RT Journal Article SR Electronic T1 S-Adenosylmethionine and Methylthioadenosine Inhibit β-Catenin Signaling by Multiple Mechanisms in Liver and Colon Cancer JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 77 OP 86 DO 10.1124/mol.114.095679 VO 87 IS 1 A1 Tony W. H. Li A1 Hui Peng A1 Heping Yang A1 Steven Kurniawidjaja A1 Parizad Panthaki A1 Yuhua Zheng A1 José M. Mato A1 Shelly C. Lu YR 2015 UL http://molpharm.aspetjournals.org/content/87/1/77.abstract AB S-Adenosylmethionine (SAMe), the principal methyl donor that is available as a nutritional supplement, and its metabolite methylthioadenosine (MTA) exert chemopreventive properties against liver and colon cancer in experimental models. Both agents reduced β-catenin expression on immunohistochemistry in a murine colitis-associated colon cancer model. In this study, we examined the molecular mechanisms involved. SAMe or MTA treatment in the colitis-associated cancer model lowered total β-catenin protein levels by 47 and 78%, respectively. In an orthotopic liver cancer model, increasing SAMe levels by overexpressing methionine adenosyltransferase 1A also reduced total β-catenin levels by 68%. In both cases, lower cyclin D1 and c-Myc expression correlated with lower β-catenin levels. In liver (HepG2) and colon (SW480, HCT116) cancer cells with constitutively active β-catenin signaling, SAMe and MTA treatment inhibited β-catenin activity by excluding it from the nuclear compartment. However, in liver (Huh-7) and colon (RKO) cancer cells expressing wild-type Wnt/β-catenin, SAMe and MTA accelerated β-catenin degradation by a glycogen synthase kinase 3-β–dependent mechanism. Both agents lowered protein kinase B activity, but this was not mediated by inhibiting phosphoinositide 3-kinase. Instead, both agents increased the activity of protein phosphatase 2A, which inactivates protein kinase B. The effect of MTA on lowering β-catenin is direct and not mediated by its conversion to SAMe, as blocking this conversion had no influence. In conclusion, SAMe and MTA inhibit Wnt/β-catenin signaling in colon and liver cancer cells regardless of whether this pathway is aberrantly induced, making them ideal candidates for chemoprevention and/or chemotherapy in these cancers.