miR-432 Induces NRF2 Stabilization by Directly Targeting KEAP1

NF-E2-related factor 2 (NRF2) is a master transcriptional regulator that integrates cellular stress responses and is negatively regulated by Kelch-like ECH-associated protein 1 (KEAP1) at the post-translational level. In human cancers, aberrantly stabilized NRF2, by the mutation of either NRF2 or KEAP1 or by the potential inhibition of autophagy, plays a vital role in tumor growth and chemoresistance through the activation of target genes. MicroRNAs (miRNA) are endogenous small noncoding RNAs that can negatively regulate gene expression by interfering with translation and/or stability of target transcripts. However, miRNA-mediated regulation of the NRF2-KEAP1 pathway under physiological conditions is poorly understood. Here, miR-432-3p positively regulates NRF2 activity through the downregulation of KEAP1 by a direct-binding mechanism to the coding region of KEAP1. Overexpression of miR-432-3p resulted in a decreased sensitivity of esophageal squamous cell carcinoma (ESCC) cells to chemotherapy drugs including cisplatin (CDDP). Conversely, the inhibition of miR-432-3p expression by the CRISPR/Cas9 system resulted in an increased sensitivity of ESCC cells to CDDP. Furthermore, miR-432-3p was overexpressed in primary ESCC tumors (55 of 84, 65.5%) and a negative correlation between the expression level of KEAP1 and miR-432-3p in primary ESCC tumors was observed.