Abstract 3171: Hyperactive MAPK dysregulation of microRNAs contributes to the ER-negative phenotype in breast cancer

Abstract We have previously shown that hyperactive MAPK (hMAPK) signaling in breast cancer results in repression of estrogen receptor (ER) expression and regulates genes thought to contribute to the aggressive phenotypes displayed by ER- breast cancers. An hMAPK gene expression signature previously described by our lab is strongly represented in many ER- breast cancers, and has been shown to be present in a subset of ER+ tumors which have low levels of ER mRNA. In investigating the mechanisms underlying this hMAPK mediated repression of ER, we found that ER mRNA was rapidly destabilized by hMAPK suggesting that microRNAs might play an important role in the hMAPK downregulation of ER and contribution to breast cancer aggression. Using a breast cancer cell-line model of hMAPK signaling, we identified a broad signature of 128 microRNAs that complements our previous gene expression signature. We analyzed microRNA expression data from two independent breast tumor datasets in which we were able to also characterize tumors according to representation of the hMAPK mRNA signature, and were able to further truncate our hMAPK microRNA signature into a more compact and biologically relevant signature. We show that this hMAPK microRNA signature associates strongly with ER-negative status and increased tumor grade and importantly, is significantly associated with increased recurrence and reduced overal survival, and at 5 year timepoints serves as a better prognostic indicator for recurrence or survival than ER status. Several microRNAs that we identified as upregulated in the hMAPK microRNA signature have been experimentally validated to target the 3′UTR of ER and contribute to the destabilization of the ER transcript, including miR-221/222 and miR-22. We further investigated the role that the microRNAs within this hMAPK microRNA signature occupy in facilitating down-regulation of ER and progression toward more aggressive breast cancer. Use of a reporter construct containing elements of the 3′UTR of the estrogen receptor with binding sites for several of these microRNAs suggested that hMAPK signaling utilizes microRNA regulatory pathways to contribute to the downregulation of ER. Using our cell line model of hMAPK signaling in breast cancer we employed a variety of techniques, including microRNA mimics, antagomirs, and pathway modeling to interrogate potential mechanisms by which these hMAPK microRNAs act to deregulate ER and other important genes and pathways involved in breast cancer. In summary, we demonstrate that, in addition to established mechanisms hMAPK signaling in breast cancer contributes to ER-negativity and tumor aggressiveness by deregulation of microRNAs and their associated pathways. These data support the importance of hMAPK microRNAs as important players in breast cancer pathogenesis, and suggest that microRNAs or microRNA pathways may offer a unique therapeutic window for breast cancer. 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 3171. doi:1538-7445.AM2012-3171