Purification and activation of recombinant p38 isoforms alpha, beta, gamma, and delta

Effects of a dual inhibitor of tumor necrosis factor-alpha and interleukin-1 on lipopolysaccharide-induced lung injury in rats: involvement of the p38 mitogen-activated protein kinase pathway

OBJECTIVE

Sepsis is a major cause of adult respiratory distress syndrome. In this study, we evaluated the effect of FR167653, which is a potent suppressant of tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 production, on lipopolysaccharide (LPS)-induced lung injury and lethality in rats, and we examined the involvement of p38 mitogen-activated protein (MAP) kinase in the action of FR167653.

DESIGN

Prospective, randomized study.

SETTING

Animal research facility in a university.

SUBJECTS

Male Sprague-Dawley rats weighing 200-270 g.

INTERVENTIONS

All the animals were assigned to one of the following four groups: control group, FR-only group, LPS-only group, and LPS/FR group. Animals in the LPS-only and LPS/FR groups received 6 mg/kg of LPS intravenously. The animals in the FR-only and LPS/FR groups also received an infusion of FR167653 at 0.2 mg x kg(-1) x hr(-1), commencing 30 mins before the LPS (or vehicle) injection and continuing for 5.5 hrs.

MEASUREMENTS AND MAIN RESULTS

LPS significantly induced the accumulation of pulmonary neutrophils and lung edema, both of which were significantly attenuated by treatment with FR167653. FR167653 also significantly decreased the LPS-induced lethality. Histologically, tissue damage was milder in the LPS/FR group than in the LPS-only group. Serum concentrations of TNF-alpha and IL-1beta and plasma concentrations of thromboxane B2 were all suppressed in the LPS/FR group compared with the LPS-only group. Western blot analysis revealed that FR167653 inhibited the phosphorylation of p38 MAP kinase in lung tissues.

CONCLUSIONS

FR167653 administration decreased serum TNF-alpha and IL-1beta concentrations, which was associated with decreased lung injury and lethality. The mechanism responsible for the decreased TNF-alpha and IL-1 may be related to the inhibitory effect of FR167653 on p38 MAP kinase activation.

Marathon running transiently increases c-Jun NH2-terminal kinase and p38 activities in human skeletal muscle

We examined the pattern of activation and deactivation of the stress-activated protein kinase signalling molecules c-Jun NH2-terminal kinase (JNK) and p38 kinase in skeletal muscle in response to prolonged strenuous running exercise in human subjects. Male subjects (n = 14; age 32 +/- 2 years; VO2,max 60 +/- 2 ml kg-1 min-1) completed a 42.2 km marathon (mean race time 3 h 35 min). Muscle biopsies were obtained 10 days prior to the marathon, immediately following the race, and 1, 3 and 5 days after the race. The activation of JNK and p38, including both p38alpha and p38gamma, was measured with immune complex assays. The phosphorylation state of p38 (alpha and gamma) and the upstream regulators of JNK and p38, mitogen-activated protein kinase kinase 4 (MKK4) and mitogen-activated protein kinase kinase 6 (MKK6), were assessed using phosphospecific antibodies. JNK activity increased 7-fold over basal level immediately post-exercise, but decreased back to basal levels 1, 3 and 5 days after the exercise. p38gamma phosphorylation (4-fold) and activity (1.5-fold) increased immediately post-exercise and returned to basal levels at 1, 3 and 5 days following exercise. In contrast, p38alpha phosphorylation and activity did not change over the time course studied. MKK4 and MKK6 phosphorylation increased and decreased in a trend similar to that observed with JNK activity and p38gamma phosphorylation. Prolonged running exercise did not affect JNK, p38alpha, or p38gamma protein expression in the days following the race. This study demonstrates that both JNK and p38 intracellular signalling cascades are robustly, yet transiently increased following prolonged running exercise. The differential activation of the p38 isoforms with exercise in human skeletal muscle indicates that these proteins may have distinct functions in vivo.

Mechanical stress-initiated signal transductions in vascular smooth muscle cells

Mechanical force is an important modulator of cellular morphology and function in a variety of tissues, and is particularly important in cardiovascular systems. Vascular smooth muscle cell (VSMC) hypertrophy and proliferation contribute to the development of atherosclerosis, hypertension, and restenosis, where mechanical forces are largely disturbed. How VSMCs sense and transduce the extracellular mechanical signals into the cell nucleus resulting in quantitative and qualitative changes in gene expression is an interesting and important research field. Recently, it has been demonstrated that mechanical stress rapidly induced phosphorylation of platelet-derived growth factor (PDGF) receptor, activation of integrin receptor, stretch-activated cation channels, and G proteins, which might serve as mechanosensors. Once mechanical force is sensed, protein kinase C and mitogen-activated protein kinases (MAPKs) were activated, leading to increased c-fos and c-jun gene expression and enhanced transcription factor AP-1 DNA-binding activity. Interestingly, physical forces also rapidly resulted in expression of MAPK phosphatase-1 (MKP-1), which inactivates MAPKs. Thus, mechanical stresses can directly stretch the cell membrane and alter receptor or G protein conformation, thereby initiating signalling pathways, usually used by growth factors. These findings have significantly enhanced our knowledge of the pathogenesis of arteriosclerosis and provided promising information for therapeutic interventions for vascular diseases.

The p38 signal transduction pathway: activation and function

The p38 signalling transduction pathway, a Mitogen-activated protein (MAP) kinase pathway, plays an essential role in regulating many cellular processes including inflammation, cell differentiation, cell growth and death. Activation of p38 often through extracellular stimuli such as bacterial pathogens and cytokines, mediates signal transduction into the nucleus to turn on the responsive genes. p38 also transduces signals to other cellular components to execute different cellular responses. In this review, we summarize the characteristics of the major components of the p38 signalling transduction pathway and highlight the targets of this pathway and the physiological function of the p38 activation.

Differential Expression and Activation of p38 Mitogen-Activated Protein Kinase α, β, γ, and δ in Inflammatory Cell Lineages

Four p38 mitogen-activated protein kinases (p38α, β, γ, δ) have been described. To understand the role of p38 family members in inflammation, we determined their relative expression in cells that participate in the inflammatory process. Expression was measured at the level of mRNA by reverse-transcriptase PCR and protein by Western blot analysis. p38α was the dominant form of p38 in monocytes; expression of p38δ was low and p38β was undetected. In macrophages, p38α and p38δ were abundant, but p38β was undetected. p38α and p38δ were also expressed by neutrophils, CD4+ T cells, and endothelial cells. Again, p38β was not detected in neutrophils, although low amounts were present in CD4+ T cells. In contrast, p38β was abundant in endothelial cells. p38γ protein was not detected in any cell type, although p38γ mRNA was present in endothelial cells. Immunokinase assays showed a strong activation of p38α and a lesser activation of p38δ in LPS-stimulated macrophages. Abs specific for mono- and dual-phophorylated forms of p38 suggested that LPS induces dual phosphorylation of p38α, but primarily mono-phosphorylation of p38δ. IL-1β activated p38α and p38β in endothelial cells. However, p38α was the more activated form based on kinase assays and phosphorylation analysis. Expression and activation patterns of p38α in macrophages and endothelial cells suggest that p38α plays a major role in the inflammatory response. Additional studies will be needed to define the contribution of p38δ to macrophage, neutrophil, and T cell functions, and of p38β to signaling in endothelial cells and T cells.