title: Degradation of interleukin 8 by the serine protease MucD of Pseudomonas aeruginosa.
abstract: We investigated the influence of the type III effector, ExoS, on the host epithelial cell response to Pseudomonas aeruginosa infection, and we found that disruption of the exoS gene caused a significant increase in the amount of interleukin-8 (IL-8) in the culture medium of Caco-2 cells. We show that IL-8 was degraded in the culture medium following infection of the cells with the wild-type (PAO1), but not the exoS knock-out (the ΔexoS) strain. Purified ExoS protein itself did not degrade IL-8. We next show that IL-8 degradation by PAO1 was inhibited by the addition of serine protease inhibitors. These results strongly suggest that a bacterial serine protease that degrades IL-8 is expressed and secreted into the culture medium of Caco-2 cells infected with PAO1, and that the expression of this protein is repressed in cells infected with the ΔexoS strain. The PAO1 genome encodes 28 different protease genes, including two serine proteases: PA3535 and mucD. PA3535 and mucD gene knock-outs were constructed (ΔmucD and ΔPA3535), and ΔmucD but not ΔPA3535 showed reduced IL-8 degradation. To understand the significance of IL-8 degradation, we next evaluated neutrophil infiltration in lungs excised from mice intranasally infected with the P. aeruginosa strains. Increased neutrophil infiltration was observed in PAO1-infected mice, but not in ΔexoS- or ΔmucD-infected mice. Taken together, our results suggest that P. aeruginosa escapes from phagocytic killing due to IL-8 degradation following the secretion of the MucD serine protease, whose expression appears to be influenced by ExoS.
authors.affiliation: Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, 5 Misasagi-Nakauchicho, Yamashina, Kyoto 607-8414, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Okuda
authors.forename: Naoki
authors.initials: N
authors.lastname: Hayashi
authors.forename: Soichi
authors.initials: S
authors.lastname: Tanabe
authors.forename: Shu
authors.initials: S
authors.lastname: Minagawa
authors.forename: Naomasa
authors.initials: N
authors.lastname: Gotoh
mesh_terms: D036002:ADP Ribose Transferases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism; D018938:Caco-2 Cells; D005260:Female; D055786:Gene Knockout Techniques; D006651:Histocytochemistry; D054884:Host-Pathogen Interactions; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism*; D008168:Lung / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D020556:Neutrophil Infiltration; D018410:Pneumonia, Bacterial / Q000382:microbiology; D011552:Pseudomonas Infections / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D016209:Interleukin-8; D036002:ADP Ribose Transferases; C444820:exoenzyme S; C097649:MucD protein, Pseudomonas aeruginosa; D012697:Serine Endopeptidases