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Abstract

NF-κB signaling is frequently deregulated in a variety of cancers and is constitutively active in estrogen receptor negative breast cancer subtypes. These molecular subtypes of breast cancer are associated with poor overall survival. During my PhD work, I focused on mechanisms of NF-κB regulation in breast cancer by miRNAs, key regulators of eukaryotic gene expression, which bind their target mRNAs via seed sequences and inhibit gene expression at the post transcriptional level. In a previous study, miR-30c-2-3p was found to be one of the strongest negative regulators of NF-κB signaling in a genome-wide miRNA screen. I uncovered the underlying molecular mechanisms by which miR-30c-2-3p regulates NF-κB signaling and cell cycle progression in breast cancer by combining in vitro data with publically available breast cancer patient datasets. I could show that miR-30c-2-3p directly targets TRADD, an adaptor protein of the TNFR/NF-κB signaling pathway as well as the cell cycle protein, CCNE1. Ectopic expression of miR-30c-2-3p downregulated essential cytokines IL8, IL6 and CXCL1, reduced cell proliferation, and invasion in MDA-MB-231 breast cancer cells. RNAi-induced silencing of TRADD phenocopied the effects on invasion and cytokine expression also observed with miR-30c-2-3p, while inhibition of CCNE1 phenocopied the effects of the miRNA on cell proliferation. The tumor suppressive role of miR-30c-2-3p was confirmed in a cohort of 781 breast tumors with matched mRNA and miRNA expression data where higher expression of miR-30c-2-3p was associated with better survival. Furthermore an anticorrelation with expression of target genes and miR-30c-2-3p was seen in these breast cancer patients. These findings are important in the context of breast cancer where NF-κB signaling has been implicated to play a role in tumor initiation, progression, metastasis and resistance to chemotherapy. During my thesis work I could establish that miR-30c-2-3p negatively regulates both NF-κB signaling and cell cycle progression, that are two important signaling pathways frequently deregulated in breast cancer. As a result, miR-30c-2-3p directly effects several hallmarks of cancer cells, i.e., proliferation, expression of inflammatory cytokines as well as invasion, and can be potentially used for therapeutic intervention in miRNA based cancer therapy.