Abstract 2090: MicroRNAs 221/222 and genistein mediated regulation of ARHI tumor suppressor gene in prostate cancer

ARHI, an imprinted tumor suppressor gene, is expressed in normal immortalized prostate epithelial cells, but is dramatically down-regulated in prostate cancer cell lines. Here we investigated the mechanisms of ARHI silencing in prostate cancer through microRNA and genistein (a dietary isoflavone from soy) mediated pathways. First, we evaluated ARHI mRNA levels by real time PCR using Q-PCR slice (48 prostate tumor and normal adjacent tissues) and protein levels by immunostaining of prostate tissue array (36 cancer, 8 matched normal adjacent tissue and 4 bone metastases). Both experiments showed down-regulation of ARHI in prostate cancer tissues compared to adjacent normal tissues. To understand the functional significance of ARHI down-regulation with regard to tumorigenesis, ARHI was over-expressed in prostate cancer PC-3 cells by introduction of ARHI plasmid followed by functional studies. Over-expression of ARHI can inhibit cell proliferation, colony formation, invasion and induced caspase-independent apoptosis. Further studies on new mechanism of ARHI down regulation showed a significant inverse relationship between ARHI and miR-221 & 222 which were up-regulated in cancer cell lines. Transfection of miR-221 & 222 inhibitors into PC-3 cells caused a significant induction of ARHI expression. A direct interaction of miR-221 or 222 with a target site on the 3′UTR of ARHI was confirmed by a dual luciferase pMIR-REPORT assay. Finally, we also found that genistein up-regulated ARHI by down regulating miR-221 & 222 in PC-3 cells. In conclusion, ARHI is a tumor suppressor gene down regulated in prostate cancer, and over-expression of ARHI can inhibit cell proliferation, colony formation and invasion. This study demonstrates for the first time that prostate cancer cells have elevated levels of miR-221 & 222 which bind to the 3′UTR of ARHI contributing to its down regulation. Genistein, a potential non-toxic chemopreventive agent restores expression of ARHI and may be an important dietary therapeutic agent for treating prostate cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2090.