Melittin induces PTCH1 expression by down-regulating MeCP2 in human hepatocellular carcinoma SMMC-7721 cells

Abstract

Hepatocellular carcinoma (HCC) has a high mortality rate worldwide and still remains to be a noticeable public health problem. Therefore, new remedies are urgently needed. Melittin, a major component of bee venom, is known to suppress cell growth in various cancers including HCC. However, the mechanism of the anticancer effect of melittin on HCC has not been fully elucidated. It has been reported that Methyl-CpG binding protein 2 (MeCP2) plays a key role in tumor proliferation, apoptosis, migration and invasion. In the present study, we found the high expression of MeCP2 in human HCC tissues and in the SMMC-7721 cell line. MeCP2 silencing inhibited cell proliferation, while over-expression of MeCP2 promoted cell growth in SMMC-7721 cells. It indicates that MeCP2 may be an attractive target for human HCC. We further found that melittin could inhibit cell proliferation by reducing MeCP2 expression in vitro. Interestingly, the inhibitory effect of melittin on cell proliferation was due to a delay in G0/G1 cell cycle progression, without influencing cell apoptosis. Next, we investigated the potential molecular mechanisms and found that MeCP2 could modulate Shh signaling in SMMC-7721 cells. Further study indicates that melittin may induce the demethylation of PTCH1 promoter, resulting in the increased expression of PTCH1. Furthermore, the expression of Shh and GLI1 was significantly lowered upon treatment of melittin. These results suggest that melittin can block Shh signaling in vitro. In short, these results indicate that melittin inhibits cell proliferation by down-regulating MeCP2 through Shh signaling in SMMC-7721 cells.