MiRNAs have been shown to regulate numerous cellular functions including metastasis of cancer cells, and are considered promising biomarkers of disease. The major tight junction protein of epithelial cells, claudin 1, is down regulated or absent in human invasive breast cancer and is therefore considered a putative tumor suppressor. However, claudin 1 has now been shown to be highly expressed in the basal-like molecular subtype and in vitro studies revealed that claudin 1 can regulate breast cancer cell motility and proliferation. To gain further understanding of how claudin 1 mediates its activities in breast cancer, we examined changes in global micro RNA (miRNA) gene expression when claudin 1 was over-expressed in the phenotypically basal-like human breast cancer (HBC) cell line MDA-MB231.

Using next generation sequencing, followed by qPCR validation, we identified seven miRNAs (miR-9-5p, miR-9-3p, miR- let-7c, miR-127-3p, miR-99a-5p, miR-129-5p, and miR-146a-5p) whose expression were altered as a consequence of claudin 1 over expression. Most of these miRNAs were down regulated and associated with tumor suppression in a variety of cancers including breast. Additionally, using gene expression profiling analysis of the claudin 1 over expressing clones, we identified a number of down regulated EMT related genes, including PDGFRB and CDH1 (E- cadherin). Expression of these genes is frequently lost during breast tumor progression. Interestingly, SPP1 and SERPINE 1, genes often associated with tumor cell migration and motility, were up regulated in the claudin 1 over expressing clones. Employing the miRNA target prediction program miRWalk, a number of validated miRNA target sites were identified on some of these deregulated genes. A target site for miR-9-5p was identified on the CDH1 sequence, whereas a target site of miR-99-5p was identified on SERPINE 1. Altogether, over 500 target genes have been validated as targets for the deregulated miRNAs.

Overall, we show for the first time that in HBC, claudin 1 can alter the dynamics of a number of miRNAs involved in tumor progression. Moreover, our data provides further evidence to suggest that claudin 1 has the potential to be a useful biomarker that identifies a subset of tumors, within the aggressive but currently poorly characterized basal-like subtype. Our study also suggests that miRNAs may be used in conjunction with claudin 1 to better characterize these cancers. Further studies are now warranted to determine the role of these miRNAs in facilitating the function of claudin 1 in breast cancer.

Citation Format: Anne AA Blanchard, Anna Majer, Sarah Medina, Stephanie A. Booth, Yvonne Myal. Claudin 1 expression levels affect miRNA dynamics in human basal-like breast cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1923.