E-Cadherin loss associated with EMT promotes radioresistance in human tumor cells

• Published in: Radiotherapy and oncology Vol. 99; no. 3; pp. 392 - 397
• Main Authors: Theys, Jan, Jutten, Barry, Habets, Roger, Paesmans, Kim, Groot, Arjan J, Lambin, Philippe, Wouters, Brad G, Lammering, Guido, Vooijs, Marc
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier Ireland Ltd 01.06.2011
• Subjects: Analysis of Variance; Blotting, Western; Cadherins - metabolism; Cell Hypoxia; Cell Line, Tumor; Cell Survival - radiation effects; Cell Transformation, Neoplastic; E-Cadherin; EMT; Epithelial Cells - metabolism; Epithelial Cells - pathology; Gene Expression Regulation, Neoplastic; Hematology, Oncology and Palliative Medicine; Humans; Immunoenzyme Techniques; Mesoderm - metabolism; Mesoderm - pathology; Microenvironment; Neoplasms - genetics; Neoplasms - metabolism; Neoplasms - pathology; Phenotype; Radiation Tolerance; Radioresistance; Real-Time Polymerase Chain Reaction; Signal Transduction; Tumor hypoxia; Tumor Microenvironment; Tumor hypoxia; Radioresistance; Microenvironment; EMT; E-Cadherin
• ISSN: 0167-8140; 1879-0887
• DOI: 10.1016/j.radonc.2011.05.044

Abstract Background and purpose Hypoxia is a hallmark of solid cancers and associated with metastases and treatment failure. During tumor progression epithelial cells often acquire mesenchymal features, a phenomenon known as epithelial-to-mesenchymal transition (EMT). Intratumoral hypoxia has been linked to EMT induction. We hypothesized that signals from the tumor microenvironment such as growth factors and tumor oxygenation collaborate to promote EMT and thereby contribute to radioresistance. Materials and methods Gene expression changes under hypoxia were analyzed using microarray and validated by qRT-PCR. Conversion of epithelial phenotype upon hypoxic exposure, TGFβ addition or oncogene activation was investigated by Western blot and immunofluorescence. Cell survival following ionizing radiation was assayed using clonogenic survival. Results Upon hypoxia, TGFβ addition or EGFRvIII expression, MCF7, A549 and NMuMG epithelial cells acquired a spindle shape and lost cell–cell contacts. Expression of epithelial markers such as E-cadherin decreased, whereas mesenchymal markers such as vimentin and N-cadherin increased. Combining hypoxia with TGFβ or EGFRvIII expression, lead to more rapid and pronounced EMT-like phenotype. Interestingly, E-cadherin expression and the mesenchymal appearance were reversible upon reoxygenation. Mesenchymal conversion and E-cadherin loss were associated with radioresistance. Conclusions Our findings describe a mechanism by which the tumor microenvironment may contribute to tumor radioresistance via E-cadherin loss and EMT.