Cyclin D1 affects epithelial–mesenchymal transition in epithelial ovarian cancer stem cell-like cells

BACKGROUND: The association of cancer stem cells with epithelial–mesenchymal transition (EMT) is receiving attention. We found in our previous study that EMT existed from CD24− phenotype cells to their differentiated cells. It was shown that cyclin D1 functioned in sustaining self-renewal independent of CDK4/CDK6 activation, but its effect on the EMT mechanism in ovarian cancer stem cells is unclear. METHODS: The anchorage-independent spheroids from ovarian adenocarcinoma cell line 3AO were formed in a serum-free medium. CD24− and CD24+ cells were isolated by fluorescence-activated cell sorting. Cell morphology, viability, apoptosis, and migratory ability were observed. Stem-related molecule Bmi-1, Oct-4 and EMT-related marker E-cadherin, and vimentin expressions were analyzed. Cyclin D1 expression in CD24− phenotype enriched spheroids was knocked down with small interfering RNA, and its effects on cell proliferation, apoptosis, migration ability, and EMT-related phenotype after transfection were observed. RESULTS: In our study, CD24− cells presented stronger proliferative, anti-apoptosis capacity, and migratory ability, than CD24+ cells or parental cells. CD24− cells grew with a scattered spindle-shape within 3 days of culture and transformed into a cobblestone-like shape, identical to CD24+ cells or parental cells at 7 days of culture. CD24− cells or spheroids highly expressed cyclin D1, Bmi-1, and vimentin, and seldom expressed E-cadherin, while CD24+ or parental cells showed the opposite expression. Furthermore, cyclin D1-targeted small interfering RNA resulted in decreased vimentin expression in spheroids. Transfected cells also exhibited an obvious decrease in cell viability and migration, but an increase in cell apoptosis. CONCLUSION: Cancer stem cell-like cells possess mesenchymal characteristics and EMT ability, and cyclin D1 involves in EMT mechanism, suggesting that EMT of cancer stem cell-like cells may play a key role in invasion and metastasis of ovarian cancer.