IPS-1 plays an essential role in stress granule formation induced by dsRNA through interacting with PKR and mediating its activation

Abstract

Formation of cytoplasmic stress granules (SGs) and innate immune response are two distinct cellular responses to stresses. Our study investigated involvement of four innate immune proteins, retinoic acid-inducible gene I (RIG-I), melanoma differentiation-associated gene 5 (MDA5), IFN-β promoter stimulator (IPS-1) and protein kinase regulated by dsRNA (PKR) in the formation of SGs. Knockdown of IPS-1 or PKR significantly decreased the SG formation induced by dsRNA. IPS-1 depletion markedly attenuated the phosphorylation of PKR and eIF2α triggered by dsRNA, and IPS-1 facilitated the in vitro autophosphorylation of PKR. In IPS-1 depleted cells, the dsRNA-mediated association of PKR with its dsRNA binding domains or full length PKR was significantly abrogated, suggesting IPS-1 might be involved in PKR dimerization. By co-immunoprecipitation and pulldown assays, our data demonstrated that IPS-1 directly binds to PKR via its CARD domain, suggesting that effect of IPS-1 on SG formation might exert through interacting with PKR and mediating its activation. PKR was recruited into SGs upon activation while majority of IPS-1 protein formed clusters on mitochondrial membrane. Our work provides first evidence that innate signaling molecule IPS-1 plays an essential role in SG formation.