Silencing of the EPHB3 tumor-suppressor gene in human colorectal cancer through decommissioning of a transcriptional enhancer.
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/β-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.
Institute of Molecular Medicine and Cell Research, Faculty of Biology, Institute of Pathology, University Medical Center, Department of Hematology and Oncology, University Medical Center, Freiburg Institute for Advanced Studies, and BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-University Freiburg, D-79117 Freiburg, Germany.
Sabine
S
Jägle
Kerstin
K
Rönsch
Sylvia
S
Timme
Hana
H
Andrlová
Miriam
M
Bertrand
Marcel
M
Jäger
Amelie
A
Proske
Monika
M
Schrempp
Afsheen
A
Yousaf
Tom
T
Michoel
Robert
R
Zeiser
Martin
M
Werner
Silke
S
Lassmann
Andreas
A
Hecht
D000818:Animals; D017209:Apoptosis / Q000235:genetics; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D059447:Cell Cycle Checkpoints / Q000235:genetics; D002454:Cell Differentiation / Q000235:genetics; D015179:Colorectal Neoplasms / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D019073:HT29 Cells; D006801:Humans; D020935:MAP Kinase Signaling System / Q000235:genetics; D051379:Mice; D014411:Neoplastic Stem Cells / Q000378:metabolism / Q000473:pathology; D036223:Receptor, EphB3 / Q000235:genetics* / Q000378:metabolism; D051880:Receptors, Notch / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D014158:Transcription, Genetic; D051153:Wnt Proteins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism
D051792:Basic Helix-Loop-Helix Proteins; D036223:Receptor, EphB3; D051880:Receptors, Notch; D051153:Wnt Proteins; D051176:beta Catenin; C065501:ASCL2 protein, human
EPHB2; Ephrin signaling; metastasis; tumor progression