MicroRNA-320 suppresses the stem cell-like characteristics of prostate cancer cells by downregulating the Wnt/beta-catenin signaling pathway I-Shan Hsieh1, Kung-Chao Chang2, Yao-Tsung Tsai1, Jhen-Yu Ke3, Pei-Jung Lu4, Kuen-Haur Lee5, Shauh-Der Yeh6, Tse-Ming Hong4, and Yuh-Ling Chen1,3,*

Prostate cancer (PCa) is a leading cause of mortality and morbidity in men worldwide, and emerging evidence suggests that the CD44high prostate tumor-initiating cells (TICs) are associated with its poor prognosis. Although microRNAs are frequently dysregulated in human cancers, the influence of microRNAs on PCa malignancy and whether targeting TIC-associated microRNAs inhibit PCa progression remain unclear. In this study, we found that miR-320 is significantly downregulated in PCa. Overexpression of miR-320 in PCa cells decreases PCa tumorigenesis in vitro and in vivo. Global gene expression profiling of miR-320-overexpressing PCa cells reveals that downstream target genes of Wnt/β-catenin pathway and cancer stem cell markers are significantly decreased. MicroRNA-320 inhibits β-catenin expression by targeting the 3′-untranslated region of β-catenin mRNA. The reduction of miR-320 associated with increased β-catenin was also found in CD44high subpopulation of prostate cancer cells and clinical PCa specimens. Interestingly, knockdown of miR-320 significantly increases the cancer stem-like properties, such as tumorsphere formation, chemoresistance and tumorigenic abilities, although enriching the population of stem-like TICs among PCa cells. Furthermore, increased miR-320 expression in prostate stem-like TICs significantly suppresses stem cell-like properties of PCa cells. These results support that miR-320 is a key negative regulator in prostate TICs, and suggest developing miR-320 as a novel therapeutic agent may offer benefits for PCa treatment.