ARHI is an imprinted tumor suppressor gene and is downregulated in various malignancies. However, ARHI expression, function, and mechanisms of action in prostate cancer have not been reported. Here, we report that ARHI mRNA and protein levels were downregulated in prostate cancer tissues compared with adjacent normal tissues. Overexpression of ARHI inhibited cell proliferation, colony formation, invasion, and induced apoptosis. Further studies on a new mechanism of ARHI downregulation showed a significant inverse relationship between ARHI and miR-221 and 222, which were upregulated in prostate cancer cell lines. Transfection of miR-221 and 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 upregulates ARHI by downregulating miR-221 and 222 in PC-3 cells. In conclusion, ARHI is a tumor suppressor gene downregulated in prostate cancer, and overexpression of ARHI can inhibit cell proliferation, colony formation, and invasion. This study demonstrates for the first time that prostate cancer cells have decreased level of ARHI which could be caused by direct targeting of 3'UTR of ARHI by miR221/222. Genistein, a potential nontoxic chemopreventive agent, restores expression of ARHI and may be an important dietary therapeutic agent for treating prostate cancer.
©2010 AACR