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The host-encoded Heme Regulated Inhibitor (HRI) facilitates virulence-associated activities of bacterial pathogens.

ABSTRACT: Here we show that cells lacking the heme-regulated inhibitor (HRI) are highly resistant to infection by bacterial pathogens. By examining the infection process in wild-type and HRI null cells, we found that HRI is required for pathogens to execute their virulence-associated cellular activities. Specifically, unlike wild-type cells, HRI null cells infected with the gram-negative bacterial pathogen Yersinia are essentially impervious to the cytoskeleton-damaging effects of the Yop virulence factors. This effect is due to reduced functioning of the Yersinia type 3 secretion (T3S) system which injects virulence factors directly into the host cell cytosol. Reduced T3S activity is also observed in HRI null cells infected with the bacterial pathogen Chlamydia which results in a dramatic reduction in its intracellular proliferation. We go on to show that a HRI-mediated process plays a central role in the cellular infection cycle of the Gram-positive pathogen Listeria. For this pathogen, HRI is required for the post-invasion trafficking of the bacterium to the infected host cytosol. Thus by depriving Listeria of its intracellular niche, there is a highly reduced proliferation of Listeria in HRI null cells. We provide evidence that these infection-associated functions of HRI (an eIF2? kinase) are independent of its activity as a regulator of protein synthesis. This is the first report of a host factor whose absence interferes with the function of T3S secretion and cytosolic access by pathogens and makes HRI an excellent target for inhibitors due to its broad virulence-associated activities.

SUBMITTER: Shrestha N

PROVIDER: S-EPMC3707855 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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The host-encoded Heme Regulated Inhibitor (HRI) facilitates virulence-associated activities of bacterial pathogens.

Shrestha Niraj N Boucher Justin J Bahnan Wael W Clark Emily S ES Rosqvist Roland R Fields Kenneth A KA Khan Wasif N WN Schesser Kurt K

PloS one 20130710 7

Here we show that cells lacking the heme-regulated inhibitor (HRI) are highly resistant to infection by bacterial pathogens. By examining the infection process in wild-type and HRI null cells, we found that HRI is required for pathogens to execute their virulence-associated cellular activities. Specifically, unlike wild-type cells, HRI null cells infected with the gram-negative bacterial pathogen Yersinia are essentially impervious to the cytoskeleton-damaging effects of the Yop virulence factor ...[more]

PMID: 23874749

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Project description:BackgroundSickle cell disease (SCD) poses a significant health challenge and therapeutic approaches often target fetal hemoglobin (HbF) to ameliorate symptoms. Hydroxyurea, a current therapeutic option for SCD, has shown efficacy in increasing HbF levels. However, concerns about myelosuppression and thrombocytopenia necessitate the exploration of alternative compounds. Heme-regulated inhibitor (HRI) presents a promising target for pharmacological intervention in SCD due to its association with HbF modulation. This study systematically screened compounds for their potential inhibitory functions against HRI.MethodsSmall-molecule compounds from 17 plants commonly utilized in traditional SCD management were subjected to in silico screening against HRI. Molecular docking was performed, and free binding energy calculations were determined using molecular mechanics with generalized born and surface area (MMGBSA). The lead compounds were subjected to molecular dynamics simulation at 100 ns. Computational quantum mechanical modelling of the lead compounds was subsequently performed. We further examined the pharmacodynamics, pharmacokinetic and physiological properties of the identified compounds.ResultsFive potential HRI inhibitors, including kaempferol-3-(2G-glucosyrutinoside), epigallocatechin gallate, tiliroside, myricetin-3-O-glucoside, and cannabiscitrin, with respective docking scores of -16.0, -12.17, -11.37, -11.56 and 11.07 kcal/mol, were identified. The MMGBSA analysis of the complexes yielded free-binding energies of -69.76, -71.17, -60.44, 53.55, and - 55 kcal/mol, respectively. The identified leads were stable within HRI binding pocket for the duration of 100 ns simulation.ConclusionsThe study successfully identified five phytoligands with potential inhibitory effects on HRI, opening avenues for their use as modulators of HbF in SCD patients. This finding holds promise for advancing treatment strategies in SCD. However, additional preclinical analyses are warranted to validate the chemotherapeutic properties of the lead compounds.

Project description:The kidney and bladder expresses a variety of powerful defense mechanisms to limit urinary infection including iron scavenging, a process called "nutritional immunity". We previously demonstrated that bladder and kidney epithelia generates the archetype of the urinary iron defense, a lipocalin called NGAL which binds Enterochelin, a bacterial siderophore. However, because urinary bacteria can evade the bacteriostatic effects of NGAL by modifying Enterochelin and by producing additional siderophores, other mechanisms of "nutritional immunity" are anticipated. To study the defense in the kidney, we used a cell type specific method of RNA isolation in mouse (adapted from Gay et al, Oregon). A promiscuous form of phosphoribosyltransferase (UPRT) was cloned into the Rosa26 locus using a floxed-stop design which we activated in a cell specific fashion with Atp6v1b1-Cre. Thiouracil was introduced 12hr and 24hrs after urinary tract infection. Isolation of RNA directly from intercalated revealed synthetic (Npas1-Bmal1-Alas), transport (Hrg1, Flvcr1) and metabolic enzymes (Hmox1) of heme metabolism. Hmox1 was detected in the kidney with a luciferase based reporter (Contag et al, Stanford) after infection. CO production was detected in vivo and in AtpCre-mTmG FACS isolated intercalated cells in vitro using a novel metal-based probe synthesized at Columbia (adapted from Liu et al, China). Urinary bacteria (UPEC) with heme transport mutations were not competitive in the colonization of the kidney but conversely were markedly stimulated by iron, suggesting bacterial-host competition for heme capture and metabolism. In fact, infection upregulated both heme synthetic and metabolic genes, suggesting that CO production is induced by infection. Exposure to CO terminated the growth of UPEC. In sum, we have identified an unusual iron trafficking system in the collecting ducts that mirrors the nutritional requirements of UPEC to achieve pyelonephritis. Many of these components are specific to the intercalated cells, consistent with the notion that these cells defend the urinary tract from infection.

Dataset Information

The host-encoded Heme Regulated Inhibitor (HRI) facilitates virulence-associated activities of bacterial pathogens.

Publications

The host-encoded Heme Regulated Inhibitor (HRI) facilitates virulence-associated activities of bacterial pathogens.

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