Phd in LIFE SCIENCE

Thesis title: Role of microRNAs in Proliferation, Senescence and Cancer: Implications for RNA-aided therapy

MicroRNAs (miRNAs) are short non-coding RNAs involved in the regulation of around 60% of genes affecting various cellular and biological processes, including immunological regulation, metabolic control, cell cycle, and stem cell development. Different diseases or particular physiological conditions have an altered expression of miRNAs; some of them are overexpressed whereas others are underexpressed in comparison with the miRNA patterns in homeostasis. Additionally, miRNAs may play both oncogenic and tumor-suppressive roles. The goal of the fascinating field of cancer treatment known as immunotherapy is to use body's own immune system to discover and eliminate tumor cells. Immune-Checkpoint (IC) inhibition, for instance, is a novel strategy that is rapidly gaining traction in clinical and preclinical investigations as an adjuvant and alternative to established cancer therapies. Nevertheless, despite promising improvements, relapse occurs in many cases and after an initial response, acquired resistance arises in most patients. Furthermore, the role of adipose-derived mesenchymal stem cells (ASCs) as potential therapeutic agents in regenerative medicine and specifically in cancer is largely unexplored. The time-consuming operations necessary to use them in clinical applications make ASCs senescent and less proliferative, reducing their therapeutic usefulness. Several ASC enhancement strategies have been proposed to help these cells preserve their important characteristics, and the use of the miRNAs is among them. Indeed, an ever-increasing evidence suggest that, in almost all human health disorders, miRNAs could be useful as modulators of drug resistance and/or therapeutics for medical intervention. This dissertation aimed to examine functions of specific miRNAs in various biological systems, tumoral or not. The final purpose is to understand if it is possible to use miRNAs to overcome therapeutic problems and increase treatment efficiency. Specifically, in an EBV-associated lymphomas system, we found that the virus-encoded protein, EBNA2, upregulates a miRNA, miR-24-3p, that targets a stimulatory IC, ICOSL, reducing its expression. By using a miRNA inhibitor, my data show that the levels of the ICOSL can be restored in lymphoma cells. In ovarian cancer (OC) model, we found that expression of the inhibitory IC, PD-L1, and, miR-200c are inversely correlated. Through upregulation of this miRNA, we could downregulate not only PD-L1 but also two other oncogenes, namely, β-catenin and c-myc, eventually increasing the therapeutic efficacy of PARP inhibitors and irradiation. In a type of OC expressing high levels of miR-200c-3p, in silico analyses revealed that this miRNA is inversely correlated with PPP3CC expression. The bioinformatics analysis was experimentally validated and we found that PPP3CC is a tumor suppressor. The inhibition of miR-200c-3p led to PPP3CC increase and consequently, to a decreased proliferation and metastases and increased apoptosis of OC cells. Finally, in a non-tumor system, miR-200c-3p was used to modulate ASCs stemness. The data show that this miRNA regulates stemness, senescence and immunomodulatory properties of these cells. Taken together, these findings provide insights how miRNAs could be employed to regulate ICs, hold in check the adverse effects of conventional chemotherapy and increase its efficiency by employing novel miRNA based combinatorial therapeutic approaches.