Downregulation of endogenous TRAIL and its effect on the human cancer cell line KELLY.

umor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to exert an unexpected pro-survival, pro-proliferative and pro-invasive effect on a subset of human cancer cell lines. Recent clinical studies report that increased expression of endogenous TRAIL is associated with decreased disease-specific survival in renal cell carcinoma and cholangiocarcinoma which are resistant to TRAIL induced apoptosis. The present work investigated the role of endogenous TRAIL as an intrinsic growth factor in apoptosis-resistant human cancer cells. Several cell lines derived from solid human tumors were studied, among them the neuroblastoma cell line KELLY, a cancer cell line resistant to TRAIL-induced apoptosis. First, to investigate whether TRAIL-knockdown could inhibit cell growth, the use of small interfering RNAs (siRNA) for endogenous TRAIL was established and a successful knockdown was verified on both mRNA and protein level. Second, the functional impact of the knockdown of endogenous TRAIL was investigated by measuring cell growth and cell death after transfection: Interestingly, the human neuroblastoma cell line KELLY unexpectedly showed markedly reduced cell growth upon knockdown of endogenous TRAIL. Furthermore, knockdown of TRAIL induced cell death in KELLY cells, which was dependent on caspase-signaling and rescued by the addition of soluble TRAIL. Thus, endogenous TRAIL functions as an intrinsic survival and growth factor in the neuroblastoma cell line KELLY. The present work provided first evidence that the expression of endogenous TRAIL can be specifically downregulated through siRNA knockdown to inhibit survival and growth of cancer cells in-vitro, which are resistant to TRAIL induced apoptosis. The present data strongly supports the potential of endogenous TRAIL to function as a novel therapeutic target in cancer therapy. In the light of the emerging clinical use of siRNAs for cancer therapy, targeting TRAIL by RNA interference may provide a valuable treatment approach for patients with cancers resistant to TRAIL induced apoptosis and high expression levels of endogenous TRAIL