부산대학교 도서관

Simple Summary: M1 and M3 muscarinic receptors, M1R and M3R, play important roles in health and disease. Previously, we found opposite patterns of expression in colon cancer for the genes encoding M1R and M3R. Likewise, M1R and M3R deficiency had opposite effects in a mouse colon cancer model. Based on these observations, we hypothesized that activating M1R might inhibit the growth of colon cancer cells. Here, we confirmed divergent expression of M1R and M3R protein in progressive colon cancer. Then, we discovered that in contrast to M3R activators, treating human colon cancer cells with M1R activators inhibited cell growth. The effects of M1R activation appeared to be mediated by a signaling pathway downstream of the receptor. Notably, M1R activation was more effective than conventional chemotherapy agents at inhibiting colon cancer cell growth and combining these agents augmented this action. We believe our findings support further investigation of selective M1R activators as treatments for advanced colon cancer. M3 muscarinic receptor (M3R) activation stimulates colon cancer cell proliferation, migration, and invasion; M3R expression is augmented in colon cancer and ablating M3R expression in mice attenuates colon neoplasia. Several lines of investigation suggest that in contrast to these pro-neoplastic effects of M3R, M1R plays an opposite role, protecting colon epithelial cells against neoplastic transformation. To pursue these intriguing findings, we examined the relative expression of M1R versus M3R in progressive stages of colon neoplasia and the effect of treating colon cancer cells with selective M1R agonists. We detected divergent expression of M1R and M3R in progressive colon neoplasia, from aberrant crypt foci to adenomas, primary colon cancers, and colon cancer metastases. Treating three human colon cancer cell lines with two selective M1R agonists, we found that in contrast to the effects of M3R activation, selective activation of M1R reversibly inhibited cell proliferation. Moreover, these effects were diminished by pre-incubating cells with a selective M1R inhibitor. Mechanistic insights were gained using selective chemical inhibitors of post-muscarinic receptor signaling molecules and immunoblotting to demonstrate M1R-dependent changes in the activation (phosphorylation) of key downstream kinases, EGFR, ERK1/2, and p38 MAPK. We did not detect a role for drug toxicity, cellular senescence, or apoptosis in mediating M1R agonist-induced attenuated cell proliferation. Lastly, adding M1R-selective agonists to colon cancer cells augmented the anti-proliferative effects of conventional chemotherapeutic agents. Collectively, these results suggest that selective M1R agonism for advanced colon cancer, alone or in combination with conventional chemotherapy, is a therapeutic strategy worth exploring. [ABSTRACT FROM AUTHOR]