期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：13
页码：4886-4891
DOI：10.1073/pnas.1314523111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The protein tyrosine kinase Ephrin type-B receptor 3 (EPHB3) counteracts tumor-cell dissemination by regulating intercellular adhesion and repulsion and acts as tumor/invasion suppressor in colorectal cancer. This protective mechanism frequently collapses at the adenoma-carcinoma transition due to EPHB3 transcriptional silencing. Here, we identify a transcriptional enhancer at the EPHB3 gene that integrates input from the intestinal stem-cell regulator achaete-scute family basic helix-loop-helix transcription factor 2 (ASCL2), Wnt/{beta}-catenin, MAP kinase, and Notch signaling. EPHB3 enhancer activity is highly variable in colorectal carcinoma cells and precisely reflects EPHB3 expression states, suggesting that enhancer dysfunction underlies EPHB3 silencing. Interestingly, low Notch activity parallels reduced EPHB3 expression in colorectal carcinoma cell lines and poorly differentiated tumor-tissue specimens. Restoring Notch activity reestablished enhancer function and EPHB3 expression. Although essential for intestinal stem-cell maintenance and adenoma formation, Notch activity seems dispensable in colorectal carcinomas. Notch activation even promoted growth arrest and apoptosis of colorectal carcinoma cells, attenuated their self-renewal capacity in vitro, and blocked tumor growth in vivo. Higher levels of Notch activity also correlated with longer disease-free survival of colorectal cancer patients. In summary, our results uncover enhancer decommissioning as a mechanism for transcriptional silencing of the EPHB3 tumor suppressor and argue for an antitumorigenic function of Notch signaling in advanced colorectal cancer.
