Colon adenocarcinoma-derived cells that express induced-pluripotent stem cell markers possess stem cell function

Abstract

Aims Much work has been done to find markers of cancer stem cells (CSCs) that distinguish them from the tumor bulk cells and normal cells. Recent CSC research has applied the induced pluripotent stem cell (iPSC) concept. In this study, we investigated the expression of a panel of iPSC markers in primary colon adenocarcinoma (CA)-derived cell lines. Materials and methods Expression of iPSC markers by CA-derived primary cell lines was interrogated using immunocytochemistry, western blotting and RT-qPCR. The stem cell function of these cells was then assessed in vitro using differentiation and tumorsphere assays. Results Expression of iPSC markers OCT4, SOX2, NANOG, KLF4 and c-MYC was more widespread in high-grade CA (HGCA) cell lines than low-grade CA (LGCA) cell lines, as demonstrated by western blotting and RT-qPCR. These cells could be induced to differentiate down the three embryonic lineages. Cells derived from HGCA were more capable of forming tumorspheres than those derived from LGCA. EpCAM sorting revealed that a population enriched for EpCAMHigh cells formed larger tumorspheres than EpCAMLow cells. Pluripotency markers, SSEA4 and TRA-1-60, were co-expressed by a small subpopulation of cells that also co-expressed SOX2 in 75% and OCT4 in 50% of the cell lines. Conclusions CA-derived primary cell lines contain tumorsphere-forming cells which express key pluripotency genes and can differentiate down 3 embryonic lineages, suggesting a pluripotent CSC-like phenotype. There appear to be two iPSC-like subpopulations, one with high EpCAM expression which forms larger tumorspheres than another with low EpCAM expression. Furthermore, these cells can be characterized based on iPSC marker expression, as we have previously demonstrated in the original CA tumor tissues.