Regnase-1, a rapid response ribonuclease regulating inflammation and stress responses.

RNA-binding proteins (RBPs) are central players in post-transcriptional regulation and immune homeostasis. The ribonuclease and RBP Regnase-1 exerts critical roles in both immune cells and non-immune cells. Its expression is rapidly induced under diverse conditions including microbial infections, treatment with inflammatory cytokines and chemical or mechanical stimulation. Regnase-1 activation is transient and is subject to negative feedback mechanisms including proteasome-mediated degradation or mucosa-associated lymphoid tissue 1 (MALT1) mediated cleavage. The major function of Regnase-1 is promoting mRNA decay via its ribonuclease activity by specifically targeting a subset of genes in different cell types. In monocytes, Regnase-1 downregulates IL-6 and IL-12B mRNAs, thus mitigating inflammation, whereas in T cells, it restricts T-cell activation by targeting c-Rel, Ox40 and Il-2 transcripts. In cancer cells, Regnase-1 promotes apoptosis by inhibiting anti-apoptotic genes including Bcl2L1, Bcl2A1, RelB and Bcl3. Together with up-frameshift protein-1 (UPF1), Regnase-1 specifically cleaves mRNAs that are active during translation by recognizing a stem-loop (SL) structure within the 3'UTRs of these genes in endoplasmic reticulum-bound ribosomes. Through this mechanism, Regnase-1 rapidly shapes mRNA profiles and associated protein expression, restricts inflammation and maintains immune homeostasis. Dysregulation of Regnase-1 has been described in a multitude of pathological states including autoimmune diseases, cancer and cardiovascular diseases. Here, we provide a comprehensive update on the function, regulation and molecular mechanisms of Regnase-1, and we propose that Regnase-1 may function as a master rapid response gene for cellular adaption triggered by microenvironmental changes.