MiR-139-5p reverses CD44+/CD133+-associated multidrug resistance by downregulating NOTCH1 in colorectal carcinoma cells

MiRNAs may promote or inhibit tumor recurrence and drug resistance. MiR-139-5p is reportedly downregulated in colorectal cancer patient samples, but it is unknown whether and how miR-139-5p regulates drug resistance. Cancer stem cells (CSCs) are postulated to be important promoters of multiple drug resistance (MDR). In this study, we established a MDR cell model which strongly expressed the CSC-associated biomarkers CD44 and CD133. MiR-139-5p expression was reduced in MDR cell lines, while overexpression of miR-139-5p reversed CD44+/CD133+-associated MDR. We also identified NOTCH1, an important protein for stem cell maintenance and function, as a direct target of miR-139-5p, both in vitro and in a knockout mouse model. Notch1 expression was upregulated in tumor samples and inversely correlated with expression of miR-139-5p. Silencing NOTCH1 exerted an effect similar to overexpression of miR-139-5p by inhibiting the CD44+ and CD133+ population and reversing the drug-resistant phenotype. In conclusion, miR-139-5p downregulated NOTCH1 signaling to reverse CD44+/CD133+-associated MDR in colorectal cancer cells. Given this insight into the miRNA regulation of MDR, miR-139-5p could be a promising therapeutic target for colorectal cancer therapy.