Non-Canonical Wnt Receptor ROR2 Suppresses Prostate Cancer Metastasis

Prostate cancer (PCa) ranks the 5th most common cancer in the world. Receptor tyrosine-kinase like orphan receptor 2 (ROR2) is a regulator of non-canonical Wnt signaling. Expression of mRNA and protein of ROR2 was analyzed in clinical samples with qRT-PCR and IHC staining. Tranwell assays and wound healing assay were performed to determine the roles of ROR2 on migration and invasion of PCa cells. Micro-Western Array MWA platform was introduced to determine downstream signaling network regulated by ROR2. Analysis of ROR2 gene expression level in a total of 249 normal prostate tissues, benign prostate hyperplasia BPH, and prostate tumors revealed that ROR2 mRNA level is the lowest in metastatic PCa. IHC staining analysis of 48 PCa tissues indicated that ROR2 expression inversely correlated to aggressiveness of PCa. PCa cell lines express higher ROR2 lower ROR2 and higher Wnt5a than normal non-malignant prostate epithelial cell line. Over-expression of ROR2 in PCa cells significantly elevated E-cadherin, but suppressed vimentin, MMP-9, and nuclear β-catenin proteins. Elevation of ROR2 decreased the cell migration and invasion ability of PCa cells as determined by transwell and wound healing assays. MWA revealed that over-expression of ROR2 augmented protein expression of PIAS3, but diminished the abundance of Wnt5a, Stat3, vimentin, c-Myc, Dvl-2 in PCa cells. Wnt5a treatment suppressed Wnt signaling in non-malignant prostate cells as determined by TCF-LEF transcriptional activity assay, while knockdown of ROR2 in these prostate cells blocked the suppressive effect of Wnt5a. Elevation of ROR2 suppressed Wnt5a level via down-regulation of SP1, c-fos and NF-κB p65, thus impeding WNT5A transcriptional activity. Knockdown of PIAS3 or treatment with EGF in PC-3 cells partially restored cell migration and elevated protein expression of MMP-9. ROR2 is a potential therapeutic target for advanced PCa.