Expression of epithelial cell iron-related genes upon infection by Neisseria meningitidis

Department of Cell & Developmental Biology, Oregon Health and Science University, Portland, Oregon, United States
Cellular Microbiology (Impact Factor: 4.92). 06/2004; 6(5):473-84. DOI: 10.1111/j.1462-5822.2004.00376.x
Source: PubMed


Infection by the obligate human pathogens Neisseria meningitidis (MC) and Neisseria gonorrhoeae (GC) reduces the expression of host epithelial cell transferrin receptor 1 (TfR-1) (Bonnah et al., 2000, Cellular Microbiology 2: 207-218). In addition, the rate and pattern of TfR-1 cycling is altered, leading to diminished uptake of Tf-iron by infected host cells. As Tf-iron is important for maintaining iron homeostasis in the eukaryotic cell, these findings raised the possibility that Neisseria infection might affect further pathways of epithelial cell iron metabolism. We used a specialized cDNA microarray platform, the 'IronChip', to investigate the expression of genes involved in iron transport, storage and regulation. We show that mRNA expression of several host genes involved in iron homeostasis is altered. Surprisingly, the general mRNA expression profile of infected cells closely resembled that of uninfected cells grown in an iron-limited environment. An important exception to this profile is TfR-1, the mRNA level of which is strongly reduced. Low TfR-1 expression may be explained in part by decreased activity of the iron-regulatory proteins (IRPs) in MC-infected cells, which may result in the destabilization of TfR-1 mRNA. Intriguingly, low IRP activity contrasts with the decrease in H-ferritin protein levels in infected cells. This finding suggests that low IRP activity may be responsible in part for the decrease in TfR-1 mRNA levels. A discussion of these novel findings in relation to MC infection and virulence is provided.

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Available from: Caroline A Enns, Sep 10, 2014
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    • "Microarrays (comprising a limited number of inflammation, adhesion and iron-homeostasis genes) were used to investigate the host response of ME-180 epithelial-like human cervical carcinoma [14] and A431 human epidermoid carcinoma cells [15] to N. meningitidis. Bonnah et al. [14] showed that the mRNA expression of several host genes involved in iron homeostasis were altered upon infection with meningococci, while Plant et al. [15] showed that there was an induction of chemokine receptors and cytokines such as CXCR-4, CXCR-5, IL1A, IL1B, IL18 and IFN-γ , with most of the host genes induced early in infection. "
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    ABSTRACT: Both Neisseria meningitidis and the closely related bacterium Neisseria lactamica colonise human nasopharyngeal mucosal surface, but only N. meningitidis invades the bloodstream to cause potentially life-threatening meningitis and septicaemia. We have hypothesised that the two neisserial species differentially modulate host respiratory epithelial cell gene expression reflecting their disease potential. Confluent monolayers of 16HBE14 human bronchial epithelial cells were exposed to live and/or dead N. meningitidis (including capsule and pili mutants) and N. lactamica, and their transcriptomes were compared using whole genome microarrays. Changes in expression of selected genes were subsequently validated using Q-RT-PCR and ELISAs. Live N. meningitidis and N. lactamica induced genes involved in host energy production processes suggesting that both bacterial species utilise host resources. N. meningitidis infection was associated with down-regulation of host defence genes. N. lactamica, relative to N. meningitidis, initiates up-regulation of proinflammatory genes. Bacterial secreted proteins alone induced some of the changes observed. The results suggest N. meningitidis and N. lactamica differentially regulate host respiratory epithelial cell gene expression through colonisation and/or protein secretion, and that this may contribute to subsequent clinical outcomes associated with these bacteria.
    Preview · Article · Oct 2011 · PLoS ONE
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    • "This expression analysis demonstrated for the first time that the gonococcal tonB-exbBexbD operon is cotranscribed into a single, polycistronic operon and that the genes are coregulated by iron availability. Previous studies have demonstrated that neisserial infection results in a host cell expression pattern similar to that of iron-starved cells (Bonnah et al., 2004; Larson et al., 2004). The fact that TonB expression increased in iron-deplete growth conditions (Fig. 3A), suggests increased expression of this protein within the ironlimiting environment of infected cervical cells. "
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    ABSTRACT: Neisseria gonorrhoeae has evolved a repertoire of iron acquisition systems that facilitate essential iron uptake in the human host. Acquisition of iron requires both the energy-harnessing cytoplasmic membrane protein, TonB, as well as specific outer membrane TonB-dependent transporters (TdTs.) Survival within host epithelial cells is important to the pathogenesis of gonococcal disease and may contribute to the persistence of infection. However, the mechanisms by which gonococci acquire iron within this intracellular niche are not currently understood. In this study, we investigated the survival of gonococcal strain FA1090 within ME180 human cervical epithelial cells with respect to high affinity iron acquisition. Intracellular survival was dependent upon iron supplied by the host cell. TonB was expressed in the host cell environment and this protein was critical to gonococcal intracellular survival. Furthermore, expression of the characterized outer membrane transporters TbpA, FetA and LbpA and putative transporters TdfG, TdfH and TdfJ were not necessary for intracellular survival. Conversely, intracellular survival was dependent on expression of the putative transporter, TdfF. Expression of TdfF was detected in the presence of epithelial cell culture media containing fetal bovine serum. Expression was further modulated by iron availability. To our knowledge, this study is the first to demonstrate the specific requirement for a single iron transporter in the survival of a bacterial pathogen within host epithelial cells.
    Preview · Article · Dec 2006 · Molecular Microbiology
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    • "Ferritin levels in human cells are also regulated posttranscriptionally by iron-regulatory proteins (IRPs) that bind to ferritin mRNA and repress ferritin translation (Ponka, 1999). Our laboratory has found that MC infection reduces IRP-binding activity (Bonnah et al ., 2004), a result that apparently rules out post-transcriptional regulation as a factor in ferritin reduction. As the diminished levels of ferritin shown by the ELISA were not the result of repression of transcription or translation, we next determined whether ferritin turnover was accelerated in infected cells. "
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    ABSTRACT: In order to colonize humans and cause disease, pathogenic bacteria must assimilate iron from their host. The vast majority of non-haem iron in humans is localized intracellularly, within the storage molecule ferritin. Despite the vast reserves of iron within ferritin, no pathogen has been demonstrated previously to exploit this molecule as an iron source. Here, we show that the Gram-negative diplococcus Neisseria meningitidis can trigger rapid redistribution and degradation of cytosolic ferritin within infected epithelial cells. Indirect immunofluorescence microscopy revealed that cytosolic ferritin is aggregated and recruited to intracellular meningococci (MC). The half-life of ferritin within cultured epithelial cells was found to decrease from 20.1 to 5.3 h upon infection with MC. Supplementation of infected epithelial cells with ascorbic acid abolished ferritin redistribution and degradation and prevented intracellular MC from replicating. The lysosomal protease inhibitor leupeptin slowed ferritin turnover and also retarded MC replication. Our laboratory has shown recently that MC can interfere with transferrin uptake by infected cells (Bonnah R.A., et al., 2000, Cell Microbiol 2: 207-218) and that, perhaps as a result, the infected cells have a transcriptional profile indicative of iron starvation (Bonnah, R.A., et al., 2004, Cell Microbiol 6: 473-484). In view of these findings, we suggest that accelerated ferritin degradation occurs as a response to an iron starvation state induced by MC infection and that ferritin degradation provides intracellular MC with a critical source of iron.
    Full-text · Article · Sep 2004 · Molecular Microbiology
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