Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.25.1 (proteasome)
 28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two pathogenic mechanisms of Pseudomonas aeruginosa corneal infections are discussed, one involving bacterial exoenzymes, the other involving polymorphonuclear leukocyte (PMN)-derived lysosomal enzymes. The objective of the present study was (1) to show the relative importance of the two mechanisms and (2) to evaluate the effect of active immunization against P. aeruginosa exoenzymes on ocular damage. Rabbits were immunized against P. aeruginosa alkaline protease (AP) or elastase (Ela) and challenged with the respective enzymes. Corneal damage was studied by light photography (LP). In another group, rabbits were immunized against AP, Ela and exotoxin A (ExoA) and challenged with P. aeruginosa strains PA01 or PA103. Corneal damage was studied with LP, light microscopy, and electron microscopy. Immunized animals were totally protected against intracorneal inoculation of P. aeruginosa proteases. Twelve hr and 24 hr after challenge with whole bacteria, immunized rabbits revealed less corneal damage than non-immunized animals. However, after 48 hr corneal damage (ie severe corneal ulceration) was comparable in both groups. The study suggests that corneal damage involving lysosomal enzymes from stimulated PMN is more important after bacterial infection than direct damage by P. aeruginosa exoenzymes.
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PMID:Relevance of host-derived and bacterial factors in Pseudomonas aeruginosa corneal infections. 330 11

Mast cells are recognized not only as the major effector cells of type I hypersensitivity reactions but also as an important player of innate immune response against bacterial infection. Type I IFNs are also involved in the response against bacterial infection. However, the role of type I IFNs and their associated Janus kinase Tyk2 in mast cell functions remains to be determined. In this study, we addressed this issue using Tyk2-deficient (Tyk2(-/-)) bone marrow-derived mast cells (BMMCs). When BMMCs from wild-type (WT) mice were stimulated with IFN-alpha, they expressed mRNA for IFN-gamma-inducible protein 10 (IP-10) and monocyte chemoattractant protein-5 (MCP-5). Interestingly, IFN-alpha-induced expression of IP-10 and MCP-5 was severely decreased in Tyk2(-/-) BMMCs. In addition, IFN-alpha-induced Stat1 phosphorylation was decreased in Tyk2(-/-) BMMCs. On the other hand, IFN-alpha-induced Stat1 phosphorylation and IP-10 and MCP-5 expression were normal in Tyk2(-/-) fibroblasts. These results indicate that IFN-alpha induces the expression of TNF-alpha and the chemokines IP-10 and MCP-5 in mast cells and thatTyk2 plays a nonredundant role in IFN-alpha signaling in mast cells.
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PMID:Tyk2 is essential for IFN-alpha-induced gene expression in mast cells. 1516 80

The Skp2 oncoprotein belongs to the family of F-box proteins that function as substrate recognition factors for SCF (Skp1, cullin, F-box protein) E3 ubiquitin-ligase complexes. Binding of the substrate to the SCFSkp2 complex catalyzes the conjugation of ubiquitin molecules to the bound substrate, resulting in multi-ubiquitination and rapid degradation by the 26 S proteasome. Using Skp2 as bait in a yeast two-hybrid screen, we have identified UBP43 as a novel substrate for Skp2. UBP43 belongs to the family of ubiquitin isopeptidases and specifically cleaves ISG15, a ubiquitin-like molecule that is induced by cellular stresses, such as type 1 interferons (IFN), nephrotoxic damage, and bacterial infection. UBP43 was originally identified as an up-regulated gene in knock-in mice expressing an acute myelogenous leukemia fusion protein, AML1-ETO, as well as in melanoma cell lines treated with IFN-beta. The phenotype of UBP43 knockout mice includes shortened life span, hypersensitivity to IFN, and neuronal damage, suggesting that tight regulation of ISG15 conjugation is critical for normal cellular function. In this study, we demonstrate that UBP43 is ubiquitinated in vivo and accumulates in cells treated with proteasome inhibitors. We also show that Skp2 promotes UBP43 ubiquitination and degradation, resulting in higher levels of ISG15 conjugates. In Skp2-/- mouse cells, levels of UBP43 are consistently up-regulated, whereas levels of ISG15 conjugates are reduced. Our results demonstrate that the SCFSkp2 is involved in controlling UBP43 protein levels and may therefore play an important role in modulating type 1 IFN signaling.
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PMID:The ISG15 isopeptidase UBP43 is regulated by proteolysis via the SCFSkp2 ubiquitin ligase. 1534 34

Bacterial infection elicits hypertriglyceridemia attributed to increased hepatic production of very low-density lipoprotein (VLDL) particles and decreased peripheral metabolism. The mechanisms underlying VLDL overproduction in sepsis are as yet unclear, but seem to be fed/fasted state-dependent. To learn more about this, we investigated hepatocytes isolated from fasted rats, made endotoxic by 1 mg/kg lipopolysaccharide (LPS) injection, for their ability to secrete the VLDL protein and lipid components. The results were then related to lipogenesis markers and expression of genes critical to VLDL biogenesis. Endotoxic rats showed increased levels of serum VLDL-apoB (10-fold), -triglyceride (2-fold), and -cholesterol (2-fold), whereby circulating VLDL were lipid-poor particles. Similarly, VLDL-apoB secretion by isolated endotoxic hepatocytes was approximately 85% above control, whereas marginal changes in the output of VLDL-lipid classes occurred. This was accompanied by a substantial rise in apoB and a moderate rise in MTP mRNA levels, but with basal de novo formation and efficiency of secretion of triglycerides, cholesterol and cholesteryl esters. These results indicate that during periods of food restriction, endotoxin does not enhance lipid provision to accomplish normal lipidation of overproduced apoB molecules, though this does occur to a sufficient extent to pass the proteasome checkpoint and secretion of lipid-poor, type 2 VLDL takes place.
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PMID:Impaired response of VLDL lipid and apoB secretion to endotoxin in the fasted rat liver. 1671 89

Glycogen synthase kinase-3 (GSK-3) is a key player in various important signaling pathways in animals. The activity of GSK-3 is known to be modulated by protein phosphorylation and differential complex formation. However, little information is available regarding the function and regulation of plant GSK-3/shaggy-like kinases (GSKs). Analysis of the in vivo kinase activity of MsK1, a GSK from Medicago sativa, revealed that MsK1 is active in healthy plants and that MsK1 activity is down-regulated by the elicitor cellulase in a time- and dose-dependent manner. Surprisingly, cellulase treatment triggered the degradation of the MsK1 protein in a proteasome-dependent manner suggesting a novel mechanism of GSK-3 regulation. Inhibition of MsK1 kinase activity and degradation of the protein were two successive processes that could be uncoupled. In a transgenic approach, stimulus-induced inhibition of MsK1 was impeded by constant replenishment of MsK1 by a strong constitutive promoter. MsK1 overexpressing plants exhibited enhanced disease susceptibility to the virulent bacterial pathogen Pseudomonas syringae. MAP kinase activation in response to pathogen infection was compromised in plants with elevated MsK1 levels. These data strongly suggest that tight regulation of the plant GSK-3, MsK1, may be important for innate immunity to limit the severity of virulent bacterial infection.
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PMID:A Proteasome-regulated glycogen synthase kinase-3 modulates disease response in plants. 1717 44

The last few years have seen important advances in defining the mechanisms that cells use to monitor changes in cholesterol levels and regulate lipid metabolism. This work has unraveled a feedback system that enables cholesterol and certain sterol intermediates to regulate the proteolysis and transport of specific membrane proteins. The sterol regulatory element-binding protein (SREBP) family of transcription factors is at the center of this feedback system. These membrane-embedded proteins are activated by ER-to-Golgi transport followed by limited proteolysis. In addition, both the activation of the SREBPs and the stability of the rate-limiting enzyme in cholesterol synthesis are regulated by the ubiquitin-proteasome system in a sterol-dependent manner. The ubiquitin-proteasome system also regulates the degradation of active SREBPs. Recent work also highlights the important role of this regulatory system in several organisms, ranging from yeast to humans. In addition, the SREBP pathway has been found to regulate a diverse set of cellular processes, including phagocytosis, cell cycle progression, oxygen sensing and survival in response to bacterial infection. These advances illustrate the wide-ranging roles that SREBPs and membrane biogenesis have in cell biology.
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PMID:SREBP in signal transduction: cholesterol metabolism and beyond. 1730 6

The Pseudomonas aeruginosa-derived alkaline protease (AprA), elastase A (LasA), elastase B (LasB) and protease IV are considered to play an important role in pathogenesis of this organism. Although the sequence analysis of P. aeruginosa genome predicts the presence of several genes encoding other potential proteases in the genome, little has been known about the proteases involving in pathogenesis. Recently, Porphyromonas gingivalis gingipains and Serratia marcescens serralysin have been shown to activate protease-activated receptor 2 (PAR-2), thereby modulating host inflammatory and immune responses. Accordingly, we hypothesized that unknown protease(s) from P. aeruginosa would also modulate such responses through PARs. In this study, we found that P. aeruginosa produces a novel large exoprotease (LepA) distinct from known proteases such as AprA, LasA, LasB and protease IV. Sequence analysis of LepA showed a molecular feature of the proteins transported by the two-partner secretion pathway. Our results indicated that LepA activates NF-kappaB-driven promoter through human PAR-1, -2 or -4 and cleaves the peptides corresponding to the tethered ligand region of human PAR-1, -2 and -4 at a specific site with exposure of their tethered ligands. Considered together, these results suggest that LepA would require PARs to modulate various host responses against bacterial infection.
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PMID:A novel secreted protease from Pseudomonas aeruginosa activates NF-kappaB through protease-activated receptors. 1833 90

The obligate intracellular pathogen Chlamydia trachomatis is the most common cause of sexually transmitted bacterial disease. It secretes a protease known as chlamydial protease/proteasome-like activity factor (CPAF) that degrades many host molecules and plays a major role in Chlamydia pathogenesis. Here, we show that mature CPAF is a homodimer of the catalytic domains, each of which comprises two distinct subunits. Dormancy of the CPAF zymogen is maintained by an internal inhibitory segment that binds the CPAF active site and blocks its homodimerization. CPAF activation is initiated by trans-autocatalytic cleavage, which induces homodimerization and conformational changes that assemble the catalytic triad. This assembly leads to two autocatalytic cleavages and removal of the inhibitory segment, enabling full CPAF activity. CPAF is covalently bound and inhibited by the proteasome inhibitor lactacystin. These results reveal the activation mechanism of the CPAF serine protease and suggest new opportunities for anti-Chlamydia drug development.
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PMID:Structural basis for activation and inhibition of the secreted chlamydia protease CPAF. 1906 54

NF-kappaB (nuclear factor kappaB) has a pivotal role in many cellular processes, including the inflammatory and immune responses and, therefore, its activation is tightly regulated by the IKK (IkappaB kinase) complex and by IkappaBalpha degradation. When Shigella bacteria multiply within epithelial cells they release peptidoglycans, which are recognized by Nod1 and stimulate the NF-kappaB pathway, thus leading to a severe inflammatory response. Here, we show that IpaH9.8, a Shigella effector possessing E3 ligase activity, dampens the NF-kappaB-mediated inflammatory response to the bacterial infection in a unique way. IpaH9.8 interacts with NEMO/IKKgamma and ABIN-1, a ubiquitin-binding adaptor protein, promoting ABIN-1-dependent polyubiquitylation of NEMO. Consequently, polyubiquitylated NEMO undergoes proteasome-dependent degradation, which perturbs NF-kappaB activation. As NEMO is essential for NF-kappaB activation, we propose that the polyubiquitylation and degradation of NEMO during Shigella infection is a new bacterial strategy to modulate host inflammatory responses.
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PMID:A bacterial E3 ubiquitin ligase IpaH9.8 targets NEMO/IKKgamma to dampen the host NF-kappaB-mediated inflammatory response. 2001 Aug 14

During infection, pathogenic bacteria manipulate the host cell in various ways to allow their own replication, propagation and escape from host immune responses. Post-translational modifications are unique mechanisms that allow cells to rapidly, locally and specifically modify activity or interactions of key proteins. Some of these modifications, including phosphorylation and ubiquitylation, can be induced by pathogens. However, the effects of pathogenic bacteria on SUMOylation, an essential post-translational modification in eukaryotic cells, remain largely unknown. Here we show that infection with Listeria monocytogenes leads to a decrease in the levels of cellular SUMO-conjugated proteins. This event is triggered by the bacterial virulence factor listeriolysin O (LLO), which induces a proteasome-independent degradation of Ubc9, an essential enzyme of the SUMOylation machinery, and a proteasome-dependent degradation of some SUMOylated proteins. The effect of LLO on Ubc9 is dependent on the pore-forming capacity of the toxin and is shared by other bacterial pore-forming toxins like perfringolysin O (PFO) and pneumolysin (PLY). Ubc9 degradation was also observed in vivo in infected mice. Furthermore, we show that SUMO overexpression impairs bacterial infection. Together, our results reveal that Listeria, and probably other pathogens, dampen the host response by decreasing the SUMOylation level of proteins critical for infection.
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PMID:Listeria monocytogenes impairs SUMOylation for efficient infection. 3235 Apr 66


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