The Stem Cell Marker CD133 Associates with Enhanced Colony Formation and Cell Motility in Colorectal Cancer

CD133 is a membrane molecule that has been, controversially, reported as a CSC marker in colorectal cancer (CRC). In this study, we sought to clarify the expression and role of CD133 in CRC. Initially the size of the CD133−expressing (CD133+) population in eight well-described CRC cell lines was measured by flow cytometry and was found to range from 0% to >95%. The cell line HT29 has a CD133+ population of >95% and was chosen for functional evaluation of CD133 after gene knockdown by RNA interference. A time course assay showed that CD133 inhibition had no significant effect on cell proliferation or apoptosis. However, CD133 knockdown did result in greater susceptibility to staurosporine-induced apoptosis (p = 0.01) and reduction in cell motility (p<0.04). Since gene knockdown may cause “off-target” effects, the cell line SW480 (which has a CD133+ population of 40%) was sorted into pure CD133+ and CD133− populations to allow functional comparison of isogenic populations separated only by CD133 expression. In concordance with the knockdown experiments, a time course assay showed no significant proliferative differences between the CD133+/CD133− populations. Also greater resistance to staurosporine-induced apoptosis (p = 0.008), greater cell motility (p = 0.03) and greater colony forming efficiency was seen in the CD133+ population than the CD133− population in both 2D and 3D culture (p<0.0001 and p<0.003 respectively). Finally, the plasticity of CD133 expression in tumour cells was tested. Quantitative PCR analysis showed there was transcriptional repression in the CD133− population of SW480. Prolonged culture of a pure CD133− population resulted in re-emergence of CD133+ cells. We conclude that CD133 expression in CRCs is associated with some features attributable to stemness and that there is plasticity of CD133 expression. Further studies are necessary to delineate the mechanistic basis of these features

Characterization of the Hoechst 33342 side population from normal and malignant human renal epithelial cells

The fundamental changes which predispose for renal cell carcinoma (RCC) are poorly characterized. It is hypothesized that “cancer stem cells” may be influential in carcinogenesis, and the epithelial side population (SP) is enriched for stemlike cells in other epithelial cancers. In this study, we have isolated and characterized the SP and non-SP (NSP) populations from normal (NK) and malignant (RCC) human kidney tissue. NK specimens were taken from patients undergoing non-renal cancer surgery and paired malignant and macroscopically normal tissue samples were taken from patients undergoing surgery for RCC. The Hoechst 33342 dye efflux technique was used to isolate epithelial SP and NSP from normal and malignant human renal tissue. Cellular subpopulations were phenotyped for lineage, cell cycle, and putative stem cell markers, and functionally characterized using in vitro colony-forming and proliferation assays. The SP constituted 3.8 ± 0.4 and 5.9 ± 0.9% of epithelial cells in NK and RCC, respectively, of which 14.1 ± 3.5 and 13.2 ± 3.6% were shown to be in G0. SP cells demonstrated greater proliferative potential in colony-forming efficiency, long-term culture, and spheroids assays and were shown to be maintained upon tissue culture passage. We have shown that the renal SP is enriched for quiescent cells, with a high proliferative capacity and stemlike properties. The population is, however, heterogeneous, confirming that the terms “SP cell” and “stem cell” cannot be used interchangeably