Norcantharidin induces apoptosis in HeLa cells through caspase, MAPK, and mitochondrial pathways.

Aim: To investigate the mechanism of norcantharidin (NCTD)-induced HeLa cell apoptosis.

Methods: HeLa cell growth inhibition was measured by MTT method. Apoptosis was detected by Hoechst 33258 staining and agarose gel electrophoresis. Caspase activities were assayed using caspase apoptosis detection kit. Western blot analysis was used to evaluate the level of ICAD, ERK/p-ERK, JNK/p-JNK, and Bcl-X(L)/Bax expression.

Results: Norcantharidin inhibited HeLa cell growth in a time- and dose-dependent manner. HeLa cells treated with norcantharidin showed typical characteristics of apoptosis including the morphological changes and DNA fragmentation. Caspase family inhibitor (z-VAD-fmk), caspase-8, -9 inhibitor (z-IETD-fmk, Ac-LEHD-CHO, respectively) and caspase-3 inhibitor (z-DEVD-fmk) partially prevent norcantharidin-induced apoptosis, but initiator caspase-1 inhibitor (Ac-YVAD-fmk) did not. The activities of caspase-3, -8, and -9 were up-regulated after norcantharidin treatment. Furthermore, NCTD-induced activation of caspase-3 resulted in the degradation of the inhibitor of caspase-activated DNase (ICAD). Up-regulation of mitochondrial Bax expression and down-regulation of Bcl-x(L) expression also participated in the apoptosis induced by NCTD. Although p38 MAPK inhibitor (SB203580) failed to block cell death, ERK MAPK inhibitor (PD98059) and JNK MAPK inhibitor (SP600125) had marked inhibitory effects on norcantharidin-induced apoptosis. Moreover, the phosphorylation of JNK were up-regulated followed by delayed ERK phosphorylation after treatment with NCTD, suggesting that ERK and JNK were both responsible for NCTD-induced apoptosis in HeLa cells and worked at different stages.

Conclusion: The cytotoxic effect of NCTD on HeLa cells was mainly due to apoptosis. The anti-tumor mechanism of NCTD might involve caspses, mitochondrial, and MAPKs pathways.