Crosstalk between Wnt and Notch signaling in colonic epithelium.

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Wnt and Notch pathways are known to function together to regulate proliferation and differentiation of intestinal epithelium ; however, the molecular mechanism of their functional interplay remains unclear. In this study, we aimed at investigating the signaling crosstalk between these two pathways in colonic epithelium. First, by using several human colon cancer-derived cell lines, we have demonstrated that the expression of Hath1, a bHLH transcription factor known to be involved in Notch signaling, is regulated by the proteasome-mediated protein degradation that is under the control of Wnt signaling. We also showed that this post-translational regulation of Hath1 by Wnt/Notch signals is important for cell fate determination of colonic cells. Second, in order to investigate the crosstalk between Wnt/Notch signals, we have established a novel method to isolate and culture normal colonic epithelium in vitro. By this method, colonic cells continuously grow and the Lgr5+colonic stem cells preferentially expand as a result of Wnt/Notch activation. We also showed for the first time that the cultured colonic cells are able to regenerate damaged epithelium in recipient mice when transplanted. These data would built a basis for the future study to elucidate molecular mechanism that govern the interplay of Wnt/Notch signals to regulate the regenerative properties and/or malignant transformation of colonic epithelial cells.