Yagüe, ErnestoKumar, UttomUttomKumar2022-11-252022-10-312022-11-252021-06almahttp://hdl.handle.net/10044/1/100582Breast cancer is a heterogenous disease with some subtypes posing a significant treatment challenge due to lack of targeted therapies and chemoresistance, particularly triple-negative metaplastic breast carcinoma (MBC). Here, I report a novel triple-negative MBC derived cell line, BAS, which showed a molecular and phenotypic diversity to the only existing metaplastic HS578T cells. To gain insight behind the chemotherapeutic resistance, I generated doxorubicin (HS-DOX, BAS-DOX) and paclitaxel (HS-TX, BAS-TX) resistant derivatives of both HS578T and BAS cells. Drug sensitivity assays indicated that doxorubicin- and paclitaxel-resistant cells showed a truly multidrug resistant (MDR) phenotype. Both BAS-DOX and BAS-TX showed significant up-regulation of transcription factor FOXC1 and its experimental down-regulation re-sensitized cells to doxorubicin and paclitaxel. Moreover, experimental modulation of FOXC1 expression in MCF-7 and MDA-MB-231 cells corroborated its role in MDR. Genome-wide expression analyses identified up-regulation of TGFB2 in both BAS-DOX and BAS-TX cells. Pharmacological inhibition of the TGF-β pathway reduced FOXC1 expression and increased drug sensitivity in both BAS-DOX and BAS-TX cells. MicroRNA (miR) expression profiling identified higher endogenous miR-495-3p levels in parental BAS cells that were significantly down-regulated in both BAS MDR cells. Over-expression of miR-495-3p in BAS MDR cells led to re-sensitization to doxorubicin and paclitaxel and down-regulation of TGFB2 and FOXC1, whereas miR-495-3p inhibition in parental BAS cells led to opposite effects. Moreover, miR expression analysis in breast cancer clinical samples identified a miR signature discriminating MBC from invasive ductal carcinoma (IDC). Additionally, transcription factor FOXA1 also contributes to the MDR in breast cancer cells. Experimental down-regulation of FOXA1 in MCF-7 and T47D cells increased doxorubicin and paclitaxel sensitivity, whereas its over-expression in MDA-MB-231 cells increased resistance to both drugs. Overall, the present study reveals some novel regulators of chemoresistance in breast cancer cells and thus opens the exploration of new therapeutic strategies.Creative Commons Attribution NonCommercial NoDerivatives LicenceThesis or dissertationhttps://doi.org/10.25560/100582