Differential regulation of TNFalpha and GM-CSF induced activation of P38 MAPK in neutrophils and eosinophils

Atypical p38 Signaling, Activation, and Implications for Disease

The mitogen-activated protein kinase (MAPK) p38 is an essential family of kinases, regulating responses to environmental stress and inflammation. There is an ever-increasing plethora of physiological and pathophysiological conditions attributed to p38 activity, ranging from cell division and embryonic development to the control of a multitude of diseases including retinal, cardiovascular, and neurodegenerative diseases, diabetes, and cancer. Despite the decades of intense investigation, a viable therapeutic approach to disrupt p38 signaling remains elusive. A growing body of evidence supports the pathological significance of an understudied atypical p38 signaling pathway. Atypical p38 signaling is driven by a direct interaction between the adaptor protein TAB1 and p38α, driving p38 autophosphorylation independent from the classical MKK3 and MKK6 pathways. Unlike the classical MKK3/6 signaling pathway, atypical signaling is selective for just p38α, and at present has only been characterized during pathophysiological stimulation. Recent studies have linked atypical signaling to dermal and vascular inflammation, myocardial ischemia, cancer metastasis, diabetes, complications during pregnancy, and bacterial and viral infections. Additional studies are required to fully understand how, when, where, and why atypical p38 signaling is induced. Furthermore, the development of selective TAB1-p38 inhibitors represents an exciting new opportunity to selectively inhibit pathological p38 signaling in a wide array of diseases.

Apocynin prevents GM-CSF-induced-ERK1/2 activation and -neutrophil survival independently of its inhibitory effect on the phagocyte NADPH oxidase NOX2

Neutrophils are key cells in innate immunity and inflammation. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is known to enhance many neutrophil functions such as reactive oxygen species (ROS) production, degranulation and cell survival via the activation of the ERK1/2 pathway. ERK1/2 pathway activation is redox sensitive and could be modulated by ROS. In order to investigate whether NADPH oxidase NOX2-derived ROS could contribute to GM-CSF-induced ERK1/2 phosphorylation, we tested the effect of two selective NOX2 inhibitors, diphenylene iodonium (DPI) and apocynin. Results showed that, while both DPI and apocynin strongly inhibited neutrophil ROS production, only apocynin, but not DPI, inhibited GM-CSF-induced ERK1/2 phosphorylation, suggesting that ROS are not involved in this process. Apocynin did not affect GM-CSF-induced p38MAPKinase phosphorylation, another redox sensitive kinase. Interestingly, apocynin inhibited GM-CSF-induced MEK1/2 and AKT phosphorylation without affecting fMLF-induced phosphorylation of these proteins. GM-CSF is known to inhibit neutrophils apoptosis and to promote cell survival via the AKT-ERK1/2 pathway. In this regard, we found that apocynin also inhibited GM-CSF-induced anti-apoptotic effect in neutrophils. These results suggest that NADPH oxidase NOX2-derived ROS are not involved in GM-CSF-induced ERK1/2 phosphorylation and that apocynin inhibits GM-CSF-induced ERK1/2 phosphorylation pathway independently of its inhibitory action on NADPH oxidase NOX2. Thus, apocynin can exert an anti-inflammatory effect not only by limiting neutrophil ROS production but also by decreasing neutrophil survival at inflammatory site.

Inhibitory effect of Zanthoxylum bungeanum seed oil on ovalbumin‑induced lung inflammation in a murine model of asthma

The present study aimed to investigate the therapeutic efficacy of Zanthoxylum bungeanum seed oil (Z. seed oil) to alleviate airway inflammation in asthmatic mice. The asthmatic mice were treated with vehicle, ovalbumin (OVA), or OVA + Z. seed oil (2 g/kg) for between 24 h and 14 days. Following treatment, inflammatory cell infiltration and pulmonary tissue damage were assessed by hematoxylin and eosin staining, and immunohistochemistry. The expression levels of pro‑inflammatory cytokines, chemokines, adhesion molecules and mitogen activated protein kinase signaling proteins were measured by enzyme‑linked immunosorbent assays, reverse transcription quantitative‑polymerase chain reaction and western blot analysis. In asthmatic mice, administration of Z. seed oil attenuated lung tissue injury and airway remodeling, and inhibited the infiltration of leukocytes and eosinophils into the airway by reducing the expression levels of inflammatory cytokines and chemokines compared with OVA‑treated mice (P<0.05). Z. seed oil also reduced the levels of inflammatory chemokine and adhesion molecules via downregulation of extracellular signal‑regulated kinase and activation of c‑JUN N‑terminal kinase in the Z. seed‑treated mice compared with OVA‑treated mice (P<0.05). Thus, data from the present study indicates that Z. seed oil can suppress pulmonary inflammation and tissue injury during asthma, and suggests that it may be used to effectively treat allergen‑induced asthma.

Cholesterol selectively regulates IL-5 induced mitogen activated protein kinase signaling in human eosinophils

Eosinophils function contributes to human allergic and autoimmune diseases, many of which currently lack curative treatment. Development of more effective treatments for eosinophil-related diseases requires expanded understanding of eosinophil signaling and biology. Cell signaling requires integration of extracellular signals with intracellular responses, and is organized in part by cholesterol rich membrane microdomains (CRMMs), commonly referred to as lipid rafts. Formation of these organizational membrane domains is in turn dependent upon the amount of available cholesterol, which can fluctuate widely with a variety of disease states. We tested the hypothesis that manipulating membrane cholesterol content in primary human peripheral blood eosinophils (PBEos) would selectively alter signaling pathways that depend upon membrane-anchored signaling proteins localized within CRMMs (e.g., mitogen activated protein kinase [MAPK] pathway), while not affecting pathways that signal through soluble proteins, like the Janus Kinase/Signal Transducer and Activator of Transcription [JAK/STAT] pathway. Cholesterol levels were increased or decreased utilizing cholesterol-chelating methyl-β-cyclodextrin (MβCD), which can either extract membrane cholesterol or add exogenous membrane cholesterol depending on whether MβCD is preloaded with cholesterol. Human PBEos were pretreated with MβCD (cholesterol removal) or MβCD+Cholesterol (MβCD+Chol; cholesterol delivery); subsequent IL-5-stimulated signaling and physiological endpoints were assessed. MβCD reduced membrane cholesterol in PBEos, and attenuated an IL-5-stimulated p38 and extracellular-regulated kinase 1/2 phosphorylation (p-p38, p-ERK1/2), and an IL-5-dependent increase in interleukin-1β (IL-1β) mRNA levels. In contrast, MβCD+Chol treatment elevated PBEos membrane cholesterol levels and basal p-p38, but did not alter IL-5-stimulated phosphorylation of ERK1/2, STAT5, or STAT3. Furthermore, MβCD+Chol pretreatment attenuated an IL-5-induced increase in cell survival at 48 hours, measured as total cellular metabolism. The reduction in cell survival following cholesterol addition despite unaltered STAT phosphorylation contradicts the current dogma in which JAK/STAT activation is sufficient to promote eosinophil survival, and suggests an additional, unidentified mechanism critically regulates IL-5-mediated human PBEos survival.

A role for mitogen kinase kinase 3 in pulmonary inflammation validated from a proteomic approach

Proteomics is a powerful tool to ascertain which proteins are differentially expressed in the context of disease. We have used this approach on inflammatory cells obtained from patients with asthma to ascertain whether novel drugs targets could be illuminated and to investigate the role of any such target in a range of in vitro and in vivo models of inflammation. A proteomic study was undertaken using peripheral blood mononuclear cells from mild asthmatic subjects compared with healthy subjects. The analysis revealed an increased expression of the intracellular kinase, mitogen activated protein kinase (MKK3), and the function of this protein was investigated further in preclinical models of inflammation using MKK3 knockout mice. We describe a 3.65 fold increase in the expression of MKK3 in CD8(+) T lymphocytes obtained from subjects with asthma compared with healthy subjects using a proteomic approach which we have confirmed in CD8(+), but not in CD4(+) T lymphocytes or human bronchial epithelial cells from asthmatic patients using a Western blot technique. In wild type mice, bacterial lipopolysaccharide (LPS) caused a significant increase in MKK3 expression and significantly reduced airway neutrophilia in MKK3(-/-) mice (median, 25, 75% percentile; wild/LPS; 5.3 (0.7-9.9) × 10(5) cells/mL vs MKK3(-/-)/LPS; 0 (0-1.9) × 10(5) cells/mL, P < 0.05). In contrast, eosinophilia in sensitized wild type mice challenged with allergen (0.5 (0.16-0.65) × 10(5) cells/mL) was significantly increased in MKK3(-/-) mice (2.2 (0.9-3.5) × 10(5) cells/mL, P < 0.05). Our results suggest that asthma is associated with MKK3 over-expression in CD8(+) cells. We have also demonstrated that MKK3 may be critical for airway neutrophilia, but not eosinophilia, suggesting that this may be a target worthy of further consideration in the context of diseases associated with neutrophil activation such as severe asthma and COPD.

The effect of functional MAPKAPK2 copy number variation CNV-30450 on elevating nasopharyngeal carcinoma risk is modulated by EBV infection

Mitogen-activated protein kinase-activated protein kinase 2 (MAPKAPK2) is recognized as oncogenic and simulative role on tumorigenesis by virtue of abnormal expression in cancer including nasopharyngeal carcinoma (NPC). We hypothesized that the copy number variation (CNV)-30450, which duplicates the MAPKAPK2 promoter, may affect MAPKAPK2 expression and be associated with NPC risk. In two independent case-control panels of southern and eastern Chinese with a total of 1590 NPC patients and 1979 cancer-free controls, we investigated the association between CNV-30450 and NPC risk by genotyping the CNV-30450 with the TaqMan assay, and tested its biological effect. Consistent findings were observed in the two populations, that the increased copy number of CNV-30450 was associated with increased risk of NPC (3/4-copy versus 2-copy: odds ratio = 1.28, 95% confidence interval = 1.10-1.49), in which lies a biological mechanism that the adverse genotypes enhanced the promoter activity of MAPKAPK2 and elevated MAPKAPK2 expression. Moreover, the CNV-30450 adverse genotypes significantly interacted with Epstein-Barr virus (EBV) infection on increasing NPC risk (P = 0.035), and the genotype-phenotype correlation was only significant in EBV-positive cases (P = 0.037) but not in EBV-negative ones (P = 0.366). These data suggest that the functional CNV-30450 in the MAPKAPK2 promoter elevates the NPC risk with a modulation by EBV infection, which may be an indicator of susceptibility to NPC.

SUMMARY

This case-control study suggests that the functional CNV-30450 in the MAPKAPK2 promoter elevates the NPC risk with a modulation by EBV infection, which may be an indicator of susceptibility to NPC.

A functional copy-number variation in MAPKAPK2 predicts risk and prognosis of lung cancer

Mitogen-activated protein kinase-activated protein kinase 2 (MAPKAPK2) may promote cancer development and progression by inducing tumorigenesis and drug resistance. To assess whether the copy-number variation g.CNV-30450 located in the MAPKAPK2 promoter has any effect on lung cancer risk or prognosis, we investigated the association between g.CNV-30450 and cancer risk in three independent case-control studies of 2,332 individuals with lung cancer and 2,457 controls and the effects of g.CNV-30450 on cancer prognosis in 1,137 individuals with lung cancer with survival data in southern and eastern Chinese populations. We found that those subjects who had four copies of g.CNV-30450 had an increased cancer risk (odds ratio = 1.94, 95% confidence interval [CI] = 1.61-2.35) and a worse prognosis for individuals with lung cancer (with a median survival time of only 9 months) (hazard ratio = 1.47, 95% CI = 1.22-1.78) compared with those with two or three copies (with a median survival time of 14 months). Meanwhile, four copies of g.CNV-30450 significantly increased MAPKAPK2 expression, both in vitro and in vivo, compared with two or three copies. Our study establishes a robust association between the functional g.CNV-30450 in MAPKAPK2 and risk as well as prognosis of lung cancer, and it presents this functional copy-number variation as a potential biomarker for susceptibility to and prognosis for lung cancer.

A novel TNFR1-triggered apoptosis pathway mediated by class IA PI3Ks in neutrophils

The most common form of neutrophil death is apoptosis. In the present study, we report surprising differences in the molecular mechanisms used for caspase activation between FAS/CD95-stimulated and TNF receptor 1 (TNFR1)-stimulated neutrophils. Whereas FAS-induced apoptosis was followed by caspase-8 activation and required Bid to initiate the mitochondrial amplification loop, TNF-α-induced apoptosis involved class IA PI3Ks, which were activated by MAPK p38. TNF-α-induced PI3K activation resulted in the generation of reactive oxygen species, which activated caspase-3, a mechanism that did not operate in neutrophils without active NADPH oxidase. We conclude that in neutrophils, proapoptotic pathways after TNFR1 stimulation are initiated by p38 and PI3K, but not by caspase-8, a finding that should be considered in anti-inflammatory drug-development strategies.

Two additive mechanisms impair the differentiation of 'substrate-selective' p38 inhibitors from classical p38 inhibitors in vitro

Background

The success of anti-TNF biologics for the treatment of rheumatoid arthritis has highlighted the importance of understanding the intracellular pathways that regulate TNF production in the quest for an orally-available small molecule inhibitor. p38 is known to strongly regulate TNF production via MK2. The failure of several p38 inhibitors in the clinic suggests the importance of other downstream pathways in normal cell function. Recent work has described a 'substrate-selective' p38 inhibitor that is able to preferentially block the activity of p38 against one substrate (MK2) versus another (ATF2). Using a combined experimental and computational approach, we have examined this mechanism in greater detail for two p38 substrates, MK2 and ATF2.

Results

We found that in a dual (MK2 and ATF2) substrate assay, MK2-p38 interaction reduced the activity of p38 against ATF2. We further constructed a detailed kinetic mechanistic model of p38 phosphorylation in the presence of multiple substrates and successfully predicted the performance of classical and so-called 'substrate-selective' p38 inhibitors in the dual substrate assay. Importantly, it was found that excess MK2 results in a stoichiometric effect in which the formation of p38-MK2-inhibitor complex prevents the phosphorylation of ATF2, despite the preference of the compound for the p38-MK2 complex over the p38-ATF2 complex. MK2 and p38 protein expression levels were quantified in U937, Thp-1 and PBMCs and found that [MK2] > [p38].

Conclusion

Our integrated mechanistic modeling and experimental validation provides an example of how systems biology approaches can be applied to drug discovery and provide a basis for decision-making with limited chemical matter. We find that, given our current understanding, it is unlikely that 'substrate-selective' inhibitors of p38 will work as originally intended when placed in the context of more complex cellular environments, largely due to a stoichiometric excess of MK2 relative to p38.

MAPKAPK-2 signaling is critical for cutaneous wound healing

Cutaneous wound healing is a complex process, which is heavily dependent on successful inflammatory action. Mitogen-activated protein kinase (MAPK)-activated protein kinase-2 (MAPKAPK-2 or MK2), a major substrate of p38 MAPK, has been shown to be a major player in multiple inflammatory diseases, but its role in cutaneous wound healing has not yet been explored. In this study, by comparing excisional wounds made on the backs of MK2 knockout (KO) and MK2 wild-type (WT) mice, we found that the kinetics of wound healing are significantly affected by the absence of MK2 (P=0.010 to P<0.001). Histological examination showed a higher level of acanthosis of the migrating wound keratinocyte layer as well as a higher level of collagen deposition in the granulation tissue of the wounds from MK2 WT mice compared with those from MK2 KO mice. Interestingly, although MK2 did not influence macrophage and neutrophil infiltration of the wounds, the expression of many cytokines and chemokines was significantly affected at different days post wounding. Furthermore, the delayed healing rate of wounds in MK2 KO mice can be significantly improved by passive transfer of macrophages with intact MK2. Overall, these results show a critical role for MK2 gene expression in macrophages participating in the process of cutaneous wound healing.

A potent and selective p38 inhibitor protects against bone damage in murine collagen-induced arthritis: a comparison with neutralization of mouse TNFalpha

BACKGROUND AND PURPOSE

The p38 kinase regulates the release of proinflammatory cytokines including tumour-necrosis factor-alpha (TNFalpha) and is regarded as a potential therapeutic target in rheumatoid arthritis (RA). Using the novel p38 inhibitor Org 48762-0, we investigated the therapeutic potential of p38 inhibition and compared this to anti-mouse (m)TNFalpha antibody treatment in murine collagen-induced arthritis (CIA).

EXPERIMENTAL APPROACH

Pharmacological profiles of Org 48762-0 were characterized in kinase assays, cellular assays and in lipopolysaccharide (LPS)-induced inflammation in mice. The effects of Org 48762-0 and of mTNFalpha-neutralization on established arthritis were examined in murine CIA.

KEY RESULTS

Org 48762-0 potently inhibited p38alpha kinase with a high degree of kinase selectivity. In cellular assays, Org 48762-0 reduced LPS-induced TNFalpha release. Oral administration of Org 48762-0 in mice showed drug-like pharmacokinetic properties and inhibited LPS-induced cytokine production. These pharmacological characteristics of Org 48762-0 prompted a comparison of therapeutic efficacy with mTNFalpha-neutralization in CIA. Org 48762-0 and anti-mTNFalpha antibody treatment equally inhibited development of arthritis when evaluated macroscopically. Radiological analyses revealed protection against bone damage for both treatments, although statistical difference was reached with Org 48762-0 treatment only. Further, micro-computed tomographical and histopathological analyses confirmed the protective effects of Org 48762-0 on joint damage.

CONCLUSIONS AND IMPLICATIONS

Pharmacological targeting of p38 kinase provided good protection against joint tissue damage in CIA. In our experiments, neutralization of mTNFalpha produced less prominent suppression of bone damage. Our data suggest a therapeutic potential for selective and potent p38 inhibitors in RA.