Inhibition of the β-Catenin/Tcf Signaling by Caffeoylquinic Acids in Sweet Potato Leaf through down Regulation of the Tcf-4 Transcription

Sweet potato leaves contain the highest levels of functional polyphenols. In this study the effects of the sweet potato leaf extract and its contents, such as mono (3, 4, and 5)-caffeoylquinic acid (CQA), di-CQA (4,5-diCQA, 3,5-diCQA, and 3,4-diCQA) and caffeic acid (CA), were evaluated on the beta-catenin/Tcf-4 signaling in human colorectal cancer HCT116 cells. The extract and the CQA derivatives inhibited the beta-catenin/Tcf-4 signaling, and the inhibition of the di-CQA (with two caffeoyl groups) was higher than that of the mono-CQA (one-caffeoyl group) and CA, suggesting that the caffeoyl structure in the presence of a catechol group plays a significant role in interfering with the beta-catenin/Tcf-4 signaling. In addition, the CQA derivatives had no effect on the beta-catenin protein expression, but all test compounds inhibited the expression of the Tcf-4 transcription, and the inhibition of the di-CQA derivatives was stronger than those of the mono-CQA derivatives as well as the beta-catenin/Tcf-4 transcriptional activity. These compounds can modulate the downstream Wnt signaling pathway, suggesting that sweet potato leaves can be a protective food for colorectal cancer.