Characterization of cancer stem cells in hepatocellular carcinoma

Abstract

Hepatocellular carcinoma (HCC) is the third most common cause of death from cancer worldwide due to the challenges in both its diagnosis and treatment. According to recent studies, HCC tumors, like many other solid tumors are initiated and maintained by a subpopulation of cells called “cancer stem cells (CSCs)” or "tumor-initiating cells (TICs)". HCC stem cells can be identified by the expression of cardinal CD markers such as CD133 (Prominin-1) and epithelial cell adhesion molecule (EpCAM). This study primarily focuses on the investigation of mechanisms involved in the generation of HCC stem cell sub-population using a panel of 15 HCC cell lines. Preliminary data indicates that four cell lines (27%) display CD133+ stem cell populations at frequencies ranging from 8 to 90% when tested by flow cytometry. Among these CD133 positive cell lines, two isogenic cell line with different positivity levels prompted us to focus on two specific cell lines;, i) parental HepG2 cell line and its clone, which was transfected with four copies of hepatitis B virus (HBV), namely ii) HepG2-2215. With tumorigenicity assay induced in atymic nude mice, data revealed that HepG2-2215 that had higher CD133+ ratio, showed higher and rapid tumor formation than parental HepG2 that had much lower CD133+ sub-cellular proportion. Microarray analyses were performed to underpin the mechanisms of in CD133+ cell number variations of these two cell lines. Our initial findings suggested that FGFR signaling pathway might have played a role. To investigate these findings, FGFR signaling pathway was inhibited via potent inhibitor as well as knock down with siRNA. However, preliminary data did not indicate these presumptions and further studies are needed to clarify the relationship between FGFR signaling and CSC formation in HCC. Also, role of suppressive oligodeoxynucleotide (ODN) was studied to see the effects of suppression of DNAdriven immunostimulation. Findings showed that suppressive ODN decreased CD133 levels, which indicates the difference between these two cell lines may arise from the HBV transfection of HepG2-2215 cell line which can produce HBV particles. However, further investigation is needed to understand the relationship between HBV infection and CSC population in HCC.