Abstract 3055: miR-495 functions as a novel regulator of the estrogen and progesterone receptorsin human breast cancers.

The estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2, also known as ErbB-2 or c-neu) are the major biomarkers that define the classification and treatment options for patients with breast cancers. ER and PR positive breast cancers are more likely to respond to hormonal therapy. HER2 positive breast cancers are more likely to respond to trastuzumab targeted therapy. On the other end, triple negative breast cancers (TNBC) which lack ER and PR and do not overexpress HER2 do not respond well to hormonal therapy or HER2 targeted therapy and are associated with poor prognosis. Once patients with TNBC develop chemoresistance or relapse, there is no additional treatment option available. The key for developing novel therapeutics in TNBC is to elucidate the exact mechanisms by which these receptors undergo silencing, especially ER and PR. MicroRNAs (miRNAs), a class of small noncoding RNAs, have been shown to be important gene regulators in all biological processes including breast carcinogenesis and progression. Through an in silico analysis of the latest miRNAs database with four different miRNA algorithms, we have identified 11 putative miRNAs that target all 3′-untranslated regions (3’-UTRs) of the ER, PR and HER2 genes. miR-495 was one of the putative miRNAs that has been verified to be a significant regulator of ER and PR. Ectopic expression of miR-495 mimics in BT474 and MDA-MB-361 breast cancer cells greatly reduced ER and PR protein expression, but not HER2 expression. Enforced expression of a miR-495 inhibitor or antigomiR-495 in MDA-MB-361 breast cancer cells significantly elevated ER and PR expression. More importantly, miR-495 markedly inhibited the luciferase activities of both ER and PR reporters that contained the wild-type 3’-UTRs of ER and PR. miR-495 could not, however, affect the luciferase activities of the mutant ER and PR reporters that had been deleted the seed sequences in the 3’-UTRs of ER and PR, indicating that ER and PR are direct downstream targets of miR-495. miR-495 expression in primary breast cancers was assessed by in situ hybridization on a tissue microarray that containing 97 cases of randomly selected breast cancers. miR-495 levels were upregulated in thirteen breast cancers (13.4%). Among these 13 cases, 6 were TNBCs (46.2%), 2 were ER/PR low expressing breast cancers and 1 was ER/PR negative HER2 positive breast cancer. Therefore, miR-495 is a novel negative regulator of ER and PR and is upregulated in primary TNBC. Selective inhibition of miR-495 expression in TNBC with miR-495 inhibitors or antigomiR-495 may restore ER and PR expression. Citation Format: Xiao-Feng Le, Hui Ling, Maggie Mao, Xinna Zhang, Shu Zhang, George A. Calin, Yun Wu, Robert C. Bast. miR-495 functions as a novel regulator of the estrogen and progesterone receptorsin human breast cancers. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3055. doi:10.1158/1538-7445.AM2013-3055