Trichosanthin induced apoptosis in HL-60 cells via mitochondrial and endoplasmic reticulum stress signaling pathways

Trichosanthin suppresses HeLa cell proliferation through inhibition of the PKC/MAPK signaling pathway

Trichosanthin (TCS) possesses a broad spectrum of biological and pharmacological activities, including anti-tumor activities. Our previous studies have shown that TCS inhibits HeLa cell proliferation by activating the apoptotic pathway. In particular, the transcriptional factor cAMP response element binding (CREB) protein plays a pivotal role in apoptotic HeLa cells. However, no information, to date, is available about the signaling pathways involved in the inhibition of cell proliferation induced by TCS. The present study showed that PKA and PKC activities were significantly inhibited by TCS treatment. However, specific inhibitor of PKA activity failed to affect the inhibition of HeLa cell proliferation induced by TCS, even in the presence of cAMP agonists. In contrast, PKC activator/inhibitor significantly attenuated/enhanced the inhibitory effect of TCS on cell proliferation. In particular, the reversed effect of cAMP agonist on cell proliferation was partly prevented by PKC, ERK1/2, and p38 MAPK blockade. Consistent with these results, the reversed effect of cAMP agonists on CREB phosphorylation was significantly decreased by inhibitors of these kinases, but not PKA inhibitor. Therefore, our results suggested that HeLa cell proliferation was inhibited by TCS via suppression of PKC/MAPK signaling pathway.

CREB-mediated Bcl-2 expression in trichosanthin-induced Hela cell apoptosis

Bcl-2 plays a pivotal role in the control of cell death and is down-regulated in trichosanthin (TCS)-induced cell apoptosis. Because Bcl-2 expression is regulated by the transcription factor cyclic AMP response element-binding protein (CREB), we investigated the role of CREB activation in TCS-induced Hela cells apoptosis. Our results showed that TCS-caused Hela cell apoptosis was accompanied by the decrease of Bcl-2 and phosphorylated CREB protein levels. Interesting, this inhibitive effect can be abolished by the combined treatment of TCS/cAMP agonists. Furthermore, TCS-mediated Bcl-2 protein was abrogated by the suppression of CREB expression with antisense treatment, and blocking the interaction between CREB-binding protein and the Bcl-2 cyclic AMP-responsive element (CRE) by a CRE decoy oligonucleotide. Therefore, these data support the hypothesis that CREB plays a critical role in the regulation of Bcl-2 expression in TCS-induced Hela cell death.