapoptotic regulators. Regarding the antiapoptotic mechanisms, we have recently demonstrated that human alphaA– and alphaB–crystallins prevent staurosporine–induced apoptosis through interactions with Bax and Bcl–XS to sequester their translocation into mitochondria (Mao et al., 2003, Cell Death & Differentiation, in press). Here, we demonstrate that human alphaA– and alphaB–crystallins prevent UVA–induced apoptosis through regulation of RAF/MEK/ERK and AKT signaling pathways. Methods: Human alphaA–, alphaB–crystallins and the related vector–transfected stable expression clones were established with human lens epithelial cells under G418 screening. Expression of human alphaA– and alphaB–crystallins was determined with Western blot and fluorescence microscopy. The transfected cells were irradiated with UVA with doses previously shown to be implicated in cataractogenesis. Apoptosis in each type of cell was determined by Hoechst staining, and regulation of RAF/MEK/ERK and AKT pathways were analyzed by Western blot analysis. Results: UVA irradiation activated RAF/MEK/ERK pathway, which was necessary for UVA–induced apoptosis. AlphaB–crystallin repressed activation of this pathway. In contrast, alphaA–crystallin activated AKT pathway to counteract UVA–induced apoptosis. Conclusions: Our results for the first time demonstrate that the two alpha–crystallins display differential functional mechanisms in preventing UVA–induced apoptosis. Supported by the Hormel Foundation, University of Minnesota Graduate School and Lotus Scholar Professorship funds from Hunan Normal University. None.

Keywords: crystallins • apoptosis/cell death • cell death/apoptosis