Article
Wnt/β-catenin signaling mediates resistance of colorectal cancer cells to radiation
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Authors
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Emil Kendziorra
- University Medical Center Göttingen, General and Visceral Surgery, Göttingen
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Kerstin Ahlborn
- University Medical Center Göttingen, General and Visceral Surgery, Göttingen
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Melanie Spitzner
- University Medical Center Göttingen, General and Visceral Surgery, Göttingen
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Georg Emons
- University Medical Center Göttingen, General and Visceral Surgery, Göttingen
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Margret Rave-Fränk
- University Medical Center Göttingen, Radiotherapy and Radiooncology, Göttingen
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Jochen Gaedcke
- University Medical Center Göttingen, General and Visceral Surgery, Göttingen
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Heinz Becker
- University Medical Center Göttingen, General and Visceral Surgery, Göttingen
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Tobias Pukrop
- University Medical Center Göttingen, Hematology/Oncology, Göttingen
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B. Michael Ghadimi
- University Medical Center Göttingen, General and Visceral Surgery, Göttingen
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Thomas Ried
- National Cancer Institute, National Institutes of Healt, Genetics Branch, Center for Cancer Research, Bethesda, MD
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Marian Grade
- University Medical Center Göttingen, General and Visceral Surgery, Göttingen
| Published: | May 20, 2011 |
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Outline
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Introduction: The clinical response of locally advanced rectal cancers to preoperative chemoradiotherapy is very heterogeneous. To determine the molecular characteristics underlying this heterogeneous response, we recently used gene expression microarrays to profile a series of responsive and resistant rectal carcinomas and identified TCF7L2, the main downstream effector of the Wnt/β-catenin pathway, as over-expressed in the resistant tumors. The aim of this study was to functionally evaluate whether TCF7L2 mediates resistance to irradiation.
Materials and methods: TCF7L2 was silenced in three colorectal cancer cell lines (SW837, SW480 and HT-29) using shRNA constructs. Stable knockdown was confirmed using Western blot analysis, and selected single-cell clones (SCC) were irradiated at 0, 1, 2, 4, 6 and 8 Gy. To gain further insight into the underlying molecular mechanisms, follow-up experiments were performed in SW837 and HT-29.
Results: RNAi-mediated silencing of TCF7L2 led to a significant radiosensitization in SW837 and SW480 SCCs, whereas no effect was observed in HT-29. This radiosensitization was the consequence of an increased fraction of cells in the G2/M phase at time of radiation exposure, and an impaired DNA double strand repair, evaluated using immunohistochemical staining of γH2AX foci. Finally, using the TOPFLASH/FOPFLASH reporter assay, we could show that untransfected SW837 cells exhibited higher basal Wnt/β-catenin pathway activity and inducibility compared with untransfected HT-29 cells.
Conclusion: TCF7L2 was previously shown to be over-expressed in rectal cancers that were resistant to preoperative chemoradiotherapy. These data suggest TCF7L2 as a potential therapeutic target whose modification may be harnessed to sensitize Wnt/ß-catenin-dependent, resistant tumor cells to radiation. We have therefore uncovered an as yet unappreciated role of canonical Wnt/ß-catenin signaling as a mediator of resistance to multimodal treatment.
