CANCER STEM CELLS BIOMARKERS DISCOVERY FOR COLORECTAL CANCER: THE ROLE OF miRNAs

The present doctoral work is divided into two parts, aimed to clarify the role of cancer stem cells (CSCs) in colorectal cancer (CRC), by studying miRNAs. In the first phase of the study, through an in-depth literature revision, a set of miRNAs with a diagnostic and prognostic value in the CRC was selected. The levels of these miRNAs were then analyzed on serum, healthy and cancerous tissue of a restricted group of CRC patients, divided into two groups by presence or absence of metastasis. The same miRNAs were analyzed on cell models: a healthy control (cell line CCD-18Co), and three models of colon cancer: HCT-116, HT-29, and T-84, in standard conditions and enriched in CSCs. Our results indicate that miRNAs can be used as CSC markers of CRC and invite to deepen the roles of miR-21, miR-210, miR-10b, miR-31b, and miR-18a. In parallel, the serum miRNoma of patients at different CRC stages was analyzed, allowing to highlight a possible protective role of mir-486-5p against the progression of CRC. Then its levels were measured in the feces of a different group of patients compared to healthy controls, and a control case meta-analysis was performed from data available on the GEO dataset. The results showed the hyperexpression of miR-486-5p in the feces and serum of the patients with an opposite result in the tissues. To further analyze the behavior of miR-486-5p, it was analyzed in CSCs and non-CSCs cell models. The analysis showed a drastic decrease in the expression of miR-486-5p in the CSCs. Then the effect of forced expression of miR-486-5p or its inhibition was studied on HCT-116 (CSCs and non-CSCs), by studying the stem cell factors, and the four main CSCs-related pathways, showing an inhibitory effect of miR-486-5p on the stem phenotype of these cells. Theses results provide a step forward in understanding the role of miR-486-5p in CRC and CSC and suggest its diagnostic and prognostic power in combination with other CRC biomarkers