Hypoxia, Snail and incomplete epithelial-mesenchymal transition in breast cancer.
BACKGROUND
Hypoxia is an element of the tumour microenvironment that impacts upon numerous cellular factors linked to clinical aggressiveness in cancer. One such factor, Snail, a master regulator of the epithelial-mesenchymal transition (EMT), has been implicated in key tumour biological processes such as invasion and metastasis. In this study we set out to investigate regulation of EMT in hypoxia, and the importance of Snail in cell migration and clinical outcome in breast cancer.


METHODS
Four breast cancer cell lines were exposed to 0.1% oxygen and expression of EMT markers was monitored. The migratory ability was analysed following Snail overexpression and silencing. Snail expression was assessed in 500 tumour samples from premenopausal breast cancer patients, randomised to either 2 years of tamoxifen or no adjuvant treatment.


RESULTS
Exposure to 0.1% oxygen resulted in elevated levels of Snail protein, along with changes in vimentin and E-cadherin expression, and in addition increased migration of MDA-MB-468 cells. Overexpression of Snail increased the motility of MCF-7, T-47D and MDA-MB-231 cells, whereas silencing of the protein resulted in decreased migratory propensity of MCF-7, MDA-MB-468 and MDA-MB-231 cells. Moreover, nuclear Snail expression was associated with tumours of higher grade and proliferation rate, but not with disease recurrence. Interestingly, Snail negativity was associated with impaired tamoxifen response (P=0.048).


CONCLUSIONS
Our results demonstrate that hypoxia induces Snail expression but generally not a migratory phenotype, suggesting that hypoxic cells are only partially pushed towards EMT. Furthermore, our study supports the link between Snail and clinically relevant features and treatment response.
Department of Laboratory Medicine, Center for Molecular Pathology, Malmö University Hospital, Lund University, Malmö SE-205 02, Sweden.
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Lundgren
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Nordenskjöld
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Landberg
D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology*; D048708:Cell Growth Processes / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics / Q000502:physiology; D018572:Disease-Free Survival; D004847:Epithelial Cells / Q000473:pathology; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D053208:Kaplan-Meier Estimate; D008648:Mesoderm / Q000473:pathology; D010100:Oxygen / Q000008:administration & dosage / Q000378:metabolism; D015398:Signal Transduction; D000071250:Snail Family Transcription Factors; D013629:Tamoxifen / Q000494:pharmacology; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D014162:Transfection
D014408:Biomarkers, Tumor; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors; D013629:Tamoxifen; D010100:Oxygen