IAP-family protein Survivin inhibits caspase activity and apoptosis induced by Fas (CD95), Bax, caspases, and anticancer drugs

Survivin is a member of the inhibitor of apoptosis protein (IAP) family. We investigated the antiapoptotic mechanism of Survivin, as well as its expre ssion in 60 human tumor cell Lines used for the National Cancer Institute's anticancer drug screening program. In cotransfection experiments, cell dea th induced by Bar or Fas (CD 95) was partially inhibited (mean +/- SD, 65% +/- 8%) by Sunivin, whereas XIAP, another IAP family member, almost complet ely blocked cell death (93% +/- 4%) under the same conditions. Survivin and XIAP also protected 293 cells from apoptosis induced by overexpression of procaspase-3 and -7 and inhibited the processing of these zymogens into act ive caspases. In vitro binding experiments indicated that, like other IAP-f amily proteins, Survivin binds specifically to the terminal effector cell d eath proteases, caspase-3 and -7, but not to the proximal initiator proteas e caspase-8. Using a cell-free system in which cytosolic extracts were deri ved from control- or Survivin-transfected cells and where caspases were act ivated either by addition of cytochrome c and dATP or by adding recombinant active caspase-8, Survivin was able to substantially reduce caspase activi ty, as measured by cleavage of a tetrapeptide substrate, AspGluValAsp-amino fluorocoumarin. Similar results were obtained in intact cells when Survivin was overexpressed by gene transfection and caspase activation was induced by the anticancer drug etoposide. Sunivin was expressed in all 60 cancer ce ll lines analyzed, with highest levels in breast and lung cancers and lowes t Levels in renal cancers. These findings indicate that Survivin, which is commonly expressed in human tumor cell lines, can bind the effector cell de ath proteases caspase-3 and -7 in vitro and inhibits caspase activity and c ell death in cells exposed to diverse apoptotic stimuli. Although quantitat ive differences may exist, these observations suggest commonality in the me chanisms used by IAP-family proteins to suppress apoptosis.