MIR-7 targets pax6 and modulates bladder cancer cell migration

Transitional cell carcinoma (TCC) of the bladder is one of the 10 most common cancers in Australia. Bladder cancer incidence increases with the age and is 3-4 times as common in males compared to females. Invasive bladder cancer is the major cause of death among people diagnosed with urothelial cancer. The work presented in this thesis aims to better understand the development and progression of bladder cancer in humans. This thesis focuses on the role played by miR-7 and its downstream target Pax6, using a novel cell model of human bladder transitional cell carcinoma. This model consists of TSU-Pr1 and TSU-Pr1-B2, two highly related cell lines that were originally derived from the T24 bladder cancer cell line. TSU-Pr1-B2 is a subline of TSU-Pr1 that was generated through in vivo selection for metastatic cells following systemic inoculation. In the present study, a low expression level of miR-7 was observed in the epithelial-like TSU-Pr1-B2 cells compared to the more mesenchymal-like TSU-Pr1 cells. Overexpression of miR-7 in TSU-Pr1-B2 cells inhibited cell migration and reduced cell speed in vitro. Bioinformatic analyses predicted four putative miR-7 binding sites in the Pax6 3’ UTR. This interaction was confirmed using a luciferase reporter assay. Further experiments showed that knock-down of Pax6 in TSU-Pr1-B2 cells also impaired cell migration and decreased cell speed in vitro. These results suggested that miR-7 decreased cell migration in vitro by down-regulating Pax6. Integrin-Linked Kinase (ILK) was identified as a potential novel downstream target of Pax6. ILK promoter activity decreased when Pax6 was overexpressed. Therefore, I postulated that Pax6 could regulate ILK, providing a novel pathway for miR-7 mediated regulation of bladder cancer progression. This study provides new insights in the molecular mechanisms mediating migration of urothelial cancer cells and implicates a miR-7/Pax6/ILK signalling pathway in this process.