Microrna-198: A novel tumor suppressor in prostate cancer.

Abstract

92 Background: microRNAs (miRNAs) are small non-coding RNA molecules which act as repressors of gene function, and have been identified as playing substantial roles in cancer as both tumor suppressors and oncogenes. miR-198 has been reported to be down-regulated in several cancers, with low expression associated with worse overall survival. In addition, miR-198 has demonstrated tumor suppressor effects by altering several hallmarks of cancer. Despite compelling evidence in other cancers, miR-198's role in prostate cancer aggression has not yet been evaluated. Methods: Experiments were conducted by overexpressing miR-198 in three prostate cancer cell lines: DU145, LNCaP and 22RV1. To examine miR-198's effect on hallmarks of cancer in vitro, we used standard protocols to assay proliferation, colony formation, cell cycle profile, migration, and invasive potential. Gene array, qPCR, western blotting, and siRNA knockdown experiments were used to establish miR-198 downstream targets. Results: Overexpression of the candidate tumor suppressor miR-198 diminished proliferation in all prostate cancer cell lines and significantly impaired colony formation in soft agar. Subsequently, miR-198 expression was also demonstrated to reduce growth and tumor formation in vivo using LNCaP xenografts. Gene arrays and in silico target prediction identified several candidate targets, none of which have been previously linked to miR-198. MIB1, an E3 ubiquitin ligase, was the only target we have since identified to be reduced with miR-198 overexpression at both the RNA and protein levels. Knockdown of MIB1 recapitulated miR-198's effects on proliferation and colony formation, and further experiments are underway to demonstrate a direct binding relationship. An additional gene array with MIB1 siRNA will be performed to highlight pathways through which MIB1/miR-198 suppress tumorigenesis. Conclusions: Our evidence supports miR-198 as an important tumor suppressor in prostate cancer, with elevated expression impairing proliferation, colony formation, and in vivo tumor formation. This investigation into miR-198 highlights a potential role as a prostate cancer biomarker, or as a potential target of therapeutics to restore miRNA activity.