Abstract 2295: miR-342 modulates ID4 expression in breast cancer

Abstract

Abstract Integration of the results from a transcriptome profiling of coding and non coding RNAs (miRNA) on familial (BRCA1- or BRCA2-mutated, or BRCAX) and sporadic breast cancers identified possible miRNA-dependent mechanisms associated with the different BRCA groups analyzed. Among the miRNA/target gene pairs found, we focused on that composed by miR-342 and ID4 gene. ID4 is a negative regulator of B-HLH transcription factors frequently expressed in cancer and miR-342 is deregulated in many cancers, including breast. All of our groups had relatively high expression of miR-342 and low expression of ID4, except for one subgroup of BRCAX cases (named BRCAXa, comprising cases with clinical characteristics similar to BRCA1) that had reciprocal expression patterns of this pair. We evaluated the expression levels of the putative pair in different breast cancer cell lines and found that ID4 gene expression was on average higher in estrogen receptor negative (ER-) cells; on the contrary, miR-342 had higher expression in estrogen receptor positive (ER+) cells. The direct binding of miR-342 to the 3′ UTR of ID4 and its potential inhibitory effect was functionally validated using a reporter luciferase system. Reciprocal expression of miR-342 and ID4 was then confirmed in vitro in the triple negative MDA-MB-231 cell line, that, similarly to the BRCAXa subgroup, had low expression of miR-342 and where miR-342 introduction reduced ID4 protein levels. ID4 is a negative regulator of BRCA1 and modulation of its expression in breast cancer is inversely related with that of BRCA1. Being ID4 a target of miR-342, we hypothesized a relationship between these two genes and the miRNA and that low levels of miR-342 could provide a mechanism for increasing ID4 that negatively regulates BRCA1 expression. Analysis of their levels in our cases supported this thesis. In the BRCAXa class lower levels of miR-342 were associated with reduced expression of BRCA1. We hypothesized that down-regulation of ID4 through miR-342 could provide a mechanism for increasing BRCA1 expression. We tested this hypothesis in the MDA-MB-231 cells, where we found miR-342 mediated downregulation of ID4, but no increase in the expression of BRCA1 at either gene or protein levels. These results showed that ID4 is a validated target of miR342 and propose a role of miR-342 in familial breast cancer where it could impair expression of ID4. Targets of ID4 different than BRCA1 can be altered in the BRCAXa subgroup. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2295. doi:1538-7445.AM2012-2295