Transcription factor AP-1 regulation by mitogen-activated protein kinase signal transduction pathways

Ischemic preconditioning triggers tyrosine kinase signaling: a potential role for MAPKAP kinase 2

Myocardial adaptation to ischemia has been shown to activate protein tyrosine kinase, potentiating activation of phospholipase D, which leads to the stimulation of mitogen-activated protein (MAP) kinases and MAP kinase-activated protein (MAPKAP) kinase 2. The present study sought to further examine the signal transduction pathway for the MAPKAP kinase 2 activation during ischemic adaptation. Isolated perfused rat hearts were adapted to ischemic stress by repeated ischemia and reperfusion. Hearts were pretreated with genistein to block tyrosine kinase, whereas SB-203580 was used to inhibit p38 MAP kinases. Western blot analysis demonstrated that p38 MAP kinase is phosphorylated during ischemic stress adaptation. Phosphorylation of p38 MAP kinase was blocked by genistein, suggesting that activation of p38 MAP kinase during ischemic adaptation is mediated by a tyrosine kinase signaling pathway. MAPKAP kinase 2 was estimated by following in vitro phosphorylation with recombinant human heat shock protein 27 as specific substrate for MAPKAP kinase 2. Again, both genistein and SB-203580 blocked the activation of MAPKAP kinase 2 during myocardial adaptation to ischemia. Immunofluorescence microscopy with anti-p38-antibody revealed that p38 MAP kinase is primarily localized in perinuclear regions. p38 MAP kinase moves to the nucleus after ischemic stress adaptation. After ischemia and reperfusion, cytoplasmic striations in the myocytes become obvious, indicating translocation of p38 MAP kinase from nucleus to cytoplasm. Corroborating these results, myocardial adaptation to ischemia improved the left ventricular functions and reduced myocardial infarction that were reversed by blocking either tyrosine kinase or p38 MAP kinase. These results demonstrate that myocardial adaptation to ischemia triggers a tyrosine kinase-regulated signaling pathway, leading to the translocation and activation of p38 MAP kinase and implicating a role for MAPKAP kinase 2.

Exercise stimulates c-Jun NH2 kinase activity and c-Jun transcriptional activity in human skeletal muscle

Exercise causes selective changes in gene expression leading to alterations in the structure and function of human skeletal muscle. However, little is known about the specific signaling pathways that enable exercise to modulate gene regulatory events. We determined the effects of exercise on c-Jun NH2-terminal kinase (JNK) activity, a signaling molecule involved in the regulation of transcription. Biopsies of vastus lateralis muscle were taken from eight subjects at rest and after 60 min of cycle ergometer exercise. Exercise increased JNK activity in all subjects (5.9 +/- 1.8 fold above basal). JNK activation was associated with an increased expression of its downstream nuclear target c-Jun mRNA. When two additional subjects were studied using a one-legged exercise protocol, JNK activity increased only in the exercising leg, indicating that exercise-induced JNK signaling represents an intrinsic response of the contracting muscle, rather than a systemic response to exercise. These studies demonstrate that the JNK pathway may serve as a link between contractile activity and transcriptional responses in human skeletal muscle.

Extracellular signal-regulated protein kinase/Jun kinase cross-talk underlies vascular endothelial cell growth factor-induced endothelial cell proliferation

Ligand binding to vascular endothelial cell growth factor (VEGF) receptors activates the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK) and c-Jun N-terminal protein kinase (JNK). Possible cross-communication of ERK and JNK effecting endothelial cell (EC) actions of VEGF is poorly understood. Incubation of EC with PD 98059, a specific mitogen-activated protein kinase kinase inhibitor, or transfection with Y185F, a dominant negative ERK2, strongly inhibited VEGF-activated JNK. JNK was also activated by ERK2 expression in the absence of VEGF, inhibited 82% by co-transfection with dominant negative SEK-1, indicating upstream activation of JNK by ERK. VEGF-stimulated JNK activity was also reversed by dominant negative SEK-1. Other EC growth factors exhibited similar cross-activation of JNK through ERK. VEGF stimulated the nuclear incorporation of thymidine, reversed 89% by PD 98059 and 72% by Y185F. Dominant negative SEK-1 or JNK-1 also significantly reduced VEGF-stimulated thymidine incorporation. Expression of wild type Jip-1, which prevents JNK nuclear translocation, inhibited VEGF-induced EC proliferation by 75%. VEGF stimulated both cyclin D1 synthesis and Cdk4 kinase activity, inhibited by PD 98059 and dominant negative JNK-1. Important events for VEGF-induced G1/S progression and cell proliferation are enhanced through a novel ERK to JNK cross-activation and subsequent JNK action.

Oxidant Stress Incites Spreading of Macrophages via Extracellular Signal-Regulated Kinases and p38 Mitogen-Activated Protein Kinase

Cultured macrophages exhibit spreading in response to external stimuli. It is relevant to in vivo morphologic changes of macrophages during extravasation, migration, and differentiation. The present study was performed to elucidate molecular mechanisms that regulate spreading of macrophages. Redox is a crucial factor that modulates a wide range of cell function. We found that macrophages undergo spreading in response to oxidant stress caused by hydrogen peroxide or an oxidant generating agent menadione. To identify signaling pathways involved, a role of mitogen-activated protein (MAP) kinases was investigated. Western blot analysis showed that treatment of macrophages with menadione rapidly induced phosphorylation of extracellular signal-regulated kinases (ERK1, ERK2) and p38 MAP kinase, but not c-Jun N-terminal kinase (JNK). Pharmacologic inhibition of either ERK or p38 activation blunted the macrophage spreading. Similarly, transfection with dominant-negative mutants of ERKs or a mutant p38 significantly suppressed the oxidant-triggered spreading. ERKs and p38 are known to activate serum response element (SRE) via phosphorylation of the ternary complex factor Elk-1. To further identify downstream events, we focused on a role of SRE. Stimulation of macrophages with menadione induced activation of SRE. Intervention in the SRE activation by a dominant-negative mutant of Elk-1 inhibited the menadione-induced spreading. These results suggest that oxygen radical metabolites, the well-known mediators for tissue injury, incite spreading of macrophages via the MAP kinase-SRE signaling pathways.

Stress-activated protein kinase/Jun N-terminal kinase is required for interleukin (IL)-1-induced IL-6 and IL-8 gene expression in the human epidermal carcinoma cell line KB

The cytokine interleukin-1 (IL-1) is a major inflammatory hormone which activates a broad range of genes during inflammation. The signaling mechanisms triggered by IL-1 include activation of several distinct protein kinase systems. The stress-activated protein kinase (SAPK), also termed Jun N-terminal kinase (JNK), is activated particularly strongly by the cytokine. In an attempt to delineate its role in activation of gene expression by IL-1, we inhibited the IL-1-induced SAPK/JNK activity by stable overexpression of either a catalytically inactive mutant of SAPKbeta (SAPKbeta(K-R)) or antisense RNA to SAPKbeta in human epidermal carcinoma cells. A detailed analysis of signal transduction in those cells showed that activation of neither NFkappaB nor p38 mitogen-activated protein kinase was affected, suggesting that we achieved specific blockade of the SAPK/JNK. In untransfected and vector-transfected KB cells, IL-1 induced a strong increase in expression of IL-6 and IL-8 mRNA, along with the synthesis of high amounts of the proteins. In two KB cell clones stably overexpressing the mutant SAPKbeta(K-R), and three clones stably overexpressing antisense RNA to SAPKbeta, expression of IL-6 and IL-8 in response to IL-1 was strongly reduced at both the mRNA and protein level. These data indicate that the SAPK/JNK pathway provides an indispensable signal for IL-1-induced expression of IL-6 and IL-8.

Agonist stimulation of B1 and B2 kinin receptors causes activation of the MAP kinase signaling pathway, resulting in the translocation of AP-1 in HEK 293 cells

In response to bradykinin, phosphorylated MAP kinases (ERK-1 and ERK-2) were abundantly increased in HEK 293 cells, which overexpress the rat B2 kinin receptor. In a similar way des-Arg9-bradykinin stimulation of B1 kinin receptor-overexpressing HEK 293 cells caused activation of the same species of MAP kinase. Furthermore, nuclear translocation of transcription factor AP-1 was also found in the cells after stimulation with either agonist. PD98059, a MAP kinase kinase (MEK-1) inhibitor, blocked the agonist-induced AP-1 translocation as well as the phosphorylation of the MAP kinases. This communication provides the first evidence for both B1 and B2 kinin receptors mediating the MAP kinase signaling pathway to activate AP-1.

Protein kinase G mediates vascular endothelial growth factor-induced Raf-1 activation and proliferation in human endothelial cells

Vascular endothelial growth factor (VEGF) is an endothelium-specific, secreted protein that acts as a vasodilator, angiogenic peptide, and hyperpermeability factor. Recent reports have shown that nitric oxide synthase inhibitors block proliferation and microvascular hyperpermeability induced by VEGF. This study examined the mechanisms by which nitric oxide and its downstream signals mediate the VEGF-induced proliferative response in human umbilical vein endothelial cells (HUVECs). Nitric oxide synthase blockade by Nomega-nitro-L-arginine methyl ester prevented both the proliferative effect of VEGF and Raf-1 activation by VEGF as measured by cell counting and the capacity of immunoprecipitated Raf-1 to phosphorylate syntide 2, a Raf-1-specific synthetic substrate. VEGF-induced proliferation and Raf-1 kinase activity were also inhibited by Rp-8-pCPT-cGMPs and KT5823, inhibitors of the regulatory and catalytic subunits of cGMP-dependent protein kinase (PKG), respectively. The ability of PKG to stimulate proliferation was verified by the observation that the PKG activator, 8-pCPT-cGMPs, stimulated both Raf-1 kinase activity and endothelial proliferation in a dose-dependent manner. Furthermore, recombinant catalytically active PKG phosphorylated and activated Raf-1 in a reconstituted system. Finally, Raf-1 immunoprecipitated from VEGF-stimulated endothelial cells coprecipitated with PKG, indicating a direct protein-protein interaction in activated cells. We conclude that VEGF induces increases in both proliferation and Raf-1 kinase activity in HUVECs and these activities are dependent on NO and its downstream effector, PKG.

Stress-induced Fas ligand expression in T cells is mediated through a MEK kinase 1-regulated response element in the Fas ligand promoter

T lymphocytes undergo apoptosis in response to a variety of stimuli, including exposure to UV radiation and gamma-irradiation. While the mechanism by which stress stimuli induce apoptosis is not well understood, we have previously shown that the induction of Fas ligand (FasL) gene expression by environmental stress stimuli is dependent on c-Jun N-terminal kinase (JNK) activation. Using inducible dominant-active (DA) JNK kinase kinase (MEKK1) expression in Jurkat cells, we map a specific MEKK1-regulated response element to positions -338 to -316 of the Fas ligand (FasL) promoter. Mutation of that response element abrogated MEKK1-mediated FasL promoter activation and interfered in stress-induced activation of that promoter. Using electrophoretic mobility shift assays, we demonstrate that activator protein 1 (AP-1) binding proteins, namely, activating transcription factor 2 (ATF2) and c-Jun, bind to the MEKK1 response element. Transient transfection of interfering c-Jun and ATF2 mutants, which lack the consensus JNK phosphorylation sites, abrogated the transcriptional activation of the FasL promoter, demonstrating the involvement of these transcription factors in the regulation of the FasL promoter. Taken together, our data indicate that MEKK1 and transcription factors regulated by the JNK pathway play a role in committing lymphocytes to undergo apoptosis by inducing FasL expression via a novel response element in the promoter of that gene.

Activation of MAPKs in human bronchial epithelial cells exposed to metals

We have previously shown that in vitro exposure to metallic compounds enhances expression of interleukin (IL)-6, IL-8, and tumor necrosis factor-alpha in human bronchial epithelial cells. To characterize signaling pathways involved in metal-induced expression of inflammatory mediators and to identify metals that activate them, we studied the effects of As, Cr, Cu, Fe, Ni, V, and Zn on the mitogen-activated protein kinases (MAPK) extracellular receptor kinase (ERK), c-Jun NH2-terminal kinase (JNK), and P38 in BEAS cells. Noncytotoxic concentrations of As, V, and Zn induced a rapid phosphorylation of MAPK in BEAS cells. Activity assays confirmed marked activation of ERK, JNK, and P38 in BEAS cells exposed to As, V, and Zn. Cr and Cu exposure resulted in a relatively small activation of MAPK, whereas Fe and Ni did not activate MAPK under these conditions. Similarly, the transcription factors c-Jun and ATF-2, substrates of JNK and P38, respectively, were markedly phosphorylated in BEAS cells treated with As, Cr, Cu, V, and Zn. The same acute exposure to As, V, or Zn that activated MAPK was sufficient to induce a subsequent increase in IL-8 protein expression in BEAS cells. These data suggest that MAPK may mediate metal-induced expression of inflammatory proteins in human bronchial epithelial cells.

Proliferation and differentiation of human osteoblastic cells associated with differential activation of MAP kinases in response to epidermal growth factor, hypoxia, and mechanical stress in vitro

In an attempt to elucidate the specificity of pathways from environmental stress to cellular outcome via mitogen activated protein kinases (MAPKs) activation, we examined the responsiveness of cultured human osteoblastic periodontal ligament (PDL) cells to epidermal growth factor (EGF), hypoxia, and mechanical stress, in terms of cell proliferation, differentiation, and associated activation of three different types of MAPK. Cell proliferation was promoted in the presence of 10ng/ml of EGF or in hypoxic conditions (5% O2), whereas it was inhibited by cyclic stretch (9% strain, 6 cycles/min), which was used as a model of mechanical stress. Conversely, the alkaline phosphatase activity, a marker for osteoblastic differentiation of the cells, was increased by cyclic stretch but decreased by EGF and hypoxia. The mitogenic response of PDL cells to EGF or hypoxia was associated with the selective phosphorylation and activation of extracellular-related kinase (ERK) 1/2, while phosphorylation and activation of c-Jun N-terminal kinase (JNK) was observed in mechanical stretch loaded cells. No such changes were seen in p38 protein. These findings suggested that stress-responsive changes in proliferation and osteoblastic differentiation of PDL cells are selectively mediated by ERK 1/2 and by JNK, respectively, and that a balance between these two pathways determines the cell fate.

ADD1/SREBP-1c mediates insulin-induced gene expression linked to the MAP kinase pathway

The aim of this study was to define the role of sterol regulatory element binding protein (SREBP)-1c, the human homologue to ADD1 (adipocyte determination- and differentiation-dependent factor 1), in insulin-induced gene expression. Transfection studies using SREBP-1-deficient cells and a LDL receptor promoter fragment containing the ADD1/SREBP-1c binding side showed that the effects of insulin and PDGF were abolished compared to control cells and completely reconstituted by overexpressing ADD1/SREBP-1c. Overexpression of upstream activators of MAP kinases, like MEKK1 or MEK1, demonstrated that ADD1/SREBP-1c-mediated effects of insulin and PDGF might be linked to the MAP kinase cascade. The recombinant N-terminal domain of ADD1/SREBP-1c was phosphorylated predominantly on serine and slightly on threonine residues by MAP kinases ERK1 and ERK2 in vitro. This was reversible by alkaline phosphatase. We conclude that ADD1/SREBP-1c mediates gene regulatory effects of insulin as well as PDGF and that this signalling is linked to the MAP kinase cascade.

p38 Mitogen-activated protein kinase mediates the transcriptional induction of the atrial natriuretic factor gene through a serum response element. A potential role for the transcription factor ATF6

In various cell types certain stresses can stimulate p38 mitogen-activated protein kinase (p38 MAPK), leading to the transcriptional activation of genes that contribute to appropriate compensatory responses. In this report the mechanism of p38-activated transcription was studied in cardiac myocytes where this MAPK is a key regulator of the cell growth and the cardiac-specific gene induction that occurs in response to potentially stressful stimuli. In the cardiac atrial natriuretic factor (ANF) gene, a promoter-proximal serum response element (SRE), which binds serum response factor (SRF), was shown to be critical for ANF induction in primary cardiac myocytes transfected with the selective p38 MAPK activator, MKK6 (Glu). This ANF SRE does not possess sequences typically required for the binding of the Ets-related ternary complex factors (TCFs), such as Elk-1, indicating that p38-mediated induction through this element may take place independently of such TCFs. Although p38 did not phosphorylate SRF in vitro, it efficiently phosphorylated ATF6, a newly discovered SRF-binding protein that is believed to serve as a co-activator of SRF-inducible transcription at SREs. Expression of an ATF6 antisense RNA blocked p38-mediated ANF induction through the ANF SRE. Moreover, when fused to the Gal4 DNA-binding domain, an N-terminal 273-amino acid fragment of ATF6 was sufficient to support trans-activation of Gal4/luciferase expression in response to p38 but not the other stress kinase, N-terminal Jun kinase (JNK); p38-activating cardiac growth promoters also stimulated ATF6 trans-activation. These results indicate that through ATF6, p38 can augment SRE-mediated transcription independently of Ets-related TCFs, representing a novel mechanism of SRF-dependent transcription by MAP kinases.

TNF Receptor-Associated Factor-3 Signaling Mediates Activation of p38 and Jun N-Terminal Kinase, Cytokine Secretion, and Ig Production Following Ligation of CD40 on Human B Cells

CD40 engagement induces a variety of functional outcomes following association with adaptor molecules of the TNF receptor-associated factor (TRAF) family. Whereas TRAF2, -5, and -6 initiate NF-κB activation, the outcomes of TRAF3-initiated signaling are less characterized. To delineate CD40-induced TRAF3-dependent events, Ramos B cells stably transfected with a dominant negative TRAF3 were stimulated with membranes expressing recombinant CD154/CD40 ligand. In the absence of TRAF3 signaling, activation of p38 and control of Ig production were abrogated, whereas Jun N-terminal kinase activation and secretion of IL-10, lymphotoxin-α, and TNF-α were partially blocked. By contrast, induction of apoptosis, activation of NF-κB, generation of granulocyte-macrophage CSF, and up-regulation of CD54, MHC class II, and CD95 were unaffected by the TRAF3 dominant negative. Together, these results indicate that TRAF3 initiates independent signaling pathways via p38 and JNK that are associated with specific functional outcomes.

Hepatocyte growth factor-induced expression of ornithine decarboxylase, c-met, and c-myc is differently affected by protein kinase inhibitors in human hepatoma cells HepG2

Binding of hepatocyte growth factor (HGF) to its receptor Met induces autophosphorylation and activation of the tyrosine kinase activity. In HGF-treated HepG2 cells, we studied: (i) the expression patterns of early (c-myc, c-jun, and c-fos) and delayed-early (ornithine decarboxylase and c-met) response genes and (ii) the possible involvement of protein kinase transducers in the control of the expression of c-met and of other genes eventually induced downstream. c-met and c-myc mRNAs peaked 1-2 h after HGF, while c-jun and c-fos mRNAs slightly increased at 1 h. Ornithine decarboxylase activity was induced earlier (4 h) than the mRNA (8-10 h). The transducers involved in HGF-triggered gene inductions were investigated using different protein kinase inhibitors: genistein for the receptor tyrosine kinase, herbimycin A for the nonreceptor tyrosine kinase (pp60(c-src)), wortmannin for phosphatidylinositol 3-kinase (PI3K) and H7 for protein kinase C (PKC). The similarity of responses to PKC inhibition led to suppose that c-myc and ornithine decarboxylase mRNAs were induced sequentially along the same transduction pathway triggered by HGF. Ornithine decarboxylase activity seemed to be largely regulated by phosphorylation(s). The mRNA expression of c-jun was likely to undergo a negative regulation through a mechanism involving PI3K, while that of c-met seemed to be almost independent from various protein kinases (PI3K, pp60(c-src), and PKC).

Lithium stimulates gene expression through the AP-1 transcription factor pathway

Lithium, a monovalent cation, is the mainstay in the treatment of manic-depressive (MDI) illness, but despite extensive research, its mechanism of action remains to be elucidated. Since lithium requires chronic administration for therapeutic efficacy, and because its beneficial effects last well beyond its discontinuation, it has been postulated that lithium may exert major effects at the genomic level. In the present study we found that lithium, at therapeutically relevant concentrations, increases AP-1 DNA binding activity in human SH-SY5Y cells and rat C6 glioma cells. Additionally, in both SY5Y and C6 cells transiently transfected with a reporter gene vector driven by an SV40 promoter, lithium increased the activity of the reporter gene in a time- and concentration-dependent manner. Furthermore, mutations in the AP-1 sites of the reporter gene promoter significantly attenuated lithium's effects. These data indicate that lithium stimulates gene expression through the AP-1 transcription factor pathway, effects which may play a role in its long-term mood-stabilizing effects.

Involvement of Ras in Bruton's tyrosine kinase-mediated JNK activation

Defects in Bruton's tyrosine kinase (Btk) result in B cell immunodeficiencies in humans and mice. Recent studies showed that Btk is required for maximal activation of JNK, a family of stress-activated protein kinases, induced by several extracellular stimuli including interleukin (IL)-3. On the other hand, IL-3-induced JNK activation is dependent on Ras. In the present study we have investigated whether Ras is involved in Btk-mediated JNK activation in BaF3 mouse pro-B cells. Overexpression of wild-type Btk protein in these cells enhanced JNK activation upon IL-3 stimulation, whereas expression of kinase-dead Btk partially suppressed JNK activation. Induced expression of the dominant negative Ras(N17) in the cells overexpressing wild-type Btk suppressed JNK activation. Importantly, overexpression of Btk enhanced the level of the GTP-bound, active form of Ras in response to IL-3 stimulation. Btk overexpression also increased the Shc-Grb2 association induced by IL-3 stimulation. Expression of either N17Ras or V12Ras did not impose any effects on Btk kinase activity. These data collectively indicate that Ras plays a role of an intermediary signaling protein in Btk-mediated JNK activation induced by the IL-3 signaling pathway.

Epigallocatechin suppression of proliferation of vascular smooth muscle cells: correlation with c-jun and JNK

1. The mechanisms of the antiproliferative effect of epigallocatechin, one of the catechin derivatives found in green tea, in vascular smooth muscle cells were studied. The proliferative response was determined from the uptake of tritiated thymidine. 2. In the concentration range of 10(-6) to 10(-4) M, catechin, epicatechin, epigallocatechin, epicatechin gallate and epigallocatechin, epigallocatechin gallate, concentration-dependently inhibited the proliferative response stimulated by serum in rabbit cultured vascular smooth muscle cells. Catechin and epicatechin were less effective in inhibiting the serum-stimulated smooth muscle cell proliferation, indicating that the galloyl group may be important for full inhibitory activity. 3. Epigallocatechin (EGC) inhibited the proliferative responses in different cells including rat aortic smooth muscle cells (A7r5 cells), rabbit cultured aortic smooth muscle cells, human coronary artery smooth muscle cells, and human CEM lymphocytes in a concentration-dependent manner. The possible mechanisms of the antiproliferative effect of EGC were further studied in A7r5 cells. 4. The membranous protein tyrosine kinase activity stimulated by serum in A7r5 cells was significantly reduced by 10(-5) M EGC. In contrast, the cytosolic protein kinase C activity stimulated by phorbol ester was unaffected by directly incubating with EGC (10(-6)-10(-4) M). 5. We also performed Western blot analysis using the anti-phosphotyrosine monoclonal antibody PY20. EGC (10(-5) M) reduced the levels of tyrosine phosphorylated proteins with different molecular weights, indicating that EGC may inhibit the protein tyrosine kinase activity or stimulate the protein phosphatase activity. 6. Reverse transcription-polymerase chain reaction analysis of c-fos, c-jun and c-myc mRNA levels demonstrated that c-jun mRNA level after serum-stimulation was significantly reduced by 10(-5) M EGC. However, the reduction of c-fos and c-myc mRNA levels by 10(-5) M EGC did not achieve significance. 7. Western blot analysis using the antibody against JNK (c-jun N-terminal kinase) and ERK (extracellular signal-regulated kinase) demonstrated that the level of phosphorylated JNK1, but not phosphorylated ERK1 and ERK2, was reduced by 10(-5) M EGC. Direct measurement of kinase activity by immune complex kinase assay confirmed that JNK1 activity was inhibited by EGC treatment. These results demonstrate that EGC preferentially reduced the activation of JNK/SAPK (stress-activated protein kinase) signal transduction pathway. 8. It is suggested that the antiproliferative effect of epigallocatechin on vascular smooth muscle cells may partly be mediated through inhibition of protein tyrosine kinase activity, reducing c-jun mRNA expression and inhibiting JNK1 activation. Tea catechins may be useful as a template for the development of drugs to prevent the pathological changes of atherosclerosis and post-angioplasty restenosis.

Regulation of human alcohol dehydrogenase gene ADH7: importance of an AP-1 site

The structure and function of the human alcohol dehydrogenase 7 (ADH7) promoter were analyzed. A promoter fragment extending to bp -232 functioned well in H4IIE-C3, CV-1, and HeLa cells, whereas the region extending further upstream to bp -799 had no significant effect on activity. We identified cis-acting elements in the proximal 232 bp and examined their effect on promoter activity. Mutation of site A, where c-Jun bound, caused a drastic decrease in the promoter activity in H4IIE-C3 and CV-1 cells, suggesting that AP-1 plays an important role in the regulation of ADH7. Mutation of site B also caused a large drop in promoter activity in both cell lines; C/EBPalpha can bind to this site, but because the site affects activity approximately equally in CV-1 cells that lack C/EBPalpha and in H4IIE-C3 cells that contain low levels, other proteins are likely to play the major roles in vivo. Mutation of site C, where C/EBP bound and c-Jun bound weakly, had different effects in the two cell lines: in H4IIE-C3 cells, the site C mutation did not significantly increase promoter activity, whereas in CV-1 cells, which lack C/EBPalpha, it led to a doubling of activity. Surprisingly, cotransfection of the wild-type promoter with C/EBPa or C/EBPbeta led to a decrease in promoter activity, which might in part explain the lack of activity of ADH7 in adult liver.

The mitogen-activated protein kinase pathway contributes to vanadate toxicity in vascular smooth muscle cells

Vanadate has been considered in the treatment of diabetes because of its insulin-like effects. However, it has severe toxic effects in both animal and man. In cultured cells, vanadate can either cause death or be growth stimulatory, depending on the cell type and growth conditions. Here, we report that in baboon aortic smooth muscle cells (SMCs), vanadate induced p42/p44 mitogen-activated protein kinase (MAPK) activity. This effect was abolished in the presence of the specific MAPK kinase (MAPKK) inhibitor PD098059. Although activation of p42/p44MAPK/MAPKK is generally thought to be necessary for proliferation, in SMCs, vanadate did not promote DNA synthesis and inhibited thymidine incorporation stimulated by platelet-derived growth factor (PDGF)-BB in a dose dependent fashion (IC50: 30 microM). Prolonged exposure to vanadate exerted cytotoxic effects. Cells retracted, rounded up and detached from the substratum. These vanadate-induced morphological changes were blocked in the presence of PD098059. The addition of PDGF-BB further activated p42/p44MAPK/MAPKK in the presence of vanadate and substantially increased vanadate toxicity. We conclude from these observations that activation of the p42/p44MAPK/MAPKK signalling module contributes to the cytotoxic effects induced by vanadate.

A conserved p38 mitogen-activated protein kinase pathway regulates Drosophila immunity gene expression

Accumulating evidence suggests that the insect and mammalian innate immune response is mediated by homologous regulatory components. Proinflammatory cytokines and bacterial lipopolysaccharide stimulate mammalian immunity by activating transcription factors such as NF-kappaB and AP-1. One of the responses evoked by these stimuli is the initiation of a kinase cascade that leads to the phosphorylation of p38 mitogen-activated protein (MAP) kinase on Thr and Tyr within the motif Thr-Gly-Tyr, which is located within subdomain VIII. We have investigated the possible involvement of the p38 MAP kinase pathway in the Drosophila immune response. Two genes that are highly homologous to the mammalian p38 MAP kinase were molecularly cloned and characterized. Furthermore, genes that encode two novel Drosophila MAP kinase kinases, D-MKK3 and D-MKK4, were identified. D-MKK3 is an efficient activator of both Drosophila p38 MAP kinases, while D-MKK4 is an activator of D-JNK but not D-p38. These data establish that Drosophila indeed possesses a conserved p38 MAP kinase signaling pathway. We have examined the role of the D-p38 MAP kinases in the regulation of insect immunity. The results revealed that one of the functions of D-p38 is to attenuate antimicrobial peptide gene expression following exposure to lipopolysaccharide.

Molecular cloning and characterization of a human protein kinase that specifically activates c-Jun N-terminal kinase

The c-Jun N-terminal kinases (JNKs), also called stress-activated protein kinases (SAPKs), belong to the mitogen-activated protein kinase (MAPK) gene super-family. Like all the MAPKs, JNKs are activated through dual phosphorylation of a theronine residue and a tyrosine residue by a dual specificity kinase such as JNKK1/MKK4/SEK1. Here, we report the molecular cloning and characterization of hJNKK2 alpha, a human homolog of the recently reported murine MKK7 alpha. hJNKK2 alpha belongs to the MAPK kinase gene family and is expressed in many adult tissues. It is nearly identical to a recently reported human JNKK2 at the kinase domain but with major differences in both amino- and carboxyl-terminal sequences, suggesting that hJNKK2 alpha may be an alternative spliced form of this kinase. Expression of hJNKK2 alpha, but not its related kinases JNKK1/MKK4/SEK1, MEK1, MKK3, or MKK6, leads to strong activation of JNK in several cell lines. No activation of ERK or p38 kinases was observed with this kinase. An in-vitro kinase assay demonstrated that JNK1 activation by hJNKK2 alpha requires phosphorylation of the theronine and tyrosine residues at positions 183 and 185 in JNK1. Furthermore, hJNKK2 alpha activated the JNK-dependent signal transduction pathway in vivo by induction of c-Jun- and ATF2-mediated gene transcription. In conclusion, we have cloned the human homolog of murine MKK7 alpha, which may be an alternative spliced form of human JNKK2 involved in transducing specific upstream signals to regulate JNK activity in vivo.

DNA binding of activator protein-1 is increased in human mesangial cells cultured in high glucose concentrations

Human mesangial cells (HMC) grown in high glucose environments synthesize excessive amounts of extracellular matrix proteins (ECM). The promoter regions of certain ECM genes contain TPA (phorbol ester)-responsive element (TRE) motifs that bind the transcription factor, activator protein-1 (AP-1), a complex of Jun and other phosphoproteins. AP-1 binding to the TRE promoter is regulated by the quantity, composition and post-translational modifications of proteins in the AP-1 complex. We report an increased binding of AP-1 to TRE oligonucleotides in HMC cultured chronically (5 days) in high glucose environments (30 mM d-glucose). This increased binding is not due to differences in the nuclear quantity of AP-1 proteins or in the composition of the AP-1 complex when compared to AP-1 proteins from cells grown in normal glucose (5 mM d-glucose). A 30 mM l-glucose environment also increased AP-1 binding, but to a degree less than d-glucose. The increased AP-1 binding was partly reversed by treatment of HMC with Calphostin C or Bisindolylmaleimide I suggesting a partial role of the protein kinase C (PKC) pathway in mediating AP-1 binding. AP-1 binding was unaffected by treatment of cells with the MEK inhibitor PD 98059. In addition, increased AP-1 binding persisted for at least 48 hours after media glucose concentrations were normalized. The level of Jun-NH2-terminal kinase (JNK) activity and the phosphorylation of the JNK kinase, SEK1, were unchanged by chronic high glucose concentrations. These studies suggest that in HMC cultured in chronic high glucose, post-translational modifications increase the binding of AP-1 to the TRE motif.

Bruton's tyrosine kinase-mediated interleukin-2 gene activation in mast cells. Dependence on the c-Jun N-terminal kinase activation pathway

Cross-linking of the high affinity IgE receptor (FcepsilonRI) on mast cells induces secretion of cytokines, including interleukin (IL)-2, through transcriptional activation of cytokine genes. Previously, defects in the gene coding for Bruton's tyrosine kinase (Btk) were shown to result in defective cytokine production in mast cells, and thereby mice carrying btk mutations exhibited diminished anaphylactic reactions in response to IgE and antigen. In this study, we provide evidence that the transcription factors involved in the IL-2 gene expression in T cells are also required for maximal activation of the IL-2 gene in FcepsilonRI-stimulated mast cells. Among them, AP-1 (Jun/Fos) and NF-AT were identified as candidate transcription factors that are regulated by Btk. Consistent with our previous data indicating that Btk regulates stress-activated protein kinases, c-Jun N-terminal kinase (JNK), c-Jun and other JNK-regulatable transcription factors are activated by FcepsilonRI cross-linking in a Btk-dependent manner. Further, FcepsilonRI-induced IL-2 gene activation is dependent on c-Jun and a component, SEK1, of its upstream activation pathway. Collectively, these data demonstrate that Btk regulates the transcription of the IL-2 gene through the JNK-regulatable transcription factors in FcepsilonRI-stimulated mast cells.

Interaction of transcription factors with serum response factor. Identification of the Elk-1 binding surface

Serum response elements (SREs) play important roles in transforming extracellular signals into specific nuclear responses. The SRE-binding protein, serum response factor (SRF), plays a pivotal role in this process. Several transcription factors have been shown to interact with SRF and thereby create distinct complexes with different regulatory potentials. The ETS domain transcription factor Elk-1 is one such protein and serves to integrate distinct mitogen-activated protein kinase cascades at SREs. Elk-1 uses a short hydrophobic surface presented on the surface of an alpha-helix to interact with SRF. In this study we have used site-directed mutagenesis to identify residues in SRF that comprise the Elk-1 binding surface. The Elk-1 binding surface is composed of residues that lie on a hydrophobic surface-exposed groove located at the junction of the MADS box and C-terminal SAM motif. Different residues are implicated in interactions between SRF and the transcription factor Fli-1, indicating that although some overlap with the Elk-1 binding surface occurs, their interaction surfaces on SRF are distinct. Our data are consistent with the hypothesis that the SRF DNA-binding domain acts as docking site for multiple transcription factors that can bind to small surface-exposed patches within this domain.

Mechanism of sodium arsenite-mediated induction of heme oxygenase-1 in hepatoma cells. Role of mitogen-activated protein kinases

Heme oxygenase-1 is an inducible enzyme that catalyzes heme degradation and has been proposed to play a role in protecting cells against oxidative stress-related injury. We investigated the induction of heme oxygenase-1 by the tumor promoter arsenite in a chicken hepatoma cell line, LMH. We identified a heme oxygenase-1 promoter-driven luciferase reporter construct that was highly and reproducibly expressed in response to sodium arsenite treatment. This construct was used to investigate the role of mitogen-activated protein (MAP) kinases in arsenite-mediated heme oxygenase-1 gene expression. In LMH cells, sodium arsenite, cadmium, and heat shock, but not heme, induced activity of the MAP kinases extracellular-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38. To examine whether these MAP kinases were involved in mediating heme oxygenase-1 gene expression, we utilized constitutively activated and dominant negative components of the ERK, JNK, and p38 MAP kinase signaling pathways. Involvement of an AP-1 site in arsenite induction of heme oxygenase-1 gene expression was studied. We conclude that the MAP kinases ERK and p38 are involved in the induction of heme oxygenase-1, and that at least one AP-1 element (located -1576 base pairs upstream of the transcription start site) is involved in this response.

Signal transduction by the c-Jun N-terminal kinase (JNK)--from inflammation to development

The c-Jun amino-terminal kinase (JNK) group of MAP kinases has been identified in mammals and insects. JNK is activated by exposure of cells to cytokines or environmental stress, indicating that this signaling pathway may contribute to inflammatory responses. Genetic and biochemical studies demonstrate that this signaling pathway also regulates cellular proliferation, apoptosis, and tissue morphogenesis. A functional role for JNK is therefore established in both the cellular response to stress and in many normal physiological processes.

A novel interaction between inhibitory melatonin receptors and protein kinase C-dependent signal transduction in ovine pars tuberalis cells

This study revealed an important and unexpected finding: namely, that inhibitory melatonin receptors can inhibit a phorbol 12,13 myristate acetate (PMA)-induced, protein kinase C (PKC)-dependent increase in c-fos messenger RNA expression in ovine pars tuberalis (PT) cells. PMA induces dose-dependent stimulation of c-fos expression that is attenuated by melatonin in a dose-dependent and pertussis toxin-sensitive manner. The effect of 100 nM PMA is blocked by Ro31-8220 (1 microM), yet is not mimicked by 4alpha-PMA (100 nM). PMA (100 nM) induces PKC activity in PT cells (P < 0.05) within 5 min, but melatonin has no effect on this response. PMA (100 nM) stimulates both phospholipase D and mitogen-activated protein kinase (MAPK) (p42/44) activities in PT cells, but melatonin has no effect on these responses. The results indicate that neither of these second-messenger activities contribute to the melatonin-sensitive pathway of c-fos activation. The MEK (MAPK kinase) inhibitor, PD98059 (50 microM), does not block the induction of c-fos by PMA, although at the same dose it inhibits PMA-mediated activation of p42/44 MAPK by 50-70%, and activation by forskolin or insulin-like growth factor-I by 100%. These data suggest that p42/44 MAPK may not be the primary mediator of PKC-dependent c-fos induction. In contrast to the effect of melatonin on PMA-mediated c-fos induction in PT cells, in L cells stably transfected with the sheep Mel1 alphabeta receptor, melatonin potentiates the c-fos response in a pertussis toxin-sensitive manner. These data indicate the tissue-specific nature of melatonin receptor signaling, and reveal that a pertussis toxin-sensitive pathway can block PKC-mediated c-fos induction in PT cells.

Notch inhibition of E47 supports the existence of a novel signaling pathway

E47 is a widely expressed transcription factor that activates B-cell-specific immunoglobulin gene transcription and is required for early B-cell development. In an effort to identify processes that regulate E47, and potentially B-cell development, we found that activated Notch1 and Notch2 effectively inhibit E47 activity. Only the intact E47 protein was inhibited by Notch-fusion proteins containing isolated DNA binding and activation domains were unaffected-suggesting that Notch targets an atypical E47 cofactor. Although overexpression of the coactivator p300 partially reversed E47 inhibition, results of several assays indicated that p300/CBP is not a general target of Notch. Notch inhibition of E47 did not correlate with its ability to activate CBF1/RBP-Jkappa, the mammalian homolog of Suppressor of Hairless, a protein that associates physically with Notch and defines the only known Notch signaling pathway in drosophila. Importantly, E47 was inhibited independently of CBF1/RPB-Jkappa by Deltex, a second Notch-interacting protein. We provide evidence that Notch and Deltex may act on E47 by inhibiting signaling through Ras because (i) full E47 activity was found to be dependent on Ras and (ii) both Notch and Deltex inhibited GAL4-Jun, a hybrid transcription factor whose activity is dependent on signaling from Ras to SAPK/JNK.

Unexpected suppression of alpha-smooth muscle actin, the activation marker of mesangial cells, by pp60v-src tyrosine kinase

Cultured mesangial cells constitutively express alpha-smooth muscle actin (alpha-SMA), a marker of cellular activation. We unexpectedly found that tyrosine kinase pp60v-src, a known activator for a wide range of signalling cascades, suppressed the alpha-SMA expression in mesangial cells. The present study was conducted to elucidate molecular events involved in this phenomenon. Transfection with a reporter plasmid revealed that the serum response element (SRE), the cis-element required for alpha-SMA expression, was constitutively active in mesangial cells. When mesangial cells were transfected with pp60v-src, activity of both SRE and the alpha-SMA promoter was down-regulated. This was associated with depressed levels of phosphorylated extracellular signal-regulated kinases (ERKs), but not c-Jun N-terminal kinase. Selective inhibition of ERKs by PD098059 abrogated constitutive SRE activity, leading to suppressed alpha-SMA expression. These results uncovered a novel potential of pp60v-src for suppression of alpha-SMA via intervention in the ERK-SRE signalling pathway.

Differential targeting of MAP kinases to the ETS-domain transcription factor Elk-1

The activation of MAP kinase (MAPK) signal transduction pathways results in the phosphorylation of transcription factors by the terminal kinases in these cascades. Different pathways are activated by mitogenic and stress stimuli, which lead to the activation of distinct groups of target proteins. The ETS-domain transcription factor Elk-1 is a substrate for three distinct classes of MAPKs. Elk-1 contains a targeting domain, the D-domain, which is distinct from the phosphoacceptor motifs and is required for efficient phosphorylation and activation by the ERK MAPKs. In this study, we demonstrate that members of the JNK subfamily of MAPKs are also targeted to Elk-1 by this domain. Targeting via this domain is essential for the efficient and rapid phosphorylation and activation of Elk-1 both in vitro and in vivo. The ERK and JNK MAPKs use overlapping yet distinct determinants in the D-domain for targeting to Elk-1. In contrast, members of the p38 subfamily of MAPKs are not targeted to Elk-1 via this domain. Our data therefore demonstrate that different classes of MAPKs exhibit differential requirements for targeting to Elk-1.

Retinoic acid inhibits induction of c-Jun protein by ultraviolet radiation that occurs subsequent to activation of mitogen-activated protein kinase pathways in human skin in vivo

Human skin is exposed daily to solar ultraviolet (UV) radiation. UV induces the matrix metalloproteinases collagenase, 92-kD gelatinase, and stromelysin, which degrade skin connective tissue and may contribute to premature skin aging (photoaging). Pretreatment of skin with all-trans retinoic acid (tRA) inhibits UV induction of matrix metalloproteinases. We investigated upstream signal transduction pathways and the mechanism of tRA inhibition of UV induction of matrix metalloproteinases in human skin in vivo. Exposure of human skin in vivo to low doses of UV activated EGF receptors, the GTP-binding regulatory protein p21Ras, and stimulated mitogen-activated protein (MAP) kinases, extracellular signal-regulated kinase (ERK), c-Jun amino-terminal kinase (JNK), and p38. Both JNK and p38 phosphorylated, and thereby activated transcription factors c-Jun and activating transcription factor 2 (ATF-2), which bound to the c-Jun promoter and upregulated c-Jun gene expression. Elevated c-Jun, in association with constitutively expressed c-Fos, formed increased levels of transcription factor activator protein (AP) 1, which is required for transcription of matrix metalloproteinases. Pretreatment of human skin with tRA inhibited UV induction of c-Jun protein and, consequently, AP-1. c-Jun protein inhibition occurred via a posttranscriptional mechanism, since tRA did not inhibit UV induction of c-Jun mRNA. These data demonstrate, for the first time, activation of MAP kinase pathways in humans in vivo, and reveal a novel posttranscriptional mechanism by which tRA antagonizes UV activation of AP-1 by inhibiting c-Jun protein induction. Inhibition of c-Jun induction likely contributes to the previously reported prevention by tRA of UV induction of AP-1-regulated matrix-degrading metalloproteinases in human skin.

Signal transduction via the mitogen-activated protein kinase pathway induced by binding of coagulation factor VIIa to tissue factor

The putative role of tissue factor (TF) as a receptor involved in signal transduction is indicated by its sequence homology to cytokine receptors (Bazan, J. F. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 6934-6938). Signal transduction induced by binding of FVIIa to cells expressing TF was studied with baby hamster kidney (BHK) cells stably transfected with TF and with a reporter gene construct encoding a luciferase gene under transcriptional control of tandem cassettes of signal transducer and activator of transcription (STAT) elements and one serum response element (SRE). FVIIa induced a significant luciferase response in cells expressing TF, BHK(+TF), but not in cells without TF. The BHK(+TF) cells responded to the addition of FVIIa in a dose-dependent manner, whereas no response was observed with active site-inhibited FVIIa, which also worked as an antagonist to FVIIa-induced signaling. Activation of the p44/42 MAPK pathway upon binding of FVIIa to TF was demonstrated by suppression of signaling with the specific kinase inhibitor PD98059 and demonstration of a transient p44/42 MAPK phosphorylation. No stimulation of p44/42 MAPK phosphorylation was observed with catalytically inactive FVIIa derivatives suggesting that the catalytic activity of FVIIa was obligatory for activation of the MAPK pathway. Signal transduction caused by a putative generation of FXa activity was excluded by experiments showing that FVIIa/TF-induced signaling was not quenched by tick anticoagulant protein, just as addition of FXa could not induce phosphorylation of p44/42 MAPK in BHK(+TF) cells. These results suggest a specific mechanism by which binding of FVIIa to cell surface TF independent of coagulation can modulate cellular functions and possibly play a role in angiogenesis and tumor metastasis as indicated by several recent observations.

YopJ of Yersinia pseudotuberculosis is required for the inhibition of macrophage TNF-alpha production and downregulation of the MAP kinases p38 and JNK

Exposure of macrophages to lipopolysaccharide (LPS) leads to production of the pro-inflammatory cytokine, tumour necrosis factor alpha (TNF-alpha). Previous studies have suggested that pathogenic Yersinia spp. inhibit LPS-mediated production of TNF-alpha in macrophages, and that one of the Yop proteins secreted by the plasmid-encoded type III pathway is required for this activity. We found that TNF-alpha production was inhibited when J774A.1 murine macrophages were infected with wild-type Y. pseudotuberculosis but not with an isogenic ysc mutant defective for Yop secretion. We inactivated multiple yop genes to identify which of these factors are required for the inhibition of TNF-alpha production. A mutant unable to express yopJ was defective for the inhibition of TNF-alpha production. Production of TNF-alpha is regulated at the transcriptional and translational levels by several mitogen-activated protein (MAP) kinases. The MAP kinases p38 and JNK underwent sustained activation in macrophages infected with the yopJ mutant. Conversely, p38 and JNK were downregulated in macrophages infected with the wild-type strain. The ability of the yopJ mutant to downregulate p38 and JNK and to inhibit production of TNF-alpha was restored by the expression of yopJ+ in trans. Therefore, YopJ is required for Y. pseudotuberculosis to downregulate MAP kinases and inhibit the production of TNF-alpha in macrophages.

The Shp-2 tyrosine phosphatase has opposite effects in mediating the activation of extracellular signal-regulated and c-Jun NH2-terminal mitogen-activated protein kinases

Shp-2 is a widely expressed cytoplasmic tyrosine phosphatase with two SH2 domains. A targeted mutant allele of the Shp-2 gene with a deletion of 65 amino acids in the NH2-terminal SH2 domain was created that leads to embryonic lethality at mid-gestation in homozygous mutant mice. To define the Shp-2 function in cell signaling, we have established mutant fibroblast cell lines, and have examined the effect of the Shp-2 mutation on extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) mitogen-activated protein (MAP) kinase pathways. Insulin-like growth factor (IGF)-I-induced ERK activation was completely abolished, while ERK activity upon platelet-derived growth factor and epidermal growth factor stimulation was significantly reduced and shortened in mutant cells. Stimulation of ERK by phorbol 12-myristate 13-acetate was not affected in mutant cells, but the phorbol 12-myristate 13-acetate-induced ERK activity decayed much faster compared with that in wild-type cells. In contrast, JNK activation upon heat shock was significantly enhanced in Shp-2 mutant cells. Based on these results, we conclude that Shp-2 plays differential positive regulatory roles in various mitogenic signaling pathways leading to ERK activation, and that Shp-2 is a negative effector in JNK activation by cellular stress. This is the first evidence that a tyrosine phosphatase has opposite effects in mediating the activation of ERK and JNK MAP kinases.

The Elk-1 ETS-domain transcription factor contains a mitogen-activated protein kinase targeting motif

The phosphorylation of transcription factors by mitogen-activated protein kinases (MAP) is a pivotal event in the cellular response to the activation of MAP kinase signal transduction pathways. Mitogenic and stress stimuli activate different pathways and lead to the activation of distinct groups of target proteins. Elk-1 is targeted by three distinct MAP kinase pathways. In this study, we demonstrate that the MAP kinase ERK2 is targeted to Elk-1 by a domain which is distinct from, and located N-terminally to, its phosphoacceptor motifs. Targeting via this domain is essential for the efficient and rapid phosphorylation of Elk-1 in vitro and full and rapid activation in vivo. Specific residues involved in ERK targeting have been identified. Our data indicate that the targeting of different classes of MAP kinases to their nuclear substrates may be a common mechanism to increase the specificity and efficiency of this signal transduction pathway.

Constitutive activation of c-Jun N-terminal kinase by a mutant epidermal growth factor receptor

Epidermal growth factor receptor (EGF) variant type III (EGFRvIII) is a constitutively active, naturally occurring mutation of the EGF receptor that is found in many types of human tumors. When overexpressed in NIH3T3 fibroblasts, EGFRvIII induces transformation by enhancing cell growth and reducing apoptosis. Analysis of downstream signaling pathways has revealed that extracellular signal-regulated kinase activity is down-regulated, raising doubt as to the significance of this pathway in promoting transformation. We investigated whether the c-Jun N-terminal kinase (JNK) pathway was affected by EGFRvIII. NIH3T3 cells expressing EGFRvIII exhibited a high basal level of JNK activity, which was not present in cells overexpressing the normal EGF receptor. Treatment of cells overexpressing EGFRvIII with inhibitors of the EGF receptor or phosphatidylinositol 3-kinase resulted in the down-regulation of JNK activity. Furthermore, the down-regulation of JNK activity was associated with a loss of properties related to transformation, and there was no evidence for JNK activity in the promotion of apoptosis in these cells. These findings implicate constitutive activation of the JNK pathway in transformation by EGFRvIII.

Selective activation of p38 mitogen-activated protein (MAP) kinase isoforms by the MAP kinase kinases MKK3 and MKK6

The cellular response to treatment with proinflammatory cytokines or exposure to environmental stress is mediated, in part, by the p38 group of mitogen-activated protein (MAP) kinases. We report the molecular cloning of a novel isoform of p38 MAP kinase, p38 beta 2. This p38 MAP kinase, like p38 alpha, is inhibited by the pyridinyl imidazole drug SB203580. The p38 MAP kinase kinase MKK6 is identified as a common activator of p38 alpha, p38 beta 2, and p38 gamma MAP kinase isoforms, while MKK3 activates only p38 alpha and p38 gamma MAP kinase isoforms. The MKK3 and MKK6 signal transduction pathways are therefore coupled to distinct, but overlapping, groups of p38 MAP kinases.

Inflammatory cytokines induce the expression of basic fibroblast growth factor (bFGF) isoforms required for the growth of Kaposi's sarcoma and endothelial cells through the activation of AP-1 response elements in the bFGF promoter

BACKGROUND

The growth of Kaposi's sarcoma (KS) spindle cells is dependent on a number of inflammatory cytokines as well as the autocrine growth factor, basic fibroblast growth factor (bFGF). Moreover, inflammatory cytokines, found at increased levels in KS lesions, promote bFGF production in KS and endothelial cells.

OBJECTIVES

To determine the induction of bFGF isoforms, role of bFGF in cell growth and activation of the bFGF promoter by inflammatory cytokines.

DESIGN AND METHOD

3H-Thymidine uptake, bFGF immunoblotting and transfection of dominant-negative MAP kinase components were used to study the effect of cytokines on the bFGF promoter, bFGF isoform expression and proliferation of KS cells.

RESULTS

Treatment with oncostatin M (OSM), interleukin (IL)-1 and tumor necrosis factor (TNF)-alpha induced the expression of 18, 22 and 24 kDa bFGF isoforms in KS and human umbilical vein endothelial cells (HUVEC). Antisense bFGF oligonucleotides interfered in the induction of KS cell proliferation by individual cytokines. OSM, IL-1 and TNF-alpha induced the transcriptional activation of a bFGF promoter reporter gene in parallel with the activation of an AP-1 reporter. Dominant-negative ERK and dominant-negative JNK mutants interfered in cytokine-induced activation of these reporters in accordance with the role of the MAP kinase cascades in individual cytokine signaling pathways.

CONCLUSIONS

OSM, IL-1 and TNF-alpha induce KS cell growth by inducing the expression of various bFGF isoforms. Moreover, bFGF production by KS and HUVEC is dependent on the activation of the ERK and JNK cascades, which result in the transcriptional activation of the bFGF promoter.

Topical glucocorticoids and the skin--mechanisms of action: an update

The topical glucocorticoids (GCs) represent the treatment of choice for many types of inflammatory dermatoses. Despite the extensive use of this class of drugs as first line therapy the mechanism of their action is uncertain. It is clear that the multiplicity of actions of the topical GCs is an important facet of their scope in the treatment of dermal disorders. The aim of this update is to review past and current theories regarding how these agents might work. Current understanding of the molecular mechanisms of GC action has advanced significantly over the past decade with the realisation that multiple systems are responsible for transduction of GC effects at a molecular level. The two primary modes of action are via interaction directly with DNA or indirectly through modulation of specific transcription factors: the endpoint in both cases being modulation of specific protein synthesis. Both of these mechanisms will be discussed. In particular this review will concentrate on the possibility that a GC-inducible protein, termed lipocortin 1, may have a significant role to play in the anti-inflammatory actions of these drugs. Additionally it has become apparent that several inflammatory enzymes induced in inflammation are sites of inhibitory action of the GCs, and the possibility that this occurs in the skin will be discussed paying particular attention to the inducible phospholipase A2, nitric oxide synthase and cyclooxygenase systems.

Nuclear accumulation of NFAT4 opposed by the JNK signal transduction pathway

The nuclear factor of activated T cells (NFAT) group of transcription factors is retained in the cytoplasm of quiescent cells. NFAT activation is mediated in part by induced nuclear import. This process requires calcium-dependent dephosphorylation of NFAT caused by the phosphatase calcineurin. The c-Jun amino-terminal kinase (JNK) phosphorylates NFAT4 on two sites. Mutational removal of the JNK phosphorylation sites caused constitutive nuclear localization of NFAT4. In contrast, JNK activation in calcineurin-stimulated cells caused nuclear exclusion of NFAT4. These findings show that the nuclear accumulation of NFAT4 promoted by calcineurin is opposed by the JNK signal transduction pathway.

Stat1 serine phosphorylation occurs independently of tyrosine phosphorylation and requires an activated Jak2 kinase

Gamma interferon (IFN-gamma) induces both tyrosine and serine phosphorylation of Stat1. Stat1 serine phosphorylation is required for maximal transcriptional activity of Stat1. In this report, we present evidence that Stat1 tyrosine phosphorylation is not a prerequisite for Stat1 serine phosphorylation, although an active Jak2 kinase is required for both phosphorylation events. Stat1 serine phosphorylation occurs with a more delayed time course than tyrosine phosphorylation. The occurrence of serine phosphorylation without tyrosine phosphorylation suggests that serine phosphorylation takes place in the cytoplasm. Experiments performed with cells expressing either dominant-negative or constitutively active Ras protein indicated that the Ras-mitogen-activated protein kinase pathway is probably not involved in IFN-gamma-induced Stat1 serine phosphorylation. Finally, a kinase capable of correct Stat1 serine phosphorylation was detected in partially purified cytoplasmic extracts from both IFN-gamma-treated and untreated cells.

Proteinase inhibitors I and II from potatoes specifically block UV-induced activator protein-1 activation through a pathway that is independent of extracellular signal-regulated kinases, c-Jun N-terminal kinases, and P38 kinase

Solar UV irradiation is the causal factor for the increasing incidence of human skin carcinomas. The activation of the transcription factor activator protein-1 (AP-1) has been shown to be responsible for the tumor promoter action of UV light in mammalian cells. We demonstrate that proteinase inhibitor I (Inh I) and II (Inh II) from potato tubers, when applied to mouse epidermal JB6 cells, block UV-induced AP-1 activation. The inhibition appears to be specific for UV-induced signal transduction for AP-1 activation, because these inhibitors did not block UV-induced p53 activation nor did they exhibit any significant influence on epidermal growth factor-induced AP-1 transactivation. Furthermore, the inhibition of UV-induced AP-1 activity occurs through a pathway that is independent of extracellular signal-regulated kinases and c-Jun N-terminal kinases as well as P38 kinases. Considering the important role of AP-1 in tumor promotion, it is possible that blocking UV-induced AP-1 activity by Inh I or Inh II may be functionally linked to irradiation-induced cell transformation.

Absence of excitotoxicity-induced apoptosis in the hippocampus of mice lacking the Jnk3 gene

Excitatory amino acids induce both acute membrane depolarization and latent cellular toxicity, which often leads to apoptosis in many neurological disorders. Recent studies indicate that glutamate toxicity may involve the c-Jun amino-terminal kinase (JNK) group of mitogen-activated protein (MAP) kinases. One member of the JNK family, Jnk3, may be required for stress-induced neuronal apoptosis, as it is selectively expressed in the nervous system. Here we report that disruption of the gene encoding Jnk3 in mice caused the mice to be resistant to the excitotoxic glutamate-receptor agonist kainic acid: they showed a reduction in seizure activity and hippocampal neuron apoptosis was prevented. Although application of kainic acid imposed the same level of noxious stress, the phosphorylation of c-Jun and the transcriptional activity of the AP-1 transcription factor complex were markedly reduced in the mutant mice. These data indicate that the observed neuroprotection is due to the extinction of a Jnk3-mediated signalling pathway, which is an important component in the pathogenesis of glutamate neurotoxicity.

Inhibition of ultraviolet B-induced activator protein-1 (AP-1) activity by aspirin in AP-1-luciferase transgenic mice

Aspirin is under consideration as a promising chemopreventative agent for human cancers. To study the usefulness of aspirin as a chemopreventative agent for UV-induced human skin cancer, we investigated the effect of aspirin on UVB-induced activator protein-1 (AP-1) activity. In the JB6 cell culture system, aspirin or sodium salicylate (SA) inhibited UVB-induced AP-1 activity in a dose-dependent manner; this inhibitory effect occurred only in cells pretreated with aspirin or SA before UVB irradiation but not cells treated with aspirin or SA after UVB irradiation. Furthermore, these inhibitory effects on UVB-induced AP-1 activity appeared to be mediated through blocking of activation of MAP kinase family members, including extracellular signal-regulated protein kinases, c-Jun N-terminal kinases, and p38. It was not due to absorption of UVB light by aspirin. In the skin of AP-1-luciferase transgenic mice, UVB irradiation induced a rapid increase in AP-1 activity, which reached the peak at 48 h post-UVB irradiation. The topical pretreatment of mouse skin with aspirin markedly blocked the UVB-induced AP-1 transactivation in vivo. These data provide the first evidence that aspirin and SA are inhibitors of UV-induced signal transduction and thus could be used as a chemopreventative agent for skin cancer.

Activation of CD95 (APO-1/Fas) signaling by ceramide mediates cancer therapy-induced apoptosis

We report here that anticancer drugs such as doxorubicin lead to induction of the CD95 (APO-1/Fas) system of apoptosis and the cellular stress pathway which includes JNK/SAPKs. Ceramide, which accumulates in response to different types of cellular stress such as chemo- and radiotherapy, strongly induced expression of CD95-L, cleavage of caspases and apoptosis. Antisense CD95-L as well as dominant-negative FADD inhibited ceramide- and cellular stress-induced apoptosis. Fibroblasts from type A Niemann-Pick patients (NPA), genetically deficient in ceramide synthesis, failed to up-regulate CD95-L expression and to undergo apoptosis after gamma-irradiation or doxorubicin treatment. In contrast, JNK/SAPK activity was still inducible by doxorubicin in the NPA cells, suggesting that activation of JNK/SAPKs alone is not sufficient for induction of the CD95 system and apoptosis. CD95-L expression and apoptosis in NPA fibroblasts were restorable by exogenously added ceramide. In addition, NPA fibroblasts undergo apoptosis after triggering of CD95 with an agonistic antibody. These data demonstrate that ceramide links cellular stress responses induced by gamma-irradiation or anticancer drugs to the CD95 pathway of apoptosis.

Modulation of cellular AP-1 DNA binding activity by heat shock proteins

Recent studies have indicated that ubiquitously expressed molecular chaperones of the heat shock protein (Hsp) class may have an additional, nuclear, role in the regulation of gene expression. Experiments on cellular transcription factors derived from the rat adrenal gland have now shown that Hsps modulate in vitro DNA binding activity of the AP-1 factor. Both Hsc70 (p73) and Hsp70 (p72) were demonstrated to exert this effect through a mechanism that appears to be independent of both redox, and phosphorylation state. Further studies on the effect of Hsps on recombinant Fos/Jun protein binding activity indicated that the mechanism of action involves a selective attenuation of high affinity c-Fos:c-Jun binding as compared with c-Jun homodimer binding activity. Because cellular and physiological stress are associated with the induction of both AP-1 and Hsps it is apparent that Hsps may play a modulatory role in the regulation of AP-1 responsive genes.

c-Jun amino-terminal kinase is regulated by Galpha12/Galpha13 and obligate for differentiation of P19 embryonal carcinoma cells by retinoic acid

Retinoic acid induces P19 mouse embryonal carcinoma cells to differentiate to endoderm and increases expression of the heterotrimeric G-protein subunits Galpha12 and Galpha13. Retinoic acid was found to induce differentiation and sustained activation of c-Jun amino-terminal kinase, but not of ERK1,2 or of p38 mitogen-activated protein kinases. Much like retinoic acid, expression of constitutively active forms of Galpha12 and Galpha13 induced differentiation and constitutive activation of c-Jun amino-terminal kinase. Expression of the dominant negative form of c-Jun amino-terminal kinase 1 blocked both the activation of c-Jun amino-terminal kinase and the induction of endodermal differentiation in the presence of retinoic acid. These data implicate c-Jun amino-terminal kinase as a downstream element of activation of Galpha12 or Galpha13 obligate for retinoic acid-induced differentiation.

Activation of the hematopoietic progenitor kinase-1 (HPK1)-dependent, stress-activated c-Jun N-terminal kinase (JNK) pathway by transforming growth factor beta (TGF-beta)-activated kinase (TAK1), a kinase mediator of TGF beta signal transduction

Transforming growth factor beta (TGF-beta)-activated kinase (TAK1) is known for its involvement in TGF-beta signaling and its ability to activate the p38-mitogen-activated protein kinase (MAPK) pathway. This report shows that TAK1 is also a strong activator of c-Jun N-terminal kinase (JNK). Both the wild-type and a constitutively active mutant of TAK1 stimulated JNK in transient transfection assays. Mitogen-activated protein kinase kinase 4 (MKK4)/stress-activated protein kinase/extracellular signal-regulated kinase (SEK1), a dual-specificity kinase that phosphorylates and activates JNK, synergized with TAK1 in activating JNK. Conversely, a dominant-negative (MKK4/SEK1 mutant inhibited TAK1-induced JNK activation. A kinasedefective mutant of TAK1 effectively suppressed hematopoietic progenitor kinase-1 (HPK1)-induced JNK activity but had little effect on germinal center kinase activation of JNK. There are two additional MAPK kinase kinases, MEKK1 and mixed lineage kinase 3 (MLK3), that are also downstream of HPK1 and upstream of MKK4/SEK mutant. However, because the dominant-negative mutants of MEKK1 and MLK3 did not inhibit TAK1-induced JNK activity, we conclude that activation of JNK1 by TAK1 is independent of MEKK1 and MLK3. In addition to TAK1, TGF-beta also stimulated JNK activity. Taken together, these results identify TAK1 as a regulator in the HPK1 --> TAK1 --> MKK4/SEK1 --> JNK kinase cascade and indicate the involvement of JNK in the TGF-beta signaling pathway. Our results also suggest the potential roles of TAK1 not only in the TGF-beta pathway but also in the other HPK1/JNK1-mediated pathways.