Identification of NOD2 as a novel target of RNA-binding protein HuR: evidence from NADPH oxidase-mediated HuR signaling in diabetic nephropathy.

Although our recent studies have demonstrated that NOD2 is one of the critical components of a signal transduction pathway that links renal injury to inflammation in diabetic nephropathy (DN), the regulatory mechanisms for NOD2 expression under hyperglycemia have not yet been elucidated. Considering that NOD2 mRNA from different species bears a long 3'-UTR with various AU-rich elements, the present study was designed to investigate the potential contribution of the RNA-binding protein human antigen R (HuR) on the posttranscriptional regulation of NOD2 expression. In this study, we first found upregulation of HuR in the kidney from DN subjects, which was correlated with proteinuria, indicating a role for HuR in the pathogenesis of DN. In vitro, high glucose (HG) induced a distinct increase in cytoplasmic HuR in rat glomerular mesangial cells. By RNA EMSA, we found that HuR bound to the 3'-UTR of NOD2, and HuR silencing reduced HG-induced NOD2 expression and mRNA stability. Mechanistically, we further found that NADPH oxidase-mediated redox signaling contributed to the expression and translocation of HuR and NOD2 mRNA stability. Finally, we evaluated the role of HuR showing that in vivo gene silencing of HuR by intrarenal lentiviral gene delivery ameliorated renal injury as well as reducing NOD2 expression in diabetic rats. Collectively, our studies demonstrate that HuR acts as a key posttranscriptional regulator of NOD2 expression, suggesting that targeting of HuR-NOD2 signaling might be crucial for the treatment of DN.