Maria Elena Bicchieri

An emerging notion in the breast cancer field is that cancer stem cells (CSCs) are responsible for the degree of aggressiveness of the tumor and disease relapse. Therefore, the development of novel therapeutic strategies that specifically target the CSCs population could be the key to achieve an effective cure for breast cancer. Recent research has highlighted the role of microRNAs as key regulators of SC selfrenewal. The overall goal of this project was to identify key miRNA “modifiers” of breast cancer SC self-renewal with the purpose of identifying those involved in the regulation of stemcell traits and bona fide novel therapeutic targets. We used a lentiviral microRNA library to perform a functional whole-genome screening based on the self-renewal ability of CSCs on a breast cancer cell line. The screening yielded to 20 candidate microRNAs selected as potential modifiers of selfrenewal. A proof-of-principle validation revealed that 6 out of 10 tested cloned, confirmed their effects even when analyzed as single clones, underlining the potentiality of the whole-genome phenotype screening. We focused our attention on the two most promising candidates and, in order to search for the mechanism through which these microRNAs exert their function, we performed an RNA-seq analysis. We revealed that one microRNA in particular was able to control independently different pathway related to self-renewal, migration and proliferation, suggesting that this miRNA could effectively act at multiple levels to silence the selfrenewal potential of cancer stem cells and, likely, inhibit the proliferation and migratory ability of the tumor, too.