SWAP70, actin-binding protein, function as an oncogene targeting tumor-suppressive miR-145 in prostate cancer.

BACKGROUND: MiR-145 is down-regulated in various human cancers. We previously demonstrated that some actin-binding proteins were targeted by several microRNAs (miRNAs), including miR-145, in bladder and prostate cancer (CaP). The aim of this study is to determine a novel oncogenic gene targeted by miR-145 by focusing on actin-binding proteins in CaP.

METHODS: We focused on the SWAP switching B-cell complex 70 kDa subunit (SWAP70), which is an F-actin binding protein involved in activating B-cell transformation. A luciferase reporter assay was used to identify the actual binding sites between miR-145 and SWAP70 mRNA. Cell viability was evaluated by cell proliferation, wound healing, and matrigel invasion assays in si-SWAP70 transfectants. A total of 75 clinical prostate specimens were subjected to immunohistochemistry of SWAP70.

RESULTS: Molecular target searches of this miRNA and the luciferase reporter assay showed that SWAP70 was directly regulated by miR-145. Silencing of SWAP70 studies demonstrated significant inhibitions of cell migration and invasion in CaP cell lines. The SWAP70 positive-staining was significantly higher in percentage in the CaP than in benign prostate hyperplasia tissue.

CONCLUSIONS: Down-regulation of miR-145 was a frequent event in CaP, and it may have a tumor suppressive function. SWAP70 may be a target of miR-145, and it might have a potential oncogenic function. The novel molecular networks though which miR-145 acts, may provide new insights into the underlying molecular mechanisms of CaP.