Melittin, a major component of bee venom, sensitizes human hepatocellular carcinoma cells to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis by activating CaMKII-TAK1-JNK/p38 and inhibiting IkappaBalpha kinase-NFkappaB.

Promoting apoptosis is a strategy for cancer drug discovery. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in a wide range of malignant cells. However, several cancers, including human hepatocellular carcinoma (HCC), exhibit a major resistance to TRAIL-induced cell death. Melittin, a water-soluble 26-amino acid peptide derived from bee venom of Apis mellifera, can exert toxic or inhibitory effects on many types of tumor cells. Here we report that melittin can induce apoptosis of HCC cells by activating Ca2+/calmodulin-dependent protein kinase, transforming growth factor-beta-activated kinase 1 (TAK1), and JNK/p38 MAPK. We show that melittin-induced apoptosis can be inhibited by calcium chelator, by inhibitors for Ca2+/calmodulin-dependent protein kinase, JNK and p38, and by dominant negative TAK1. In the presence of melittin, TRAIL-induced apoptosis is significantly increased in TRAIL-resistant HCC cells, which may be attributed to melittin-induced TAK1-JNK/p38 activation and melittin-mediated inhibition of IkappaBalpha kinase-NFkappaB. Our data suggest that melittin can synergize with TRAIL in the induction of HCC cell apoptosis by activating the TAK1-JNK/p38 pathway but inhibiting the IkappaBalpha kinase-NFkappaB pathway. Therefore, the combination of melittin with TRAIL may be a promising therapeutic approach in the treatment of TRAIL-resistant human cancer.