Type I interferon-driven susceptibility to Mycobacterium tuberculosis is mediated by IL-1Ra.

The bacterium Mycobacterium tuberculosis (Mtb) causes tuberculosis and is responsible for more human mortality than any other single pathogen1. Progression to active disease occurs in only a fraction of infected individuals and is predicted by an elevated type I interferon (IFN) response2-7. Whether or how IFNs mediate susceptibility to Mtb has been difficult to study due to a lack of suitable mouse models6-11. Here, we examined B6.Sst1S congenic mice that carry the 'susceptible' allele of the Sst1 locus that results in exacerbated Mtb disease12-14. We found that enhanced production of type I IFNs was responsible for the susceptibility of B6.Sst1S mice to Mtb. Type I IFNs affect the expression of hundreds of genes, several of which have previously been implicated in susceptibility to bacterial infections6,7,15-18. Nevertheless, we found that heterozygous deficiency in just a single IFN target gene, Il1rn, which encodes interleukin-1 receptor antagonist (IL-1Ra), is sufficient to reverse IFN-driven susceptibility to Mtb in B6.Sst1S mice. In addition, antibody-mediated neutralization of IL-1Ra provided therapeutic benefit to Mtb-infected B6.Sst1S mice. Our results illustrate the value of the B6.Sst1S mouse to model IFN-driven susceptibility to Mtb, and demonstrate that IL-1Ra is an important mediator of type I IFN-driven susceptibility to Mtb infections in vivo

The Copper-Responsive RicR Regulon Contributes to Mycobacterium tuberculosis Virulence

ABSTRACT As with most life on Earth, the transition metal copper (Cu) is essential for the viability of the human pathogen Mycobacterium tuberculosis. However, infected hosts can also use Cu to control microbial growth. Several Cu-responsive pathways are present in M. tuberculosis, including the regulated in copper repressor (RicR) regulon, which is unique to pathogenic mycobacteria. In this work, we describe the contribution of each RicR-regulated gene to Cu resistance in vitro and to virulence in animals. We found that the deletion or disruption of individual RicR-regulated genes had no impact on virulence in mice, although several mutants had Cu hypersensitivity. In contrast, a mutant unable to activate the RicR regulon was not only highly susceptible to Cu but also attenuated in mice. Thus, these data suggest that several genes of the RicR regulon are required simultaneously to combat Cu toxicity in vivo or that this regulon is also important for resistance against Cu-independent mechanisms of host defense. IMPORTANCE Mycobacterium tuberculosis is the causative agent of tuberculosis, killing millions of people every year. Therefore, understanding the biology of M. tuberculosis is crucial for the development of new therapies to treat this devastating disease. Our studies reveal that although host-supplied Cu can suppress bacterial growth, M. tuberculosis has a unique pathway, the RicR regulon, to defend against Cu toxicity. These findings suggest that Cu homeostasis pathways in both the host and the pathogen could be exploited for the treatment of tuberculosis

Prokayrotic Ubiquitin-Like Protein (Pup) Proteome of Mycobacterium tuberculosis

Prokaryotic ubiquitin-like protein (Pup) in Mycobacterium tuberculosis (Mtb) is the first known post-translational small protein modifier in prokaryotes, and targets several proteins for degradation by a bacterial proteasome in a manner akin to ubiquitin (Ub) mediated proteolysis in eukaryotes. To determine the extent of pupylation in Mtb, we used tandem affinity purification to identify its “pupylome”. Mass spectrometry identified 55 out of 604 purified proteins with confirmed pupylation sites. Forty-four proteins, including those with and without identified pupylation sites, were tested as substrates of proteolysis in Mtb. Under steady state conditions, the majority of the test proteins did not accumulate in degradation mutants, suggesting not all targets of pupylation are necessarily substrates of the proteasome under steady state conditions. Four proteins implicated in Mtb pathogenesis, Icl (isocitrate lyase), Ino1 (inositol-1-phosphate synthase), MtrA (Mtb response regulator A) and PhoP (phosphate response regulator P), showed altered levels in degradation defective Mtb. Icl, Ino1 and MtrA accumulated in Mtb degradation mutants, suggesting these proteins are targeted to the proteasome. Unexpectedly, PhoP was present in wild type Mtb but undetectable in the degradation mutants. Taken together, these data demonstrate that pupylation regulates numerous proteins in Mtb and may not always lead to degradation

Cytokinins beyond plants: synthesis by Mycobacterium tuberculosis

Mycobacterium tuberculosis (M. tuberculosis) resides mainly inside macrophages, which produce nitric oxide (NO) to combat microbial infections. Earlier studies revealed that proteasome-associated genes are required for M. tuberculosis to resist NO via a previously uncharacterized mechanism. Twelve years later, we elucidated the link between proteasome function and NO resistance in M. tuberculosis in Molecular Cell, 57 (2015), pp. 984–994. In a proteasome degradation-defective mutant, Rv1205, a homologue of the plant enzyme LONELY GUY (LOG) that is involved in the synthesis of phytohormones called cytokinins, accumulates and as a consequence results in the overproduction of cytokinins. Cytokinins break down into aldehydes that kill mycobacteria in the presence of NO. Importantly, this new discovery reveals for the first time that a mammalian bacterial pathogen produces cytokinins and leaves us with the question: why is M. tuberculosis, an exclusively human pathogen, producing cytokinins

Role for Nucleotide Excision Repair in Virulence of Mycobacterium tuberculosis

Mutations in Mycobacterium tuberculosis uvrB result in severe sensitivity to acidified nitrite, a source of nitric oxide (6). In this study, we show that a uvrB mutant is exquisitely sensitive to UV light but not to several sources of reactive oxygen species in vitro. Furthermore, a uvrB mutant was attenuated in mice as judged by an extension of life span. Attenuation in mice was partially reversed by genetic inactivation of nitric oxide synthase 2 (iNOS) and almost completely reversed in mice lacking both iNOS and phagocyte oxidase. Thus, a gene predicted to encode a key element of DNA repair is required for resistance of M. tuberculosis to both reactive nitrogen and reactive oxygen species in mice

Prokaryotic Ubiquitin-Like Protein Provides a Two-Part Degron to Mycobacterium Proteasome Substrates▿ †

Prokaryotic ubiquitin-like protein (Pup) is a posttranslational modifier that targets proteins for degradation by the mycobacterial proteasome. We show that the disordered amino terminus of Pup is required for degradation, while the helical carboxyl terminus mediates its attachment to proteins. Thus, Pup has distinct regions that either interact with pupylation enzymes or initiate proteasomal degradation