Abstract 2292: Tumor suppressive miR-124 targets androgen receptor and inhibits proliferation of prostate cancer cells

Abstract

Abstract Recent studies have revealed that miR-124 functions as a tumor suppressor and is downregulated in several types of human cancer. Until now, however, whether miR-124 is involved in prostate cancer (CaP) is totally unknown. In order to explore the role of miR-124 in CaP, we detected the expression level of miR-124 in prostate cell lines and clinical prostatic tissues using qPCR, and observed a reduced expression of miR-124 in all malignant cell lines tested and in a majority of clinical CaP samples examined, compared to that in the benign cell lines and in benign prostatic hyperplasia (BPH), suggesting that miR-124 is a putative tumor suppressor gene. Since the 3′UTR of androgen receptor (AR) mRNA contains a broadly conserved miR-124-binding site, experiments were performed to validate miR-124-mediated regulation of AR. We found that transfection of synthetic miR-124 mimic (miR-124m) downregulated the AR protein level and its downsteam effectors PSA and miR-125b. To verify that the miR-124 binding site is responsible for regulation by miR-124, the AR 3β UTR was cloned into the pRIM Reporter-luciferase vector, and cotransfected with miR-124m into CaP cells. We observed that transfection of miR-124m resulted in 40% reduction of luciferase activity, indicating a direct interaction between miR-124 and AR mRNA. We then examined whether clinical CaP samples having low level of miR-124 overexpress the AR using IHC analysis, and found a reverse correlation between miR-124 and AR expression levels in 7 of 8 CaP samples. These data suggest that miR-124 targets the AR and down-regulation of miR-124 results in increased expression of the AR in CaP cells. In addition, we tested whether miR-124 inhibits the growth of CaP cells, and found that treatment with miR-124m induced significant inhibition of cell proliferation compared to treatment with miR-NC control. We also evaluated the effect of miR-124 on tumorigenesis of 22Rv1 CaP cells that were transiently transfected with miR-124m. We observed that tumors derived from miR-124-transfected 22Rv1 cells grew substantially slowly, when compared to miR-NC tumors. Taken together, our data suggest that miR-124 is a potential tumor suppressor gene in CaP, and restoration of miR-124 expression may represent a novel therapeutic strategy in CaP therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2292. doi:1538-7445.AM2012-2292