MECHANISMS OF MIR-3189-3P-MEDIATED ANTITUMORAL ACTIVITY IN BREAST CANCER

Background: Brest cancer is one of the most diffused tumors worldwide. In US, breast cancer represents 30% of all newly diagnosed cancers in female and remain the second leading cause of death, with new 281,550 diagnosed cases in women. Invasive breast cancer can be divided into four subtypes, among which HR+ is the most common and the less aggressive. On the contrary, TNBC is the most aggressive subtype and the one with the worst prognosis. TNBC is characterized by the lack of estrogen receptor, progesterone receptor, and HER2. Consequently, TNBC cannot be treated with the available hormone therapies and receptor targeted treatments. Currently, even if some TNBCs do benefit from immunotherapy and PARP inhibitors, surgery and chemotherapy appear to remain the first-line treatments. The regulatory oncoprotein c-MYC regulate several pathways and is generally overexpressed in many tumors including TNBCs, making it a promising therapeutic target. Nevertheless, c-MYC is currently considered a non-drugable target. MiRNAs are small endogenous ncRNAs, 18-25 bp long, that are able to regulate gene expression and our lab previously characterized miR-3189-3p as a miRNA with a strong anticancer activity against different tumor types, including glioblastoma and melanoma. Because of the role demonstrated in these tumors, we wanted to investigate the effect of miR-3189-3p in breast cancer. Methods: in this work, we used MDA-MB-231 cell line transiently transfected with miR-3189-3p or scramble control. The functional role of the miRNA was assessed by cell proliferation, cell migration and cell invasion assays. The miR-3189-3p gene target 4E-BP1 3’UTR was validated by luciferase assays. MiRNA-mediated c-MYC downregulation was assessed by Real time PCR and Western Blots. The role of 4E-BP1 in the miRNA-mediated effects was assessed through its overexpression or downregulation. The role of miR-3189-3p on the metabolism was assessed using the Seahorse XF96 Flux Analyzer. Results: We demonstrated that overexpression of miR-3189-3p reduces cell proliferation, migration and invasion. Additionally, although MYC 3’UTR is not a predicted target for miR-3189-3p, we discovered that our miRNA is able to downregulate c-MYC protein levels by targeting 4E-BP1 in normal growth conditions and in stress conditions. Indeed, miR-3189-3p has a negative effect on cap-dependent and cap-independent translation. Finally, we found that miR-transfected cells show a different metabolism at their basal state, increasing both oxygen metabolism and glycolysis. Conclusion: Overall, results indicated that miR-3189-3p targets translational regulatory proteins that negatively affect expression of c-MYC, suggesting that miR-3189-3p can be a valuable therapeutic approach against a malignancy with few treatment options.