284 MIR-145 FUNCTIONS AS TUMOR SUPPRESSOR AND REGULATES ACTIN-BINDING PROTEINS (FSCN1 AND SWAP70) IN PROSTATE CANCER

Abstract

INTRODUCTION AND OBJECTIVES: MicroRNAs are small non-coding RNAs that negatively regulate protein-coding genes involved in the development of various malignancies. Down-regulation of miR-145 has been reported in many types of human cancer, including prostate cancer (PCa). In the last meeting, we demonstrated that miR-145 was the most down-regulated microRNA in bladder cancer and had a tumor suppressive function through targeting an actin-binding protein, FSCN1. Increasing evidence indicates that the miR-145 functions as a tumor suppressive miRNA and causes cell viability inhibitions in human cancer cells. However, there is limited knowledge of its targets in PCa. The aim of this study is to identify target genes of miR-145 based on gene expression analysis of miR-145-transfected PCa cells. METHODS: For genome-wide screening for target genes silenced by miR-145 in PCa, we performed oligo-microarray analysis of miR-145 transfectants (PC3, DU145) compared to miR-negative control transfectants. We employed web-based software in order to search for putative target genes of miR-145, and we focused on fascin homolog 1 (FSCN1) and SWAP switching B-cell complex 70kDa subunit (SWAP70), which is also known as F-actin binding protein involved in activating B cell transformation. The luciferase reporter assay was used to confirm the actual binding sites between miR-145 and FSCN1/ SWAP70 mRNA. Cell viability was evaluated by cell proliferation, wound healing, and matrigel invasion assays in si-FSCN1 and siSWAP70 transfectants. A total of 75 clinical prostate specimens were subjected to immunohistochemistry of SWAP70. RESULTS: The mRNA and protein expression of FSCN1 and SWAP70 were markedly repressed in the miR-145 transfectants. The luciferase reporter assay demonstrated that miR-145 was directly bound to the specific sites of FSCN1 and SWAP70 mRNA. Significant inhibitions of cell proliferation, invasion and migration were observed in the si-FSCN1 and the si-SWAP70 transfectants (p 0.0001) as well as the miR-145 transfectants (p 0.0001). The immunohistochemical score of SWAP70 in PCa specimens was significantly higher than that in benign prostate hyperplasia specimens (p 0.0169). CONCLUSIONS: Our data suggest that tumor suppressive miR-145 directory regulates both FSCN1 and SWAP70 that might have oncogenic functions associated with actin-promoting cell motility and malignant transformation in PCa. These pathways may play critical roles in PCa development and serve as a novel therapeutic target in PCa.