XIAP underlies apoptosis resistance of renal cell carcinoma cells

X-linked inhibitor of apoptosis (XIAP), a key member of the inhibitors of apoptosis protein family, can inhibit apoptosis by directly binding to the initiator caspase-9, −3 and −7, thereby promoting tumor cell survival during tumor progression. In the present study, XIAP basal expression levels were investigated and its contribution to the resistance to apoptosis was evaluated, in the RCC cell lines exposed to apoptosis-inducing drugs. This was investigated by histological methods and western blot analysis. Using RNA interference, elimination of XIAP in Caki-1 cells was also studied, and its contribution to the sensitivity to apoptosis induced through the intrinsic pathway was observed. Differences in XIAP expression were detected between ClearCa-2 and ClearCa-6 cell lines. ClearCa-6 cells with lower expression of XIAP were more sensitive to apoptosis-inducing drugs, compared with ClearCa-2 cells. However, the levels of XIAP expression in both cell lines were stable during apoptosis. Furthermore, a Caki-1 cell line with no XIAP expression was used, and was demonstrated to be more sensitive to the apoptosis induced by the mitochondrial pathway. These results suggested that downregulation of XIAP expression could enhance the sensitivity of RCC cells to apoptosis, and the basal expression of XIAP during apoptosis is stable. This may provide novel insight for targeted gene therapy against XIAP, in the clinic.