MicroRNA-122 targets δ-catenin to suppress the tumorigenic potential of prostate cancer cells.

δ-Catenin is expressed abundantly in various human cancers, including prostate, brain, breast, and lung carcinomas, and is recognized as an oncogene that promotes cancer cell growth and tumorigenesis. Although several transcriptional and post-translational pathways for δ-catenin regulation have been identified in cancer cells, the potential effects of microRNA-mediated regulation remain elusive. Here, we used a δ-catenin 3'-UTR luciferase reporter assay to identify regulatory microRNAs. Subsequent bioinformatics analyses and molecular studies revealed that overexpression of miR-122 downregulated δ-catenin expression significantly via targeted binding to a seed sequence in the 3'-UTR region of δ-catenin, and suppressed the invasion, migration, and proliferation of prostate cancer cells in vitro. In a TRAMP-C2 mouse syngeneic prostate tumor model, stable expression of miR-122 decreased both δ-catenin expression and tumor growth. Mechanistically, overexpression of miR-122 inhibited the expression of δ-catenin-mediated downstream factors significantly in prostate cancer cells, including c-myc and cyclin D1. In cells overexpressing miR-122, there was no additive or synergistic effect of siRNA-mediated knockdown of δ-catenin on cell invasiveness, and overexpression of miR-122 alone had a more pronounced suppressive effect on cell invasion than knockdown of δ-catenin alone. These results suggest that miR-122 acts as tumor suppressor in prostate cancer, mainly by downregulating δ-catenin expression, but also by targeting other factors. Indeed, subsequent experiments showed that overexpression of miR-122 reduced the levels of the mRNAs encoding myc, snail, and VEGF in prostate cancer cells. Overall, our findings demonstrate that targeting of δ-catenin by miR-122 represses the motility and tumorigenesis of prostate cancer cells, indicating a tumor suppressive effect of this miRNA in prostate cancer.