Abstract
[Purpose] Heat shock protein 27 (HSP27) is implicated in diverse biological functions. We have reported that HSP27 has a role in protecting human cells against UVC lethality. We identified annexin II as an HSP27-interacting protein. In this study, we sought to confirm the combined roles of HSP27 and annexin II in cell death after UVC irradiation.
[Methods] We used two human cell lines, UVC-sensitive RSa and its variant UVC-resistant APr-1. After UVC irradiation, the cellular amounts of annexin II protein were analyzed by Western blotting in those cells transfected with HSP27 cDNA and siRNA for HSP27. In those cells with up- or down-regulation of HSP27 or annexin II proteins, sensitivity to UVC irradiation was analyzed by colony formation assay. The capacity to remove UVC-damaged DNA was measured using antibody against the damage.
[Results and Conclusion] In RSa cells, expression of annexin II decreased after UVC irradiation, and over-production of annexin II in RSa cells resulted in increased resistance to UVC lethality. Transfection of RSa cells with HSP27 cDNA caused an increase in their resistance to UVC lethality and prevented the decline in annexin II expression. By contrast, APr-1 cells showed no decline in annexin II expression after UVC irradiation, while HSP27 siRNA-transfected APr-1 cells showed a decline and were sensitized to UVC lethality. The complex of HSP27 and annexin II was relocalized from the postnuclear to the nuclear fraction after UVC irradiation in APr-1 cells. Furthermore, annexin II siRNA-transfected APr-1 cells showed a decreased capacity to remove UVC-damage and were sensitized to UVC lethality. These results suggested that annexin II expression is involved in the repair of UVC-damaged DNA and the UVC susceptibility of human cells. As well, HSP27 appeared to regulate annexin II expression and/or localization after UVC irradiation as a molecular chaperone.
