KSRP suppresses cell invasion and metastasis through miR-23a-mediated EGR3 mRNA degradation in non-small cell lung cancer.

KH-type splicing regulatory protein (KSRP) is a single-strand RNA binding protein which regulates mRNA stability either by binding to AU-rich elements (AREs) of mRNA 3'UTR or by facilitating miRNA biogenesis to target mRNA. Unlike its well-characterized function at the molecular level in maintaining RNA homeostasis, the role of KSRP in cancer progression remains largely unknown. Here we investigate the role of KSRP in non-small cell lung cancer (NSCLC). We first examined KSRP expression by immunohistochemistry in a cohort containing 196 NSCLC patients and observed a strong positive correlation between KSRP expression and survival of NSCLC patients. Multivariate analysis further identified KSRP as an independent prognostic factor. Manipulating KSRP expression significantly affected in vitro cell mobility and in vivo metastatic ability of NSCLC cells. Microarray analysis identified an ARE-containing gene, EGR3, as a downstream effector of KSRP in NSCLC. Interestingly, we found that KSRP decreased EGR3 mRNA stability in an ARE-independent manner. By screening KSRP-regulated miRNAs in NSCLC cells, we further found that miR-23a directly binds to EGR3 3'UTR, reducing EGR3 expression and thereby inhibiting NSCLC cell mobility. Our findings implicate a targetable KSRP/miR-23a/EGR3 signaling axis in advanced tumor phenotypes.