Monocytic activation of protein tyrosine kinase, protein kinase A and protein kinase C induced by porins isolated from Salmonella enterica serovar Typhimurium

Biology and Diseases of Swine

Swine are used in biomedical research as models for biomedical research and for teaching. This chapter covers normative biology and behavior along with common and emerging swine diseases. Xenotransplantation is discussed along with similarities and differences of swine immunology.

Microbe-host interactions: structure and role of Gram-negative bacterial porins

Gram negative bacteria have evolved many mechanisms of attaching to and invading host epithelial and immune cells. In particular, many outer membrane proteins (OMPs) are involved in this initial interaction between the pathogen and their host. The outer membrane (OM) of Gram-negative bacteria performs the crucial role of providing an extra layer of protection to the organism without compromising the exchange of material required for sustaining life. The OM, therefore, represents a sophisticated macromolecular assembly, whose complexity has yet to be fully elucidated. This review will summarize the structural information available for porins, a class of OMP, and highlight their role in bacterial pathogenesis and their potential as therapeutic targets. The functional role of porins in microbe-host interactions during various bacterial infections has emerged only during the last few decades, and their interaction with a variety of host tissues for adhesion to and invasion of the cell and for evasion of host-defense mechanisms have placed bacterial porins at the forefront of research in bacterial pathogenesis. This review will discuss the role that porins play in activating immunological responses, in inducing signaling pathways and their influence on antibiotic resistance mechanisms that involve modifications of the properties of the OM lipid barrier.

PAMPs, PRRs and the genomics of gram negative bacterial recognition in fish

Understanding the mechanisms that underpin pathogen recognition and subsequent orchestration of the immune response in fish is an area of significant importance for both basic research and management of health in aquaculture. In recent years much attention has been given to the identification of pattern recognition receptors (PRRs) in fish, however, characterisation of interactions with specific pathogen-associated molecular patterns (PAMPs) is still incomplete. Microarray studies have significantly contributed to functional studies and early descriptions of PAMP-PRR driven activation of specific response cassettes in the genome have been obtained although much is left to be done. In this review we will address gram negative (G-negative) bacterial recognition in fish addressing contributing factors such as structure-function relationships between G-negative PAMPs, current knowledge of fish PRRs and the input achieved by microarray-based studies ranging from in vivo infection studies to directed in vitro PAMP-cell studies. Finally we revisit the endotoxic recognition paradigm in fish and suggest a series of future perspectives that could contribute toward the further elucidation of G-negative bacterial recognition across the highly diverse group of vertebrates that encompass the fishes.

Cellular cholesterol involvement in Src, PKC, and p38/JNK transduction pathways by porins

Biological membranes are described as a mosaic of different domains where interactions between membrane components induce the formation of subdomains with different characteristics and functions. Lipids play an important role in the formation of lipid-enriched microdomains where they dynamically associate to form platforms important for membrane protein sorting and construction of signaling complexes. Cholesterol confined in lipid domains is a crucial component required by microorganisms, directly or indirectly, to enter or exit the intracellular compartment. Cellular activation mediated by superficial bacterial component may be modified by local cholesterol depletion. Therefore, new perspectives for unconventional therapeutic intervention in Gram-negative infections may be envisaged. We tested this hypothesis by using methyl-beta-cyclodextrin (mbetaCD) as a cholesterol-complexing agent to alter the U937 plasma membrane cholesterol content. Our results demonstrate that cholesterol depletion of U937 cells inhibited Salmonella enterica serovar Typhimurium porins-mediated phosphorylation of Src kinase family, protein kinase C (PKC), JNK, and p38, while cholesterol repletion restored the phosphorylation. Lipopolysaccharide (LPS) extracted from the same bacterial strain has been used as a control. Our data demonstrate that the lack of activation of signal transduction pathway observed following cholesterol depletion differently modulates the release of interleukin-6 (IL-6) or tumor necrosis factor-alpha (TNF-alpha), suggesting that Src, associated to lipid domains, may represent an important pathway in Gram-negative-induced cellular signal.

STAT1 and STAT3 phosphorylation by porins are independent of JAKs but are dependent on MAPK pathway and plays a role in U937 cells production of interleukin-6

A group of transcription factors, termed signal transducers and activators of transcription (STATs), appears to orchestrate the downstream events propagated by cytokine/growth factor interactions with their cognate receptors. Similarly, cytoplasmic Janus kinases (JAKs) seem to play a critical role in diverse signal transduction pathways that govern cellular survival, proliferation, differentiation and apoptosis. In this work, we analysed the effects of the Salmonella enterica serovar Typhimurium porins on signaling by the JAK/STAT pathway and IL-6 release in U937 cells. Porins and LPS of membrane from Gram-negative bacteria are factors implicated in septic shock. In our assays porins induce interleukin-6 (IL-6) release (110+/-2.6pg/ml) 24h after stimulation and STAT1/STAT3 tyrosine (Tyr701/Tyr705) and serine (Ser727) phosphorylation after 15min. By using several selective inhibitors we demonstrate that porins modulate the activation of STAT1/STAT3 through mitogen activated protein kinases (MAPKs) and not JAKs. Furthermore, we demonstrated that STAT1 and STAT3 are not involved in the modulation of IL-6 release in U937 cells stimulated with porins. Inhibition of tyrosine/serine phosphorylation mediated by MAPKs of STAT1 and STAT3 decrease the IL-6 secretion following porin stimulation. Therefore, suggesting a key role of this pathway in phosphorylation of Ser 727 in STAT1 and STAT3. These results are confirmed by porin or LPS-induced nuclear translocation of STAT1 and STAT3 in U937 cells.

Salmonella enterica serovar Typhimurium ompS1 and ompS2 mutants are attenuated for virulence in mice

Salmonella enterica serovar Typhimurium mutants with mutations in the ompS1 and ompS2 genes, which code for quiescent porins, were nevertheless highly attenuated for virulence in a mouse model, indicating a role in pathogenesis. Similarly, a strain with a mutation in the gene coding for LeuO, a positive regulator of ompS2, was also attenuated.

OmpD but not OmpC is involved in adherence ofSalmonella entericaserovar Typhimurium to human cells

Conflicting reports exist regarding the role of porins OmpC and OmpD in infections due to Salmonella enterica serovar Typhimurium. This study investigated the role of these porins in bacterial adherence to human macrophages and intestinal epithelial cells. ompC and ompD mutant strains were created by transposon mutagenesis using P22-mediated transduction of Tn10 and Tn5 insertions, respectively, into wild-type strain 14028. Fluorescein-labeled wild-type and mutant bacteria were incubated with host cells at various bacteria to cell ratios for 1 h at 37 °C and analyzed by flow cytometry. The mean fluorescence intensity of cells with associated wild-type and mutant bacteria was used to estimate the number of bacteria bound per host cell. Adherence was also measured by fluorescence microscopy. Neither assay showed a significant difference in binding of the ompC mutant and wild-type strains to the human cells. In contrast, the ompD mutant exhibited lowered binding to both cell types. Our findings suggest that OmpD but not OmpC is involved in the recognition of Salmonella serovar Typhimurium by human macrophages and intestinal epithelial cells.Key words: Salmonella, adherence, porins, intestinal epithelial cells, macrophage.

Interleukin-8 production by THP-1 cells stimulated by Salmonella enterica serovar Typhimurium porins is mediated by AP-1, NF-κB and MAPK pathways

Interleukin-8 (IL-8) is released in response to inflammatory stimuli, such as bacterial products. Either porins or lipopolysaccharide (LPS) stimulated THP-1 cells to release IL-8 after 24 h. We have previously reported that stimulation of monocytic cells with Salmonella enterica serovar Typhimurium porins led to the activation of mitogen-activated protein kinase cascades and of protein tyrosine kinases (PTKs). In this report, we demonstrate, using two potent and selective inhibitors of MEK activation by Raf-1 (PD-098059) and p38 (SB-203580), that both ERK1/2 and p38 pathways play a key role in the production of IL-8 by porins and LPS. Porin-stimulated expression of activating protein 1 (AP-1) and correlated IL-8 release is also inhibited by PD-098059 or SB-203580 indicating that the Raf-1/MEK1-MEK2/MAPK cascade is required for their activation. Also PTKs modulate the pathway that control IL-8 gene expression, in fact its expression is abolished by tyrphostin. By using N-acetyl-leucinyl-leucinyl-norleucinal-H (ALLN) an inhibitor of nuclear factor-kappaB (NF-kappaB) activity, we also observed IL-8 release modulation. Our results elucidate some of the molecular mechanisms by which AP-1 and NF-kappaB regulate IL-8 release and open new strategies for the design of specific molecules that will modulate IL-8 effects in various infectious diseases.

Eukaryotic cell signaling and transcriptional activation induced by bacterial porins

The protein composition of the outer membrane of Gram-negative bacteria consists of about 20 immunochemically distinct proteins, termed outer membrane proteins (OMPs). Apart from their structural role, OMPs have been shown to have other functions, particularly with regard to transport, and have been classified as permeases and porins. Porins, during their interaction with the host, are immunogenic and also directly stimulate several cellular functions. Porins work both as molecules present on the bacterial surface and as molecules released by bacteria. Lipopolysaccharide and OMPs, the major structural macromolecular constituents of the outer membrane, carry out a fundamental role in the pathogenesis of Gram-negative infections. This brief review describes the multiple facets of the biological activities of porins both in vitro and in vivo, particularly focusing on their ability to induce the expression of cytokines and other factors that modulate cellular activities with either pathological or adaptive consequences. This brief discussion will focus on the signal transmission mechanisms induced by bacterial porins.