Molecular cloning and functional characterization of porcine stimulator of interferon genes (STING)

The stimulator of interferon genes (STING) of human/mouse has been identified recently as an adaptor that links virus-sensing receptors to interferon regulatory factor 3 (IRF3) activation. Here we report the cloning and characterization of porcine STING (poSTING). The full-length poSTING cDNA sequence encodes 378 amino acids and contains one endoplasmic reticulum (ER) retention motif, RAR. Phylogenetic analysis revealed that poSTING, together with bovine STING, is more closely related to the human than to mouse STING. poSTING mRNA expression was mainly detected in the spleen, lymph node and lung. Enhanced green fluorescence protein (EGFP)-labeled poSTING was found to reside predominantly in the ER, and also in the mitochondrial membrane in PK-15 cells. Over-expression of poSTING activated both IRF3 and nuclear factor kappaB (NF-kappaB) transcription factors to induce IFN-beta production, while knockdown of poSTING significantly inhibited poly(I:C)- and poly(dAT:dAT)-induced IFN-beta promoter activation and IFN-beta mRNA production. Furthermore, the pseudorabies virus (PRV), a dsDNA virus, has been shown to activate the IFN-beta promoter in a poSTING-dependent way in porcine cell lines. Altogether, these results indicate that STING is an important regulator of porcine innate immune signaling. The results will help better understand the biological role(s) of STING in innate immunity during evolution.