Characterization of the structure and function of a new mitogen-activated protein kinase (p38beta)

Delayed induction of p38 MAPKs in reactive astrocytes in the brain of mice after KA-induced seizure

Activation of p38 mitogen-activated protein kinase (p38 MAPK) has been implicated in pathological changes in inflammatory and apoptotic processes in various cell types including neurons. Here we report the delayed induction of p38 MAPKs in the brain of mice following kainic acid (KA)-induced seizure. The immunoreactivities of p38alpha and p38beta MAPKs were markedly increased in the brain 4 days after KA administration, especially in the areas undergoing selective neuronal loss. In particular, p38beta was dramatically increased in reactive astrocytes of CA3 and CA1 regions of hippocampus with its enriched localization in the nucleus of astrocytes. The induction of p38beta was sustained for more than 10 days after KA-treatment. Pre-administration of the selective neuronal nitric oxide synthase (nNOS) inhibitor, 7-nitroindazole (7-NI), which suppressed the delayed neuronal death as well as astrogliosis in hippocampus of seizure-experienced animals, dramatically repressed the delayed induction of p38beta MAPK in astrocytes. The repression was reversed by the co-injection with L-arginine (L-arg), a substrate for NOS, which coincided with the aggravation of neuronal death. Together, these data suggested a role of p38 MAPK signal pathway in delayed neuronal death and/or in reactive gliosis in mice with KA-induced seizure.

p38beta MAP kinase protects rat mesangial cells from TNF-alpha-induced apoptosis

p38 MAP kinases (p38) and c-Jun N-terminal protein kinases (JNK) have been associated with TNF-alpha-induced apoptosis. However, recent studies indicate that an early but brief activation of JNK and/or p38 may actually protect some cells from TNF-alpha-induced apoptosis. Whether the activation of JNK and p38 provides a pro- or anti-apoptotic signal for TNF-alpha has been controversial. In this study, we investigated the role of p38 in the regulation of TNF-alpha cytotoxicity in rat mesangial cells. Treatment of the cells with TNF-alpha alone had little effect on their viability, but they became very sensitive to apoptosis when treated with TNF-alpha in the presence of the p38 inhibitor SB 203580. These results suggested that the p38 pathway is critical for mesangial cells to survive the toxic effect of TNF-alpha. Using adenovirus-mediated gene transfer technique, we further demonstrated that p38beta, but not p38alpha, is essential to protect the cells from TNF-alpha toxicity. It has been speculated that there is a synergetic interaction between the p38 and the nuclear factor-kappaB (NF-kappaB) pathways in protecting certain cells from apoptosis. However, expression of neither p38beta nor its dominant negative mutant in mesangial cells interfered with TNF-alpha-induced translocation of NF-kappaB, the initial step of NF-kappaB activation. While it is unclear whether p38beta regulates NF-kappaB transcription activity at other steps, it is apparent that p38beta does not affect TNF-alpha-induced NF-kappaB activation at the stage of nuclear translocation.

The in vivo role of p38 MAP kinases in cardiac remodeling and restrictive cardiomyopathy

Stress-induced mitogen-activated protein kinase (MAP) p38 is activated in various forms of heart failure, yet its effects on the intact heart remain to be established. Targeted activation of p38 MAP kinase in ventricular myocytes was achieved in vivo by using a gene-switch transgenic strategy with activated mutants of upstream kinases MKK3bE and MKK6bE. Transgene expression resulted in significant induction of p38 kinase activity and premature death at 7-9 weeks. Both groups of transgenic hearts exhibited marked interstitial fibrosis and expression of fetal marker genes characteristic of cardiac failure, but no significant hypertrophy at the organ level. Echocardiographic and pressure-volume analyses revealed a similar extent of systolic contractile depression and restrictive diastolic abnormalities related to markedly increased passive chamber stiffness. However, MKK3bE-expressing hearts had increased end-systolic chamber volumes and a thinned ventricular wall, associated with heterogeneous myocyte atrophy, whereas MKK6bE hearts had reduced end-diastolic ventricular cavity size, a modest increase in myocyte size, and no significant myocyte atrophy. These data provide in vivo evidence for a negative inotropic and restrictive diastolic effect from p38 MAP kinase activation in ventricular myocytes and reveal specific roles of p38 pathway in the development of ventricular end-systolic remodeling.

Tissue-specific induction of E-selectin in glomeruli is augmented following diabetes mellitus

We recently demonstrated that induction of adhesion molecules is tissue, cell type, and blood vessel size specific. We examined here whether the glomeruli, a peculiar vascular system, express adhesion molecules in a specific manner in the murine kidney. In addition, since serum levels of soluble adhesion molecules have been reported to be elevated in diabetic patients, we examined the influence of diabetes mellitus on the induction of adhesion molecules in the kidney. Analysis of E-selectin mRNA expression by in situ hybridization indicated that it was selectively induced in glomeruli by intravenous administration of interleukin-1beta, while ICAM-1 mRNA expression was seen diffusely in endothelium lining the small arteries and capillaries or in glomeruli, and VCAM-1 mRNA expression was most prominent in endothelial cells of larger blood vessels. Induction of E-selectin mRNA expression in glomeruli by proinflammatory stimuli was augmented in streptozotocin-induced diabetic mice as compared with control mice, while ICAM-1 or VCAM-1 mRNA induction was only slightly influenced. Furthermore, immunohistochemical analysis showed that selective expression of E-selectin in glomeruli was augmented predominantly in epithelial cells, depending on the duration of diabetes mellitus, in KK-Ay mice. These findings suggest that glomerulus-specific expression of E-selectin is related to the development of diabetic nephropathy.

Retinoblastoma protein interacts with ATF2 and JNK/p38 in stimulating the transforming growth factor-beta2 promoter

Two highly related transcription factors, ATF2 and ATFa, enhance the activity of the Transforming Growth Factor beta2 (TGF-beta2) promoter via a partial cAMP response element in transfected CHO cells. The retinoblastoma protein (Rb) also activates this promoter and enhances the stimulatory effects of ATF2 but causes near extinction of the effects of ATFa. The site on Rb required for its effects alone and in combination with the ATFs has been mapped mainly to the A/B pockets but the C pocket is also implicated. Whereas MKK7 or JNK expression enhances the actions of both ATFs, MKK6 or p38 expression only augments the effects of ATF2. Immunoprecipitation with Rb antibodies of lysates from transfected cells brings down expressed ATF2 but not ATFa. Expressed JNK and p38 are also found in the anti-Rb immunoprecipitates. ATF2 antibodies bring down expressed Rb, JNK and p38 and expression of Rb enhances the immunoprecipitation of both JNK and p38 by ATF2 antibodies. The results suggest that Rb is acting as a matchmaker by bridging either JNK or p38 with their common substrate ATF2 and, hence, facilitating its activation. Consistent with this suggestion, expression of Rb enhances the phosphorylation of ATF2 in CHO cells.

The Usf-1 transcription factor is a novel target for the stress-responsive p38 kinase and mediates UV-induced Tyrosinase expression

The stress-activated signalling cascade leading to phosphorylation of the p38 family of kinases plays a crucial role during development and in the cellular response to a wide variety of stress-inducing agents. Although alterations in gene expression characteristic of the stress response require the regulation of key transcription factors by the p38 family, few downstream targets for this signalling pathway have been identified. By examining the ability of pigment cells to respond to UV irradiation as part of the UV-induced tanning response, we show that while the microphthalmia-associated transcription factor Mitf regulates basal Tyrosinase expression, it is the ubiquitous basic helix-loop-helix-leucine zipper transcription factor Usf-1 that is required for the UV activation of the Tyrosinase promoter. Consistent with this we demonstrate that Usf-1 is phosphorylated and activated by the stress-responsive p38 kinase. The results suggest that activation of Usf-1 by p38 at a wide variety of viral and cellular promoters will provide a link between stimuli as diverse as UV irradiation, glucose, viral infection and pro-inflammatory cytokines, and the changes in gene expression associated with the stress response.

Salicylates inhibit flavivirus replication independently of blocking nuclear factor kappa B activation

Flaviviruses comprise a positive-sense RNA genome that replicates exclusively in the cytoplasm of infected cells. Whether flaviviruses require an activated nuclear factor(s) to complete their life cycle and trigger apoptosis in infected cells remains elusive. Flavivirus infections quickly activate nuclear factor kappa B (NF-kappaB), and salicylates have been shown to inhibit NF-kappaB activation. In this study, we investigated whether salicylates suppress flavivirus replication and virus-induced apoptosis in cultured cells. In a dose-dependent inhibition, we found salicylates within a range of 1 to 5 mM not only restricted flavivirus replication but also abrogated flavivirus-triggered apoptosis. However, flavivirus replication was not affected by a specific NF-kappaB peptide inhibitor, SN50, and a proteosome inhibitor, lactacystin. Flaviviruses also replicated and triggered apoptosis in cells stably expressing IkappaBalpha-DeltaN, a dominant-negative mutant that antagonizes NF-kappaB activation, as readily as in wild-type BHK-21 cells, suggesting that NF-kappaB activation is not essential for either flavivirus replication or flavivirus-induced apoptosis. Salicylates still diminished flavivirus replication and blocked apoptosis in the same IkappaBalpha-DeltaN cells. This inhibition of flaviviruses by salicylates could be partially reversed by a specific p38 mitogen-activated protein (MAP) kinase inhibitor, SB203580. Together, these results show that the mechanism by which salicylates suppress flavivirus infection may involve p38 MAP kinase activity but is independent of blocking the NF-kappaB pathway.

The p38 mitogen-activated protein kinase mediates cytoskeletal remodeling in pulmonary microvascular endothelial cells upon intracellular adhesion molecule-1 ligation

Changes in the cytoskeleton of endothelial cells (ECs) play important roles in mediating neutrophil migration during inflammation. Previous studies demonstrated that neutrophil adherence to TNF-alpha-treated pulmonary microvascular ECs induced cytoskeletal remodeling in ECs that required ICAM-1 ligation and oxidant production and was mimicked by cross-linking ICAM-1. In this study, we examined the role of ICAM-1-induced signaling pathways in mediating actin cytoskeletal remodeling. Cross-linking ICAM-1 induced alterations in ICAM-1 distribution, as well as the filamentous actin rearrangements and stiffening of ECs shown previously. ICAM-1 cross-linking induced phosphorylation of the p38 mitogen-activated protein kinase (MAPK) that was inhibited by allopurinol and also induced an increase in the activity of the p38 MAPK that was inhibited by SB203580. However, SB203580 had no effect on oxidant production in ECs or ICAM-1 clustering. ICAM-1 cross-linking also induced phosphorylation of heat shock protein 27, an actin-binding protein that may be involved in filamentous actin polymerization. The time course of heat shock protein 27 phosphorylation paralleled that of p38 MAPK phosphorylation and was completely inhibited by SB203580. In addition, SB203580 blocked the EC stiffening response induced by either neutrophil adherence or ICAM-1 cross-linking. Moreover, pretreatment of ECs with SB203580 reduced neutrophil migration toward EC junctions. Taken together, these data demonstrate that activation of p38 MAPK, mediated by xanthine oxidase-generated oxidant production, is required for cytoskeletal remodeling in ECs induced by ICAM-1 cross-linking or neutrophil adherence. These cytoskeletal changes in ECs may in turn modulate neutrophil migration toward EC junctions.

Akt down-regulation of p38 signaling provides a novel mechanism of vascular endothelial growth factor-mediated cytoprotection in endothelial cells

Vascular endothelial growth factor (VEGF) utilizes a phosphoinositide 3-kinase (PI 3-kinase)/Akt signaling pathway to protect endothelial cells from apoptotic death. Here we show that PI 3-kinase/Akt signaling promotes endothelial cell survival by inhibiting p38 mitogen-activated protein kinase (MAPK)-dependent apoptosis. Blockade of the PI 3-kinase or Akt pathways in conjunction with serum withdrawal stimulates p38-dependent apoptosis. Blockade of PI 3-kinase/Akt also led to enhanced VEGF activation of p38 and apoptosis. In this context, the pro-apoptotic effect of VEGF is attenuated by the p38 MAPK inhibitor SB203580. VEGF stimulation of endothelial cells or infection with an adenovirus expressing constitutively active Akt causes MEKK3 phosphorylation, which is associated with decreased MEKK3 kinase activity and down-regulation of MKK3/6 and p38 MAPK activation. Conversely, activation-deficient Akt decreases VEGF-stimulated MEKK3 phosphorylation and increases MKK/p38 activation. Activation of MKK3/6 is not dependent on Rac activation since dominant negative Rac does not decrease p38 activation triggered by inhibition of PI 3-kinase. Thus, cross-talk between the Akt and p38 MAPK pathways may regulate the level of cytoprotection versus apoptosis and is a new mechanism to explain the cytoprotective actions of Akt.

Signalling for survival and death in neurones: the role of stress-activated kinases, JNK and p38

The pathways involved in neuronal survival or death have been extensively studied mainly in cell lines. Recent evidence has suggested that activation of the stress activated pathways, jun N-terminal kinase (JNK) and p38 may play important roles in neuronal cell death or regeneration. In this review we will discuss these pahtways in detail. We will examine the evidence that these pathways are important in neuronal cell death. Finally we will review the evidence that inhibitors of these pathways have a neuroprotective effect both in vitro and in vivo.

Decreased p38 MAPK activity in end-stage failing human myocardium: p38 MAPK alpha is the predominant isoform expressed in human heart

Short duration exposure to cellular stresses have been shown to activate p38 mitogen-activated protein kinase (MAPK) in cultured rat ventricular cardiomyocytes and isolated perfused hearts; however, effects of chronic stress on p38 MAPK are not well understood. This study determined whether alterations in the p38 MAPK pathway occurred prior to end-stage human heart failure. The p38 MAPK alpha isoform was detectable in human cardiac tissue. However, carefully controlled analysis of protein and message in this study demonstrated an absence of the p38 MAPK beta -isoform. Low levels of message for the non-SB203580 sensitive p38 MAPK gamma and delta isoforms were also detected in both normal and failing human myocardium. Ischemic and idiopathic end-stage failing human hearts were compared to non-failing hearts for both p38 alpha MAPK protein level and total p38 MAPK activity. Western blotting techniques demonstrated no significant changes in total p38 alpha MAPK content. However, approximately 75% decreases in active/phosphorylated p38 MAPK (P<0.005) were observed in both ischemic and idiopathic failing hearts compared to non-failing hearts. In-gel kinase assays confirmed that activated p38 MAPK, detected by Western blotting, phosphorylated its potential downstream targets. When compared to non-failing hearts, approximately 46% decreases in p38 MAPK phosphorylation of mitogen-activated protein kinase-activated protein kinase-2 (MAPKAPK-2) were observed in ischemic and idiopathic failing hearts (P=0.03 and P=0.04 respectively). Active p38 MAPK was localized to sarcomeric structures in the cytosol of myocytes by confocal immunofluorescence microscopy. The correlation between decreased MAPKAPK-2 phosphorylation and loss of active p38 MAPK in failing human myocytes suggests that decreases in the activation of p38 MAPK alpha, the predominant cardiac isoform, occur prior to end-stage heart failure.

MEK6 regulates human involucrin gene expression via a p38alpha - and p38delta -dependent mechanism

A signaling cascade that includes protein kinase C (PKC), Ras, and MEKK1 regulates involucrin (hINV) gene expression in epidermal keratinocytes (Efimova, T., LaCelle, P., Welter, J. F., and Eckert, R. L. (1998) J. Biol. Chem. 273, 24387-24395 and Efimova, T., and Eckert, R. L. (2000) J. Biol. Chem. 275, 1601-1607). Because signal transfer downstream of MEKK1 may involve several MAPK kinases (MEKs), it is important to evaluate the regulatory role of each MEK isoform. In the present study we evaluate the role of MEK6 in transmitting this signal. Constitutively active MEK6 (caMEK6) increases hINV promoter activity and increases endogenous hINV levels. The caMEK6-dependent increase in gene expression is inhibited by the p38 MAPK inhibitor, SB203580, and is associated with a marked increase in p38alpha MAPK activity; JNK and ERK kinases are not activated. In addition, hINV gene expression is inhibited by dominant-negative p38alpha and increased when caMEK6 and p38alpha are co-expressed. caMEK6 also activates p38delta, but p38delta inhibits the caMEK6-dependent activation. These results suggest that MEK6 increases hINV gene expression by regulating the balance between activation of p38alpha, which increases gene expression, and p38delta, which decreases gene expression.

Ray38p, a homolog of a purine motif triple-helical DNA-binding protein, Stm1p, is a ribosome-associated protein and dissociated from ribosomes prior to the induction of cycloheximide resistance in Candida maltosa

Cycloheximide (CYH) resistance in Candida maltosa is dependent on the induction of a ribosomal protein, Q-type L41, the 56th residue of which is glutamine, not proline as in ordinary P-type L41. We found that a 38-kDa protein in a wild-type C. maltosa ribosomal fraction became undetectable upon CYH treatment but detectable again with the establishment of CYH resistance by the induction of Q-type L41. We cloned a gene coding for this protein and named it RAY38 (ribosome-associated protein of yeast). Ray38p is a homolog of a purine motif triple-helical DNA-binding protein, Stm1p, and has a putative RNA-binding motif RGG. The ribosome-associated Ray38p was phosphorylated at serine and threonine residues, and Ray38p that was dissociated from ribosome by CYH treatment was highly phosphorylated in threonine residues. A ray38 null mutant recovered faster from CYH-caused growth stasis than the wild-type strain, suggesting that the dissociation of Ray38p from ribosome facilitates the induction of CYH resistance in C. maltosa.

Transient activation of c-Jun NH2-terminal kinase by growth factors influences survival but not apoptosis of human thyrocytes

Activation of c-Jun NH2-terminal kinase (JNK), a member of the mitogen-activated protein kinase (MAPK) family, is involved in apoptosis or cell proliferation. We have previously demonstrated that ionizing radiation or thyroid-stimulating hormone activated JNK without linking to thyroid cell apoptosis. To clarify the involvement of JNK activation in thyroid cell survival, we investigated the effects of various growth factors on induction of JNK activation in cultured human thyroid cells. JNK activation was observed at 30 minutes after fetal bovine serum (FBS) stimulation and returned to basal level at 240 minutes. Epidermal growth factor (EGF), transforming growth factor-beta (TGF-beta) and hepatocyte growth factor (HGF) also induced JNK activation, but did not trigger apoptotic cell death. Furthermore, we observed high basal activation of JNK in four of five human thyroid cancer cell lines. Overexpression of c-Met, an HGF receptor, was observed in two of the four cell lines with high basal JNK activity. Our results suggest that JNK activation does not induce apoptosis but is associated with survival or transformation of human thyroid cells.

Suppression of the clinical and cytokine response to endotoxin by RWJ-67657, a p38 mitogen-activated protein-kinase inhibitor, in healthy human volunteers

Sepsis resulting in multiorgan failure and death is still a major problem in intensive care medicine, despite extensive attempts to interfere in the supposed underlying mechanism of a deranged immune system. This is not only due to the persistent lacunae in knowledge about the immune system in sepsis but also due to the lack of sufficient instruments for intervention. Inhibitors of the p38 mitogen-activated protein kinase (p38MAPK) have been used to study the signalling pathway of the immune response. In vitro and animal studies have demonstrated that blocking p38MAPK could mitigate the pro-inflammatory response and improve survival after endotoxaemia. Using an endotoxaemia model in healthy human volunteers we evaluated the attenuation of clinical and cytokine response to endotoxin after inhibition of p38MAPK by an oral dose of RWJ-67657, a pyrindinyl imidazole. We measured the clinical parameters temperature, blood pressure and heart rate. The proinflammatory cytokines tumour necrosis factor-alpha, interleukin-6 and interleukin-8 were measured by ELISA at various points during a 24-h period. Drug toxicity was evaluated by routine clinical and laboratory examinations. After a single dose dose of RWJ-67657 the temperature and blood pressure response remained at the basal level. The inhibition of TNF-alpha, IL-6 and IL-8 response was a dose dependent. With the maximum dosage, reduction in peak serum levels of the proinflammatory cytokines was greater than 90%. There was no drug-related toxicity.

INTERPRETATION

We conclude that inhibition of p38MAPK by RWJ-67657 might be a tool to intervene in the deranged immune response in sepsis and other inflammatory diseases.

The antihyperglycemic drug alpha-lipoic acid stimulates glucose uptake via both GLUT4 translocation and GLUT4 activation: potential role of p38 mitogen-activated protein kinase in GLUT4 activation

The cofactor of mitochondrial dehydrogenase complexes and potent antioxidant alpha-lipoic acid has been shown to lower blood glucose in diabetic animals. alpha-Lipoic acid enhances glucose uptake and GLUT1 and GLUT4 translocation in 3T3-L1 adipocytes and L6 myotubes, mimicking insulin action. In both cell types, insulin-stimulated glucose uptake is reduced by inhibitors of p38 mitogen-activated protein kinase (MAPK). Here we explore the effect of alpha-lipoic acid on p38 MAPK, phosphatidylinositol (PI) 3-kinase, and Akt1 in L6 myotubes. alpha-Lipoic acid (2.5 mmol/l) increased PI 3-kinase activity (31-fold) and Akt1 (4.9-fold). Both activities were inhibited by 100 nmol/l wortmannin. alpha-Lipoic acid also stimulated p38 MAPK phosphorylation by twofold within 10 min. The phosphorylation persisted for at least 30 min. Like insulin, alpha-lipoic acid increased the kinase activity of the alpha (2.8-fold) and beta (2.1-fold) isoforms of p38 MAPK, measured by an in vitro kinase assay. Treating cells with 10 micromol/l of the p38 MAPK inhibitors SB202190 or SB203580 reduced the alpha-lipoic acid-induced stimulation of glucose uptake by 66 and 55%, respectively. In contrast, SB202474, a structural analog that does not inhibit p38 MAPK, was without effect on glucose uptake. In contrast to 2-deoxyglucose uptake, translocation of GLUT4myc to the cell surface by either alpha-lipoic acid or insulin was unaffected by 20 micromol/l of SB202190 or SB203580. The results suggest that inhibition of 2-deoxyglucose uptake in response to alpha-lipoic acid by inhibitors of p38 MAPK is independent of an effect on GLUT4 translocation. Instead, it is likely that regulation of transporter activity is sensitive to these inhibitors.

p38 MAP kinase negatively regulates cyclin D1 expression in airway smooth muscle cells

We have demonstrated that platelet-derived growth factor (PDGF) stimulates p38 mitogen-activated protein (MAP) kinase activation in bovine tracheal myocytes, suggesting that p38 is involved in growth regulation. We therefore examined whether p38 regulates expression of cyclin D1, a G(1) cyclin required for cell cycle traversal. The chemical p38 inhibitors SB-202190 and SB-203580 each increased basal and PDGF-induced cyclin D1 promoter activity and protein abundance. Overexpression of a dominant negative allele of MAP kinase kinase-3 (MKK3), an upstream activator of p38alpha, had similar effects. Conversely, active MKK3 and MKK6, both of which increase p38alpha activity, each decreased transcription from the cyclin D1 promoter. Together, these data demonstrate that p38 negatively regulates cyclin D1 expression. We tested whether p38 regulates cyclin D1 expression via inhibition of extracellular signal-regulated kinase (ERK) activation. Chemical inhibitors of p38 induced modest ERK phosphorylation and activation. However, dominant negative MKK3 was insufficient to activate ERK, and active MKK3 and MKK6 did not attenuate platelet-derived growth factor-mediated ERK activation. These data are consistent with the notion that p38alpha negatively regulates cyclin D1 expression via an ERK-independent pathway.

Intracellular pathways involved in TNF-alpha and superoxide anion release by Abeta(1-42)-stimulated primary human macrophages

In this study, the intracellular signal transduction pathways leading to the production of TNF-alpha and superoxide anions by amyloid-beta-stimulated primary human monocyte-derived macrophages was investigated. Using Western blotting and specific inhibitors it is shown that both ERK 1/2 and p38 MAPK signal transduction pathways as well as PKC are involved in the amyloid-beta-stimulated superoxide anion production. In contrast, only ERK 1/2 MAPK seems to be involved in TNF-alpha production: questioning the connection between PKC and ERK 1/2 activation. Our results suggest the use of ERK 1/2 MAPK inhibitors in the prevention of macrophage activation in the context of Alzheimer's disease.

Mitogen-activated protein (MAP) kinase pathways: regulation and physiological functions

Mitogen-activated protein (MAP) kinases comprise a family of ubiquitous proline-directed, protein-serine/threonine kinases, which participate in signal transduction pathways that control intracellular events including acute responses to hormones and major developmental changes in organisms. MAP kinases lie in protein kinase cascades. This review discusses the regulation and functions of mammalian MAP kinases. Nonenzymatic mechanisms that impact MAP kinase functions and findings from gene disruption studies are highlighted. Particular emphasis is on ERK1/2.

Role of p38 MAP kinase in LPS-induced airway inflammation in the rat

We investigated the effect of the p38 kinase inhibitor SB 203580 on airway inflammation induced by aerosolized lipopolysaccharide (LPS) in male Wistar rats. SB 203580 significantly inhibited (ED(50)=15.8 mg kg(-1)) plasma levels of TNF-alpha in rats challenged with LPS (1.5 mg kg(-1), i.p.). Aerosolized LPS induced a peak in TNF-alpha levels and the initiation of a neutrophilic response in bronchoalveolar lavage (BAL) fluid at the 2 h time point. Furthermore, the 4 h time point was associated with the peak in IL-1beta levels and the initial plateau of neutrophilia observed in the BAL fluid. SB 203580 (100 mg kg(-1)), had no effect on peak TNF-alpha levels or the associated neutrophilia in the BAL. Interestingly, the PDE 4 inhibitor RP 73401 (100 mg kg(-1)) significantly reduced both TNF-alpha levels and neutrophilic inflammation. However, the BAL fluid from rats pre-treated with either compound significantly inhibited TNF-alpha release from cultured human monocytes 18 h after LPS treatment (83.6 and 44.5% inhibition, respectively). Alternatively, SB 203580 (100 mg kg(-1)) produced dose-related inhibition of BAL IL-1beta levels (67.5% inhibition, P<0.01) and BAL neutrophilia (45.9% inhibition, P<0.01) 4 h after LPS challenge. P38 protein was present in lung tissue and the level of expression was not affected by LPS treatment. P38 kinase appears to be involved in the release of IL-1beta and the sustained neutrophilic response in the BAL fluid. This data may suggest a role for p38 inhibitors in the treatment of airway inflammatory diseases in which neutrophilia is a feature of the lung pathology.

Mammalian mitogen-activated protein kinase signal transduction pathways activated by stress and inflammation

The molecular details of mammalian stress-activated signal transduction pathways have only begun to be dissected. This, despite the fact that the impact of these pathways on the pathology of chronic inflammation, heart disease, stroke, the debilitating effects of diabetes mellitus, and the side effects of cancer therapy, not to mention embryonic development, innate and acquired immunity, is profound. Cardiovascular disease and diabetes alone represent the most significant health care problems in the developed world. Thus it is not surprising that understanding these pathways has attracted wide interest, and in the past 10 years, dramatic progress has been made. Accordingly, it is now becoming possible to envisage the transition of these findings to the development of novel treatment strategies. This review focuses on the biochemical components and regulation of mammalian stress-regulated mitogen-activated protein kinase (MAPK) pathways. The nuclear factor-kappa B pathway, a second stress signaling paradigm, has been the subject of several excellent recent reviews (258, 260).

MEK7-dependent activation of p38 MAP kinase in keratinocytes

Previous studies suggest that a PKC/Ras/MEKK1 cascade regulates involucrin (hINV) gene expression in human epidermal keratinocytes. MEK7, which is expressed in epidermis, has been identified as a member of this cascade (Efimova, T., LaCelle, P., Welter, J. F., and Eckert, R. L. (1998) J. Biol. Chem. 273, 24387-24395 and Efimova, T., and Eckert, R. L. (2000) J. Biol. Chem. 275, 1601-1607). However, the kinase that functions downstream of MEK7 has not been identified. Our present studies show that MEK7 expression in keratinocytes markedly activates p38alpha and modestly activates JNK. Activation of p38 MAPK by MEK7 is a novel finding, as previous reports have assigned MEK7 as a JNK regulator. We also demonstrate that this regulation is physiologically important, as the p38alpha- and JNK-dependent activities regulate hINV promoter activity and expression of the endogenous hINV gene.

Regulation of activating transcription factor-2 in early stage of the adipocyte differentiation program

p38beta mitogen-activated protein kinase activity is required for the differentiation of 3T3-L1 fibroblasts into adipocytes. Activating transcription factor-2 (ATF-2) is efficiently phosphorylated and activated by p38beta kinase. These findings led us to examine a regulatory role of ATF-2 in adipocyte differentiation. The induction of ATF-2 protein precedes the expression of the transcription factors, peroxisome proliferator-activated receptor (PPAR) gamma and CCAAT/enhancer-binding protein (C/EBP) alpha. Consistent with early activation of p38beta kinase, the phosphorylation of ATF-2 was also detected in early stage of adipocyte differentiation. ATF-2 regulated gene transcription of PPARgamma, which was synergistically enhanced by p38beta kinase and C/EBPbeta proteins expression. Ectopic expression of ATF-2 in 3T3-L1 cells induced the endogenous PPARgamma protein levels. These results suggest that ATF-2 plays a role in a primary regulator of adipocyte differentiation with C/EBPbeta through promoting adipogenesis-inducing transcription factors including PPARgamma and becomes associated earlier in the differentiation program as mitotic clonal expansion proceeds and the cells become initially differentiated.

A novel mitogen-activated protein kinase is responsive to Raf and mediates growth factor specificity

The proto-oncogene Raf is a major regulator of growth and differentiation. Previous studies from a number of laboratories indicate that Raf activates a signaling pathway that is independent of the classic MEK1,2-ERK1,2 cascade. However, no other signaling cascade downstream of Raf has been identified. We describe a new member of the mitogen-activated protein kinase family, p97, an ERK5-related kinase that is activated and Raf associated when cells are stimulated by Raf. Furthermore, p97 is selectively responsive to different growth factors, providing a mechanism for specificity in cellular signaling. Thus, p97 is activated by the neurogenic factor fibroblast growth factor (FGF) but not the mitogenic factor epidermal growth factor (EGF) in neuronal cells. Conversely, the related kinase ERK5 is activated by EGF but not FGF. p97 phosphorylates transcription factors such as Elk-1 and Ets-2 but not MEF2C at transactivating sites, whereas ERK5 phosphorylates MEF2C but not Elk-1 or Ets-2. Finally, p97 is expressed in a number of cell types including primary neural and NIH 3T3 cells. Taken together, these results identify a new signaling pathway that is distinct from the classic Raf-MEK1,2-ERK1,2 kinase cascade and can be selectively stimulated by growth factors that produce discrete biological outcomes.

PKC delta mediates ionizing radiation-induced activation of c-Jun NH(2)-terminal kinase through MKK7 in human thyroid cells

The thyroid gland is one of the most sensitive organs in ionizing radiation (IR)-induced carcinogenesis. To determine, therefore, the specific cascade of IR-induced signal transduction in human thyroid cells, we investigated the functional role of protein kinase C (PKC), especially its interlocking activation of c-Jun NH(2)-terminal kinase (JNK) pathway. In the present study, using adenovirus expression vectors for diverse dominant-negative (DN) types of PKC isoforms (alpha, beta2, delta, epsilon and zeta) expressed in primary cultured human thyroid cells, only DN/PKC delta suppressed IR-induced JNK activation. In addition, Rottlerin, a PKC delta specific inhibitor, inhibited IR-induced JNK activation. IR-induced activation of transcription factor AP-1, downstream target of JNK, was also attenuated by DN/PKC delta. To examine the involvement of upstream kinases of JNK, we performed immune-complex kinase assays of mitogen-activated protein kinase kinase 4 (MKK4) and MKK7. IR activated MKK7 but not MKK4, and this activation was inhibited by Rottlerin. Furthermore, IR-induced JNK activation was suppressed by overexpression of kinase-deficient MKK7. Our results indicate that IR selectively activates the cascade of PKC delta-MKK7-JNK-AP-1 in human thyroid cells, suggesting a not apoptotic but radio-resistant role of PKC delta in human thyroid cells following IR.

Activation of Rac1 and the p38 mitogen-activated protein kinase pathway in response to all-trans-retinoic acid

Several signaling pathways are activated by all-trans-retinoic acid (RA) to mediate induction of differentiation and apoptosis of malignant cells. In the present study we provide evidence that the p38 MAP kinase pathway is activated in a RA-dependent manner in the NB-4, acute pro-myelocytic leukemia, and the MCF-7, breast carcinoma, cell lines. RA treatment of cells induces a time- and dose-dependent phosphorylation of p38, and such phosphorylation results in activation of its catalytic domain. p38 activation is not inducible by RA in a variant NB-4 cell line, NB-4.007/6, which is resistant to the effects of RA, suggesting a role for this pathway in the induction of RA responses. Our data also demonstrate that the small G-protein Rac1 is activated by RA and functions as an upstream regulator of p38 activation, whereas the MAPKAPK-2 serine kinase is a downstream effector for the RA-activated p38. To obtain information on the functional role of the Rac1/p38/MAPKAPK-2 pathway in RA signaling, the effects of pharmacological inhibition of p38 on RA-induced gene transcription and cell differentiation were determined. Our results indicate that treatment of cells with the SB203580 inhibitor does not inhibit RA-dependent gene transcription via retinoic acid response elements or induction of Stat1 protein expression. However, treatment with SB203580 or SB202190 strongly enhances RA-dependent induction of cell differentiation and RA-regulated growth inhibitory responses. Altogether, our findings demonstrate that the Rac1/p38 MAP kinase pathway is activated in a RA-dependent manner and exhibits negative regulatory effects on the induction of differentiation.

Angiotensin II induces migration and Pyk2/paxillin phosphorylation of human monocytes

Angiotensin (Ang) II has been shown to enhance the development of atherosclerotic lesions. Migration of monocytes is an early critical step in the atherosclerotic process. To elucidate mechanisms by which Ang II promotes atherogenesis, we investigated its effects on human monocyte migration. Ang II induced migration of human peripheral blood monocytes (HPBM) and human THP-1 monocytes at concentrations between 0.01 and 1 micromol/L, with a 3.6+/-0.6-fold induction in HPBM and a 4.8+/-0.9-fold induction in THP-1 cells at 1 micromol/L Ang II (both P<0.01 versus unstimulated cells). Addition of the Ang II receptor type 1 (AT1-R) antagonist losartan (1 to 100 micromol/L) suppressed Ang II-induced migration of HPBM and THP-1 monocytes in a dose-dependent manner, demonstrating an AT1-R-mediated mechanism. Ang II-directed migration was also blocked by the Src kinase inhibitor PP2 (10 micromol/L), by the extracellular-regulated protein kinase (ERK 1/2) inhibitor PD98059 (30 micromol/L), and by the p38-MAPK inhibitor SB203580 (10 micromol/L), indicating that Src, ERK 1/2, and p38 are all involved in Ang II-induced migration of HPBM and human THP-1 monocytes. The proline-rich tyrosine kinase 2 (Pyk2) and paxillin are 2 cytoskeleton-associated proteins involved in cell movement, phosphorylated by Ang II in other cell types, and abundantly expressed in monocytes. Ang II (1 micromol/L) induced Pyk2 and paxillin phosphorylation in human THP-1 monocytes, peaking after 10 minutes for Pyk2 with a 6.7+/-0.9-fold induction and after 2 minutes for paxillin with a 3.2+/-0.4-fold induction. Ang II-induced phosphorylation of both proteins was suppressed by losartan and the Src inhibitor PP2, whereas no effect was observed with PD98059 and SB203580. This study demonstrates a novel proatherogenic action of Ang II on human monocytes by stimulating their migration, through an AT1-R-dependent process, involving signaling through Src, ERK 1/2, and p38. Furthermore, the promigratory actions of Ang II in human monocytes are associated with the phosphorylation of 2 cytoskeleton-associated proteins, Pyk2 and paxillin.

Overexpression of 12-lipoxygenase causes cardiac fibroblast cell growth

Evidence suggests that leukocyte type 12-lipoxygenase (12-LO) plays an important role in cell growth. However, the role of 12-LO in cardiac cell growth has not been tested. We have now stably overexpressed 12-LO cDNA in rat fetal cardiac fibroblasts to evaluate the role of the 12-LO pathway in cardiac cell growth. Overexpression of 12-LO increased cell [(3)H]leucine incorporation by 2.1+/-0.1-fold (P<0.01) and cell protein content by 2.2+/-0. 3-fold (P<0.01) over mock-transfected cells. These findings were confirmed in additional clones. Baicalein, a 12-LO enzyme inhibitor, dose-dependently inhibited serum-induced leucine incorporation in cardiac fibroblast cells as well as partially inhibited leucine incorporation in cells overexpressing 12-LO. 12-LO overexpression also caused cell [(3)H]thymidine incorporation to increase by 3.4+/-0.3-fold (P<0.01). Cell flow cytometry analysis showed that the size of 12-LO-overexpressing cells was markedly enlarged compared with that of mock-transfected cells. The fibronectin content of the 12-LO-overexpressing cardiac fibroblasts was also significantly increased. We next evaluated the effects of 12-LO RNA overexpression on kinase pathways linked to cellular growth. The overexpression of 12-LO enhanced extracellular signal-regulated kinase activity (4. 1+/-0.5-fold), c-Jun NH(2)-terminal kinase activity (2.9+/-0.5-fold), and p38 mitogen-activated protein kinase activity (2.2+/-0.3-fold). Pretreatment with SB202190 (100 nmol/L), a specific inhibitor of p38, prevented the increases in protein content of 12-LO-overexpressing cardiac fibroblast cells. These data clearly demonstrate that the overexpression of 12-LO causes cell growth of cardiac fibroblasts, thus supporting the role of 12-LO as a novel growth-promoting pathway in the heart.

Peroxynitrite induces GADD34, 45, and 153 VIA p38 MAPK in human neuroblastoma SH-SY5Y cells

Peroxynitrite, one of the most reactive radicals, is produced from superoxide anion and nitric oxide. A peroxynitrite generator, 3-morpholinosydonimine (SIN-1), was found to induce the expression of three different growth arrest and DNA damage-inducible (GADD) mRNA, GADD34, GADD45, and GADD153, at the early phase during cell death in human neuroblastoma SH-SY5Y cells. In addition, peroxynitrite activated p38 MAPK just before induction of three GADD mRNA. A specific inhibitor of p38 MAPK, SB202190, markedly suppressed peroxynitrite-induced expression of three GADD mRNA in SH-SY5Y cells. The expression of three GADD genes and also p38 MAPK phosphorylation were suppressed by treatment with radical scavengers, superoxide dismutase plus catalase and glutathione. Glutathione depletion by L-buthionine-S, R-sulfoximine (BSO), increased the vulnerability of the cells to peroxynitrite. These findings indicate that peroxynitrite-mediated oxidative stress activated p38 MAPK to induce three GADD genes.

Selective targeting of MAPKs to the ETS domain transcription factor SAP-1

MAPK pathways play important roles in regulating the key cellular processes of proliferation, differentiation, and apoptosis. There are multiple MAPK pathways, which are subject to different regulatory cues. It is important that these pathways maintain specificity in signaling to elicit the activation of a specific program of gene expression. MAPK-docking domains in several transcription factors have been shown to play important roles in determining the specificity and efficiency of their phosphorylation by MAPKs. Here we investigate the mechanisms by which MAPKs are targeted to the ETS domain transcription factor SAP-1. We demonstrate that SAP-1 contains two different domains that are required for its efficient phosphorylation in vitro and activation in vivo by ERK2 and a subset of p38 MAPKs. The D-domain is closely related to other MAPK-docking domains, but exhibits a novel specificity and serves to promote selective targeting of ERK2, p38alpha, and p38beta(2) to SAP-1. A second important region, the FXF motif, also plays an important role in directing MAPKs to phosphorylate SAP-1. The FXF motif promotes targeting by ERK2 and, to a lesser extent, p38alpha, but not p38beta(2). Our data therefore demonstrate that a modular system of motifs is responsible for directing specific MAPK subtypes to SAP-1, but also point to important distinctions in the mechanism of action of the D-domain and FXF motif.

Helicobacter pylori-induced prostaglandin E(2) synthesis involves activation of cytosolic phospholipase A(2) in epithelial cells

Helicobacter pylori initiates an inflammatory response and gastric diseases, which are more common in patients infected with H. pylori strains carrying the pathogenicity island, by colonizing the gastric epithelium. In the present study we investigated the mechanism of prostaglandin E(2) (PGE(2)) synthesis in response to H. pylori infection. We demonstrate that H. pylori induces the synthesis of PGE(2) via release of arachidonic acid predominately from phosphatidylinositol. In contrast to H. pylori wild type, an isogenic H. pylori strain with a mutation in the pathogenicity island exerts only weak arachidonic acid and PGE(2) synthesis. The H. pylori-induced arachidonic acid release was abolished by phospholipase A(2) (PLA(2)) inhibitors and by pertussis toxin (affects the activity of G alpha(i)/G alpha(o)). The role of phospholipase C, diacylglycerol lipase, or phospholipase D was excluded by using specific inhibitors. An inhibitor of the stress-activated p38 kinase (SB202190), but neither inhibitors of protein kinase C nor an inhibitor of the extracellular-regulated kinase pathway (PD98059), decreased the H. pylori-induced arachidonic acid release. H. pylori-induced phosphorylation of p38 kinase and cytosolic PLA(2) was blocked by SB202190. These results indicate that H. pylori induces the release of PGE(2) from epithelial cells by cytosolic PLA(2) activation via G alpha(i)/G alpha(o) proteins and the p38 kinase pathway.

Multiple signals required for cyclic AMP-responsive element binding protein (CREB) binding protein interaction induced by CD3/CD28 costimulation

The optimal activation of cAMP-responsive element binding protein (CREB), similar to the full activation of T lymphocytes, requires the stimulation of both CD3 and CD28. Using a reporter system to detect interaction of CREB and CREB-binding protein (CBP), in this study we found that CREB binds to CBP only by engagement of both CD3 and CD28. CD3/CD28-promoted CREB-CBP interaction was dependent on p38 mitogen-activated protein kinase (MAPK) and calcium/calmodulin-dependent protein kinase (CaMK) IV in addition to the previously identified extracellular signal-regulated kinase pathway. Extracellular signal-regulated kinase, CaMKIV, and p38 MAPK were also the kinases involved in CREB Ser(133) phosphorylation induced by CD3/CD28. A reconstitution experiment illustrated that optimum CREB-CBP interaction and CREB trans-activation were attained when these three kinase pathways were simultaneously activated in T cells. Our results demonstrate that coordinated activation of different kinases leads to full activation of CREB. Notably, CD28 ligation activated p38 MAPK and CaMKIV, the kinases stimulated by CD3 engagement, suggesting that CD28 acts by increasing the activation extent of p38 MAPK and CaMKIV. These results support the model of a minimum activation threshold for CREB-CBP interaction that can be reached only when both CD3 and CD28 are stimulated.

Role of mitogen-activated protein kinases in activation of human neutrophils by antineutrophil cytoplasmic antibodies

Antineutrophil cytoplasmic antibodies (ANCA) may be important in the pathophysiology of necrotizing vasculitis. ANCA activate human neutrophils primed with tumor necrosis factor-alpha (TNF-alpha) in vitro. TNF-alpha priming results in translocation of ANCA antigens to the cell surface, where they are recognized by the antibodies. The signaling mechanisms involved in TNF-alpha priming and subsequent ANCA-induced activation were investigated. TNF-alpha-primed neutrophils were stimulated with monoclonal antibodies (MAb) to human myeloperoxidase (MPO) and proteinase 3 (PR3), and with preparations of human ANCA (three patients with PR3-ANCA and two patients with MPO-ANCA). Respiratory burst was measured with superoxide dismutase-inhibitable ferricytochrome C reduction and using dihydro-rhodamine-1,2,3. Phosphorylation of p38 mitogen-activated protein kinase (p38-MAPK) and the extracellular signal-regulated kinase (ERK) were assessed by immunoblotting. ANCA-antigen translocation was studied by flow cytometry. The tyrosine phosphorylation inhibitor genistein, but not calphostin or staurosporin, resulted in a significant dose-dependent superoxide generation inhibition (11.6 +/- 1.7 nmol to 2.1 +/- 0.5 for PR3-ANCA, and 16.0 +/- 2.8 to 3.3 +/- 1.3 for MPO-ANCA). The p38-MAPK inhibitor (SB202190) and the ERK inhibitor (PD98059) diminished PR3-ANCA-mediated superoxide production dose dependently (11.6 +/- 1.7 nmol O(2)(-) to 1.9 +/- 0.6 with 50 microM SB202190 and 4.0 +/- 0.6 with 50 microM PD098059, respectively). For MPO-ANCA, the results were similar (16.0 +/- 2.8 nmol to 0.9 +/- 1.0 nmol with SB202190 and 6.4 +/- 2.4 nmol with PD98059, respectively). Western blot showed phosphorylation of both p38-MAPK and ERK during TNF-alpha priming. The p38-MAPK inhibitor and the ERK inhibitor showed the strongest effect on respiratory burst when added before TNF-alpha priming, further supporting an important role for both signaling pathways in the priming process. Flow cytometry showed that p38-MAPK inhibition decreased the translocation of PR3 (by 93 +/- 2%) and of MPO (by 64 +/- 2%). In contrast, no such effect was seen when ERK was inhibited. Thus, p38-MAPK and ERK are important for the TNF-alpha-mediated priming of neutrophils enabling subsequent ANCA-induced respiratory burst. However, both pathways show differential effects, whereby p38-MAPK controls the translocation of ANCA antigens to the cell surface.

Role of p38 MAP kinase in endothelial cell alignment induced by fluid shear stress

The p38/mitogen-activated protein (MAP) kinase-activated protein kinase 2 (MAPKAP kinase 2)/heat shock protein (HSP)25/27 pathway is thought to play a critical role in actin dynamics. In the present study, we examined whether p38 was involved in the morphological changes seen in endothelial cells (EC) exposed to shear stress. Cultured bovine aortic EC were subjected to 14 dyn/cm(2) laminar steady shear stress. Peak activation of p38, MAPKAP kinase 2, and HSP25 were sixfold at 5 min, sixfold at 5 min, and threefold at 30 min compared with static control, respectively. SB-203580 (1 microM), a specific inhibitor of p38, abolished the activation of MAPKAP kinase 2 and HSP25 as well as EC elongation and alignment in the direction of flow elicited by shear stress. The mean orientation angle of cells subjected to shear without SB-203580, with SB-203580, or static control were 17, 50, and 43 degrees, respectively (P < 0. 05). EC transfected with the dominant negative mutant of p38-alpha aligned randomly with no stress fiber formation despite exposure to shear stress. These data suggests that the pathway of p38/MAPKAP kinase 2/HSP25/27 is activated in response to shear stress, and this pathway plays an important role in morphological changes induced by shear stress.

Immunolocalization of p38 MAP kinase in mouse brain

p38 has been implicated to play a critical role in regulating apoptosis in PC12 and cerebellar granule cells, and is inactivated in cultured fetal neurons in response to insulin. Though p38 is activated in microglia after ischemia, the physiological functions of p38 in the brain are not well understood. As a first step to elucidate the physiological functions of p38 in the central nervous system, we raised a polyclonal antibody against p38 and performed immunohistochemical examination to demonstrate the localization of p38 in mouse brain. Strong p38 immunoreactivity was apparent in fiber bundles including the olfactory tract, anterior commissure, corpus callosum, cingulum, internal capsule, stria terminalis, fimbria and alveus hippocampi, fornix, stria medullaris, optic chiasm and optic tract. Although similar regions were stained with both anti-p38 and anti-neurofilament antibodies, intense p38 immunoreactivity was often observed in myelin sheath-like structures but not in axons. This is the first demonstration of the localization of p38 in the central nervous system and provides an anatomical basis for understanding physiological roles of p38.

Thyroid-stimulating hormone and cyclic AMP activate p38 mitogen-activated protein kinase cascade. Involvement of protein kinase A, rac1, and reactive oxygen species

p38 mitogen-activated protein kinases (p38-MAPKs) are activated by cytokines, cellular stresses, growth factors, and hormones. We show here that p38-MAPKs are activated upon stimulation by thyroid-stimulating hormone (TSH) or cAMP. TSH caused the phosphorylation of p38-MAPK in Chinese hamster ovary cells stably transfected with the human TSH receptor but not in wild-type Chinese hamster ovary cells. The effect of TSH was fully mimicked by the adenylyl cyclase activator, forskolin, and by a permeant analog of cAMP. The effect of forskolin was reproduced in FRTL5 rat thyroid cells. TSH also stimulated the phosphorylation of MAPK kinase 3 or 6, over the same time scale as that of p38-MAPKs. TSH and forskolin stimulated the activity of the alpha-isoform of p38-MAPK assayed by phosphorylation of the transcription factor ATF2. The activity of MAPK-activated protein kinase-2 was stimulated by TSH and forskolin. This stimulation was abolished by SB203580, a specific inhibitor of p38-MAPKs. The protein kinase A inhibitor H89 inhibited the stimulation of phosphorylation of p38-MAPKs by forskolin, whereas inhibitors of protein kinase C, p70(S6k), and phosphatidylinositol 3-kinase were ineffective. Expression of the dominant negative form of Rac1, but not that of Ras, blocked forskolin-induced p38-MAPK activation. Diphenylene iodonium, a potent inhibitor of NADPH oxidase(s), and ascorbic acid, an effective free radical scavenger, suppressed TSH- or forskolin-stimulated p38-MAPK phosphorylation, indicating that the generation of reactive oxygen species plays a key role in signaling from cAMP to p38-MAPKs. Inhibition of the p38-MAPK pathway with SB203580 partially but significantly, attenuates cAMP- and TSH-induced expression of the sodium iodide symporter in FRTL-5 cells. These results point to a new signaling pathway for the G(s)-coupled TSH receptor, involving cAMP, protein kinase A, Rac1, and reactive oxygen species and resulting in the activation of a signaling kinase cascade that includes MAPK kinase 3 or 6, p38-MAPK, and MAPK-activated protein kinase-2.

Differential activation of p38 mitogen-activated protein kinase isoforms depending on signal strength

We have investigated the ability of the mitogen-activated protein kinase (MAPK) kinase MKK6 to activate different members of the p38 subfamily of MAPKs and found that some MKK6 mutants can efficiently activate p38alpha but not p38gamma. In contrast, a constitutively active MKK6 mutant activated both p38 MAPK isoforms to similar extents. The same results were obtained upon co-expression in Xenopus oocytes and in vitro using either MKK6 immunoprecipitates from transfected cells or bacterially produced recombinant proteins. We also found that the preferential activation of p38alpha by MKK6 correlated with more efficient binding of MKK6 to p38alpha than to p38gamma. Furthermore, increasing concentrations of constitutively active MKK6 differentially activated either p38alpha alone (low MKK6 activity) or both p38alpha and p38gamma (high MKK6 activity), both in vitro and in injected oocytes. The determinants for selectivity are located at the carboxyl-terminal lobe of p38 MAPKs but do not correspond to the activation loop or common docking sequences. We also showed that different stimuli can induce different levels of endogenous MKK6 activity that correlate with differential activation of p38 MAPKs. Our results suggest that the level of MKK6 activity triggered by a given stimulus may determine the pattern of downstream p38 MAPK activation in the particular response.

Estrogen signals to the preservation of endothelial cell form and function

Estrogen is important for the primary prevention of vascular disease in young women, but the mechanisms of protection at the vascular cell are still largely unknown. Although traditionally thought of as a nuclear transcription factor, the estrogen receptor has also been identified in the cell plasma membrane to signal but serve largely undefined roles. Here we show that estradiol (E2) rapidly activates p38beta mitogen-activated protein kinase in endothelial cells (EC), which activates the mitogen-activated protein kinase-activated protein kinase-2 and the phosphorylation of heat shock protein 27. The sex steroid preserves the EC stress fiber formation and actin and membrane integrity in the setting of metabolic insult. E2 also prevents hypoxia-induced apoptosis and induces both the migration of EC and the formation of primitive capillary tubes. These effects are reversed by the inhibition of p38beta, by the expression of a dominant-negative mitogen-activated protein kinase-activated protein kinase-2 protein, or by the expression of a phosphorylation site mutant heat shock protein 27. E2 signaling from the membrane helps preserve the EC structure and function, defining potentially important vascular-protective effects of this sex steroid.

High Levels of Glucose Stimulate Angiotensinogen Gene Expression Via the P38 Mitogen-Activated Protein Kinase Pathway in Rat Kidney Proximal Tubular Cells* *This work was supported by grants from the Medical Research Council of Canada (MT-13420 to J.S.D.C. and J.G.F., and MT-12573 to J.G.F.) and from the NIH (HL-48455 to J.R.I., and D.K-50836 to S.S.T.)

The present studies investigated whether the effect of high levels of glucose on angiotensinogen (ANG) secretion and gene expression in kidney proximal tubular cells is mediated at least in part via the activation of p38 mitogen-activated protein kinase (p38 MAPK). Rat immortalized renal proximal tubular cells (IRPTCs) were cultured in monolayer. The levels of immunoreactive rat ANG (IR-rANG) secreted into the medium and the levels of cellular ANG messenger RNA were determined by a specific RIA for rat ANG and a RT-PCR assay, respectively. Phosphorylation of cellular p38 MAPK was determined by Western blot analysis using the Phospho Plus p38 MAPK antibody kit. High levels of glucose (i.e. 25 mM) and phorbol 12-myristate 13-acetate (PMA; 10(-7) M) increased the secretion of IR-rANG and cellular ANG messenger RNA as well as phosphorylation of p38 MAPK in IRPTCs. This stimulatory effect of high levels of glucose and PMA was blocked by SB 203580 (a specific inhibitor of p38 MAPK), but not by SB 202474 (a negative control of SB 203580). High levels of D-sorbitol or 2-deoxy-D-glucose (i.e. > or = 35 mM) also stimulated the phosphorylation of p38 MAPK, but did not stimulate ANG secretion or gene expression. GF 109203X (an inhibitor of protein kinase C) blocked the stimulatory effect of high levels of glucose and PMA on ANG gene expression, whereas it did not block the effect of high levels of glucose, sorbitol, or 2-deoxy-D-glucose on p38 MAPK phosphorylation in IRPTCs. These studies demonstrate that the stimulatory effect of a high level of glucose (25 mM) on ANG gene expression in IRPTCS may be mediated at least in part via activation of p38 MAPK signal transduction pathway and is protein kinase C independent.

Cisplatin and UV radiation induce activation of the stress-activated protein kinase p38gamma in human melanoma cells

The p38 alpha mitogen-activated protein kinase has been implicated in the cellular response to genotoxic agents. Here we show that another p38 family member is also activated in response to cisplatin exposure in human melanoma cells. We identified this isoform as p38gamma based on its recognition by specific antibodies and because, in contrast to p38alpha, its activity was not affected by SB203580. We also found that etoposide caused a much more discrete phosphorylation of both p38alpha and p38gamma than either cisplatin or UV treatment. These results indicate that genotoxic stresses activate several p38 isoforms whose implication in the cellular response might depend on the type of DNA damage.

Cyclic AMP activates p38 mitogen-activated protein kinase in Th2 cells: phosphorylation of GATA-3 and stimulation of Th2 cytokine gene expression

cAMP is an important second messenger with immunomodulatory properties. Elevation of intracellular cAMP in T cells, induced by agents such as IL-1alpha or PGs, inhibits T cell activation. In effector T cells, an increase in the level of intracellular cAMP inhibits cytokine production in Th1 cells but stimulates cytokine production in Th2 cells. Here we report that cAMP-induced effects in Th2 cells occur independently of the protein kinase A pathway, which is the major mediator of cAMP-induced signaling events in most cell types. Instead, cAMP stimulates activation of p38 mitogen-activated protein kinase in Th2 cells. This appears to be a Th2-selective event because cAMP barely increased p38 phosphorylation in Th1 cells. We show that in Th2 cells, cAMP promotes the production of both IL-5 and IL-13, which play distinct but critical roles in asthma pathogenesis. Our data also show that cAMP causes increased phosphorylation of the transcription factor GATA-3, which we have shown is a critical regulator of Th2 cytokine gene expression and, in turn, of airway inflammation in mice. Thus, Th2-specific GATA-3 expression and p38 mitogen-activated protein kinase activation together provide a molecular basis for the differential effects of cAMP in the two T helper cell subsets.

Signal-dependent nuclear export of a histone deacetylase regulates muscle differentiation

Members of the myocyte enhancer factor-2 (MEF2) family of transcription factors associate with myogenic basic helix-loop-helix transcription factors such as MyoD to activate skeletal myogenesis. MEF2 proteins also interact with the class II histone deacetylases HDAC4 and HDAC5, resulting in repression of MEF2-dependent genes. Execution of the muscle differentiation program requires release of MEF2 from repression by HDACs, which are expressed constitutively in myoblasts and myotubes. Here we show that HDAC5 shuttles from the nucleus to the cytoplasm when myoblasts are triggered to differentiate. Calcium/calmodulin-dependent protein kinase (CaMK) signalling, which stimulates myogenesis and prevents formation of MEF2-HDAC complexes, also induces nuclear export of HDAC4 and HDAC5 by phosphorylation of these transcriptional repressors. An HDAC5 mutant lacking two CaMK phosphorylation sites is resistant to CaMK-mediated nuclear export and acts as a dominant inhibitor of skeletal myogenesis, whereas a cytoplasmic HDAC5 mutant is unable to block efficiently the muscle differentiation program. Our results highlight a mechanism for transcriptional regulation through signal- and differentiation-dependent nuclear export of a chromatin-remodelling enzyme, and suggest that nucleo-cytoplasmic trafficking of HDACs is involved in the control of cellular differentiation.

p38MAPK inhibition enhances basal and norepinephrine-stimulated p42/44MAPK phosphorylation in rat pinealocytes

Interaction between p38MAPK and p42/44MAPK in rat pinealocytes was examined by determining the effects of p38MAPK inhibitors on the phosphorylation of p42/44MAPK using Western blot analysis. Treatment with SB202190, a specific inhibitor of p38MAPK, increased p42/44MAPK phosphorylation in a concentration-dependent manner. SB202190 also enhanced the magnitude and the duration of norepinephrine-activated p42/44MAPK phosphorylation. The effect of SB202190 on p42/44MAPK phosphorylation was abolished by PD98059 or UO126, inhibitors of MEK, suggesting that SB202190 is acting upstream of MEK in activating p42/44MAPK. The SB202190-induced phosphorylation of p42/44MAPK was not blocked by inhibitors of cGMP-dependent kinase (KT5823), protein kinase C (calphostin C) or Ca2+/calmodulin dependent kinase (KN93) suggesting that these pathways may not be involved in the effect of SB202190. SB202190 further increased p42/44MAPK phosphorylation that was stimulated by 8-bromo-cGMP, 4beta phorbol 12-myristate 13-acetate, or ionomycin. In contrast, inhibition of p42/44MAPK phosphorylation by dibutyryl-cAMP persisted when p42/44MAPK phosphorylation was increased by SB202190. Furthermore, inhibition of p42/44MAPK phosphorylation had no effect on p38MAPK activation. These results suggest that inhibition of p38MAPK causes activation of p42/44MAPK and acts synergistically with norepinephrine in the regulation of p42/44MAPK activation in rat pinealocytes.

Protein kinase C zeta plays a central role in activation of the p42/44 mitogen-activated protein kinase by endotoxin in alveolar macrophages

Human alveolar macrophages respond to endotoxin (LPS) by activation of a number of mitogen-activated protein kinase pathways, including the p42/44 (extracellular signal-related kinase (ERK)) kinase pathway. In this study, we evaluated the role of the atypical protein kinase C (PKC) isoform, PKC zeta, in LPS-induced activation of the ERK kinase pathway. Kinase activity assays showed that LPS activates PKC zeta, mitogen-activated protein/ERK kinase (MEK, the upstream activator of ERK), and ERK. LPS did not activate Raf-1, the classic activator of MEK. Pseudosubstrate-specific peptides with attached myristic acid are cell permeable and can be used to block the activity of specific PKC isoforms in vivo. We found that a peptide specific for PKC zeta partially blocked activation of both MEK and ERK by LPS. We also found that this peptide blocked in vivo phosphorylation of MEK after LPS treatment. In addition, we found that LPS caused PKC zeta to bind to MEK in vivo. These observations suggest that MEK is an LPS-directed target of PKC zeta. PKC zeta has been shown in other systems to be phosphorylated by phosphatidylinositol (PI) 3-kinase-dependent kinase. We found that LPS activates PI 3-kinase and causes the formation of a PKC zeta/PI 3-kinase-dependent kinase complex. These data implicate the PI 3-kinase pathway as an integral part of the LPS-induced PKC zeta activation. Taken as a whole, these studies suggest that LPS activates ERK kinase, in part, through activation of an atypical PKC isoform, PKC zeta.

Hypoxia differentially regulates the mitogen- and stress-activated protein kinases. Role of Ca2+/CaM in the activation of MAPK and p38 gamma

Hypoxic/ischemic trauma is a primary factor in the pathology of various vascular, pulmonary, and cerebral disease states. Yet, the signaling mechanisms by which cells respond and adapt to changes in oxygen levels are not clearly established. The effects of hypoxia on the stress- and mitogen-activated protein kinase (SAPK and MAPK) signaling pathways were studied in PC12 cells. Exposure to moderate hypoxia (5% O2) was found to progressively stimulate phosphorylation and activation of p38 gamma in particular, and also p38 alpha, two isoforms of the p38 family of stress-activated protein kinases. In contrast, hypoxia had no effect on enzyme activity of p38 beta, p38 beta 2, p38 delta, or on JNK, another stress-activated protein kinase. Prolonged hypoxia also induced phosphorylation and activation of p42/p44 MAPK, although this activation was modest when compared to NGF and UV-induced activation. We further showed that activation of p38 gamma and MAPK during hypoxia requires calcium, as treatment with Ca(2+)-free media or the calmodulin antagonist, W13, blocked the activation of p38 gamma and MAPK, respectively. These studies demonstrate that an extremely typical physiological stress (hypoxia) causes selective activation of specific elements of the SAPKs and MAPKs, and identifies Ca+2/CaM as a critical upstream activator.

Involvement of p38 mitogen-activated protein kinase signaling pathway in osteoclastogenesis mediated by receptor activator of NF-kappa B ligand (RANKL)

The receptor activator of NF-kappaB ligand (RANKL) induces osteoclast differentiation from bone marrow cells in the presence of macrophage colony-stimulating factor. We found that treatment of bone marrow cells with SB203580 inhibited osteoclast differentiation via inhibition of the RANKL-mediated signaling pathway. To elucidate the role of p38 mitogen-activated protein (MAP) kinase pathway in osteoclastogenesis, we employed RAW264 cells which could differentiate into osteoclast-like cells following treatment with RANKL. In a dose-dependent manner, SB203580 but not PD98059, inhibited RANKL-induced differentiation. Among three MAP kinase families tested, this inhibition profile coincided only with the activation of p38 MAP kinase. Expression in RAW264 cells of the dominant negative form of either p38alpha MAP kinase or MAP kinase kinase (MKK) 6 significantly inhibited RANKL-induced differentiation of the cells. These results indicate that activation of the p38 MAP kinase pathway plays an important role in RANKL-induced osteoclast differentiation of precursor bone marrow cells.

Adenosine induces endothelial apoptosis by activating protein tyrosine phosphatase: a possible role of p38alpha

Endothelial cell (EC) apoptosis is important in vascular injury, repair, and angiogenesis. Homocysteine and/or adenosine exposure of ECs causes apoptosis. Elevated homocysteine or adenosine occurs in disease states such as homocysteinuria and tissue necrosis, respectively. We examined the intracellular signaling mechanisms involved in this pathway of EC apoptosis. Inhibition of protein tyrosine phosphatase (PTPase) attenuated homocysteine- and/or adenosine-induced apoptosis and completely blocked apoptosis induced by the inhibition of S-adenosylhomocysteine hydrolase with MDL-28842. Consistent with this finding, the tyrosine kinase inhibitor genistein enhanced apoptosis in adenosine-treated ECs. Adenosine significantly elevated the PTPase activity in the ECs. Mitogen-activated protein kinase activities were examined to identify possible downstream targets for the upregulated PTPase(s). Extracellular signal-regulated kinase (ERK) 1 activity was slightly elevated in adenosine-treated ECs, whereas ERK2, c-Jun NH(2)-terminal kinase-1, or p38beta activities differed little. The mitogen-activated protein kinase-1 inhibitor PD-98059 enhanced DNA fragmentation, suggesting that increased ERK1 activity is a result but not a cause of apoptosis in adenosine-treated ECs. Adenosine-treated ECs had diminished p38alpha activity compared with control cells; this effect was blunted on PTPase inhibition. These results indicate that PTPase(s) plays an integral role in the induction of EC apoptosis upon exposure to homocysteine and/or adenosine, possibly by the attenuation of p38alpha activity.

The small GTPases Ras, Rac, and Cdc42 transcriptionally regulate expression of human fibroblast growth factor 1

Four distinct promoters (1A, 1B, 1C, and 1D) of fibroblast growth factor 1 (FGF1), spaced up to 70 kilobase pairs apart, direct the expression of alternatively spliced transcript variants (FGF1.A, -1. B, -1.C, and -1.D) that encode FGF1. These FGF1 transcripts can be detected in cultured cells as well as in normal and diseased tissues. These transcripts are differentially regulated in a cell-specific manner. To further delineate the biological function of multiple promoter usage by a single gene, we investigated the transcriptional regulation of these promoters by defined signaling pathways associated with cell proliferation and cell survival. Here we show a specific association of two of the FGF1 promoters, 1C and 1D, with signaling cascades of the Ras superfamily of GTPases. A serum-response element, comprised of the Ets and CArG motifs, present in promoter 1D was shown to be the target of distinct signaling cascades; the Ets motif target of Ras, Rac1, and Cdc42 regulation; and the CArG motif target of de novo protein synthesis-independent cascade. Ras and Rac1 also activated the FGF2 promoter. Further, the transcription factor Ets2 synergistically activated FGF1 gene, but not FGF2, in a Ras- and Rac1-dependent signaling pathway. In support of these conclusions high levels of intracellular FGF1 were detected in cells undergoing cytokinesis. Altogether, our results suggest that FGF1 may play a fundamental role in cell division, spreading, and migration, in addition to cell proliferation.