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Discussion In this study, we investigated the CSC phenotype in two human colon cancer cell lines HCT116 and HT29 based on their expression of surface markers, chemoresistance properties, side population phenotype and gene expression analysis. Our results confirm that both cell lines differ in their stemness properties. We propose to define the putative CSC subsets as CD44+/CD24-/CD133- in HCT116 cell line and CD24+/CD44-/CD133- in HT29 cell line. Selected cell subsets appear to be more resistant to 5-FU treatment, possess an upregulated expression of several stemness-associated genes and are able to actively exclude Rhodamine 133 dye. Moreover, they are small in size: CD44+/CD24-/CD133- accounts for 4.1% of HCT116 cells and CD24+/CD44-/CD133- accounts for 4.9% of HT29 cells. CSCs identification in vitro and in vivo is generally based upon specific surface markers expression, CD133, CD24, CD44, ESA, CD166 and CD117 being the most common markers applicable in CSC research (20, 22). Although CD133 is widely accepted as a colon CSCs marker, it’s significance in defining potential colon CSCs population is still questionable. Our results show that putative CSCs in both HCT116 and HT29 lines do not express CD133. Though it was demonstrated, that CD133+ subpopulation of colon cancer was able to initiate tumor formation (23, 24), Shmelkov et al was the first to show, that CD133 expression is not restricted to colon CSCs. Instead they discovered, that CD133 is expressed in a majority of differentiated colon epithelial cells. In addition, both CD133+ and CD133- subpopulations of colon metastatic tumor were able to initiate tumor formation in NOD/SCID mouse and CD133- formed even more aggressive and larger tumors (25). CD24 was also propose... ... middle of paper ... ... established cancer cell lines may not fully reflect the heterogeneity of individual tumors. Further studies involving tumor samples and high-resolution methods would increase the precision of tumor diversity analysis. The bigger picture of tumor heterogeneity might confer useful insights for clinical practice. Conclusions Taken together, our findings demonstrate that human colon cancer cell lines with distinct levels of aggressiveness and differentiation capacity differ in their CSC-related properties. We imply that putative CSC subset for HCT116 cell line is CD44+/CD24-/CD133- (4,1% of all cells) and for HT29 cells – CD24+/CD44-/CD133- (4,9% of all cells). Acknowledgements This study was supported by Ministry of Education and Science of Lithuania, Grant No. VP1-3.1-ŠMM-10-V-02-027. Statement of Conflict of Interest The authors state no conflicts of interest.
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