Induction of the ISR by AB5 subtilase cytotoxin drives type-I IFN expression in pDCs via STING activation

We demonstrate that exposure to the Shiga AB5 subtilase cytotoxin (SubAB) induces the unfolded protein response (UPR) in human peripheral blood mononuclear cells, concomitant with a pro-inflammatory response across distinct cell subsets. Notably, SubAB selectively induces type-I interferon (IFN) expression in plasmacytoid dendritic cells, acting synergistically with Toll-like receptor 7 stimulation. The induction of type-I IFN in response to SubAB relies on stimulator of interferon genes (STING) activation, coupled with protein synthesis inhibition mediated by protein kinase R-like endoplasmic reticulum kinase and phosphorylation of the eukaryotic translation initiation factor 2 subunit-alpha. By impeding mRNA translation through the integrated stress response, SubAB precipitates the downregulation of the negative innate signaling feedback regulator Tax1-binding protein 1. This downregulation is necessary to unleash TANK-binding kinase 1 signaling associated with STING activation. These findings shed new light on how UPR-inducing conditions may regulate the immune system during infection or pathogenesis. Overall design: To comprehensively study the impact of SubAB on human cells, we performed single-cell transcriptomics analysis of human Peripheral blood mononuclear cells ( PBMCs) submitted to different stimulatory conditions, including 6 h of SubAB (1 mg/ml) exposure and/or TLR7 stimulation with the adenine analog CL307 (1mM). Samples are mock treated (NT), SubAB-treated (Toxin), CL307-treated (CL307) or both (CL307-Toxin)