Breaking self‐regulation of Regnase‐1 promotes its own protein expression

AbstractThe RNA‐binding protein (RBP) Regnase‐1 is an endonuclease that regulates immune responses by modulating target mRNA stability. Regnase‐1 degrades a group of inflammation‐associated mRNAs, which contributes to a balanced immune response and helps prevent autoimmune diseases. Regnase‐1 also cleaves its own mRNA by binding stem‐loop (SL) RNA structures in its 3′UTR. To understand how this autoregulation is important for immune responses, we generated mice with a 2‐bp genome deletion in the target SL of the Regnase‐1 3′‐untranslated region (3′UTR). Deletion of these nucleotides inhibited SL formation and limited Regnase‐1‐mediated mRNA degradation. Mutant mice had normal hematopoietic cell differentiation. Biochemically, mutation of the 3′UTR SL increased Regnase‐1 mRNA stability and enhanced both Regnase‐1 mRNA and protein levels in mouse embryonic fibroblasts (MEFs). The expression of Il6, a Regnase‐1 target gene, was constitutively suppressed at steady‐state in mutant MEFs. Additionally, Regnase‐1 protein expression in mutant MEFs was significantly elevated compared to that in wild‐type MEFs at steady state and upon proinflammatory cytokine stimulation. These data suggest a negative feedback mechanism for Regnase‐1 expression and represent a unique mouse model to probe Regnase‐1 overexpression in vivo.