Effects of inhibitors of Toll-like receptors, protease-activated receptor-2 signalings and trypsin on influenza A virus replication and upregulation of cellular factors in cardiomyocytes

Severe influenza sometimes causes myocarditis. We recently found that influenza A virus (IAV) infection induces various cellular factors, such as proinflammatory cytokines IL-6, IL-1β and TNF-α, matrix metalloproteinases (MMPs) and ectopic trypsin in mice hearts and in H9c2 cardiomyocytes. The induction of these cellular factors in turn promotes viral replication, myocardial inflammation and cellular damage through their intracellular signal transductions in cooperation with the IAV-induced Toll-like receptors (TLRs) and proteinase-activated receptor-2 (PAR-2) signallings, although the precise nature of these interactions remain obscure. By using specific inhibitors of TLRs and PAR-2 signalings and trypsin inhibitor aprotinin, we analyzed the role of TLR signaling and PAR-2 signaling in the IAV-induced pathological changes in cardiomyocytes. Inhibitors of TLR7/8-Myeloid Differentiation factor 88-nuclear factor-B signaling and aprotinin effectively suppressed IAV-induced upregulation of proinflammatory cytokines, MMPs, trypsinogen and viral replication. Inhibitor of TLR3-Toll/interleukin-1 receptor domain-containing adaptor inducing interferons-dependent signaling predominantly suppressed the upregulation of interferon-β, a key intracellular host immune response factor. In contrast to the suppressive effect of trypsin inhibitor aprotinin on IAV replication, PAR-2 inhibitor FSY-NH2, induced marginal upregulation of trypsinogen and subsequent stimulation of IAV replication

Vascular hyperpermeability in severe influenza

Multiorgan failure with vascular hyperpermeability is the final outcome in the progression of seasonal influenza virus pneumonia and influenza-associated encephalopathy, and it is also common in infection with highly pathogenic avian influenza virus. However, the precise molecular mechanism by which influenza virus infection causes vascular endothelial cell hyperpermeability remains poorly defined. We investigated the mechanisms of hyperpermeability of human umbilical vein endothelial cells infected with influenza A virus (IAV)/Puerto Rico/8/34 (PR8) (H1N1). The levels of β-catenin, a key regulatory component of the vascular endothelial-cadherin cell adhesion complex, were markedly decreased during infection for 28 h, with increments of vascular hyperpermeability measured by transendothelial electrical resistance. Lactacystin (at 2 μM), a proteasome inhibitor, inhibited the decrease in β-catenin levels. Since the N-terminal phosphorylation of β-catenin by glycogen synthase kinase (GSK)-3β is the initiation step of proteasome-dependent degradation, we examined the effects of GSK-3β suppression by RNA interference in endothelial cells. IAV-infection-induced β-catenin degradation was significantly inhibited in GSK-3β-knockdown cells, and transfection of cells with recombinant β-catenin significantly suppressed IAV-induced hyperpermeability. These findings suggest that IAV infection induces GSK-3β-mediated β-catenin degradation in the adherens junctional complexes and induces vascular hyperpermeability. The in vitro findings of β-catenin degradation and activation of GSK-3β after IAV infection were confirmed in lungs of mice infected with IAV PR8 during the course of infection from day 0 to day 6. These results suggest that GSK-3β-mediated β-catenin degradation in adherens junctions is one of the key mechanisms of vascular hyperpermeability in severe influenza

Mechanisms of matrix metalloproteinase-9 upregulation and tissue destruction in various organs in influenza A virus infection

Severe influenza is characterized clinicopathologically by multiple organ failure, although the relationship amongst virus and host factors that influence this morbid outcome and the underlying mechanisms of action remain unclear. The present study identified marked upregulation of matrix metalloproteinase (MMP)-9 and pro-inflammatory cytokine tumor necrosis factor alpha (TNF-α) in various organs after intranasal infection of influenza A WSN virus. MMP-9 and TNF-α were upregulated in the lung, the site of initial infection, as well as in the brain and heart. The infection-induced MMP-9 upregulation was inhibited by anti-TNF-α antibodies and by anti-oxidative reagents pyrrolidine dithiocarbamate and N-acetyl-L-cysteine, which inhibit activation of nuclear factor kappa B (NF-χB), as well as by nordihydroguaiaretic acid, which inhibits activation of activator protein 1 (AP-1). In addition, MMP-9 upregulation via TNF-α was also suppressed by inhibitors of mitogen-activated protein kinases (MAPKs), such as extracellular signalregulated kinase 1/2 and p38, and partly by a c-Jun N-terminal kinase inhibitor. These results indicated that the influenza-induced MMP-9 upregulation in various organs is mediated through MAPK-NF-χB- and/or AP-1-dependent mechanisms. Strategies that neutralize TNF-α as well as inhibitors of MAPK-NF-χB- and/or AP-1-dependent pathways may be useful for suppressing the MMP-9 effect and thus preventing multiple organ failure in severe influenza

The second metal-binding site of 70 kDa heat-shock protein is essential for ADP binding, ATP hydrolysis and ATP synthesis.

The chaperone activity of Hsp70 (70 kDa heat-shock protein) in protein folding and its conformational switch, including oligomeric and monomeric interconversion, are regulated by the hydrolysis of ATP and the ATP-ADP exchange cycle. The crystal structure of human ATPase domain shows two metal-binding sites, the first for ATP binding and a second, in close proximity to the first, whose function remains unknown [Sriram, Osipiuk, Freeman, Morimoto and Joachimiak (1997) Structure 5, 403-414]. In this study, we have characterized the second metal-binding motif by site-directed mutagenesis and the kinetics of ATP and ADP binding, and found that the second metal-binding site, comprising a loop co-ordinated by His-227, Glu-231 and Asp-232, participates both in ATP hydrolysis and ATP-synthetic activities, in co-operation with the first metal-binding site. The first metal-binding site, a catalytic centre, is essential for ATP binding and the second site for ADP binding in the reactions of ATP hydrolysis and ATP synthesis

Intrinsic nucleoside diphosphate kinase-like activity as a novel function of 14-3-3 proteins

Abstract14-3-3 proteins play a role in many cellular functions as molecular chaperone and adapter proteins: they bind to and modulate several proteins involved in cell proliferation and differentiation, and also function ATP-dependently in targeting of precursors to mitochondria. We show here that 14-3-3 purified from a human lymphoblastoma and also its recombinant τ isoform exhibited intrinsic nucleoside diphosphate (NDP) kinase-like activity. 14-3-3 proteins preferentially catalyzed the transfer of the γ-phosphate group from ATP, dATP or dGTP to all nucleoside diphosphates and this transfer involved acid-labile phosphoenzyme intermediates. They also simultaneously catalyzed the reverse reaction of ATP hydrolysis. These properties of 14-3-3 are similar to those of NDP kinase, but not to those of adenylate kinase