Abstract 3951: The ERG 3′-UTR is a target of miR-145 and expression patterns of ERG isoforms are altered in prostate cancer

Abstract

Abstract Background: Prostate cancer is a leading cause of tumor mortality. In order to identify the underlying mechanisms we have analyzed microRNA (miRNA) expression profiles of primary prostate cancers and non-cancer prostate tissue. Using database analysis, we sought to identify regulatory targets of aberrantly expressed miRNAs. Material and Methods: We performed comparative miRNA expression profiling using deep sequencing of cDNA libraries and microarray analyses. Potential target genes of deregulated miRNAs were identified by database analysis and subsequently validated in vitro using reporter gene constructs. The abundance of ERG as one of the identified target genes was assessed by Western blotting using a self-generated polyclonal antiserum. Results: One of the miRNAs consistently deregulated in primary prostate cancer samples was miR-145 which was down regulated more than 1.5-fold in deep sequencing and 1.44-fold in microarray experiments (p<0.001, ANOVA). Independent target prediction databases (including miRanda, Targetscan and PicTar) indicated that the 3’ untranslated region (3’-UTR) of the ERG gene is a regulative target for miR-145. This prediction could be confirmed using a luciferase reporter gene vector containing the ERG 3’-UTR. Co-expression of the reporter gene construct with miR-145 resulted in a reduction of reporter gene activity while mutation of the miRNA binding site caused a loss of responsiveness to the respective miRNA. We generated a polyclonal antiserum directed against the 100 C-terminal amino acids of the longest ERG isoform and discovered that transient expression of miR-145 reduced the amount of ERG protein by 26% in the HEK293 cell line. Western blots of 26 corresponding pairs of prostate cancer and nonmalignant tissue samples showed, that ERG protein is overexpressed in the majority of cancer samples and that the relative abundance of several identified isoforms of ERG is altered in cancer samples. As expected, miR-145 expression was reduced in 24 of the 26 tumor samples. Conclusion: Our findings demonstrate that the 3’-UTR of ERG is one regulative target of miR-145, which is commonly deregulated in prostate cancer. The ERG gene is commonly overexpressed in prostate cancer and the relative abundance of ERG isoforms is altered in samples of primary prostate cancers. This is the first report to show that ERG is a target of miR-145. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3951. doi:10.1158/1538-7445.AM2011-3951