There has been an arousing interest in cancer stem cells (CSCs) ever since it was discovered few decades ago. CSCs are well-known by not only their ability to undergo self-renewal and differentiate into more mature cancer cells but also by their tumour-initiating ability from relatively very small number of cells. Only little investigation into the exact role of isolated populations of (CSCs) has been undertaken and the prevalence of CSCs in malignancies is still a matter of some debate and controversy. Here, we aim to identify specific CSC markers and isolate CSC sub-populations from colon cancer in order to force them from dormancy into active division, which will potentially make them more susceptible to chemotherapy.
Expression levels of several colorectal CSCs markers including CD271, SSEA1, EPCAM, Cript-1, or ABCG2 were validated under both hypoxic and normoxic conditions in SW480 and CSC480, colorectal cancer cell lines, using Flow cytometry and immunofluorescence. The relationship between hypoxia and cellular expression of Brn2, which is a transcription factor that could be a CSC marker, was explored via flow cytometry an immunofluorescence. Furthermore, correlation between CSC markers expression in primary and metastasis tissues in human colorectal cancer was examined by immunofluorescence.
ABCG2 and Cripto-1 were expressed in low levels on cell-subpopulations compared to CD271, EPCAM or SSEA1. Interestingly, all the markers expression levels were increased in a subpopulation by 72 hours under hypoxia compared to normoxia conditions. However, comparison over the time course of hypoxia; EPCAM, Cripto-1, or ABCG2 expression were decreased at 48 hours and then increased again at 72 hours. The SW480 Brn2-EGFP cell line showed a significant decreased in Brn2 positive cells between the normoxia and hypoxia samples at 24, 48, or 72 hours. We found that all markers were highly expressed in metastasis compared to primary sections in human tissues.
ABCG2 and Cripto-1 are potentially suitable markers for studying colon CSCs. Notably, colon CSCs could possibly exert a strong proportional relationship with hypoxia and metastasis. Additionally, all of the CSC markers were found to be more highly expressed in the metastatic samples compared with the polyps or primary sections.