Functional characterization of the role of cancer stem cell marker, prominin-1 (CD133), in hepatocellular carcinoma

Abstract

CD133 is a transmembrane protein that has been studied as a marker for cancer stem cells in various cancer types. In hepatocellular carcinoma (HCC), the CD133-positive cancer stem cell subtype is previously identified and characterized with more efficient ability to self-renew, differentiate, proliferate and resist to chemotherapeutic drugs than the CD133-negative counterparts. Despite the growing evidence suggests CD133 also contributes to the cancer stem cell features, the functional role of CD133 and the underlying molecular mechanisms are far from clear.

To elucidate the CD133 function, we have established stable inducible system for CD133 expression in HCC cell lines with low endogenous CD133 level. The inducible expression of CD133 was confirmed using western blotting and flow cytometry analysis. Transient and induced overexpression of CD133 significantly increased the tumorigenicity in vitro in SMMC-7721. As revealed by cell cycle analysis using SMMC-772 and HepG2, the ectopic expression of CD133 resulted in a lower G1 and higher G2/M phase population, and surprisingly, elevated the aneuploidy population.

Centrosome overduplication has been extensively studied that it results in aneuploidy, multipolar mitotic figures as well as chromosomal instability. Result from immunofluorescence in this study showed CD133 did not localized in centrosome, however, induced expression of CD133 significantly increased the multipolar metaphase cells. More interestingly, the centrosomal protein TAX1BP2, which is previously identified as the intrinsic block of centrosome duplication by our group, was down regulated through promoter suppression with ectopic expression of CD133. Moreover, gene expression profile by microarray found putative CD133-mediated regulators involved in contribution to hepatocarcinogenesis and cancer stemness.

Taken together, our work further confirmed CD133 is not only a cancer stem cell marker but also contributes to tumorigenicity, aneuploidy and multipolar mitotic figures; in addition, we addressed the importance of TAX1BP2 in HCC cancer stem cells.