Outer Membrane Protein A from Klebsiella pneumoniae Activates Bronchial Epithelial Cells: Implication in Neutrophil Recruitment

Institut National de la Santé et de la Recherche Médicale, Unité 416, Institut Pasteur, Lille, France.
The Journal of Immunology (Impact Factor: 4.92). 12/2003; 171(12):6697-705. DOI: 10.4049/jimmunol.171.12.6697
Source: PubMed


Aside from its mechanical barrier function, bronchial epithelium plays an important role both in the host defense and in the pathogenesis of inflammatory airway disorders. To investigate its role in lung defense, the effect of a bacterial cell wall protein, the outer membrane protein A from Klebsiella pneumoniae (kpOmpA) on bronchial epithelial cells (BEC) was evaluated on adhesion molecule expression and cytokine production. Moreover, the potential implication of this mechanism in kpOmpA-induced lung inflammation was also determined. Our in vitro studies demonstrated that kpOmpA strongly bound to BEAS-2B cells, a human BEC line, and to BEC primary cultures, resulting in NF-kappaB signaling pathway activation. Exposure to kpOmpA increased ICAM-1 mRNA and cell surface expression, as well as the secretion of IL-6, CXC chemokine ligand (CXCL)1, CXCL8, C-C chemokine ligand 2, CXCL10 by BEAS-2B cells, and BEC primary cultures (p < 0.005). We analyzed in vivo the consequences of intratracheal injection of kpOmpA to BALB/c mice. In kpOmpA-treated mice, a transient neutrophilia (with a maximum at 24 h) was observed in bronchoalveolar lavage and lung sections. In vivo kpOmpA priming induced bronchial epithelium activation as evaluated by ICAM-1 and CXCL1 expression, associated with the secretion of CXCL1 and CXCL5 in bronchoalveolar lavage fluids. In the lung, an increased level of the IL-6, CXCL1, CXCL5, CXCL10 mRNA was observed with a maximum at 6 h. These data showed that kpOmpA is involved in host defense mechanism by its ability to activate not only APC but also BEC, resulting in a lung neutrophilia.

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    • "Outer membrane protein A (OmpA) may act as an adhesin, invasin, or immune target, and plays a role in bacterial conjugation , bacteriophage binding, and maintenance of cellular structural integrity (Smith et al., 2007). Several OmpA-family outer membrane proteins (OMPs), including OmpA of Klebsiella pneumoniae (Pichavant et al., 2003), OmpA of Escherichia coli (Khan et al., 2003), OmpA of Acinetobacter baumannii (Choi et al., 2008), and OprF of Pseudomonas aeruginosa (Azghani et al., 2002), have been shown to be involved in pathogenesis. The ompA mutant strains of these bacteria are much less invasive to host cells than their parental strains (Azghani et al., 2002; Choi et al., 2008; Hsieh et al., 2013; Khan et al., 2003). "
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    ABSTRACT: Stenotrophomonas maltophilia is an opportunistic pathogen that is closely associated with high morbidity and mortality in debilitated and immunocompromised individuals. Therefore, to investigate the pathogenesis mechanism is urgently required. However, there are very few studies to evaluate the functional properties of outer membrane protein, which may contribute to the pathogenesis in S. maltophilia. In this study, three abundant proteins in the outer membrane fraction of S. maltophilia were identified by liquid chromatography-tandem mass spectrometry as OmpW1, MopB, and a hypothetical protein. MopB, a member of the OmpA family, was firstly chosen for functional investigation in this study because many OmpA-family proteins are known to be involved in pathogenesis and offer potential as vaccines. Membrane fractionation analyses demonstrated that MopB was indeed the most abundant outer membrane protein (OMP) in S. maltophilia. For functional studies, the mopB mutant of S. maltophilia (SmMopB) was constructed by insertional mutation. MopB deficiency resulted in a change in the protein composition of OMPs and altered the architecture of the outer membrane. The SmMopB strain exhibited reduced cytotoxicity toward L929 fibroblasts and was more sensitive to numerous stresses, including human serum, sodium dodecyl sulfate, and hydrogen peroxide compared with wildtype S. maltophilia. These results suggest that MopB may be a good candidate for the design of vaccines or anti-MopB drugs for controlling serious nosocomial infections of multidrug-resistant S. maltophilia, especially in immunosuppressed patients.
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    • "Compared to other chemokines, CXCL8 has a high affinity at these receptors [5]. ELR-CXC chemokines and other inflammatory mediators are mainly expressed by endothelial cells following bacterial activation in the airways [7] [8]. CXCR2 alone can produce a reduction in neutrophil infiltration, whilst CXCR1, and CXCR2, in combination, can regulate the neutrophil response to ELR chemokines. "
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    • "KpOmpA Unfolds and Refolds in Response to Load Structure 20, 121–127, January 11, 2012 ª2012 Elsevier Ltd All rights reserved 123 unfolding events. It may be further speculated that the stepwise unfolding of KpOmpA brings along another advantage that extracellular loops, which facilitate bacterial adhesion (Pichavant et al., 2003; Smith et al., 2007; Wang, 2002), are extracted from potential binding sites as soon as the tensile load applied becomes too high. Our experiments show that the unfolding intermediates of KpOmpA are established by single and grouped b-strands. "
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    ABSTRACT: In Klebsiella pneumoniae the transmembrane β-barrel forming outer membrane protein KpOmpA mediates adhesion to a wide range of immune effector cells, thereby promoting respiratory tract and urinary infections. As major transmembrane protein OmpA stabilizes Gram-negative bacteria by anchoring their outer membrane to the peptidoglycan layer. Adhesion, osmotic pressure, hydrodynamic flow, and structural deformation apply mechanical stress to the bacterium. This stress can generate tensile load to the peptidoglycan-binding domain (PGBD) of KpOmpA. To investigate how KpOmpA reacts to mechanical stress, we applied a tensile load to the PGBD and observed a detailed unfolding pathway of the transmembrane β-barrel. Each step of the unfolding pathway extended the polypeptide connecting the bacterial outer membrane to the peptidoglycan layer and absorbed mechanical energy. After relieving the tensile load, KpOmpA reversibly refolded back into the membrane. These results suggest that bacteria may reversibly unfold transmembrane proteins in response to mechanical stress.
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