A new study shows that Dickkopf-3 (DKK3), which is downregulated in prostate cancer cells but has an unknown role in prostate stromal cells, has cell-specific effects on protein expression. DKK3 silencing in prostate stromal cells differentially affects levels of secreted transforming growth factor-β induced (TGFBI) and extracellular matrix protein 1 (ECM1), which seem to have opposing effects in prostate cancer. These observations have implications for developing therapies targeting DKK3 for this disease.

Credit: Pat Morgan/Macmillan Publishers Limited

Immunohistochemistry of benign and malignant prostate tissue showed reduced DKK3 expression in the tumour epithelium and stroma. In vitro, DKK3 silencing in RWPE-1 prostate epithelial and WPMY-1 prostate stromal cells had cell type-specific effects. Silencing of DKK3 in WPMY-1 cells increased autocrine transforming growth factor-β (TGFβ)–mothers against decapentaplegic homolog 3 (SMAD3) signalling. Culture of DKK3-silenced RWPE-1 cells in conditioned media from control WPMY-1 cells increased the number of normal acini formed. Co-culture of DKK3-silenced WPMY-1 cells with RWPE-1 cells increased RWPE-1 proliferation.

Analysis of conditioned media from control and DKK3-silenced WPMY-1 and RWPE-1 cells revealed two proteins that were selected for further study: TGFBI and ECM1. Levels of TGFBI were elevated in media from DKK3-silenced WPMY-1 and RWPE-1 cells. Levels of ECM1 were decreased in conditioned media from DKK3-silenced WPMY-1 cells, but increased in conditioned media from DKK3-silenced RWPE-1 cells.

Acinar morphogenesis was improved in DKK3-silenced RWPE-1 cells on treatment with ECM1. In control RWPE-1 cells, ECM1 had no effect, but TGFBI reduced the numbers of normal acini formed.

PC3 cell invasion was increased when these cells were cultured in conditioned media from DKK3-silenced WPMY-1 cells, which was attenuated by treatment with a matrix metalloproteinase 2 (MMP2) inhibitor. Treatment with TGFBI increased cell invasion and ECM1 had no effect. However, ECM1 inhibited TGFBI-induced invasion.

In patient tumour samples, expression of DKK3 and TGFBI were inversely correlated. Relapse-free survival was positively correlated with DKK3 and ECM1 expression.

“We have found that DKK3 can inhibit TGFβ signalling in nonmalignant prostate cells and prostate cancer cells,” explains Robert Kypta, corresponding author. “The loss of DKK3 can result in changes that can be bad news (TGFBI) or good news (ECM1) for the patient, at least early on in the disease,” he continues. “We are currently using whole-genome approaches to compare the signals that DKK3 regulates in prostate epithelial, stromal, and cancer cells, so that we can identify common and cell type-specific effectors,” he concludes. A DKK3 vaccine for prostate cancer is currently in clinical trials.