Mitogen-activated protein kinase phosphatase-1 controls PD-L1 expression by regulating type I interferon during systemic Escherichia coli infection.

Mitogen-activated protein kinase phosphatase 1 (Mkp-1) KO mice produce elevated cytokines and exhibit increased mortality and bacterial burden following systemic Escherichia coli infection. To understand how Mkp-1 affects immune defense, we analyzed the RNA-Seq datasets previously generated from control and E. coli-infected Mkp-1+/+ and Mkp-1-/- mice. We found that E. coli infection markedly induced programmed death-ligand 1 (PD-L1) expression and that Mkp-1 deficiency further amplified PD-L1 expression. Administration of a PD-L1-neutralizing monoclonal antibody (mAb) to Mkp-1-/- mice increased the mortality of the animals following E. coli infection, although bacterial burden was decreased. In addition, the PD-L1-neutralizing mAb increased serum interferon (IFN)-γ and tumor necrosis factor alpha, as well as lung- and liver-inducible nitric oxide synthase levels, suggesting an enhanced inflammatory response. Interestingly, neutralization of IFN-α/ß receptor 1 blocked PD-L1 induction in Mkp-1-/- mice following E. coli infection. PD-L1 was potently induced in macrophages by E. coli and lipopolysaccharide in vitro, and Mkp-1 deficiency exacerbated PD-L1 induction with little effect on the half-life of PD-L1 mRNA. In contrast, inhibitors of Janus kinase 1/2 and tyrosine kinase 2, as well as the IFN-α/ß receptor 1-neutralizing mAb, markedly attenuated PD-L1 induction. These results suggest that the beneficial effect of type I IFNs in E. coli-infected Mkp-1-/- mice is, at least in part, mediated by Janus kinase/signal transducer and activator of transcription-driven PD-L1 induction. Our studies also support the notion that enhanced PD-L1 expression contributes to the bactericidal defect of Mkp-1-/- mice.

Knockout of MAPK Phosphatase-1 Exaggerates Type I IFN Response during Systemic Escherichia coli Infection.

We have previously shown that Mkp-1-deficient mice produce elevated TNF-α, IL-6, and IL-10 following systemic Escherichia coli infection, and they exhibited increased mortality, elevated bacterial burden, and profound metabolic alterations. To understand the function of Mkp-1 during bacterial infection, we performed RNA-sequencing analysis to compare the global gene expression between E. coli-infected wild-type and Mkp-1 -/- mice. A large number of IFN-stimulated genes were more robustly expressed in E. coli-infected Mkp-1 -/- mice than in wild-type mice. Multiplex analysis of the serum cytokine levels revealed profound increases in IFN-ß, IFN-γ, TNF-α, IL-1α and ß, IL-6, IL-10, IL-17A, IL-27, and GMSF levels in E. coli-infected Mkp-1 -/- mice relative to wild-type mice. Administration of a neutralizing Ab against the receptor for type I IFN to Mkp-1 -/- mice prior to E. coli infection augmented mortality and disease severity. Mkp-1 -/- bone marrow-derived macrophages (BMDM) produced higher levels of IFN-ß mRNA and protein than did wild-type BMDM upon treatment with LPS, E. coli, polyinosinic:polycytidylic acid, and herring sperm DNA. Augmented IFN-ß induction in Mkp-1 -/- BMDM was blocked by a p38 inhibitor but not by an JNK inhibitor. Enhanced Mkp-1 expression abolished IFN-ß induction by both LPS and E. coli but had little effect on the IFN-ß promoter activity in LPS-stimulated RAW264.7 cells. Mkp-1 deficiency did not have an overt effect on IRF3/7 phosphorylation or IKK activation but modestly enhanced IFN-ß mRNA stability in LPS-stimulated BMDM. Our results suggest that Mkp-1 regulates IFN-ß production primarily through a p38-mediated mechanism and that IFN-ß plays a beneficial role in E. coli-induced sepsis.