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Small proteins regulate Salmonella survival inside macrophages by controlling degradation of a magnesium transporter.

ABSTRACT: All cells require Mg²⁺ to replicate and proliferate. The macrophage protein Slc11a1 is proposed to protect mice from invading microbes by causing Mg²⁺ starvation in host tissues. However, the Mg²⁺ transporter MgtB enables the facultative intracellular pathogen Salmonella enterica serovar Typhimurium to cause disease in mice harboring a functional Slc11a1 protein. Here, we report that, unexpectedly, the Salmonella small protein MgtR promotes MgtB degradation by the protease FtsH, which raises the question: How does Salmonella preserve MgtB to promote survival inside macrophages? We establish that the Salmonella small protein MgtU prevents MgtB proteolysis, even when MgtR is absent. Like MgtB, MgtU is necessary for survival in Slc11a1 ⁺/⁺ macrophages, resistance to oxidative stress, and growth under Mg²⁺ limitation conditions. The Salmonella Mg²⁺ transporter MgtA is not protected by MgtU despite sharing 50% amino acid identity with MgtB and being degraded in an MgtR- and FtsH-dependent manner. Surprisingly, the mgtB, mgtR, and mgtU genes are part of the same transcript, providing a singular example of transcript-specifying proteins that promote and hinder degradation of the same target. Our findings demonstrate that small proteins can confer pathogen survival inside macrophages by altering the abundance of related transporters, thereby furthering homeostasis.

SUBMITTER: Yeom J

PROVIDER: S-EPMC7443967 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature

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Small proteins regulate Salmonella survival inside macrophages by controlling degradation of a magnesium transporter.

Yeom Jinki J Shao Yi Y Groisman Eduardo A EA

Proceedings of the National Academy of Sciences of the United States of America 20200804 33

All cells require Mg2+ to replicate and proliferate. The macrophage protein Slc11a1 is proposed to protect mice from invading microbes by causing Mg2+ starvation in host tissues. However, the Mg2+ transporter MgtB enables the facultative intracellular pathogen Salmonella enterica serovar Typhimurium to cause disease in mice harboring a functional Slc11a1 protein. Here, we report that, unexpectedly, the Salmonella small protein MgtR promotes MgtB deg ...[more]

PMID: 32753384

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Project description:Salmonella enterica are natural bacterial pathogens of humans and animals that cause systemic infection or gastroenteritis. During systemic infection, Salmonella generally reside within professional phagocytes, typically macrophages, whereas gastroenteritis is caused by infection of epithelial cells. We are only beginning to understand which host pathways contribute to Salmonella survival in particular cell types. We therefore sought to identify compounds that perturb Salmonella-host interactions using a chemical genetics approach. We found one small molecule, D61, that reduces Salmonella load in cell-line and primary macrophages but has no effect on Salmonella growth in epithelial cells or rich medium. We determined that in macrophages D61 induces LC3II, a marker of the autophagy pathway, and promotes aggregation of LC3II near Salmonella We found that D61 antibacterial activity depends on the VPS34 complex and on ATG5. D61 also reduced Salmonella load in the spleens and livers of infected mice. Lastly, we demonstrate that D61 antibacterial activity in macrophages is synergistic with the antibiotic chloramphenicol, but that this synergy is largely independent of the known autophagy-stimulating activity of chloramphenicol. Thus, a small molecule has anti-bacterial activity specifically in macrophages and mice based on the promotion of bacterial degradation by autophagy.Importance Autophagy is a conserved cellular response to metabolic stress and to invading pathogens. For many pathogens, including Salmonella, autophagy can play a detrimental or beneficial role during infection depending on the cellular context. We combined chemical genetics with single cell analyses and murine infection to dissect host-pathogen interactions. We identified a small molecule that reduces bacterial load in macrophages by increasing autophagic flux. This compound also reduces bacterial colonization of tissues in infected mice. These observations demonstrate the potential therapeutic utility of stimulating autophagy in cells and animals to curb infection.

Dataset Information

Small proteins regulate Salmonella survival inside macrophages by controlling degradation of a magnesium transporter.

Publications

Small proteins regulate <i>Salmonella</i> survival inside macrophages by controlling degradation of a magnesium transporter.

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