Extracellular high mobility group box 1 (HMGB1) has been demonstrated to function as a proinflammatory cytokine and induces neuronal injury in response to various pathological stimuli in central nervous system (CNS). However, the regulatory factor involved in HMGB1-mediated inflammatory signaling is largely unclear. Regulatory RNase 1 (Regnase-1) is a potent anti-inflammation enzyme that can degrade a set of mRNAs encoding proinflammatory cytokines. The present study aims to determine the role of Regnase-1 in the regulation of HMGB1-mediated inflammatory injury in CNS. Cultured microglia and rat brain were treated with recombinant HMGB1 to examine the induction of Regnase-1 expression. Moreover, the role of Regnase-1 in modulating the expression of inflammatory cytokines and neuronal injury was then investigated in microglia by specific siRNA knockdown upon HMGB1 treatment. Results showed that HMGB1 could significantly induce the de novo synthesis of Regnase-1 in cultured microglia. Consistently, Regnase-1 was elevated and found to be co-localized with microglia marker in the brain of rat treated with HMGB1. Silencing Regnase-1 in microglia enhanced HMGB1-induced expression of proinflammatory cytokines and exacerbated neuronal toxicity. Collectively, these results suggest that Regnase-1 can be induced by HMGB1 in microglia and negatively regulates HMGB1-mediated neuroinflammation and neuronal toxicity.

Posttranscriptional gene regulation is a rapid and effective way to mediate the expression of inflammatory genes. CCCH-type zinc finger proteins are nucleotide-binding molecules involved in RNA metabolism pathways such as RNA splicing, polyadenylation, and messenger RNA (mRNA) decay. Among these proteins, tristetraproline, Roquins, and Regnase-1/monocyte chemotactic protein-1-induced protein-1 have been recently reported to be responsible for mRNA instability. They bind to mRNAs harboring unique motifs and induce mRNA decay. In this review we summarize current progress regarding the specific characteristics of sequences and structures in the 3' untranslated regions of mRNAs that are recognized by tristetraproline, Roquins, and Regnase-1. The target mRNAs to be destabilized by those CCCH-type zinc finger proteins also are included. Notably, most target mRNAs encode cytokines and other inflammatory mediators, suggesting the immune regulation role of CCCH zinc finger proteins. Mice carrying a genetic null allele or modification of these genes display severe symptoms of autoimmune diseases. Taken together, data show that CCCH-type zinc finger proteins play a crucial role in regulating immune response by targeting multiple mRNAs, and including decay. Further understanding the functions of these proteins may provide new therapeutic targets for immune-related disorders in the future.

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