Effects of RCCS simulated microgravity on the ultrastructure and biological behavior of human MDA-MB-231 breast cancer cells

OBJECTIVE: The microgravity has significant effects on a variety of normal cells and tumor cells,and the changes of human MDA-MB-231 breast cancer cells cultured under stimulated microgravity conditions has only been reported sporadically.This study aimed to investigate the changes in ultrastructure,apoptosis,cycle progression and migration ability of human MDA-MB-231 breast cancer cells under stimulated microgravity conditions.METHODS: MDA-MB-231 breast cancer cells were cultured in a rotary cell culture system(RCCS) bioreactor to stimulate microgravity for 7 days. The cells were randomly divided into simulated microgravity(SMG) group and normal gravity control(NG) group,and harvested respectively after 7 days' culture. The changes in apoptosis,ultrastructure,cell cycle,and migration ability were evaluated by using flow cytometry,transmission electron microscopy,western blot analysis,and Transwell migration assay. RESULTS: The transmission electron microscope showed that human MDA-MB-231 breast cancer cells in SMG group had more secondary lysosomes than NG groups after 7 days' culture. The flow cytometry assay found that the proportion of apoptotic cells in SMG group (31.100±5.803)% were significantly increased compared to NG group (7.067±1.930)%,P=0.002. The median and interquartile spacing of the proportion of cells in G₀/G₁ phase in SMG group was 46.250%(50.878),lower than that in NG group 52.340%(57.710),P=0.027. The proportion of cells in the S phase were increased in SMG group (44.168±4.260)% compared with that in NG group (37.094±3.880)%,P=0.035. The Transwell migration assay showed that the migrated breast cancer cells in SMG group (138.333±26.502) were significantly reduced compared with that in NG group (592.667±60.929),P<0.001. The expression of Bcl-2 (0.397±0.790) and MMP9 (0.288±0.182) in SMG group was decreased compared with NG group (Bcl-2:0.654±0.136; MMP9:0.611±0.029) in human MDA-MB-231 breast cancer cells,while the expression of Cyclin D3 in SMG group (1.577±0.868) was increased compared with NG group (0.853±0.315),P<0.05. CONCLUSION: The simulated microgravity by RCCS has significantly impacts on human MDA-MB-231 breast cancer cells,the cell cycle and ultrastructure are impaired,the apoptosis is increased,the migration ability is inhibited,and the expression of Bcl-2,Cyclin D3 and MMP9 are affected.