Bone Abstracts

Wnt proteins and their cognate receptors play a significant role in malignant diseases, in particular in prostate cancer (PCa). We previously showed that WNT5A inhibits PCa cell proliferation and induces apoptosis in vitro, leading to reduced PCa growth in vivo. However, the involved receptors remain unknown. Here, we determine the role of two Wnt receptors (FZD8, RYK) and their influence on the WNT5A-induced effects on PCa cells.

The expression of the Wnt receptors Frizzled (FZD) 8 and RYK was analyzed in three human (PC3, C42B, MDA-PCa-2b) and two mouse (RM1, TRAMP-C2) PCa cell lines. RYK (CT-value 18-23) is higher expressed in all prostate cancer cell lines than FZD8 (CT-value 24-33). Further, FZD8 showed the lowest expression levels in the osteoblastic PCa cell line MDA-PCa-2b (CT-value 33). To determine which receptor mediates the pro-apoptotic and anti-proliferative effects of WNT5A in PCa, we knocked down RYK and FZD8 with specific siRNA in PC3 cells 24 h before the induction of WNT5A overexpression. Knock-down of FZD8 induced a further increase of apoptosis after WNT5A overexpression (2.2-fold, P<0.01). In contrast, knock-down of RYK fully reversed the induction of apoptosis after WNT5A overexpression (P<0.05). Interestingly, the decrease of proliferation after WNT5A overexpression was not reversed by neither knock-down of RYK nor FZD8, suggesting another receptor involved in this process. After knock-down of RYK, WNT5A was still able to suppress proliferation by 28%. Of note, FZD8 knock-down even further decreased (from 27 to 55%) proliferation after WNT5A overexpression. To validate our findings in vivo, a cDNA array containing samples from nine healthy and 39 patients with prostate cancer was evaluated for WNT5A and RYK expression. RYK mRNA expression correlated highly positively with WNT5A expression (r²=0.9309, P<0.001).

These data suggest that RYK, but not FZD8, mediates the pro-apoptotic effects of WNT5A on prostate cancer cells.