Abstract 5207: miR-491 and miR-218: Two possible tools to reduce FOXP3 expression in breast carcinomas

Abstract

Abstract The Forkhead box P3 (FOXP3) gene is a member of the forkhead/winged-helix family of transcription factors implicated in the regulation of immune system development and function. However, FOXP3 is also expressed in human epithelial cancers, where it has been reported to be associated with poor prognosis and in particular with metastasis. Aim of our work is to identify microRNAs able to regulate FOXP3 expression in breast tumors. To discover microRNAs able to regulate FOXP3 expression in breast cancer cells, an in silico analysis has been performed. Among microRNAs harboring FOXP3 seed regions, we focused our attention on miR-218 and miR-491, described to have oncosuppressive properties. Indeed, it has been reported that miR-218 expression stimulates activation of tumor suppressor genes and miR-491 expression inversely correlates with migratory potential in HCC cell lines and in vivo with metastatic potential. We therefore evaluated the ability of these microRNAs to act as oncosuppressors by targeting FOXP3 in a breast cancer model. After transient co-transfection either of miR-218 or miR-491 with FOXP3 in MDA-MB-231 cells, a significant decrease in FOXP3 expression at protein level by WB was found. To perform functional studies both in vitro and in vivo, we generated a breast cancer cell model by stable transfection of MDA-MB-231 with inducible Tet-off plasmid encoding for FOXP3 encompassing 3′UTR region, thus maintaining microRNA-mediated regulation. We demonstrated that FOXP3 expressing clones display an increased migration capacity as compared with their respective non-induced cells. Also in these stable clones a reduction of FOXP3 expression after transfection of miR-491 and miR-218 has been demonstrated by WB. Moreover, FOXP3 was confirmed to be a direct target of both microRNAs by luciferase reporter assay. We also found an inverse correlation between miR-491 levels and FOXP3 expression in human breast carcinoma specimens. Overall, these preliminary results demonstrate that microRNAs can regulate FOXP3 expression, and encourage to further investigate the biological and functional consequences of this targeting, and to exploit microRNAs as a potential therapeutic tool for FOXP3 expressing breast carcinomas. Citation Format: Martina Di Modica, Tiziana Triulzi, Viola Regondi, Marilena V. Iorio, Andrea Balsari, Elda Tagliabue, Patrizia Casalini. miR-491 and miR-218: Two possible tools to reduce FOXP3 expression in breast carcinomas. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5207. doi:10.1158/1538-7445.AM2014-5207