Wortmannin elevates tumor necrosis factor-related apoptosis-inducing ligand sensitivity in LNCaP cells through down-regulation of IAP-2 protein

Background and aim: TNF-related apoptosis-inducing ligand (TRAIL), which is a member of the tumor necrosis factor (TNF) family, has been shown to effectively induce tumor apoptosis without any detectable cytotoxic side effects. But recent studies have shown that LNCaP cells are resistant to TRAIL, because LNCaP cells express the constitutively active Akt/protein kinase B. Therefore this study examined the effect of Wortmannin, a PI-3 kinase inhibitor, and the intracellular mechanisms to TRAIL-induced apoptosis. Methods: LNCaP cells, which are resistant to apoptotic induction of TRAIL alone, were exposed to Wortmannin for 3 h and treated with the recombinant TRAIL protein for an additional 3 h. Results: TRAIL alone induced apoptosis in approximately 10% of the cells, whilst pretreatment with Wortmannin increased the TRAIL-induced apoptosis to 45%. Wortmannin alone had no effect on the tumor cell viability, but enhanced the TRAIL-induced apoptosis in a dose-dependent manner and completely blocked Akt phosphorylation. The blocking of the Akt phosphorylation decreased the IAP-2 protein expression level, which is believed to mediate the enhanced TRAIL-induced apoptosis. Conclusion: Wortmannin elevates the TRAIL sensitivity in LNCaP cells by regulating the phosphorylation of Akt and IAP-2 protein expression.