Silencing Oncogene E6/E7 in HeLa Sphere Forming Cells Inhibits Their Growth and Decreases Self-renewal Gene TGF-β Expression

) Cancer stem cells (CSCs) are believed responsible for the tumor initiation and the resistance to current cancer therapies such as chemoand radiotherapy, which also lead to tumor recurrences and metastasis. By using a 3-D sphere culture method that favors the growth of self-renewal cells, we have successfully isolated sphere forming cells (SFCs) from cervical cancer HeLa and SiHa cells. It is found that HeLa SFCs have CSCs-like nature. The HeLa SFCs are resistant to chemotherapeutic drugs such as cisplatin, doxorubicin, and epitoside. Moreover, HeLa SFCs can grow tumors after injection of 10,000 cells to NOD/SCID mice, whereas growing such tumors in the same time frame needs 1 x 10 parental HeLa cells. In addition, in vitro and in the presence of fetal calf serum, HeLa SFCs can form more and bigger colonies than their parental cells; and the differentiated SFCs become sensitive to cisplatin and doxorubicin. The HeLa SFCs show an expression pattern of CD44/CD24 at cell surface that resembles the biomarker of breast CSCs as reported. We further demonstrate that HeLaSFCs express different levels of E6/E7 genes compared to their parental HeLa cells, and the RNAi mediated gene silence of E6/E7 profoundly inhibits their cell growth and sphere formation. We have measured the self-renewal genes TGF-β and LIF expressions in HeLa SFCs and found that only TGF-β has been down-regulated after E6/E7 gene silencing, suggesting a possible new approach for the targeted cancer therapy of CSCs.