Reactive oxygen species-dependent HSP90 protein cleavage participates in arsenical As^{+ 3}- and MMA^{+ 3}-induced apoptosis through inhibition of telomerase activity via JNK activation

The effects of six arsenic compounds including As^{+ 3}, MMA^{+ 3}, DMA^{+ 3}, As^{+ 5}, MMA^{+ 5}, and DMA^{+ 5} on the viability of NIH3T3 cells were examined. As^{+ 3} and MMA^{+ 3}, but not the others, exhibited significant cytotoxic effects in NIH3T3 cells through apoptosis induction. The apoptotic events such as DNA fragmentation and chromosome condensation induced by As^{+ 3} and MMA^{+ 3} were prevented by the addition of NAC and CAT, and induction of HO-1 gene expression in accordance with cleavage of the HSP90 protein, and suppression of telomerase activity were observed in NIH3T3 cells under As^{+ 3} and MMA^{+ 3} treatments. An increase in the intracellular peroxide level was examined in As^{+ 3}- and MMA^{+ 3}-treated NIH3T3 cells, and As^{+ 3}- and MMA^{+ 3}-induced apoptotic events were blocked by NAC, CAT, and DPI addition. HSP90 inhibitors, GA and RD, significantly attenuated the telomerase activity in NIH3T3 cells with an enhancement of As^{+ 3}- and MMA^{+ 3}-induced cytotoxicity. Suppression of JNKs significantly inhibited As^{+ 3}- and MMA^{+ 3}-induced apoptosis by blocking HSP90 protein cleavage and telomerase reduction in NIH3T3 cells. Furthermore, Hb, SnPP, and dexferosamine showed no effect against As^{+ 3}- and MMA^{+ 3}-induced apoptosis, and overexpression of HO-1 protein or inhibition of HO-1 protein expression did not affect the apoptosis induced by As^{+ 3} or MMA^{+ 3}. These data provide the first evidence to indicate that apoptosis induced by As^{+ 3} and MMA^{+ 3} is mediated by an ROS-dependent degradation of HSP90 protein and reduction of telomerase via JNK activation, and HO-1 induction might not be involved.