Analyzing JNK and p38 mitogen-activated protein kinase activity

An ultrasensitive fiveplex activity assay for cellular kinases

Protein kinases are enzymes whose abundance, protein-protein interactions, and posttranslational modifications together determine net signaling activity in cells. Large-scale data on cellular kinase activity are limited, because existing assays are cumbersome, poorly sensitive, low throughput, and restricted to measuring one kinase at a time. Here, we surmount the conventional hurdles of activity measurement with a multiplexing approach that leverages the selectivity of individual kinase-substrate pairs. We demonstrate proof of concept by designing an assay that jointly measures activity of five pleiotropic signaling kinases: Akt, IκB kinase (IKK), c-jun N-terminal kinase (JNK), mitogen-activated protein kinase (MAPK)-extracellular regulated kinase kinase (MEK), and MAPK-activated protein kinase-2 (MK2). The assay operates in a 96-well format and specifically measures endogenous kinase activation with coefficients of variation less than 20%. Multiplex tracking of kinase-substrate pairs reduces input requirements by 25-fold, with ~75 µg of cellular extract sufficient for fiveplex activity profiling. We applied the assay to monitor kinase signaling during coxsackievirus B3 infection of two different host-cell types and identified multiple differences in pathway dynamics and coordination that warrant future study. Because the Akt–IKK–JNK–MEK–MK2 pathways regulate many important cellular functions, the fiveplex assay should find applications in inflammation, environmental-stress, and cancer research.

An alternative splicing program promotes adipose tissue thermogenesis

Alternative pre-mRNA splicing expands the complexity of the transcriptome and controls isoform-specific gene expression. Whether alternative splicing contributes to metabolic regulation is largely unknown. Here we investigated the contribution of alternative splicing to the development of diet-induced obesity. We found that obesity-induced changes in adipocyte gene expression include alternative pre-mRNA splicing. Bioinformatics analysis associated part of this alternative splicing program with sequence specific NOVA splicing factors. This conclusion was confirmed by studies of mice with NOVA deficiency in adipocytes. Phenotypic analysis of the NOVA-deficient mice demonstrated increased adipose tissue thermogenesis and improved glycemia. We show that NOVA proteins mediate a splicing program that suppresses adipose tissue thermogenesis. Together, these data provide quantitative analysis of gene expression at exon-level resolution in obesity and identify a novel mechanism that contributes to the regulation of adipose tissue function and the maintenance of normal glycemia.

DOI:http://dx.doi.org/10.7554/eLife.17672.001

The process of building a protein from the information encoded in a gene begins when the gene is copied to form a pre-messenger RNA molecule. This molecule is then edited to produce a final messenger RNA that is “translated” to form the protein. Different segments of the pre-messenger RNA molecule can be removed to create different messenger RNAs. This “alternative splicing” enables a single gene to produce multiple protein variants, allowing a diverse range of processes to be performed by cells.

Fat cells store energy in the form of fats and can release this energy as heat in a process called thermogenesis. This helps to regulate the body’s metabolism and prevent obesity. Vernia et al. now find that that feeding mice a high-fat diet causes widespread changes in alternative splicing in fat cells. Further bioinformatics analysis revealed that the NOVA family of splicing factors – proteins that bind to the pre-messenger RNAs to control alternative splicing – contribute to the alternative splicing of around a quarter of the genes whose splicing changes in response to a fatty diet.

Mice whose fat cells were deficient in the NOVA splicing factors displayed increased thermogenesis. As a consequence, when these animals were fed a high-fat diet, they gained less weight than animals in which NOVA proteins were present. Their metabolic activity was also better, meaning they were less likely to show the symptoms of pre-diabetes. Moreover, the activity of certain genes that are known to promote thermogenesis was greater in the fat cells that were deficient in NOVA proteins.

Overall, the results presented by Vernia et al. suggest that the normal role of NOVA proteins is to carry out an alternative splicing program that suppresses thermogenesis, which in turn may promote obesity. Drugs that are designed to target NOVA proteins and increase thermogenesis may therefore help to treat metabolic diseases and obesity. The next step is to identify the protein variants that are generated by NOVA proteins and work out how they contribute to thermogenesis.

DOI:http://dx.doi.org/10.7554/eLife.17672.002

A nuclear role for the respiratory enzyme CLK-1 in regulating mitochondrial stress responses and longevity

The coordinated regulation of mitochondrial and nuclear activities is essential for cellular respiration and its disruption leads to mitochondrial dysfunction, a hallmark of ageing. Mitochondria communicate with nuclei through retrograde signalling pathways that modulate nuclear gene expression to maintain mitochondrial homeostasis. The monooxygenase CLK-1 (human homologue COQ7) was previously reported to be mitochondrial, with a role in respiration and longevity. We have uncovered a distinct nuclear form of CLK-1 that independently regulates lifespan. Nuclear CLK-1 mediates a retrograde signalling pathway that is conserved from Caenorhabditis elegans to humans and is responsive to mitochondrial reactive oxygen species, thus acting as a barometer of oxidative metabolism. We show that, through modulation of gene expression, the pathway regulates both mitochondrial reactive oxygen species metabolism and the mitochondrial unfolded protein response. Our results demonstrate that a respiratory enzyme acts in the nucleus to control mitochondrial stress responses and longevity.

Alteration of JNK-1 signaling in skeletal muscle fails to affect glucose homeostasis and obesity-associated insulin resistance in mice

Obesity and associated metabolic disturbances, such as increased circulating fatty acids cause prolonged low grade activation of inflammatory signaling pathways in liver, skeletal muscle, adipose tissue and even in the CNS. Activation of inflammatory pathways in turn impairs insulin signaling, ultimately leading to obesity-associated type 2 diabetes mellitus. Conventional JNK-1 knock out mice are protected from high fat diet-induced insulin resistance, characterizing JNK-1-inhibition as a potential approach to improve glucose metabolism in obese patients. However, the cell type-specific role of elevated JNK-1 signaling as present during the course of obesity has not been fully elucidated yet. To investigate the functional contribution of altered JNK-1 activation in skeletal muscle, we have generated a ROSA26 insertion mouse strain allowing for Cre-activatable expression of a JNK-1 constitutive active construct (JNK^C). To examine the consequence of skeletal muscle-restricted JNK-1 overactivation in the development of insulin resistance and glucose metabolism, JNK^C mice were crossed to Mck-Cre mice yielding JNK^SM-C mice. However, despite increased muscle-specific JNK activation, energy homeostasis and glucose metabolism in JNK^SM-C mice remained largely unaltered compared to controls. In line with these findings, obese mice with skeletal muscle specific disruption of JNK-1, did not affect energy and glucose homeostasis. These experiments indicate that JNK-1 activation in skeletal muscle does not account for the major effects on diet-induced, JNK-1-mediated deterioration of insulin action and points towards a so far underappreciated role of JNK-1 in other tissues than skeletal muscle during the development of obesity-associated insulin resistance.

p38 mitogen-activated protein kinase (MAPK) first regulates filamentous actin at the 8-16-cell stage during preimplantation development

BACKGROUND INFORMATION

The MAPK (mitogen-activated protein kinase) superfamily of proteins consists of four separate signalling cascades: the c-Jun N-terminal kinase or stress-activated protein kinases (JNK/SAPK); the ERKs (extracellular-signal-regulated kinases); the ERK5 or big MAPK1; and the p38 MAPK group of protein kinases, all of which are highly conserved. To date, our studies have focused on defining the role of the p38 MAPK pathway during preimplantation development. p38 MAPK regulates actin filament formation through the downstream kinases MAPKAPK2/3 (MAPK-activated protein kinase 2/3) or MAPKAPK5 [PRAK (p38 regulated/activated kinase)] and subsequently through HSP25/27 (heat-shock protein 25/27). We recently reported that 2-cell-stage murine embryos treated with cytokine-suppressive anti-inflammatory drugs (CSAIDtrade mark; SB203580 and SB220025) display a reversible blockade of development at the 8-16-cell stage, indicating that p38 (MAPK) activity is required to complete murine preimplantation development. In the present study, we have investigated the stage-specific action and role of p38 MAPK in regulating filamentous actin during murine preimplantation development.

RESULTS

Treatment of 8-cell-stage embryos with SB203580 and SB220025 (CSAIDtrade mark) resulted in a blockade of preimplantation development, loss of rhodamine phalloidin fluorescence, MK-p (phosphorylated MAPKAPK2/3), HSP-p (phosphorylated HSP25/27) and a redistribution of alpha-catenin immunofluorescence by 12 h of treatment. In contrast, treatment of 2- and 4-cell-stage embryos with CSAIDtrade mark drugs resulted in a loss of MK-p and HSP-p, but did not result in a loss of rhodamine phalloidin fluorescence. All these effects of p38 MAPK inhibition were reversed upon removal of the inhibitor, and development resumed in a delayed but normal manner to the blastocyst stage. Treatment of 8-cell embryos with PD098059 (ERK pathway inhibitor) did not affect development or fluorescence of MK-p, HSP-p or rhodamine phalloidin.

CONCLUSION

Murine preimplantation development becomes dependent on p38 MAPK at the 8-16-cell stage, which corresponds to the stage when p38 MAPK first regulates filamentous actin during early development.

SOX7 is involved in aspirin-mediated growth inhibition of human colorectal cancer cells

AIM: To confirm the role of sex-determining region Y-box 7 (Sox7) in aspirin-mediated growth inhibition of COX-independent human colorectal cancer cells.

METHODS: The cell survival percentage was examined by MTT (Moto-nuclear cell direc cytotoxicity) assay. SOX7 expression was assessed by using reverse transcription-polymerase chain reaction and Western blotting. SB203580 was used to inhibit the p38MAPK signal pathway. SOX7 promoter activity was detected by Luciferase reporter assay.

RESULTS: SOX7 was upregulated by aspirin and was involved in aspirin-mediated growth inhibition of SW480 human colorectal cancer cells. The p38MAPK pathway played a role in aspirin-induced SOX7 expression, during which the AP1 transcription factors c-Jun and c-Fos upregulated SOX7 promoter activities.

RESULTS: SOX7 is upregulated by aspirin and is involved in aspirin-mediated growth inhibition of human colorectal cancer SW480 cells.

Dissociation of inositol-requiring enzyme (IRE1α)-mediated c-Jun N-terminal kinase activation from hepatic insulin resistance in conditional X-box-binding protein-1 (XBP1) knock-out mice

Hepatic insulin resistance has been attributed to both increased endoplasmic reticulum (ER) stress and accumulation of intracellular lipids, specifically diacylglycerol (DAG). The ER stress response protein, X-box-binding protein-1 (XBP1), was recently shown to regulate hepatic lipogenesis, suggesting that hepatic insulin resistance in models of ER stress may result from defective lipid storage, as opposed to ER-specific stress signals. Studies were designed to dissociate liver lipid accumulation and activation of ER stress signaling pathways, which would allow us to delineate the individual contributions of ER stress and hepatic lipid content to the pathogenesis of hepatic insulin resistance. Conditional XBP1 knock-out (XBP1Δ) and control mice were fed fructose chow for 1 week. Determinants of whole-body energy balance, weight, and composition were determined. Hepatic lipids including triglyceride, DAGs, and ceramide were measured, alongside markers of ER stress. Whole-body and tissue-specific insulin sensitivity were determined by hyperinsulinemic-euglycemic clamp studies. Hepatic ER stress signaling was increased in fructose chow-fed XBP1Δ mice as reflected by increased phosphorylated eIF2α, HSPA5 mRNA, and a 2-fold increase in hepatic JNK activity. Despite JNK activation, XBP1Δ displayed increased hepatic insulin sensitivity during hyperinsulinemic-euglycemic clamp studies, which was associated with increased insulin-stimulated IRS2 tyrosine phosphorylation, reduced hepatic DAG content, and reduced PKCε activity. These studies demonstrate that ER stress and IRE1α-mediated JNK activation can be disassociated from hepatic insulin resistance and support the hypothesis that hepatic insulin resistance in models of ER stress may be secondary to ER stress modulation of hepatic lipogenesis.

Requirement of JIP1-mediated c-Jun N-terminal kinase activation for obesity-induced insulin resistance

The c-Jun NH(2)-terminal kinase (JNK) interacting protein 1 (JIP1) has been proposed to act as a scaffold protein that mediates JNK activation. However, recent studies have implicated JIP1 in multiple biochemical processes. Physiological roles of JIP1 that are related to the JNK scaffold function of JIP1 are therefore unclear. To test the role of JIP1 in JNK activation, we created mice with a germ line point mutation in the Jip1 gene (Thr(103) replaced with Ala) that selectively blocks JIP1-mediated JNK activation. These mutant mice exhibit a severe defect in JNK activation caused by feeding of a high-fat diet. The loss of JIP1-mediated JNK activation protected the mutant mice against obesity-induced insulin resistance. We conclude that JIP1-mediated JNK activation plays a critical role in metabolic stress regulation of the JNK signaling pathway.

Role of the hypothalamic-pituitary-thyroid axis in metabolic regulation by JNK1

The cJun N-terminal kinase 1 (JNK1) is implicated in diet-induced obesity. Indeed, germline ablation of the murine Jnk1 gene prevents diet-induced obesity. Here we demonstrate that selective deficiency of JNK1 in the murine nervous system is sufficient to suppress diet-induced obesity. The failure to increase body mass is mediated, in part, by increased energy expenditure that is associated with activation of the hypothalamic-pituitary-thyroid axis. Disruption of thyroid hormone function prevents the effects of nervous system JNK1 deficiency on body mass. These data demonstrate that the hypothalamic-pituitary-thyroid axis represents an important target of metabolic signaling by JNK1.

Role of muscle c-Jun NH2-terminal kinase 1 in obesity-induced insulin resistance

Obesity caused by feeding of a high-fat diet (HFD) is associated with an increased activation of c-Jun NH(2)-terminal kinase 1 (JNK1). Activated JNK1 is implicated in the mechanism of obesity-induced insulin resistance and the development of metabolic syndrome and type 2 diabetes. Significantly, Jnk1(-)(/)(-) mice are protected against HFD-induced obesity and insulin resistance. Here we show that an ablation of the Jnk1 gene in skeletal muscle does not influence HFD-induced obesity. However, muscle-specific JNK1-deficient (M(KO)) mice exhibit improved insulin sensitivity compared with control wild-type (M(WT)) mice. Thus, insulin-stimulated AKT activation is suppressed in muscle, liver, and adipose tissue of HFD-fed M(WT) mice but is suppressed only in the liver and adipose tissue of M(KO) mice. These data demonstrate that JNK1 in muscle contributes to peripheral insulin resistance in response to diet-induced obesity.

Development of a homogeneous competitive immunoassay for phosphorylated protein antigen based on the enhanced fluorescence resonance energy transfer technology

We describe a homogeneous competitive immunoassay for a phosphorylated protein antigen. The assay takes advantage of the enhanced fluorescence resonance energy transfer (FRET) technology, which has a unique characteristic that the FRET signal is increased by the specific interaction of two fluorolabeled leucine zippers. We chose extracellular signal-regulated kinase (ERK) as a model antigen and constructed two molecular probes in which either anti-phosphorylation site antibody or the antigen peptide was chemically conjugated to the enhanced FRET probes. While these molecular probes indicated sufficient FRET signal without antigen, they displayed a significant change in the fluorescent spectrum by mixing with phosphorylated antigens. With this competitive enhanced FRET immunoassay, a phosphorylated ERK concentration within the range from 15 nM to 250 nM could be determined. Because the assay is very simple, it would be applied to not only in vitro assay but also in vivo detection of protein phosphorylation.

Signal transduction cross talk mediated by Jun N-terminal kinase-interacting protein and insulin receptor substrate scaffold protein complexes

Scaffold proteins have been established as important mediators of signal transduction specificity. The insulin receptor substrate (IRS) proteins represent a critical group of scaffold proteins that are required for signal transduction by the insulin receptor, including the activation of phosphatidylinositol 3 kinase. The c-Jun NH(2)-terminal kinase (JNK)-interacting proteins (JIPs) represent a different group of scaffold molecules that are implicated in the regulation of the JNK. These two signaling pathways are functionally linked because JNK can phosphorylate IRS1 on the negative regulatory site Ser-307. Here we demonstrate the physical association of these signaling pathways using a proteomic approach that identified insulin-regulated complexes of JIPs together with IRS scaffold proteins. Studies using mice with JIP scaffold protein defects confirm that the JIP1 and JIP2 proteins are required for normal glucose homeostasis. Together, these observations demonstrate that JIP proteins can influence insulin-stimulated signal transduction mediated by IRS proteins.

Mcl-1 integrates the opposing actions of signaling pathways that mediate survival and apoptosis

Mcl-1 is a member of the Bcl2-related protein family that is a critical mediator of cell survival. Exposure of cells to stress causes inhibition of Mcl-1 mRNA translation and rapid destruction of Mcl-1 protein by proteasomal degradation mediated by a phosphodegron created by glycogen synthase kinase 3 (GSK3) phosphorylation of Mcl-1. Here we demonstrate that prior phosphorylation of Mcl-1 by the c-Jun N-terminal protein kinase (JNK) is essential for Mcl-1 phosphorylation by GSK3. Stress-induced Mcl-1 degradation therefore requires the coordinated activity of JNK and GSK3. Together, these data establish that Mcl-1 functions as a site of signal integration between the proapoptotic activity of JNK and the prosurvival activity of the AKT pathway that inhibits GSK3.

Increase of reaction rate and sensitivity of low-abundance enzyme assay using micro/nanofluidic preconcentration chip

We report a novel method of increasing both the reaction rate and the sensitivity of low-abundance enzyme assay using a micro/nanofluidic preconcentration chip. The disposable preconcentration device made out of PDMS with a surface-patterned ion-selective membrane increases local enzyme/substrate concentrations for rapid monitoring of enzyme activity. As a model system, we used trypsin as the enzyme and BODIPY FL casein as the fluorogenic substrate. We demonstrated that the reaction rate of trypsin-BODIPY FL was significantly enhanced by increasing the local concentrations of both trypsin and BODIPY FL casein in the preconcentration chip. The reaction time required to turn over substrates at 1 ng/mL was only approximately 10 min compared to approximately 1 h without preconcentration, which demonstrates a significantly higher reaction rate through the increase of the concentrations of both the enzyme and substrate. Furthermore, trypsin activity can be measured down to a concentration level of 10 pg/mL, which is a approximately 100 fold enhancement in sensitivity compared to the result without the preconcentration step. This micro/nanofluidic preconcentrator chip could be used as a generic micro reaction platform to study any enzyme-substrate systems, or other biochemical reaction systems in low concentration ranges.

Modulation of interleukin-1 transcriptional response by the interaction between VRK2 and the JIP1 scaffold protein

Background

Cellular biological responses to specific stimulation are determined by a balance among signaling pathways. Protein interactions are likely to modulate these pathways. Vaccinia-related kinase-2 (VRK2) is a novel human kinase that can modulate different signaling pathways.

Principal Findings

We report that in vivo, the activity of JIP1-JNK complexes is downregulated by VRK2 in response to interleukin-1β. Also the reduction of endogenous VRK2 with shRNA increases the transcriptional response to IL-1β. The JIP1 scaffold protein assembles three consecutive members of a given MAPK pathway forming signaling complexes and their signal can be modulated by interactions with regulatory proteins that remain to be identified. Knocking-down JIP1 with siRNA resulted in elimination of the AP1 transcriptional response to IL-1β. VRK2, a member of novel Ser-Thr kinase family, is able to stably interact with JIP1, TAK1 and MKK7, but not JNK, and can be isolated forming oligomeric complexes with different proportions of TAK1, MKK7β1 and JNK. JIP1 assembles all these proteins in an oligomeric signalosome. VRK2 binding to the JIP1 signalosome prevents the association of JNK and results in a reduction in its phosphorylation and downregulation of AP1-dependent transcription.

Conclusions/Significance

This work suggests that the intracellular level of VRK2 protein can modulate the flow through a signaling pathway and alter the response from a receptor that can be distributed by more than one pathway, and thus contribute to the cellular specificity of the response by forming alternative signaling complexes. Furthermore, the effect might be more general and affect other signaling routes assembled on the JIP1 scaffold protein for which a model is proposed.

Requirement of JIP scaffold proteins for NMDA-mediated signal transduction

JIP scaffold proteins are implicated in the regulation of protein kinase signal transduction pathways. To test the physiological role of these scaffold proteins, we examined the phenotype of compound mutant mice that lack expression of JIP proteins. These mice were found to exhibit severe defects in N-methyl-D-aspartic acid (NMDA) receptor function, including decreased NMDA-evoked current amplitude, cytoplasmic Ca(++), and gene expression. The decreased NMDA receptor activity in JIP-deficient neurons is associated with reduced tyrosine phosphorylation of NR2 subunits of the NMDA receptor. JIP complexes interact with the SH2 domain of cFyn and may therefore promote tyrosine phosphorylation and activity of the NMDA receptor. We conclude that JIP scaffold proteins are critically required for normal NMDA receptor function.

Aging in rat causes hepatic hyperresposiveness to interleukin-1beta which is mediated by neutral sphingomyelinase-2

The process of aging has recently been shown to substantially affect the ability of cells to respond to inflammatory challenges. We demonstrate that aging leads to hepatic hyperresponsiveness to interleukin 1beta (IL-1beta), and we examine the factors that could be responsible for this phenomenon. IL-1beta-induced phosphorylation of c-jun N-terminal kinase (JNK) in hepatocytes isolated from aged rats was 3 times more potent than that in hepatocytes from young rats. Moreover, JNK was activated by substantially lower doses of IL-1beta. These age-related changes in JNK phosphorylation correlated with diminished IL-1beta-induced degradation of interleukin-1 receptor-associated kinase-1 (IRAK-1). Expression levels of IL1beta receptor I, total JNK, IRAK-1, and transforming growth factor-beta-activated kinase-1 (TAK-1) were not affected by aging. However, increased neutral sphingomyelinase activity was observed in hepatocytes from old animals, which we show is caused by induction of the plasma membrane localized neutral sphingomyelinase-2 (NSMase-2). We provide evidence that NSMase-2 is both required and sufficient for the onset of IL-1beta hyperresponsiveness during aging. Overexpression of NSMase-2 in hepatocytes from young rats leads both to a reduction in IRAK-1 degradation and potentiation of JNK phosphorylation, mimicking that seen in hepatocytes from old animals. More importantly, inhibition of NSMase activity in hepatocytes from aged rats using either scyphostatin or short interfering ribonucleic acid (siRNA) leads to reversion to the "young" phenotype of IL-1beta response.

CONCLUSION

These results show that the process of aging causes increased basal NSMase-2 activity in hepatocytes, which in turn leads to IRAK-1 stabilization, JNK potentiation, and ultimately IL-1beta hyperresponsiveness.

Regulation of p73-mediated apoptosis by c-Jun N-terminal kinase

The JNK (c-Jun N-terminal kinase)/mitogen-activated protein kinase signalling pathway is a major mediator of stress responses in cells, including the response to DNA damage. DNA damage also causes the stabilization and activation of p73, a member of the p53 family of transcription factors. p73, like p53, can mediate apoptosis by up-regulating the expression of pro-apoptotic genes, including Bax (Bcl2-associated X protein) and PUMA (p53 up-regulated modulator of apoptosis). Changes in p73 expression have been linked to tumour progression, particularly in neuroblastomas, whereas in tumours that feature inactivated p53 there is evidence that p73 may mediate the apoptotic response to chemotherapeutic agents. In the present study, we demonstrate a novel link between the JNK signalling pathway and p73. We use pharmacological and genetic approaches to show that JNK is required for p73-mediated apoptosis induced by the DNA damaging agent cisplatin. JNK forms a complex with p73 and phosphorylates it at several serine and threonine residues. The mutation of JNK phosphorylation sites in p73 abrogates cisplatin-induced stabilization of p73 protein, leading to a reduction in p73 transcriptional activity and reduced p73-mediated apoptosis. Our results demonstrate that the JNK pathway is an important regulator of DNA damage-induced apoptosis mediated by p73.

Metabolic stress signaling mediated by mixed-lineage kinases

Saturated free fatty acid (FFA) is a major source of metabolic stress that activates the c-Jun NH(2)-terminal kinase (JNK). This FFA-stimulated JNK pathway is relevant to hallmarks of metabolic syndrome, including insulin resistance. Here we used gene ablation studies in mice to demonstrate a central role for mixed-lineage protein kinases (MLK) in this signaling pathway. Saturated FFA causes protein kinase C (PKC)-dependent activation of MLK3 that subsequently causes increased JNK activity by a mechanism that requires the MAP kinase kinases MKK4 and MKK7. Loss of PKC, MLK3, MKK4, or MKK7 expression prevents FFA-stimulated JNK activation. Together, these data establish a signaling pathway that mediates effects of metabolic stress on insulin resistance.

Regulation of insulin-like growth factor binding protein-1 expression during aging

Insulin-like growth factor (IGF) binding protein-1 (IGFBP-1) is primarily produced in the liver during inflammation and regulates biological activities of IGF-I. Here we demonstrate that interleukin-1beta (IL-1beta) stimulates IGFBP-1 mRNA production in a dose-dependent manner in hepatocytes from Fisher 344 rats. Employment of c-Jun N-terminal kinase (JNK) inhibitor SP600125 resulted in 3-fold reduction of IGFBP-1 mRNA and protein levels, indicating that IL-1beta-induced IGFBP-1 production is mediated through JNK activation. We further show that hepatocytes from aged rats (20-22 mo), as compared to young (3-4 mo), exhibit up to 2-fold higher levels of IGFBP-1 in response to IL-1beta. IL-1beta-induced phosphorylation of JNK was also significantly higher in aged hepatocytes, and SP600125 treatment eliminated age-related differences in IGFBP-1 mRNA production. Moreover, glutathione depletion in hepatocytes from young rats potently activated JNK, as well as increased IL-1beta-induced IGFBP-1 mRNA levels, suggesting that age-related oxidative stress underlies the upregulated JNK activation and IGFBP-1 expression.

JNK2 is a positive regulator of the cJun transcription factor

The cJun NH(2)-terminal kinase (JNK) signal transduction pathway is established to be an important mechanism of regulation of the cJun transcription factor. Studies of Jnk1(-/-) and Jnk2(-/-) mice suggest that the JNK1 and JNK2 isoforms have opposite effects on cJun expression and proliferation. Here, we demonstrate, using a chemical genetic approach, that both JNK1 and JNK2 are positive regulators of these processes. We show that competition between JNK1 and JNK2 contributes to the opposite phenotypes caused by JNK1 and JNK2 deficiency. Our analysis illustrates the power of a chemical genetics approach for the analysis of signal transduction pathways and also highlights the limitations of single gene knockout strategies for the analysis of signaling pathways that are formed by a network of interacting proteins.

Analysis of mitogen-activated protein kinase activation and interactions with regulators and substrates

Mitogen-activated protein kinase (MAPK) cascades are ubiquitous signal transduction modules in eukaryotes that are of great interest and importance. Here, we summarize some useful methods for the analysis of MAPK signaling, including methods to (1) detect MAPK activation in cells, with an emphasis on using phosphorylation-state-specific antibodies raised against mammalian phosphopeptide sequences to detect the activation of MAPKs in other species; (2) estimate the cellular concentrations of MAPKs and other proteins of interest; (3) detect and quantify the stable physical association of MAPKs with their substrates and regulators, and estimate the relevant dissociation constants; (4) delineate the MAPK-binding regions or domains of MAPK-interacting proteins, with particular emphasis on the identification and verification of MAPK-docking sites. These procedures are broadly applicable to many organisms, including both yeast and mammalian cells.

Varicella-zoster virus infection of human fibroblast cells activates the c-Jun N-terminal kinase pathway

The transcription factors ATF-2 and c-Jun are important for transactivation of varicella-zoster virus (VZV) genes. c-Jun is activated by the c-Jun N-terminal kinase (JNK), a member of the mitogen-activated protein kinase pathway that responds to stress and cytokines. To study the effects of VZV on this pathway, confluent human foreskin fibroblasts were infected with cell-associated VZV for 1 to 4 days. Immunoblots showed that phosphorylated JNK and c-Jun levels increased in VZV-infected cells, and kinase assays determined that phospho-JNK was active. Phospho-JNK was detected after 24 h, and levels rose steadily over 4 days in parallel with accumulation of VZV antigen. The two main activators of JNK are MKK4 and MKK7, and levels of their active, phosphorylated forms also increased. The competitive inhibitor of JNK, SP600125, caused a dose-dependent reduction in VZV yield (50% effective concentration, congruent with 8 microM). Specificity was verified by immunoblotting; phospho-c-Jun was eliminated by 18 microM SP600125 in VZV-infected cells. Immunofluorescent confocal microscopy showed that phospho-c-Jun and most of phospho-JNK were in the nuclei of VZV-infected cells; some phospho-JNK was in the cytoplasm. MKK4, MKK7, JNK, and phospho-JNK were detected by immunoblotting in purified preparations of VZV virions, but c-Jun was absent. JNK was located in the virion tegument, as determined by biochemical fractionation and immunogold transmission electron microscopy. Overall, these results demonstrate the importance of the JNK pathway for VZV replication and advance the idea that JNK is a useful drug target against VZV.

p38 mitogen-activated protein kinase mediates the Fas-induced mitochondrial death pathway in CD8+ T cells

The p38 mitogen-activated protein kinase (MAPK) signaling pathway can be activated by a variety of stress stimuli such as UV radiation and osmotic stress. The regulation and role of this pathway in death receptor-induced apoptosis remain unclear and may depend on the specific death receptor and cell type. Here we show that binding of Fas ligand to Fas activates p38 MAPK in CD8+ T cells and that activation of this pathway is required for Fas-mediated CD8+ T-cell death. Active p38 MAPK phosphorylates Bcl-xL and Bcl-2 and prevents the accumulation of these antiapoptotic molecules within the mitochondria. Consequently, a loss of mitochondrial membrane potential and the release of cytochrome c lead to the activation of caspase 9 and, subsequently, caspase 3. Therefore, the activation of p38 MAPK is a critical link between Fas and the mitochondrial death pathway and is required for the Fas-induced apoptosis of CD8+ T cells.

The BRCA1 COOH-terminal region acts as an RNA polymerase II carboxyl-terminal domain kinase inhibitor that modulates p21WAF1/CIP1 expression

BRCA1 is involved both in positive and negative regulation of gene activity as well as in numerous other processes, such as DNA damage response and repair. We recently reported that BRCA1 inhibits RNA polymerase II carboxyl-terminal domain (CTD) phosphorylation by TFIIH and decreases serine 5 phosphorylation levels when introduced into a BRCA1(-/-) cell line. Regulation of CTD phosphorylation is crucial for proper gene expression and response to cellular stresses, such as DNA damage and transcription arrest. A key player in this process, P-TEFb, phosphorylates the CTD on serine 2 of transcriptionally engaged RNA polymerase II, and its kinase activity was shown to be up-regulated when cells are exposed to transcriptional stress such as UV irradiation. Here, we investigate the effect of BRCA1 on serine 2 phosphorylation and UV-activated P-TEFb kinase activity. We now show that BRCA1 inhibits immunoprecipitated P-TEFb kinase activity from UV-irradiated cells and preferentially decreases UV-induced serine 2 phosphorylation of soluble, rather than chromatin-bound, RNAPII. We further show that BRCA1 rescues the UV-mediated inhibition of transcriptional activity from nuclear extracts and stimulates endogenous p21 gene expression upon UV irradiation, a function that is dependent of the inhibition of CTD kinase activity. Our results suggest that BRCA1 could act as a CTD kinase inhibitor and, as such, contribute to the regulation of p21 gene expression.

Chemical genetic analysis of the time course of signal transduction by JNK

Exposure of primary murine embryonic fibroblasts to tumor necrosis factor (TNF) causes biphasic activation of the c-Jun NH(2)-terminal kinase (JNK) signaling pathway. The early phase (30 min) of the response to TNF is a large and transient increase in JNK activity. This response is followed by a second and more sustained phase of JNK activation that lasts many hours. We employed a chemical genetic strategy to dissect the functional consequences of these two phases of JNK activation. We report that both the early and late phases of JNK activation contribute to TNF-induced gene expression. In contrast, the early transient phase of JNK activation (<1 hr) can signal cell survival, while the later and more sustained phase of JNK activation (1-6 hr) can mediate proapoptotic signaling. These data indicate that the time course of JNK signaling can influence the biological response to JNK activation.

Block of C/EBP alpha function by phosphorylation in acute myeloid leukemia with FLT3 activating mutations

Mutations constitutively activating FLT3 kinase are detected in approximately 30% of acute myelogenous leukemia (AML) patients and affect downstream pathways such as extracellular signal-regulated kinase (ERK)1/2. We found that activation of FLT3 in human AML inhibits CCAAT/enhancer binding protein alpha (C/EBPalpha) function by ERK1/2-mediated phosphorylation, which may explain the differentiation block of leukemic blasts. In MV4;11 cells, pharmacological inhibition of either FLT3 or MEK1 leads to granulocytic differentiation. Differentiation of MV4;11 cells was also observed when C/EBPalpha mutated at serine 21 to alanine (S21A) was stably expressed. In contrast, there was no effect when serine 21 was mutated to aspartate (S21D), which mimics phosphorylation of C/EBPalpha. Thus, our results suggest that therapies targeting the MEK/ERK cascade or development of protein therapies based on transduction of constitutively active C/EBPalpha may prove effective in treatment of FLT3 mutant leukemias resistant to the FLT3 inhibitor therapies.

Mechanisms of cell death and neuroprotection by poloxamer 188 after mechanical trauma

The mechanisms of cell death and the progressive degeneration of neural tissue following traumatic brain injury (TBI) have come under intense investigation. However, the complex interactions among the evolving pathologies in multiple cell types obscure the causal relationships between the initial effects of the mechanical trauma at the cellular level and the long-term dysfunction and neuronal death. We used an in vitro model of neuronal injury to study the mechanisms of cell death in response to a well-defined mechanical insult and found that the majority of dead cells were apoptotic. We have previously reported that promotion of membrane repair acutely with the non-ionic surfactant poloxamer 188 (P188) restored cell viability to control values at 24 h postinjury. Here, we showed that P188 significantly inhibits apoptosis and prevents necrosis. We also examined the role of mitogen-activated protein kinases (MAPKs) in cell death. There was a rapid, transient activation of extracellular signal-regulated kinases, c-Jun N-terminal kinase, and p38s after mechanical insult. Of these, activation of the proapoptotic p38 was the greatest. Treatment with P188 inhibited p38 activation; however, direct inhibition of p38 by SB203580, which selectively inhibits the activity of the p38 MAPK, provided only partial inhibition of apoptosis and had no effect on necrosis. These data suggest that multiple signaling pathways may be involved in the long-term response of neurons to mechanical injury. Furthermore, that the membrane resealing action of P188 provides such significant protection from both necrosis and apoptosis suggests that acute membrane damage due to trauma is a critical precipitating event that is upstream of the many signaling cascades contributing to the subsequent pathology.

Genetic inhibition or activation of JNK1/2 protects the myocardium from ischemia-reperfusion-induced cell death in vivo

The c-Jun NH2-terminal kinase (JNK) branch of the mitogen-activated protein kinase signaling cascade has been implicated in the regulation of apoptosis in a variety of mammalian cell types. In the heart, disagreement persists concerning the role that JNKs may play in regulating apoptosis, since both pro- and antiapoptotic regulatory functions have been reported in cultured cardiomyocytes. Here we report the first analysis of cardiomyocyte cell death due to JNK inhibition or activation in vivo using genetically modified mice. Three separate mouse models with selective JNK inhibition were assessed for ventricular damage and apoptosis levels following ischemia-reperfusion injury. jnk1-/-, jnk2-/-, and transgenic mice expressing dominant negative JNK1/2 within the heart were each shown to have less JNK activity in the heart and less injury and cellular apoptosis in vivo following ischemia-reperfusion injury. To potentially address the reciprocal gain-of-function phenotype associated with sustained JNK activation, transgenic mice were generated that express MKK7 in the heart. These transgenic mice displayed elevated cardiac c-Jun kinase activity but, ironically, were also significantly protected from ischemia-reperfusion. Mechanistically, JNK-inhibited mice showed increased phosphorylation of the proapoptotic factor Bad at position 112, whereas MKK7 transgenic mice showed decreased phosphorylation of this site. Collectively, these results underscore the complexity associated with JNK signaling in regulating apoptosis, such that sustained inhibition or activation both elicit cellular protection in vivo, although probably through different mechanisms.

Mitogen-activated protein kinase (MAPK) blockade of bovine preimplantation embryogenesis requires inhibition of both p38 and extracellular signal-regulated kinase (ERK) pathways

Blastocyst formation, as a critical period during development, is an effective indicator of embryonic health and reproductive efficiency. Out of a number of mechanisms underlying blastocyst formation, highly conserved mitogen-activated protein kinase (MAPK) signaling has emerged as a major mechanism involved in regulating murine preimplantation embryo development. The objective of our study was to ascertain the role of MAPK signaling in regulating bovine development to the blastocyst stage. Using reverse transcriptase PCR and immunohistochemical staining procedures we have demonstrated that mRNA transcripts and polypeptides encoding p38 MAPK pathway constituents are detectable in preimplantation bovine embryos from the one-cell to the blastocyst stage. Further, the effects on bovine embryo development following inhibition of p38 α/β and extracellular signal-regulated kinase (ERK) signaling by treatment with SB220025 and U0126, respectively, were investigated. Eight-cell bovine embryos (50 per group; three replicates) were placed into treatments consisting of synthetic oviductal fluid (SOF) medium: SOF + SB202474 (inactive analogue), SOF + SB220025, SOF + U0124 (inactive analogue), SOF + U0126, and SOF + SB220025 + U0126. Inhibition of p38 MAPK or ERK signaling individually did not affect development to the blastocyst stage. However, when both pathways were blocked simultaneously there was a significant reduction (P< 0.05) in blastocyst formation, cell number and immunofluorescence of phosphorylated downstream pathway constituents. We have determined that, in variance to what was observed during murine preimplantation development, bovine early embryos progress at normal frequencies to the blastocyst stage in the presence of p38 MAPK inhibitors.

Role of MLK3 in the regulation of mitogen-activated protein kinase signaling cascades

Mixed-lineage protein kinase 3 (MLK3) is a member of the mitogen-activated protein (MAP) kinase kinase kinase group that has been implicated in multiple signaling cascades, including the NF-kappaB pathway and the extracellular signal-regulated kinase, c-Jun NH(2)-terminal kinase (JNK), and p38 MAP kinase pathways. Here, we examined the effect of targeted disruption of the murine Mlk3 gene. Mlk3(-/-) mice were found to be viable and healthy. Primary embryonic fibroblasts prepared from these mice exhibited no major signaling defects. However, we did find that MLK3 deficiency caused a selective reduction in tumor necrosis factor (TNF)-stimulated JNK activation. Together, these data demonstrate that MLK3 contributes to the TNF signaling pathway that activates JNK.

Increases in phosphorylation of SAPK/JNK and p38MAPK correlate negatively with mouse embryo development after culture in different media

OBJECTIVE

To test whether signal transduction proteins that mediate stress may be used to detect responses of embryos to different media in a prospective randomized study.

DESIGN

Controlled laboratory study.

SETTING

None.

PATIENT(S)

None.

INTERVENTION(S)

Mouse embryos isolated at E3.5 (3.5 days after fertilization) or E1.5 were cultured in different media for 24 hours or 72 hours, respectively. Expression of p38 mitogen activated protein kinases (MAPKs) and stress-activated protein kinase/Jun kinase (SAPK/JNK) phosphoproteins in the mouse embryo and their correlation with preimplantation development were studied.

MAIN OUTCOME MEASURE(S)

[1] In E3.5 embryos, SAPK/JNK and p38MAPK are phosphorylated at different levels in different media after 24 hours, with Ham's F10+BSA and M-16 having the highest intensity of both SAPK/JNK and p38MAPK phosphorylation and Quinn's cleavage medium and potassium simplex optimized medium supplemented with amino acids (KSOM+AA) the lowest intensity. [2] The stress-induced increase in phosphorylation of SAPK/JNK and p38MAPK appears to be post-translational in embryos. [3] The intensity of SAPK/JNK phosphorylation measured at E1.5+72 hours culture is inversely correlated with 4-cell/compaction rate, morula formation rate, blastocyst formation rate, and hatching rate.

RESULT(S)

SAPK/JNK and p38MAPK phosphoprotein levels, but not all forms of protein, are affected during culture of preimplantation embryos in seven different media. During culture, the rate of progress to four developmental events was assayed and each rate was inversely proportional to the level of SAPK/JNK phosphorylation measured by immunocytochemical means or Western blot analysis at the end of culture.

CONCLUSION(S)

Culture stresses embryos; different media exert different levels of stress on the embryos. There is a negative correlation between the amount of stress and the development rate. Taken together, the data suggest that SAPK/JNK phosphorylation may constitute a measure of homeostatic response to negative stimuli of media.

A multiplexed homogeneous fluorescence-based assay for protein kinase activity in cell lysates

New methods to quantify protein kinase activities directly from complex cellular mixtures are critical for understanding biological regulatory pathways. Herein, a fluorescence-based chemosensor strategy for the direct measurement of kinase activities in crude mammalian cell lysates is described. We first designed a new fluorescent peptide reporter substrate for each target kinase. These kinase chemosensors were readily phosphorylated by recombinant target enzyme and underwent a several-fold fluorescence increase upon phosphorylation. Then, using unfractionated cell lysates, a homogeneous kinase assay was developed that was reproducible, linear and highly preferential for monitoring changes in cellular activity of the target kinase. The general protocol was developed for the kinase Akt and then easily extended to measure protein kinase A (PKA) and mitogen-activated protein kinase-associated protein kinase 2 (MK2) activities. This assay platform is immediately useful for studying protein kinase signaling in crude cellular extracts.

JNK potentiates TNF-stimulated necrosis by increasing the production of cytotoxic reactive oxygen species

The c-Jun NH(2)-terminal kinase (JNK) has been implicated in both cell death and survival responses to different stimuli. Here we reexamine the function of JNK in tumor necrosis factor (TNF)-stimulated cell death using fibroblasts isolated from wild-type, Mkk4(-/-) Mkk7(-/-), and Jnk1(-/-) Jnk2(-/-) mice. We demonstrate that JNK can act to suppress TNF-stimulated apoptosis. However, we find that JNK can also potentiate TNF-stimulated necrosis by increasing the production of reactive oxygen species (ROS). Together, these data indicate that JNK can shift the balance of TNF-stimulated cell death from apoptosis to necrosis. Increased necrosis may represent a contributing factor in stress-induced inflammatory responses mediated by JNK.

An essential role of the JIP1 scaffold protein for JNK activation in adipose tissue

The c-Jun NH2-terminal kinase (JNK) is activated during obesity. One consequence of obesity is that JNK phosphorylates the adapter protein insulin receptor substrate 1 (IRS-1) on Ser 307 and inhibits signaling by the insulin receptor. JNK can therefore cause peripheral insulin resistance during obesity and may contribute to the development of type 2 diabetes. Here we report that the JNK-interacting protein 1 (JIP1) scaffold protein, which binds components of the JNK signaling module, is essential for JNK activation in the adipose tissue of obese mice. These data identify JIP1 as a novel molecular target for therapeutic intervention in the development of obesity.

BRCA1 can modulate RNA polymerase II carboxy-terminal domain phosphorylation levels

A high incidence of breast and ovarian cancers has been linked to mutations in the BRCA1 gene. BRCA1 has been shown to be involved in both positive and negative regulation of gene activity as well as in numerous other processes such as DNA repair and cell cycle regulation. Since modulation of the RNA polymerase II carboxy-terminal domain (CTD) phosphorylation levels could constitute an interface to all these functions, we wanted to directly test the possibility that BRCA1 might regulate the phosphorylation state of the CTD. We have shown that the BRCA1 C-terminal region can negatively modulate phosphorylation levels of the RNA polymerase II CTD by the Cdk-activating kinase (CAK) in vitro. Interestingly, the BRCA1 C-terminal region can directly interact with CAK and inhibit CAK activity by competing with ATP. Finally, we demonstrated that full-length BRCA1 can inhibit CTD phosphorylation when introduced in the BRCA1(-/-) HCC1937 cell line. Our results suggest that BRCA1 could play its ascribed roles, at least in part, by modulating CTD kinase components.

c-Jun N-terminal kinases (JNK) antagonize cardiac growth through cross-talk with calcineurin-NFAT signaling

The c-Jun N-terminal kinase (JNK) branch of the mitogen-activated protein kinase (MAPK) signaling pathway regulates cellular differentiation, stress responsiveness and apoptosis in multicellular eukaryotic organisms. Here we investigated the functional importance of JNK signaling in regulating differentiated cellular growth in the post-mitotic myocardium. JNK1/2 gene-targeted mice and transgenic mice expressing dominant negative JNK1/2 were determined to have enhanced myocardial growth following stress stimulation or with normal aging. A mechanism underlying this effect was suggested by the observation that JNK directly regulated nuclear factor of activated T-cell (NFAT) activation in culture and in transgenic mice containing an NFAT-dependent luciferase reporter. Moreover, calcineurin Abeta gene targeting abrogated the pro-growth effects associated with JNK inhibition in the heart, while expression of an MKK7-JNK1 fusion protein in the heart partially reduced calcineurin-mediated cardiac hypertrophy. Collectively, these results indicate that JNK signaling antagonizes the differentiated growth response of the myocardium through direct cross-talk with the calcineurin-NFAT pathway. These results also suggest that myocardial JNK activation is primarily dedicated to modulating calcineurin-NFAT signaling in the regulation of differentiated heart growth.

Mechanical strain differentially regulates endothelial nitric-oxide synthase and receptor activator of nuclear kappa B ligand expression via ERK1/2 MAPK

Exercise promotes positive bone remodeling through controlling cellular processes in bone. Nitric oxide (NO), generated from endothelial nitric-oxide synthase (eNOS), prevents resorption, whereas receptor activator of nuclear kappa B ligand (RANKL) promotes resorption through regulating osteoclast activity. Here we show that mechanical strain differentially regulates eNOS and RANKL expression from osteoprogenitor stromal cells in a magnitude-dependent fashion. Strain (0.25-2%) induction of eNOS expression was magnitude-dependent, reaching a plateau at 218 +/- 36% of control eNOS. This was accompanied by increases in eNOS protein and a doubling of NO production. Concurrently, 0.25% strain inhibited RANKL expression with increasing response up to 1% strain (44 +/- 3% of control RANKL). These differential responses to mechanical input were blocked when an ERK1/2 inhibitor was present during strain application. Inhibition of NO generation did not prevent strain-activated ERK1/2. To confirm the role of ERK1/2, cells were treated with an adenovirus encoding a constitutively activated MEK; Ad.caMEK significantly increased eNOS expression and NO production by more than 4-fold and decreased RANKL expression by half. In contrast, inhibition of strain-activated c-Jun kinase failed to prevent strain effects on either eNOS or RANKL. Our data suggest that physiologic levels of mechanical strain utilize ERK1/2 kinase to coordinately regulate eNOS and RANKL in a manner leading to positive bone remodeling.

A high-throughput quantitative multiplex kinase assay for monitoring information flow in signaling networks: application to sepsis-apoptosis

To treat complex human diseases effectively, a systems-level approach is needed to understand the interplay of environmental cues, intracellular signals, and cellular behaviors that underlie disease states. This approach requires high-throughput, multiplex techniques that measure quantitative temporal variations of multiple protein activities in the intracellular signaling network. Here, we describe a single microtiter-based format that simultaneously quantifies protein kinase activities in the phosphatidylinositol 3-kinase pathway (Akt), nuclear factor-kappaB pathway (IKK), and three core mitogen-activated protein kinase pathways (ERK, JNK1, MK2). These parallel high-throughput assays are stringently linear, redundantly specific, reproducible, and sensitive compared with classical low-throughput techniques. When applied to a model of sepsis-induced colon epithelial apoptosis, this approach identified a late phase of Akt activity as a critical mediator of cell survival that quantitatively contributed to the efficacy of insulin as an anti-apoptotic cue. Thus, sampling parallel nodes in the intracellular signaling network identified part of the molecular mechanism underlying the efficacy of insulin in the treatment of human sepsis.

Activation of extracellular signal-regulated kinase is involved in mechanical strain inhibition of RANKL expression in bone stromal cells

Mechanical input is known to regulate skeletal mass. In vitro, application of strain inhibits osteoclast formation by decreasing expression of the ligand RANKL in bone stromal cells, but the mechanism responsible for this down-regulation is unknown. In experiments here, application of 1.8% equibiaxial strain for 6 h reduced vitamin D-stimulated RANKL mRNA expression by nearly one-half in primary bone stromal cells. Application of strain caused a rapid activation of ERK1/2, which returned to baseline by 60 minutes. Adding the ERK1/2 inhibitor PD98059 30 minutes before strain delivery prevented the strain effect on RANKL mRNA expression, suggesting that activation of ERK1/2 was required for transduction of the mechanical force. Mechanical strain also activated N-terminal Jun kinase (JNK) that, in contrast, did not return to baseline during 24 h of continuous strain. This suggests that JNK may represent an accessory pathway for mechanical transduction in bone cells. Our data indicate that strain modulation of RANKL expression involves activation of MAPK pathways.

TNF-alpha inhibits SP-A gene expression in lung epithelial cells via p38 MAPK

Surfactant protein A (SP-A), the major lung surfactant-associated protein, mediates local defense against pathogens and modulates inflammation in the alveolus. Tumor necrosis factor (TNF)-alpha, a proinflammatory cytokine, inhibits SP-A gene expression in lung epithelial cells. Inhibitors of the phosphatidylinositol 3-kinase pathway, i.e., wortmannin, LY-294002, and rapamycin, did not block the inhibitory effects of TNF-alpha on SP-A mRNA levels. An inhibitor of the p44/42 mitogen-activated protein kinase (MAPK) pathway, PD-98059, was also ineffective. PD-169316 and SB-203580, inhibitors of p38 MAPK, blocked the TNF-alpha-mediated inhibition of SP-A mRNA levels. TNF-alpha increased the phosphorylation of p38 MAPK within 15 min. Anisomycin, an activator of p38 MAPK, increased p38 MAPK phosphorylation and decreased SP-A mRNA levels in a dose-dependent manner. Finally, TNF-alpha increased the phosphorylation of ATF-2, a transcription factor that is a p38 MAPK substrate. We conclude that TNF-alpha downregulates SP-A gene expression in lung epithelial cells via the p38 MAPK signal transduction pathway.