Investigating the role of the secreted tumour suppressor Dickkopf-3 in stromal-epithelial interactions in prostate cancer

DKK3 is a tumour suppressor gene encoding a secreted protein, Dkk-3, which is found in benign prostate and prostate cancer stroma. Dkk-3 maintains normal prostate epithelial acinar morphogenesis by limiting TGF-β/Smad/matrix metalloproteinase signalling. The role of stromal Dkk-3 was investigated in this thesis. The human prostate stromal cell line, WPMY-1, secreted a high level of Dkk-3 that was further increased by TGF-β. DKK3 gene silencing increased TGF-β-dependent signalling and migration, but did not affect proliferation. WPMY-1 cell co-culture and WPMY-1 cell conditioned media reduced proliferation and rescued acinar morphogenesis of the DKK3-silenced RWPE-1 prostate epithelial cells in a Dkk-3-dependent manner. DKK3-silenced WPMY-1 cell conditioned media increased PC3 prostate cancer cell invasion probably in an MMP2-dependent manner. Control and DKK3-silenced conditioned media were compared using an antibody array, identifying two proteins, TGFBI and ECM-1, that were affected by DKK3 silencing. DKK3 silencing increased TGFBI and reduced ECM-1 in WPMY-1 cell conditioned media, and increased both TGFBI and ECM-1 in RWPE-1 cell conditioned media. Purified recombinant TGFBI, but not ECM1, increased PC3 cell invasion, and purified ECM1, but not TGFBI, increased normal acinar morphogenesis of DKK3-silenced RWPE-1 cells. Immunohistochemical analysis of Dkk-3, TGFBI and ECM-1 in prostate cancer showed significantly lower levels of Dkk-3 in prostate cancer than in benign epithelium and in tumour stroma compared to benign stroma. TGFBI levels were higher in prostate cancer than in benign prostate epithelium and were inversely correlated with Dkk-3 expression. ECM-1 was highly expressed in cancer, and correlated with Dkk-3 and TGFBI levels in low-Gleason-score cancer stroma. Together, these in vitro studies and the immunohistochemical data support a model in which stromal Dkk-3 plays a protective role in prostate cancer, and the downregulation of Dkk-3 leads to an increased expression of TGFBI, which may promote prostate tumour cell invasion.Open Acces