8-Chloro-adenosine sensitizes a human hepatoma cell line to TRAIL-induced apoptosis by caspase-dependent and -independent pathways

Abstract

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of the tumor necrosis factor (TNF) super-family, induces apoptosis in various cancer cells with little or no effect on normal cells. 8-Chloro-adenosine (8-Cl-Ado) is a potential anti-cancer chemical agent now in clinical trail phase II, though its molecular mechanism remains poorly understood. In the present study, we report that 8-Cl-Ado can promote TRAIL killing activity in the hepatoma cell line BEL-7402 in dose- and time-dependent manner when jointly used in vitro. We showed that the expression of death receptor DR5, but not DR4 was up-regulated and the decoy receptor DcR1 was down-regulated in the cells treated with 8-Cl-Ado and the recombinant soluble TRAIL (rsTRAIL, 95-281 a.a.). Further experiments demonstrated that caspase-family inhibitor z-VAD-fmk prevented the cells from apoptosis induced by co-treatment with 8-Cl-Ado and rsTRAIL for 6 h, however, apoptosis occurred in the cells cultured for 24 h, suggesting that co-treatment induce a caspase-dependent and -independent signaling pathway in the BEL-7402 cells. This phenomenon was confirmed by cleavage analysis of caspase-3 and poly(ADP-ribose) polymerase (PARP), and ROS (reactive oxygen species) assay, respectively. Moreover, transcriptional activity test showed that NF-kappaB was inhibited in the BEL-7402 cells during co-treatment. Our results provided evidence for the first time that 8-Cl-Ado sensitizes the human hepatoma cells BEL-7402 to rsTRAIL-induced apoptosis by up-regulating DR5 expression, inactivating the NF-kappaB activity, and signaling by the caspase-dependent and -independent pathway.