TGF-β isoforms induce EMT independent migration of ovarian cancer cells

Background: Transforming growth factor beta (TGF-β) plays major roles in tumorigenesis by regulating cell growth, epithelial-to-mesenchymal transition (EMT), migration/invasion and metastasis. The epithelial markers E-cadherin, claudin-3 and claudin-4, commonly decreased in human adenocarcinomas are actually up regulated during ovarian carcinogenesis. In human ovarian cancer TGF-β1 may either suppress or promote tumor progression, but whether other TGF-β isoforms (TGF-β2 and TGF-β3) exert similar effects is not known.

Methods: In this study we investigated the ability of the TGF-β isoforms (TGF-β1-3) to induce proliferation and migration by BrdU labeling, scratch wound and trans-filter migration assays in the human serous adenocarcinoma cell-line NIH-OVCAR3. Transepithelial resistance was measured and EMT observed by light-microscopy. Expression of adherens-, tight-junction and EMT-related transcription factors was analyzed by qRT-PCR and immunoblotting.

Results: All TGF-β isoforms dose-dependently inhibited NIH-OVCAR3 cell growth, stimulated tumor cell migration with similar efficiency. The mesenchymal marker N-cadherin and claudin-1 expression was induced and occludin down regulated. However, migrating cells retained an epithelial shape and E-cadherin expression. The E-cadherin repressor SNAIL mRNA levels remained low independently of TGF-β1-3 treatment while ZEB1 expression was enhanced.

Conclusions: TGF-β1, TGF-β2 and TGF-β3 promote migration of NIH-OVCAR3 ovarian cancer cells independently of cell proliferation and without conversion to a complete EMT phenotype. Epithelial ovarian cancer commonly metastasis to the surrounding tissue or inside the peritoneum rather than invading blood vessels to set distance metastasis. Our result raises the question whether ovarian cancer primarily spread via collective migration than via single cell invasion.