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NOD2, RIP2 and IRF5 play a critical role in the type I interferon response to Mycobacterium tuberculosis.

Pandey AK, Yang Y, Jiang Z, Fortune SM, Coulombe F, Behr MA, Fitzgerald KA, Sassetti CM, Kelliher MA - PLoS Pathog. (2009)

Bottom Line: Like many intracellular pathogens, a significant fraction of the transcriptional response to Mycobacterium tuberculosis infection depends on these type I interferons, but the recognition pathways responsible remain elusive.This response is only partially impaired by the loss of Irf3 and therefore, differs fundamentally from those stimulated by bacterial DNA, which depend entirely on this transcription factor.This difference appears to result from the unusual peptidoglycan produced by mycobacteria, which we show is a uniquely potent agonist of the Nod2/Rip2/Irf5 pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, MA, USA.

ABSTRACT
While the recognition of microbial infection often occurs at the cell surface via Toll-like receptors, the cytosol of the cell is also under surveillance for microbial products that breach the cell membrane. An important outcome of cytosolic recognition is the induction of IFNalpha and IFNbeta, which are critical mediators of immunity against both bacteria and viruses. Like many intracellular pathogens, a significant fraction of the transcriptional response to Mycobacterium tuberculosis infection depends on these type I interferons, but the recognition pathways responsible remain elusive. In this work, we demonstrate that intraphagosomal M. tuberculosis stimulates the cytosolic Nod2 pathway that responds to bacterial peptidoglycan, and this event requires membrane damage that is actively inflicted by the bacterium. Unexpectedly, this recognition triggers the expression of type I interferons in a Tbk1- and Irf5-dependent manner. This response is only partially impaired by the loss of Irf3 and therefore, differs fundamentally from those stimulated by bacterial DNA, which depend entirely on this transcription factor. This difference appears to result from the unusual peptidoglycan produced by mycobacteria, which we show is a uniquely potent agonist of the Nod2/Rip2/Irf5 pathway. Thus, the Nod2 system is specialized to recognize bacteria that actively perturb host membranes and is remarkably sensitive to mycobacteria, perhaps reflecting the strong evolutionary pressure exerted by these pathogens on the mammalian immune system.

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Multiple cytosolic pathways lead to IFNβ induction.A. BMDM derived from wt, rip2−/− and nod2−/− mice were infected with virulent Mtb H37Rv (Rv) or with an ESX1 mutant (ΔESX1) at an MOI of 10 for 4 h. RNA was harvested, and IFNβ mRNA levels were quantified using real time PCR. Gene expression of IFNβ is reported as copy number per 1,000 copies of β-actin. Samples were assayed in triplicate; error bars represent the standard deviation. The experiment shown is representative of at least three. B. BMDM derived from wt, rip2−/− and nod2−/− mice were infected with virulent Mtb H37Rv (Rv) or with an ESX1 mutant (ΔESX1) at an MOI of 10 for 4 h. RNA was harvested, and RANTES mRNA levels were quantified using real time PCR. Gene expression of RANTES is reported as copy number per 1,000 copies of β-actin. Samples were assayed in triplicate; error bars represent the standard deviation. The experiment shown is representative of at least three.
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ppat-1000500-g005: Multiple cytosolic pathways lead to IFNβ induction.A. BMDM derived from wt, rip2−/− and nod2−/− mice were infected with virulent Mtb H37Rv (Rv) or with an ESX1 mutant (ΔESX1) at an MOI of 10 for 4 h. RNA was harvested, and IFNβ mRNA levels were quantified using real time PCR. Gene expression of IFNβ is reported as copy number per 1,000 copies of β-actin. Samples were assayed in triplicate; error bars represent the standard deviation. The experiment shown is representative of at least three. B. BMDM derived from wt, rip2−/− and nod2−/− mice were infected with virulent Mtb H37Rv (Rv) or with an ESX1 mutant (ΔESX1) at an MOI of 10 for 4 h. RNA was harvested, and RANTES mRNA levels were quantified using real time PCR. Gene expression of RANTES is reported as copy number per 1,000 copies of β-actin. Samples were assayed in triplicate; error bars represent the standard deviation. The experiment shown is representative of at least three.

Mentions: Consistent with previous work [28], we found that infection with ESX1 mutant bacteria induced significantly less IFNβ and RANTES expression than wild type bacteria (Figure 5). To test whether ESX1-mediated type I IFN expression was mediated solely via Rip2, we infected Rip2-deficient macrophages with ESX1 mutant bacteria and quantified IFNβ and RANTES mRNA levels. We found that in the absence of Rip2, the loss of ESX1 function resulted in a further decrease in IFNβ mRNA levels (Figure 5A), suggesting the presence of an additional host pathway(s) that contribute to IFNβ induction. However, Rip2 deletion had no significant effect in the absence of ESX1 (Figure 5B), supporting our biochemical evidence that NOD2 stimulation depends entirely the ESX1-dependent delivery of stimulants into the cytosol.


NOD2, RIP2 and IRF5 play a critical role in the type I interferon response to Mycobacterium tuberculosis.

Pandey AK, Yang Y, Jiang Z, Fortune SM, Coulombe F, Behr MA, Fitzgerald KA, Sassetti CM, Kelliher MA - PLoS Pathog. (2009)

Multiple cytosolic pathways lead to IFNβ induction.A. BMDM derived from wt, rip2−/− and nod2−/− mice were infected with virulent Mtb H37Rv (Rv) or with an ESX1 mutant (ΔESX1) at an MOI of 10 for 4 h. RNA was harvested, and IFNβ mRNA levels were quantified using real time PCR. Gene expression of IFNβ is reported as copy number per 1,000 copies of β-actin. Samples were assayed in triplicate; error bars represent the standard deviation. The experiment shown is representative of at least three. B. BMDM derived from wt, rip2−/− and nod2−/− mice were infected with virulent Mtb H37Rv (Rv) or with an ESX1 mutant (ΔESX1) at an MOI of 10 for 4 h. RNA was harvested, and RANTES mRNA levels were quantified using real time PCR. Gene expression of RANTES is reported as copy number per 1,000 copies of β-actin. Samples were assayed in triplicate; error bars represent the standard deviation. The experiment shown is representative of at least three.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2698121&req=5

ppat-1000500-g005: Multiple cytosolic pathways lead to IFNβ induction.A. BMDM derived from wt, rip2−/− and nod2−/− mice were infected with virulent Mtb H37Rv (Rv) or with an ESX1 mutant (ΔESX1) at an MOI of 10 for 4 h. RNA was harvested, and IFNβ mRNA levels were quantified using real time PCR. Gene expression of IFNβ is reported as copy number per 1,000 copies of β-actin. Samples were assayed in triplicate; error bars represent the standard deviation. The experiment shown is representative of at least three. B. BMDM derived from wt, rip2−/− and nod2−/− mice were infected with virulent Mtb H37Rv (Rv) or with an ESX1 mutant (ΔESX1) at an MOI of 10 for 4 h. RNA was harvested, and RANTES mRNA levels were quantified using real time PCR. Gene expression of RANTES is reported as copy number per 1,000 copies of β-actin. Samples were assayed in triplicate; error bars represent the standard deviation. The experiment shown is representative of at least three.
Mentions: Consistent with previous work [28], we found that infection with ESX1 mutant bacteria induced significantly less IFNβ and RANTES expression than wild type bacteria (Figure 5). To test whether ESX1-mediated type I IFN expression was mediated solely via Rip2, we infected Rip2-deficient macrophages with ESX1 mutant bacteria and quantified IFNβ and RANTES mRNA levels. We found that in the absence of Rip2, the loss of ESX1 function resulted in a further decrease in IFNβ mRNA levels (Figure 5A), suggesting the presence of an additional host pathway(s) that contribute to IFNβ induction. However, Rip2 deletion had no significant effect in the absence of ESX1 (Figure 5B), supporting our biochemical evidence that NOD2 stimulation depends entirely the ESX1-dependent delivery of stimulants into the cytosol.

Bottom Line: Like many intracellular pathogens, a significant fraction of the transcriptional response to Mycobacterium tuberculosis infection depends on these type I interferons, but the recognition pathways responsible remain elusive.This response is only partially impaired by the loss of Irf3 and therefore, differs fundamentally from those stimulated by bacterial DNA, which depend entirely on this transcription factor.This difference appears to result from the unusual peptidoglycan produced by mycobacteria, which we show is a uniquely potent agonist of the Nod2/Rip2/Irf5 pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, MA, USA.

ABSTRACT
While the recognition of microbial infection often occurs at the cell surface via Toll-like receptors, the cytosol of the cell is also under surveillance for microbial products that breach the cell membrane. An important outcome of cytosolic recognition is the induction of IFNalpha and IFNbeta, which are critical mediators of immunity against both bacteria and viruses. Like many intracellular pathogens, a significant fraction of the transcriptional response to Mycobacterium tuberculosis infection depends on these type I interferons, but the recognition pathways responsible remain elusive. In this work, we demonstrate that intraphagosomal M. tuberculosis stimulates the cytosolic Nod2 pathway that responds to bacterial peptidoglycan, and this event requires membrane damage that is actively inflicted by the bacterium. Unexpectedly, this recognition triggers the expression of type I interferons in a Tbk1- and Irf5-dependent manner. This response is only partially impaired by the loss of Irf3 and therefore, differs fundamentally from those stimulated by bacterial DNA, which depend entirely on this transcription factor. This difference appears to result from the unusual peptidoglycan produced by mycobacteria, which we show is a uniquely potent agonist of the Nod2/Rip2/Irf5 pathway. Thus, the Nod2 system is specialized to recognize bacteria that actively perturb host membranes and is remarkably sensitive to mycobacteria, perhaps reflecting the strong evolutionary pressure exerted by these pathogens on the mammalian immune system.

Show MeSH
Related in: MedlinePlus