Underlying the exosomal export of a specific microRNA, miR-503, and its implication in resistance to chemotherapy

The communication between cancer cells and their microenvironment is an essential aspect of cancerology. Therefore, understanding how the environment could affect the tumor cells behavior is critical for the development of new anti-cancer therapies. In this study, we focus on the communication between the endothelium and breast cancer cells during neoadjuvant chemotherapy by extracellular vesicles (EVs). Extracellular vesicles (EV) are small vesicles released by cells in the extracellular milieu that mediate cell-cell communication. In the context of cancer, EVs are potentially secreted by all cell types that compose in tumor microenvironment.
Previously, they we identified miR-503 which exhibited downregulated or upregulated levels in exosomes released from endothelial cells under tumor environment or neoadjuvant chemotherapy, respectively. Moreover, this miRNA could affect the proliferative and invasive capacity of the tumor cells. In this study, they highlighted an exosome-dependent transfer of microRNAs from endothelial to tumor cells. This suggests that there might be a specific mechanism that sorts this microRNA into extracellular vesicles.EVs.
The aim of this study is to identify the proteins involved in the export of miR-503, its impact on tumor cells behavior and how epirubicin, a chimitotherapeutic chemiotherapeutic agent, could affect it.
In order to identify determine the partners of miR-503, we pulled-down a biotinylated form of thisthe microRNA and we determined the proteins attached to miR-503 using mass spectrometry. Five proteins, named miR-EXO proteins, were identified: ANXA2, hnRNPA2B1, VIM, TSP-1 and FN1.Then, we investigated which miR-EXO proteins were involved in the export of miR-503. We showed that the treatment with epirubicin induce the release of hnRNPA2B1 from the complex and, thus, allow the sorting of the microRNA. We also showed that the chemotherapy affects the localization of hnRNPA2B1. In fact, epirubicin treatment induce a switch of hnRNPA2B1 from the cytoplasm to the nucleus. Furthermore, the miR-EXO proteins were knockdowned in endothelial cells and we determined the direct impact on breast cancer cells. The hnRNPA2B1 silencing decreases the proliferation of cancer cells. According to these results, hnRNPA2B1 could inhibit the export of miR-503 into extracellular vesicles and the treatment disrupts the complex by removing hnRNPA2B1. Future work will attempt to evaluate the impact of miR-503 export during tumor growth and the clinical relevance of our findings and the implication for breast cancer patients.