αB-crystallin is a member of the small heat shock proteins, which is abundantly expressed in various vertebrate tissues including the central nervous system. In our previous report, we showed αB-crystallin induction in activated astrocytes in the postischemic brain and in H2O2-treated primary astrocyte cultures. To investigate the functional significance of αB-crystallin induction in astrocytes, we generated a stable C6 astroglioma cell line overexpressing αB-crystallin. In these cells, hydrogen peroxide-induced apoptosis was reduced by 60% compared to parent cells. Furthermore, the repression of αB-crystallin expression by αB-crystallin siRNA transfection suppressed this protective effect, indicating that αB-crystallin is responsible for the protection against H2O2-induced apoptosis in C6 astroglioma cells. Similar level of aggravation in H2O2-induced apoptosis was observed in primary astrocyte cultures when αB-crystallin expression was suppressed by αB-crystallin siRNA transfection, confirming the importance of αB-crystallin. In addition, the induction of caspase-3 activity after H2O2 treatment was markedly suppressed in αB-crystallin-overexpressing cells, and immunoprecipitation proved binding between αB-crystallin and partially processed caspase-3 (a p24 intermediate). These results indicate that αB-crystallin confers protection against hydrogen peroxide-induced astrocytes apoptosis in part by inhibiting caspase-3 activation.
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