MiR-146a suppresses tumor growth and progression by targeting EGFR pathway and in a p-ERK-dependent manner in castration-resistant prostate cancer

BACKGROUND Castration-resistant prostate cancer (CRPC) is a leading cause of cancer-related deaths in elder men. This disease has limited therapeutic options and poor prognosis as the underlying molecular mechanisms are not clearly understood. Given the emerging roles of microRNA (miRNA) as a key regulator, we postulated that miRNA may play a significant role in CRPC formation. METHODS miR-146a levels in 15 androgen-dependent prostate cancer (ADPC) tissues and 5 CRPC tissues were measured by qRT-PCR. Effects of miR-146a in cell proliferation and migration in vitro and in vivo were evaluated by MTT assay, colony formation assay, transwell migratory assay, and tumor formation assay, respectively. RESULTS we found that miR-146a expression was significantly decreased in CRPC tissues compared to ADPC tissues. Functional analyses showed that ectopic overexpression of miR-146a in androgen-independent cell lines not only inhibited cell growth, colony formation, and migration in vitro, but also reduced tumorigenicity and angiogenesis in vivo. Mechanistic studies revealed that miR-146a repressed the expression of EGFR through binding to its 3'-untranslated region. Also, miR-146a inhibited the expression of MMP2, one of the most important genes in tumor progression. Moreover, downregulation of p-ERK expression significantly abrogated miR-146a-induced prostate cancer cell proliferation. CONCLUSIONS Our findings suggest that ubiquitous loss of miR-146a is a critical mechanism for overexpression of EGFR in CRPC, which is crucial to better understanding the pathogenesis of CRPC. Prostate 72:11711178, 2012. (C) 2011 Wiley Periodicals, Inc.