A novel regulatory axis of MSI2-AGO2/miR-30a-3p-CGRRF1 drives cancer chemoresistance by upregulating the KRAS/ERK pathway.

The KRAS/ERK pathway is crucial in cancer progression and chemotherapy resistance, yet its upstream regulatory mechanism remains elusive. We identified MSI2 as a new promoter of chemotherapy resistance in cancers. MSI2 directly binds to a specific class of mature miRNAs by recognizing the 'UAG' motif and interacts with the essential effector AGO2, highlighting MSI2 as a novel regulatory factor within the miRNA pathway. Specifically, MSI2 recruits UAG-miRNA miR-30a-3p to facilitate its loading onto AGO2, efficiently inhibiting the expression of CGRRF1. Further analysis reveals that CGRRF1 functions as a new ubiquitin E3 ligase for KRAS, mediating the ubiquitination and proteasome degradation of KRAS. Consequently, a novel regulatory axis involving MSI2-AGO2/miR-30a-3p-CGRRF1 positively regulates the KRAS/ERK pathway. Remarkably, platinum-based chemotherapy drugs significantly enhance the levels of phosphorylated ERK1/2 (p-ERK1/2) in cancer cells, and the EGFR inhibitor Gefitinib also increases p-ERK1/2 levels in Gefitinib-resistant cancer cells. Combining small-molecule inhibitors targeting MSI2, such as Ro 08-2750, efficiently alleviated chemoresistance in tumor cells exposed to Platinum and Gefitinib. These findings suggest that MSI2 could be a novel therapeutic target for developing strategies to counteract cancer resistance to treatment.