Dynamic equilibrium between cancer stem cells and non-stem cancer cells in human SW620 and MCF-7 cancer cell populations

BACKGROUND: Cancer stem cells (CSCs) paradigm suggests that CSCs might have important clinical implications in cancer therapy. Previously, we reported that accumulation efficiency of CSCs is different post low-and high-LET irradiation in 48 h. METHODS: Cancer stem cells and non-stem cancer cells (NSCCs) were sorted and functionally identified through a variety of assays such as antigen profiles and sphere formation. Inter-conversion between CSCs and NSCCs were in situ visualised. Cancer stem cells proportions were assayed over multiple generations under normal and irradiation surroundings. Supplement and inhibition of TGF-beta 1, as well as immunofluorescence assay of E-cadherin and Vimentin, were performed. RESULTS: Surface antigen markers of CSCs and NSCCs exist in an intrinsic homoeostasis state with spontaneous and in situ visualisable inter-conversions, irrespective of prior radiations. Supplement with TGF-b1 accelerates the equilibrium, whereas inhibition of TGF-beta signalling disturbs the equilibrium and significantly decreases CSC proportion. Epithelial mesenchymal transition (EMT) might be activated during the process. CONCLUSION: Our results indicate that the intrinsic inter-conversion and dynamic equilibrium between CSCs and NSCCs exist under normal and irradiation surroundings, and TGF-b might have important roles in the equilibrium through activating EMT. British Journal of Cancer (2012) 106, 1512-1519. doi:10.1038/bjc.2012.126 www.bjcancer.com Published online 3 April 2012 (C) 2012 Cancer Research UK