Protein kinase C-alpha activity is required for respiratory syncytial virus fusion to human bronchial epithelial cells

The Role of the Nrf2 Pathway in Airway Tissue Damage Due to Viral Respiratory Infections

Respiratory viruses constitute a significant cause of illness and death worldwide. Respiratory virus-associated injuries include oxidative stress, ferroptosis, inflammation, pyroptosis, apoptosis, fibrosis, autoimmunity, and vascular injury. Several studies have demonstrated the involvement of the nuclear factor erythroid 2-related factor 2 (Nrf2) in the pathophysiology of viral infection and associated complications. It has thus emerged as a pivotal player in cellular defense mechanisms against such damage. Here, we discuss the impact of Nrf2 activation on airway injuries induced by respiratory viruses, including viruses, coronaviruses, rhinoviruses, and respiratory syncytial viruses. The inhibition or deregulation of Nrf2 pathway activation induces airway tissue damage in the presence of viral respiratory infections. In contrast, Nrf2 pathway activation demonstrates protection against tissue and organ injuries. Clinical trials involving Nrf2 agonists are needed to define the effect of Nrf2 therapeutics on airway tissues and organs damaged by viral respiratory infections.

Acute Adenoviral Infection Elicits an Arrhythmogenic Substrate Prior to Myocarditis

BACKGROUND

Viral cardiac infection represents a significant clinical challenge encompassing several etiological agents, disease stages, complex presentation, and a resulting lack of mechanistic understanding. Myocarditis is a major cause of sudden cardiac death in young adults, where current knowledge in the field is dominated by later disease phases and pathological immune responses. However, little is known regarding how infection can acutely induce an arrhythmogenic substrate before significant immune responses. Adenovirus is a leading cause of myocarditis, but due to species specificity, models of infection are lacking, and it is not understood how adenoviral infection may underlie sudden cardiac arrest. Mouse adenovirus type-3 was previously reported as cardiotropic, yet it has not been utilized to understand the mechanisms of cardiac infection and pathology.

METHODS

We have developed mouse adenovirus type-3 infection as a model to investigate acute cardiac infection and molecular alterations to the infected heart before an appreciable immune response or gross cardiomyopathy.

RESULTS

Optical mapping of infected hearts exposes decreases in conduction velocity concomitant with increased Cx43Ser368 phosphorylation, a residue known to regulate gap junction function. Hearts from animals harboring a phospho-null mutation at Cx43Ser368 are protected against mouse adenovirus type-3-induced conduction velocity slowing. Additional to gap junction alterations, patch clamping of mouse adenovirus type-3-infected adult mouse ventricular cardiomyocytes reveals prolonged action potential duration as a result of decreased IK1 and IKs current density. Turning to human systems, we find human adenovirus type-5 increases phosphorylation of Cx43Ser368 and disrupts synchrony in human induced pluripotent stem cell-derived cardiomyocytes, indicating common mechanisms with our mouse whole heart and adult cardiomyocyte data.

CONCLUSIONS

Together, these findings demonstrate that adenoviral infection creates an arrhythmogenic substrate through direct targeting of gap junction and ion channel function in the heart. Such alterations are known to precipitate arrhythmias and likely contribute to sudden cardiac death in acutely infected patients.

The Role of the NRF2 Pathway in the Pathogenesis of Viral Respiratory Infections

In humans, acute and chronic respiratory infections caused by viruses are associated with considerable morbidity and mortality. Respiratory viruses infect airway epithelial cells and induce oxidative stress, yet the exact pathogenesis remains unclear. Oxidative stress activates the transcription factor NRF2, which plays a key role in alleviating redox-induced cellular injury. The transcriptional activation of NRF2 has been reported to affect both viral replication and associated inflammation pathways. There is complex bidirectional crosstalk between virus replication and the NRF2 pathway because virus replication directly or indirectly regulates NRF2 expression, and NRF2 activation can reversely hamper viral replication and viral spread across cells and tissues. In this review, we discuss the complex role of the NRF2 pathway in the regulation of the pathogenesis of the main respiratory viruses, including coronaviruses, influenza viruses, respiratory syncytial virus (RSV), and rhinoviruses. We also summarize the scientific evidence regarding the effects of the known NRF2 agonists that can be utilized to alter the NRF2 pathway.

An Update on Protein Kinases as Therapeutic Targets-Part I: Protein Kinase C Activation and Its Role in Cancer and Cardiovascular Diseases

Protein kinases are one of the most significant drug targets in the human proteome, historically harnessed for the treatment of cancer, cardiovascular disease, and a growing number of other conditions, including autoimmune and inflammatory processes. Since the approval of the first kinase inhibitors in the late 1990s and early 2000s, the field has grown exponentially, comprising 98 approved therapeutics to date, 37 of which were approved between 2016 and 2021. While many of these small-molecule protein kinase inhibitors that interact orthosterically with the protein kinase ATP binding pocket have been massively successful for oncological indications, their poor selectively for protein kinase isozymes have limited them due to toxicities in their application to other disease spaces. Thus, recent attention has turned to the use of alternative allosteric binding mechanisms and improved drug platforms such as modified peptides to design protein kinase modulators with enhanced selectivity and other pharmacological properties. Herein we review the role of different protein kinase C (PKC) isoforms in cancer and cardiovascular disease, with particular attention to PKC-family inhibitors. We discuss translational examples and carefully consider the advantages and limitations of each compound (Part I). We also discuss the recent advances in the field of protein kinase modulators, leverage molecular docking to model inhibitor-kinase interactions, and propose mechanisms of action that will aid in the design of next-generation protein kinase modulators (Part II).

Therapeutic potential of chelerythrine as a multi-purpose adjuvant for the treatment of COVID-19

Multifunctional nature of phytochemicals and their chemical diversity has attracted attention to develop leads originated from nature to fight COVID-19. Pharmacological activities of chelerythrine and its congeners have been studied and reported in the literature. This compound simultaneously has two key therapeutic effects for the treatment of COVID-19, antiviral and anti-inflammatory activities. Chelerythrine can prevent hyper-inflammatory immune response through regulating critical signaling pathways involved in SARS-CoV-2 infection, such as alteration in Nrf2, NF-κB, and p38 MAPK activities. In addition, chelerythrine has a strong protein kinase C-α/-β inhibitory activity suitable for cerebral vasospasm prevention and eryptosis reduction, as well as beneficial effects in suppressing pulmonary inflammation and fibrosis. In terms of antiviral activity, chelerythrine can fight with SARS-CoV-2 through various mechanisms, such as direct-acting mechanism, viral RNA-intercalation, and regulation of host-based antiviral targets. Although chelerythrine is toxic in vitro, the in vivo toxicity is significantly reduced due to its structural conversion to alkanolamine. Its multifunctional action makes chelerythrine a prominent compound for the treatment of COVID-19. Considering precautions related to the toxicity at higher doses, it is expected that this compound is useful in combination with proper antivirals to reduce the severity of COVID-19 symptoms.

Identifying Loci Associated With Bovine Corona Virus Infection and Bovine Respiratory Disease in Dairy and Feedlot Cattle

Bovine coronavirus (BCoV) is associated with respiratory and enteric infections in both dairy and beef cattle worldwide. It is also one of a complex of pathogens associated with bovine respiratory disease (BRD), which affects millions of cattle annually. The objectives of this study were to identify loci and heritability estimates associated with BCoV infection and BRD in dairy calves and feedlot cattle. Dairy calves from California (n = 1,938) and New Mexico (n = 647) and feedlot cattle from Colorado (n = 915) and Washington (n = 934) were tested for the presence of BCoV when classified as BRD cases or controls following the McGuirk scoring system. Two comparisons associated with BCoV were investigated: (1) cattle positive for BCoV (BCoV⁺) were compared to cattle negative for BCoV (BCoV^-) and (2) cattle positive for BCoV and affected with BRD (BCoV⁺BRD⁺) were compared to cattle negative for BCoV and BRD (BCoV^-BRD^-). The Illumina BovineHD BeadChip was used for genotyping, and genome-wide association analyses (GWAA) were performed using EMMAX (efficient mixed-model association eXpedited). The GWAA for BCoV⁺ identified 51 loci (p < 1 × 10^-5; 24 feedlot, 16 dairy, 11 combined) associated with infection with BCoV. Three loci were associated with BCoV⁺ across populations. Heritability estimates for BCoV⁺ were 0.01 for dairy, 0.11 for feedlot cattle, and 0.03 for the combined population. For BCoV⁺BRD⁺, 80 loci (p < 1 × 10^-5; 26 feedlot, 25 dairy, 29 combined) were associated including 14 loci across populations. Heritability estimates for BCoV⁺BRD⁺ were 0.003 for dairy, 0.44 for feedlot cattle, and 0.07 for the combined population. Several positional candidate genes associated with BCoV and BRD in this study have been associated with other coronaviruses and respiratory infections in humans and mice. These results suggest that selection may reduce susceptibility to BCoV infection and BRD in cattle.

Evidence of a dysregulated vitamin D endocrine system in SARS-CoV-2 infected patient's lung cells

Although a defective vitamin D endocrine system has been widely suspected to be associated in SARS-CoV-2 pathobiology, the status of the vitamin D endocrine system and vitamin D-modulated genes in lung cells of patients infected with SARS-CoV-2 remains unknown. To understand the significance of the vitamin D endocrine system in SARS-CoV-2 pathobiology, computational approaches were applied to transcriptomic datasets from bronchoalveolar lavage fluid (BALF) cells of such patients or healthy individuals. Levels of vitamin D receptor, retinoid X receptor, and CYP27A1 in BALF cells of patients infected with SARS-CoV-2 were found to be reduced. Additionally, 107 differentially expressed, predominantly downregulated genes, as potentially modulated by vitamin D endocrine system, were identified in transcriptomic datasets from patient's cells. Further analysis of differentially expressed genes provided eight novel genes with a conserved motif with vitamin D-responsive elements, implying the role of both direct and indirect mechanisms of gene expression by the dysregulated vitamin D endocrine system in SARS-CoV-2-infected cells. Protein-protein interaction network of differentially expressed vitamin D-modulated genes were enriched in the immune system, NF-κB/cytokine signaling, and cell cycle regulation as top predicted pathways that might be affected in the cells of such patients. In brief, the results presented here povide computational evidence to implicate a dysregulated vitamin D endocrine system in the pathobiology of SARS-CoV-2 infection.

Mutational analysis of structural proteins of SARS-CoV-2

SARS-CoV-2 transmissibility is higher than that of other human coronaviruses; therefore, it poses a threat to the populated communities. We investigated mutations among envelope (E), membrane (M), and spike (S) proteins from different isolates of SARS-CoV-2 and plausible signaling influenced by mutated virus in a host. We procured updated protein sequences from the NCBI virus database. Mutations were analyzed in the retrieved sequences of the viral proteins through multiple sequence alignment. Additionally, the data was subjected to ScanPROSITE to analyse if the mutations generated a relevant sequence for host signaling. Unique mutations in E, M, and S proteins resulted in modification sites like PKC phosphorylation and N-myristoylation sites. Based on structural analysis, our study revealed that the D614G mutation in the S protein diminished the interaction with T859 and K854 of adjacent chains. Moreover, the S protein of SARS-CoV-2 consists of an Arg-Gly-Asp (RGD) tripeptide sequence, which could potentially interact with various members of integrin family receptors. RGD sequence in S protein might aid in the initial virus attachment. We speculated crucial host pathways which the mutated isolates of SARS-CoV-2 may alter like PKC, Src, and integrin mediated signaling pathways. PKC signaling is known to influence the caveosome/raft pathway which is critical for virus entry. Additionally, the myristoylated proteins might activate NF-κB, a master molecule of inflammation. Thus the mutations may contribute to the disease pathogenesis and distinct lung pathophysiological changes. Further the frequently occurring mutations in the protein can be studied for possible therapeutic interventions.

New therapeutic targets for the prevention of infectious acute exacerbations of COPD: role of epithelial adhesion molecules and inflammatory pathways

Chronic respiratory diseases are among the leading causes of mortality worldwide, with the major contributor, chronic obstructive pulmonary disease (COPD) accounting for approximately 3 million deaths annually. Frequent acute exacerbations (AEs) of COPD (AECOPD) drive clinical and functional decline in COPD and are associated with accelerated loss of lung function, increased mortality, decreased health-related quality of life and significant economic costs. Infections with a small subgroup of pathogens precipitate the majority of AEs and consequently constitute a significant comorbidity in COPD. However, current pharmacological interventions are ineffective in preventing infectious exacerbations and their treatment is compromised by the rapid development of antibiotic resistance. Thus, alternative preventative therapies need to be considered. Pathogen adherence to the pulmonary epithelium through host receptors is the prerequisite step for invasion and subsequent infection of surrounding structures. Thus, disruption of bacterial-host cell interactions with receptor antagonists or modulation of the ensuing inflammatory profile present attractive avenues for therapeutic development. This review explores key mediators of pathogen-host interactions that may offer new therapeutic targets with the potential to prevent viral/bacterial-mediated AECOPD. There are several conceptual and methodological hurdles hampering the development of new therapies that require further research and resolution.

Establishment of a lethal aged mouse model of human respiratory syncytial virus infection

Human respiratory syncytial virus (HRSV) infection is a significant cause of morbidity and mortality, particularly among the children and the elderly. Despite extensive efforts, there is currently no formally approved vaccine and effective antiviral options against HRSV infection are limited. The development of vaccines and antiviral strategies for HRSV was partly hampered by the lack of an efficient lethal mouse model to evaluate the efficacy of the candidate vaccines or antivirals. In this study, we established a lethal HRSV mouse model by consecutively passaging a clinical HRSV isolate, GZ08-0. GZ08-18 was isolated from mouse bronchioalveolar lavage fluids at the 50^th passage of GZ08-0. Importantly, all GZ08-18-inoculated mice succumbed to the infection by day 7 post infection, whereas all GZ08-0-inoculated mice recovered from the infection. Subsequent investigations demonstrated that GZ08-18 replicated to a higher titer in mouse lungs, induced more prominent lung pathology, and resulted in higher expression levels of a number of key pro-inflammatory cytokines including IFN-γ, MIP-1α, and TNF-α in comparison to that of GZ08-0. The cyclophosphamide pretreatment rendered the mice more susceptible to a lethal outcome with less rounds of virus inoculation. Full genome sequencing revealed 17 mutations in GZ08-18, some of which might account for the dramatically increased pathogenicity over GZ08-0. In addition, by using ribavirin as a positive control, we demonstrated the potential application of this lethal mouse model as a tool in HRSV investigations. Overall, we have successfully established a practical lethal mouse model for HRSV with a mouse-adapted virus, which may facilitate future in vivo studies on the evaluation of candidate vaccines and drugs against HRSV.

Host-based processes as therapeutic targets for Rift Valley fever virus

Rift Valley fever virus (RVFV) is an enveloped, segmented, negative sense RNA virus that replicates within the host's cytoplasm. To facilitate its replication, RVFV must utilize host cell processes and as such, these processes may serve as potential therapeutic targets. This review summarizes key host cell processes impacted by RVFV infection. Specifically the influence of RVFV on host transcriptional regulation, post-transcriptional regulation, protein half-life and availability, host signal transduction, trafficking and secretory pathways, cytoskeletal modulation, and mitochondrial processes and oxidative stress are discussed. Therapeutics targeted towards host processes that are essential for RVFV to thrive as well as their efficacy and importance to viral pathogenesis are highlighted.

Protein Kinase C Signaling in Adenoviral Infection

Activation of protein kinase C (PKC), a serine/threonine protein kinase, ubiquitously influences cellular signal transduction and has been shown to play a role in viral entry. In this study, we explored a role for PKC in human adenovirus type 37 infection of primary human corneal fibroblasts, a major target cell for infection. We sought evidence for an interaction between PKC activation and two potential downstream targets: cSrc kinase, shown previously to play a critical role in adenovirus signaling in these cells, and caveolin-1, reported earlier to be important to entry of adenovirus type 37. Infection of fibroblasts increased PKCα phosphorylation and translocation of PKCα from the cytosol to caveolin-1 containing vesicles. Virus-induced phosphorylation of both cSrc and AKT was abolished in cell lysates pretreated with calphostin C, a chemical inhibitor of PKC. Inhibition of PKC also reduced virus associated phosphorylation of caveolin-1, while inhibition of cSrc by the chemical inhibitor PP2 reduced only caveolin-1 phosphorylation, but not PKCα phosphorylation, in lipid rafts. These results suggest a role for PKCα upstream to both cSrc and caveolin-1. Phosphorylated PKCα was found in the same endosomal fractions as phosphorylated cSrc, and PKCα was present to a greater degree in caveolin-1 pull downs from virus infected than mock infected cell lysates. Calphostin C also reduced early viral gene expression, indicating that PKCα activity may be required for viral entry. PKCα plays a central role in adenovirus infection of corneal fibroblasts and regulation of downstream molecules, including the important lipid raft component caveolin-1.

PKCδ is required for porcine reproductive and respiratory syndrome virus replication

Protein kinase C (PKC) that transduces signals to modulate a wide range of cellular functions has been shown to regulate a number of viral infections. Herein, we showed that inhibition of PKC with the PKC inhibitor GF109203X significantly impaired porcine reproductive and respiratory syndrome virus (PRRSV) replication. Inhibition of PKC led to virus yield reduction, which was associated with decreased viral RNA synthesis and lowered virus protein expression. And this inhibitory effect by PKC inhibitor was shown to occur at the early stage of PRRSV infection. Subsequently, we found that PRRSV infection activated PKCδ in PAMs and knockdown of PKCδ by small interfering RNA (siRNA) suppressed PRRSV replication, suggesting that novel PKCδ may play an important factor in PRRSV replication. Taken together, these data imply that PKC is involved in PRRSV infection and beneficial to PRRSV replication, extending our understanding of PRRSV replication.

Mucosal delivery of a double-stapled RSV peptide prevents nasopulmonary infection

Respiratory syncytial virus (RSV) infection accounts for approximately 64 million cases of respiratory disease and 200,000 deaths worldwide each year, yet no broadly effective prophylactic or treatment regimen is available. RSV deploys paired, self-associating, heptad repeat domains of its fusion protein, RSV-F, to form a fusogenic 6-helix bundle that enables the virus to penetrate the host cell membrane. Here, we developed hydrocarbon double-stapled RSV fusion peptides that exhibit stabilized α-helical structure and striking proteolytic resistance. Pretreatment with double-stapled RSV peptides that specifically bound to the RSV fusion bundle inhibited infection by both laboratory and clinical RSV isolates in cells and murine infection models. Intranasal delivery of a lead double-stapled RSV peptide effectively prevented viral infection of the nares. A chitosan-based nanoparticle preparation markedly enhanced pulmonary delivery, further preventing progression of RSV infection to the lung. Thus, our results provide a strategy for inhibiting RSV infection by mucosal and endotracheal delivery of double-stapled RSV fusion peptides.

Sustained protein kinase D activation mediates respiratory syncytial virus-induced airway barrier disruption

Understanding the regulation of airway epithelial barrier function is a new frontier in asthma and respiratory viral infections. Despite recent progress, little is known about how respiratory syncytial virus (RSV) acts at mucosal sites, and very little is known about its ability to influence airway epithelial barrier function. Here, we studied the effect of RSV infection on the airway epithelial barrier using model epithelia. 16HBE14o- bronchial epithelial cells were grown on Transwell inserts and infected with RSV strain A2. We analyzed (i) epithelial apical junction complex (AJC) function, measuring transepithelial electrical resistance (TEER) and permeability to fluorescein isothiocyanate (FITC)-conjugated dextran, and (ii) AJC structure using immunofluorescent staining. Cells were pretreated or not with protein kinase D (PKD) inhibitors. UV-irradiated RSV served as a negative control. RSV infection led to a significant reduction in TEER and increase in permeability. Additionally it caused disruption of the AJC and remodeling of the apical actin cytoskeleton. Pretreatment with two structurally unrelated PKD inhibitors markedly attenuated RSV-induced effects. RSV induced phosphorylation of the actin binding protein cortactin in a PKD-dependent manner. UV-inactivated RSV had no effect on AJC function or structure. Our results suggest that RSV-induced airway epithelial barrier disruption involves PKD-dependent actin cytoskeletal remodeling, possibly dependent on cortactin activation. Defining the mechanisms by which RSV disrupts epithelial structure and function should enhance our understanding of the association between respiratory viral infections, airway inflammation, and allergen sensitization. Impaired barrier function may open a potential new therapeutic target for RSV-mediated lung diseases.

Host cell entry of respiratory syncytial virus involves macropinocytosis followed by proteolytic activation of the F protein

Respiratory Syncytial Virus (RSV) is a highly pathogenic member of the Paramyxoviridae that causes severe respiratory tract infections. Reports in the literature have indicated that to infect cells the incoming viruses either fuse their envelope directly with the plasma membrane or exploit clathrin-mediated endocytosis. To study the entry process in human tissue culture cells (HeLa, A549), we used fluorescence microscopy and developed quantitative, FACS-based assays to follow virus binding to cells, endocytosis, intracellular trafficking, membrane fusion, and infection. A variety of perturbants were employed to characterize the cellular processes involved. We found that immediately after binding to cells RSV activated a signaling cascade involving the EGF receptor, Cdc42, PAK1, and downstream effectors. This led to a series of dramatic actin rearrangements; the cells rounded up, plasma membrane blebs were formed, and there was a significant increase in fluid uptake. If these effects were inhibited using compounds targeting Na⁺/H⁺ exchangers, myosin II, PAK1, and other factors, no infection was observed. The RSV was rapidly and efficiently internalized by an actin-dependent process that had all hallmarks of macropinocytosis. Rather than fusing with the plasma membrane, the viruses thus entered Rab5-positive, fluid-filled macropinosomes, and fused with the membranes of these on the average 50 min after internalization. Rab5 was required for infection. To find an explanation for the endocytosis requirement, which is unusual among paramyxoviruses, we analyzed the fusion protein, F, and could show that, although already cleaved by a furin family protease once, it underwent a second, critical proteolytic cleavage after internalization. This cleavage by a furin-like protease removed a small peptide from the F1 subunits, and made the virus infectious.

Respiratory Syncytial Virus (RSV) is a highly pathogenic paramyxovirus. We developed assays for RSV endocytosis, intracellular trafficking, membrane fusion, and infection. The results showed that RSV was rapidly and efficiently internalized, and that acid-independent membrane fusion occurred intracellularly after endocytosis. Cell biological studies demonstrated that endocytosis was macropinocytic, and that it was required for infection. The process involved activation of the EGF receptor and its downstream effectors including Cdc42, Pak1, and myosin II. RSV induced transient actin rearrangements accompanied by plasma membrane blebbing, elevated fluid uptake, and internalization of intact RSV particles into large macropinosomes. Expression of a dominant negative Rab5 mutant but not Rab7 decreased infection indicating that RSV penetration is intracellular, and takes place in Rab5 positive macropinosomes before fusion with endolysosomal compartments. The reason why RSV, unlike most paramyxoviruses, depended on endocytic entry was found to be the need for activation of the F protein by a second proteolytic cleavage. It occurred after endocytosis, and involved most likely a furin-like, vacuolar enzyme.

Respiratory syncytial virus infection: from biology to therapy: a perspective

Respiratory syncytial virus (RSV) is responsible for significant morbidity and mortality, particularly in infants younger than 18 months and in the elderly. To date, there are few effective treatment options available to prevent or treat RSV infections. Attractive therapeutic strategies include targeting host epithelial adhesion molecules required for RSV infection, enhancing localized cell-mediated immunity, interfering with RSV viral gene expression and developing a multigene DNA vaccine. The most recent data supporting the advantages and limitations of each of these approaches are discussed in detail. Several promising strategies offer hope for safe and effective prophylaxis and treatment of RSV infection.

Epidemiologic, experimental, and clinical links between respiratory syncytial virus infection and asthma

Virtually all children experience respiratory syncytial virus (RSV) infection at least once during the first 2 years of life, but only a few develop bronchiolitis and more severe disease requiring hospitalization, usually in the first 6 months of life. Children who recover from RSV-induced bronchiolitis are at increased risk for the development of recurrent wheeze and asthma in later childhood. Recent studies suggest that there is an association between RSV-induced bronchiolitis and asthma within the first decade of life but that this association is not significant after age 13. Despite the considerable progress made in our understanding of several aspects of respiratory viral infections, further work needs to be done to clarify the molecular mechanisms of early interactions between virus and host cell and the role of host gene products in the infection process. This review provides a critical appraisal of the literature in epidemiology and experimental research which links RSV infection to asthma. Studies to date demonstrate that there is a significant association between RSV infection and childhood asthma and that preventing severe primary RSV infections can decrease the risk of childhood asthma.

Respiratory syncytial virus induces insensitivity to beta-adrenergic agonists in mouse lung epithelium in vivo

Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis in infants and children worldwide. We wished to determine whether intratracheal administration of beta-agonists improved alveolar fluid clearance (AFC) across the distal respiratory epithelium of RSV-infected mice. Following intranasal infection with RSV strain A2, AFC was measured in anesthetized, ventilated BALB/c mice by instillation of 5% BSA into the dependent lung. We found that direct activation of protein kinase A by forskolin or 8-bromo-cAMP increased AFC at day 2 after infection with RSV. In contrast, short- and long-acting beta-agonists had no effect at either day 2 or day 4. Insensitivity to beta-agonists was not a result of elevated plasma catecholamines or lung epithelial cell beta-adrenergic receptor degradation. Instead, RSV-infected mice had significantly higher levels of phosphorylated PKCzeta in the membrane fractions of their lung epithelial cells. In addition, insensitivity to beta-agonists was mediated in a paracrine fashion by KC (the murine homolog of CXCL8) and reversed by inhibition of either PKCzeta or G protein-coupled receptor kinase 2 (GRK2). These results indicate that insufficient response to beta-agonists in RSV may be caused, at least in part, by impaired beta-adrenergic receptor signaling, as a consequence of GRK2-mediated uncoupling of beta-adrenergic receptors from adenylyl cyclase.

Legionella pneumophila-induced PKCα-, MAPK-, and NF-κB-dependent COX-2 expression in human lung epithelium

Legionella pneumophila causes community- and hospital-acquired pneumonia. Lung airway and alveolar epithelial cells comprise an important barrier against airborne pathogens. Cyclooxygenase (COX) and microsomal PGE2synthase-1 (mPGES-1)-derived prostaglandins like prostaglandin E2(PGE2) are considered as important regulators of lung function. Herein we tested the hypothesis that L. pneumophila induced COX-2 and mPGES-1-dependent PGE2production in pulmonary epithelial cells. Legionella induced the release of PGE2in primary human small airway epithelial cells and A549 cells. This was accompanied by an increased expression of COX-2 and mPGES-1 as well as an increased PLA2activity in infected cells. Deletion of the type IV secretion system Dot/Icm did not impair Legionella-related COX-2 expression or PGE2release in A549 cells. L. pneumophila induced the degradation of IκBα and activated NF-κB. Inhibition of IKK blocked L. pneumophila-induced PGE2release and COX-2 expression. We noted activation of p38 and p42/44 MAP kinase in Legionella-infected A549 cells. Moreover, membrane translocation and activation of PKCα was observed in infected cells. PKCα and p38 and p42/44 MAP kinase inhibitors reduced PGE2release and COX-2 expression. In summary, PKCα and p38 and p42/44 MAP kinase controlled COX-2 expression and subsequent PGE2release by Legionella-infected lung epithelial cells. These pathways may significantly contribute to the host response in Legionnaires' disease.

Interaction of monocytic cells with respiratory syncytial virus results in activation of NF-kappaB and PKC-alpha/beta leading to up-regulation of IL-15 gene expression

Respiratory syncytial virus (RSV) is a major human respiratory pathogen, particularly for infants. RSV is also a powerful inducer of cytokines, one of which is IL-15, an important immunoregulatory cytokine. IL-15 plays a key role in NK and T cell development and differentiation and also regulates NK cell/macrophage interaction, as well as monocyte/macrophage and granulocyte function. We have shown previously that different viruses up-regulate IL-15 gene expression in human PBMCs. Recently, we found that RSV induces the expression of IL-15 mRNA in the monocytic line THP-1. The signaling pathway involved in such virus-induced up-regulation of IL-15 has not yet been identified. We report here a study describing this mechanism. Because of the involvement of the protein kinase C (PKC) and the transcription factor NF-kappaB in the regulation of others cytokines by RSV as well as the involvement of NF-kappaB in the transactivation of IL-15, our hypothesis was that RSV induced the expression of IL-15 in THP-1 cells through the PKC and NF-kappaB activation. We demonstrate here that RSV-induced up-regulation of IL-15 expression in THP-1 cells involves the phosphorylation of PKC-alpha/beta. Further, inhibition of PKC by different specific inhibitors blocks this up-regulation. Using the electromobility shift assay, we show that the activated form of NF-kappaB binds to the IL-15 promoter sequence. We further confirm, using an ELISA assay, the involvement of p65 in the transcription of IL-15. This study, demonstrating the ability of RSV to induce IL-15 expression, might explain, at least in part, the exacerbated, inflammatory response triggered by RSV infection.