How guarantee as anti-cancer therapies, our data suggest that bacterial siderophores act as cytotoxins during infection. Clinical isolates of K. pneumoniae create 50 to 100 M Ent in pure culture (information not shown), quantities sufficient to induce the hypoxia and iron starvation responses described here. The induction of cellular stresses in response to siderophores and Lcn2 for the duration of infection may possibly cause significant pathological effects throughout infection. Even so, our final results indicate that Lcn2 can cooperate with these cellular pressure responses to induce robust cytokine release and recruit inflammatory cells to combat the bacterial source of toxic siderophores. Although the inflammatory response to siderophores and Lcn2 is activated in response to iron chelation as an alternative to a siderophore-Lcn2 complicated, the cellular responses to Ent, Ybt, and GlyEnt are distinct. Stimulation with Ybt or Ybt Lcn2 induces much more IL-8, IL-6, and CCL20 secretion and NDRG1 gene expression than equimolar stimulation with Ent or Ent Lcn2. This really is surprising, mainly because Ent has the highest identified affinity for iron. In truth, stimulation of A549 cells with growing molar concentrations of siderophores illustrates a higher threshold concentration to induce IL-8 secretion by Ybt than that by Ent (data not shown). This is consistent with the pattern shown in Fig. 4A, in which Fe-Ent induces much more NDRG1 gene expression than Fe-Ybt. Despite equimolar addition of Fe to Ent, trace cost-free Ent is capable of chelating cellular iron and inducing NDRG1 expression. GlyEnt may not induce cellular iron chelation or proinflammatory cytokine secretion because of its decreased membrane partitioning abilities (14). Addition of GlyEnt to an PI3KC2β Synonyms entirely siderophore-deficient strain of K. pneumoniae restores bacterial growth, indicating that GlyEnt is able to obtain iron for bacterial growth (52). Differential secretion of Ent, Ybt, and GlyEnt for the duration of infection may well trigger dissimilar pathological effects through triggering varied ErbB3/HER3 custom synthesis levels of cytokine production. Expression of HIF-1 protein is regulated by means of hydroxylation by prolyl hydroxylases (PHDs), a modification that targets the protein for fast proteasomal degradation (19). Because PHDs need iron as a cofactor, HIF-1 stabilization is often induced by both oxygen and iron starvation (53). Indeed, siderophores previously have been shown to induce HIF-1 stabilization (54, 55). In a earlier study, Ybt was shown to stabilize HIF-1 , but effects on inflammation have been not assessed. GlyEnt also was reported to induce HIF-1 , but this required higher concentrations of siderophores ( 200 M) (54).September 2014 Volume 82 Numberiai.asm.orgHolden et al.AEnterobactin Yersiniabactin Lipocalin two cytokinescytokinesBCIL-8 CCL20 Fe HIF-1 IL-6 Fe HIF-IL-8 CCL20 IL-FIG 7 Lcn2 acts as a sensor by modulating airway epithelial cell inflammatory cytokine secretion in response to iron chelation by unbound Ent and Ybt. (A) Modest amounts of Ent can be bound and neutralized by Lcn2, top to a low degree of Lcn2-induced cytokine secretion within the airway. Big amounts of Ent (B) or Ybt (C) evade Lcn2 binding, leading to altered host iron status and HIF-1 stabilization. The mixture of cellular iron depletion and Lcn2 signaling increases production of inflammatory cytokines, including IL-8, IL-6, and CCL20.The existing study demonstrates induction of HIF-1 stabilization by the prototypical siderophore Ent and Ent Lcn2 at physiologic concentrations. Moreover, we illustrate tha.
