title: Bacterial siderophores that evade or overwhelm lipocalin 2 induce hypoxia inducible factor 1α and proinflammatory cytokine secretion in cultured respiratory epithelial cells.
abstract: Iron is essential for many cellular processes and is required by bacteria for replication. To acquire iron from the host, pathogenic Gram-negative bacteria secrete siderophores, including enterobactin (Ent). However, Ent is bound by the host protein lipocalin 2 (Lcn2), preventing bacterial reuptake of aferric or ferric Ent. Furthermore, the combination of Ent and Lcn2 (Ent+Lcn2) leads to enhanced secretion of interleukin-8 (IL-8) compared to that induced by either stimulus alone. Modified or structurally distinct siderophores, including yersiniabactin (Ybt) and glycosylated Ent (GlyEnt, or salmochelin), deliver iron to bacteria despite the presence of Lcn2. We hypothesized that the robust immune response to Ent and Lcn2 requires iron chelation rather than the Ent+Lcn2 complex itself and also can be stimulated by Lcn2-evasive siderophores. To test this hypothesis, cultured respiratory epithelial cells were stimulated with combinations of purified siderophores and Lcn2 and analyzed by gene expression microarrays, quantitative PCR, and cytokine immunoassays. Ent caused HIF-1α protein stabilization, induced the expression of genes regulated by hypoxia-inducible factor 1α (HIF-1α), and repressed genes involved in cell cycle and DNA replication, whereas Lcn2 induced expression of proinflammatory cytokines. Iron chelation by excess Ent or Ybt significantly increased Lcn2-induced secretion of IL-8, IL-6, and CCL20. Stabilization of HIF-1α was sufficient to enhance Lcn2-induced IL-6 secretion. These data indicate that respiratory epithelial cells can respond to bacterial siderophores that evade or overwhelm Lcn2 binding by increasing proinflammatory cytokine production.
authors: Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, USA.
authors: Victoria I
authors: VI
authors: Holden
authors: Department of Pathology, University of Michigan, Ann Arbor, Michigan, USA.
authors: Steven
authors: S
authors: Lenio
authors: Department of Biostatistics, School of Public Health, University of Michigan, Ann Arbor, Michigan, USA.
authors: Rork
authors: R
authors: Kuick
authors: Department of Molecular Integrative Physiology, University of Michigan, Ann Arbor, Michigan, USA.
authors: Sadeesh K
authors: SK
authors: Ramakrishnan
authors: Department of Molecular Integrative Physiology, University of Michigan, Ann Arbor, Michigan, USA Department of Internal Medicine, Division of Gastroenterology, University of Michigan, Ann Arbor, Michigan, USA.
authors: Yatrik M
authors: YM
authors: Shah
authors: Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, USA Department of Pathology, University of Michigan, Ann Arbor, Michigan, USA mikebach@med.umich.edu.
authors: Michael A
authors: MA
authors: Bachman
mesh_terms: D000209:Acute-Phase Proteins / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology; D045744:Cell Line, Tumor; D054418:Chemokine CCL20 / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism*; D004261:DNA Replication / Q000502:physiology; D004758:Enterobactin / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007249:Inflammation / Q000378:metabolism*; D015850:Interleukin-6 / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D000071068:Lipocalin-2; D054834:Lipocalins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D017262:Siderophores / Q000378:metabolism*
chemical_list: D000209:Acute-Phase Proteins; D001426:Bacterial Proteins; C108355:CCL20 protein, human; D054418:Chemokine CCL20; D016207:Cytokines; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D015850:Interleukin-6; D016209:Interleukin-8; C489506:LCN2 protein, human; D000071068:Lipocalin-2; D054834:Lipocalins; D011518:Proto-Oncogene Proteins; D017262:Siderophores; D004758:Enterobactin