Side population cell fractions from hepatocellular carcinoma cell lines increased with tumor dedifferentiation, but lack characteristic features of cancer stem cells

Abstract

Cancer stem cells (CSCs), a minority population with stem cell-like characteristics, play important roles in cancer development and progression. Putative CSC markers, such as CD13, CD90, CD133, and epithelial cell adhesion molecule (EpCAM), and side population (SP) technique are generally used in an attempt to isolate CSCs. We aimed to clarify the relationship between CSCs and clonal dedifferentiation in hepatocellular carcinoma (HCC). We used a well-differentiated HCC cell line (HAK-1A) and a poorly differentiated HCC cell line (HAK-1B) established from a single nodule with histological heterogeneity. HAK-1B arose because of clonal dedifferentiation of HAK-1A. The SP cells and non-SP (NSP) cells were isolated from the two cell lines with a FACSAria II and used for the analyses. The SP cell fractions in HAK-1A and HAK-1B were 0.2% and 0.9%, respectively. CD90 or EpCAM was not expressed in either HAK-1A or HAK-1B, while CD13 and CD133 were expressed in HAK-1B alone. Although sphere forming ability, tumorigenicity, growth rate, and CD13 expression were higher in HAK-1B SP cells than HAK-1B NSP cells, there were no differences in drug resistance, colony forming ability, or cell cycle rates between HAK-1B SP and NSP cells, suggesting HAK-1B SP cells do not fulfill CSC criteria. Our findings suggested a possible relationship between the expression of CSC markers and clonal dedifferentiation. However, the complete features of CSC could not be identified in SP cells, and the concept of SP cells as a universal marker for CSC may not apply to HAK-1A and HAK-1B.