癌干细胞很可能来自癌变的成体干细胞，而原癌基因Bmi1在干细胞自我更新和"干性"维持中起关键作用。我们前期研究发现，高表达Bmi1基因的大鼠卵圆细胞(成体肝干细胞)可在裸鼠体内形成低分化肝癌；进一步的芯片结果提示miRNA-200b与Bmi1的表达显著负相关，miRNA靶基因预测软件也提示Bmi1可能是miRNA-200b的下游靶基因。在此基础上我们提出假设：miRNA-200b可通过靶向调控Bmi1基因进而促进成体肝干细胞向肝癌干细胞转分化。本项目拟首先通过qPCR、Western和双荧光素酶报告系统验证miRNA-200b能否靶向调控Bmi1；然后检测miRNA-200b对卵圆细胞体外自我更新、多向分化、耐受化疗药及在裸鼠体内成瘤能力的影响；最后检测miRNA-200b/Bmi1对Wnt、SHH和Notch信号通路的影响；以探明在干细胞癌变中起关键作用的基因、信号通路及上下游调控机制。

Cancer stem cells probably derived from malignant transformation of adult stem cells, while oncogene Bmi1 plays pivotal roles in the self-renewal and "stemness" maintenance of stem cells. Previouly, we have found that rat oval cells (adult liver stem cells) with high expression of Bmi1 gene produced tumors in nude mice with histological features of poorly differentiated hepatocellular carcinoma. Further, our array analysis revealed that miRNA-200b correlated negatively with Bmi1 gene. Bmi1 has also been predicted to be a potential target gene of miRNA-200b by the use of miRNA-target software prediction algorithms. Therefore, we hypothesised that miRNA-200b can promote malignant transformation of liver stem cells to liver cancer stem cells by targeted regulation of Bmi1 in oval cells. In this study, first real time PCR, Western blot and Dual-Luciferase assay were employed to validate whether Bmi1 was a target gene of miRNA-200b. Next, the effect of miRNA-200b on oval cells self-renew, multipotent differentiation, chemoresistance as well as tumorigenecity was studied in vitro and in vivo. At last, the effects of miRNA-200b/Bmi1 on Wnt, SHH and Notch signaling pathways were investigated. This study aimd to explore the key genes, signaling pathways, upstream and downstream regulatory mechanisms in malignant transformation of stem cells.