Prostate cancer stem cell fate: β-catenin and the Wnt pathway

A major problem in prostate cancer is the high relapse rate post therapy. This is believed to be due to the presence of a small number of prostate cancer stem cells within a tumour. Tumour initiation, maintenance and spreading have been attributed to this subpopulation of tumour cells. Wnt activity and β-catenin signalling have been associated with different types of cancer and microarray data from our laboratory highlighted upregulation of members of the Wnt pathway in primary prostate cancer stem cells. Therefore, the aim of this study was to determine the consequences of β-catenin downregulation on prostate cancer stem cell fate and to identify whether aberrant Wnt signalling and β-catenin levels and location play a role in prostate tumour initiation, growth and dissemination. Our strategy was to develop and use lentiviral vectors containing short-hairpin RNAs to downregulate β-catenin in prostate cancer cell lines and primary, cultured cells. This work shows that PC-3 prostate cancer cells, infected with β-catenin-shRNA-lentiviruses (PC-3v), displayed a significant downregulation of β-catenin at the protein level. These cells also exhibited reduced growth in vitro as well as a significantly lower invasiveness. In vivo, PC-3v cells showed slower tumour onset in immunocompromised mice. To assess Wnt activity in individual cells the localisation of β-catenin in prostate cancer cell lines and cultured primary cells was determined. Cells were stained for active, dephosphorylated β-catenin and various forms of phosphorylated β-catenin using immunofluorescence. Cultured, primary prostate cells were infected with a GFP containing lentivirus to establish an optimal infection protocol for primary cells. Primary cells were also infected with shRNA-containing viruses and changes in cell morphology were observed. This is the first study to examine the biological consequences of β-catenin downregulation by shRNAs in prostate cancer cell lines and prostate primary cells.