Abstract
Interleukin-24 (IL-24) is a cytokine belonging to the IL-10 gene family. This cytokine selectively induces apoptosis in cancer cells, without harming normal cells, through a mechanism involving endoplasmic reticulum (ER) stress response. TAT-IL-24-KDEL is a fusion protein that efficiently enters the tumor cells and locates in the ER. Here we report that TAT-IL-24-KDEL induced apoptosis in human cancer cells, mediated by the ER stress cell death pathway. This process was accompanied by the inhibition of the transcription of an antiapoptotic protein, survivin. The forced expression of survivin partially protected cancer cells from the induction of apoptosis by TAT-IL-24-KDEL, increased their clonogenic survival, and attenuated TAT-IL-24-KDEL-induced activation of caspase-3/7. RNA interference of survivin markedly sensitized the transformed cells to TAT-IL-24-KDEL. Survivin was expressed at higher levels among isolated clones that resistant to TAT-IL-24-KDEL. These observations show the important role of survivin in attenuating cancer-specific apoptosis induced by TAT-IL-24-KDEL. The pharmacological inhibition of survivin expression by a selective small-molecule survivin suppressant YM155 synergistically sensitized cancer cells to TAT-IL-24-KDEL-induced apoptosis in vitro and in vivo. The combined regimen caused significantly higher activation of ER stress and dysfunction of mitochondria than either treatment alone. As survivin is overexpressed in a majority of cancers, the combined TAT-IL-24-KDEL and YM155 treatment provides a promising alternative to the existing therapies.