Role of SAPK/ERK kinase-1 in the stress-activated pathway regulating transcription factor c-Jun

Viperin mRNA is a novel target for the human RNase MRP/RNase P endoribonuclease

RNase MRP is a conserved endoribonuclease, in humans consisting of a 267-nucleotide RNA associated with 7–10 proteins. Mutations in its RNA component lead to several autosomal recessive skeletal dysplasias, including cartilage-hair hypoplasia (CHH). Because the known substrates of mammalian RNase MRP, pre-ribosomal RNA, and RNA involved in mitochondrial DNA replication are not likely involved in CHH, we analyzed the effects of RNase MRP (and the structurally related RNase P) depletion on mRNAs using DNA microarrays. We confirmed the upregulation of the interferon-inducible viperin mRNA by RNAi experiments and this appeared to be independent of the interferon response. We detected two cleavage sites for RNase MRP/RNase P in the coding sequence of viperin mRNA. This is the first study providing direct evidence for the cleavage of a mRNA by RNase MRP/RNase P in human cells. Implications for the involvement in the pathophysiology of CHH are discussed.

‘In vivo’ and ‘in vitro’ activity of Larrea divaricata Cav. on EL-4 cells

Larrea divaricata is a plant widely used in folk medicine in Argentina. It has been demonstrated that an aqueous extract of L. divaricata possesses a biphasic effect on cell proliferation, at low concentrations exerts a stimulatory action and at high concentrations exerts anti-proliferative effects upon the T lymphoma BW 5147; therefore, we propose in this paper to test the effect of the extract ‘in vitro’ and ‘in vivo’ in another T-cell lymphoma named EL-4. It was analyzed ‘in vitro’ cell proliferation by tritiated thymidine uptake and the effect of the extract on tumors induced in mice analyzing tumor progression and survival.The results showed that the aqueous extract induced the proliferation of tumor cells at all the concentrations studied. The results ‘in vivo’ showed that the aqueous extract stimulated significantly the size of tumors and that untreated mice lived longer than those treated. It is important to be very careful when plant extracts are selected for the treatment of several diseases. Consequently, before using a plant extract, specific scientific studies must be undertaken on different models to certificate therapeutic and adverse effects. Moreover, it can be said that L. divaricata has a specific anti-tumor mechanism of action depending on the targets.

Specific regulation of JNK signalling by the novel rat MKK7gamma1 isoform

The c-Jun N-terminal kinases (JNKs) mediate a diversity of physiological and pathophysiological effects. Apart from isoform-specific JNK activation, upstream kinases are supposed to be the relevant regulators, which are involved in the context- and signalosome-depending functions. In the present study we report the cloning and characterization of the novel rat MKK7gamma1, a splice variant of MKK7 with an additional exon in the N-terminal region, in the neuronal pheochromocytoma cell line PC12. Transfected MKK7gamma1 increased basal JNK activity, in particular phosphorylation of JNK2. Consequently, JNK signalling was changed in mRNA-, protein- and activation-levels of JNK targets, such as transcription factors (c-Jun, p53, c-Myc), cell cycle regulators (p21, CyclinD1) and apoptotic proteins (Fas, Bim, Bcl-2, Bcl-xl). These alterations promote the sensitivity of MKK7gamma1-transfected cells towards cell death and repress cell proliferation under normal cell growth conditions. Complexes of JIP-1, MKK7 and JNK2 were the major JNK signalosomes under basal conditions. After stimulation with taxol (5muM) and tunicamycin (1.4mug/ml), MKK7gamma1- but not MKK7beta1-transfection, reduced cell death and even increased cell proliferation. Cellular stress also led to an increased phosphorylation of JNK1 and the almost complete abrogation of complexes of JIP-1, MKK7 and JNK2 in MKK7gamma1-transfected PC12 cells. Summarizing, MKK7gamma1 affects the function and activity of individual JNK isoforms and the formation of their signalosomes. This study demonstrates for the first time that one splice-variant of MKK7 tightly controls JNK signalling and effectively adapts JNK functions to the cellular context.

Activation of ASK1, downstream MAPKK and MAPK isoforms during cardiac ischaemia

p38 MAPK is activated potently during cardiac ischaemia, although the precise mechanism by which it is activated is unclear. We used the isolated perfused rat heart to investigate the signalling pathways activated upstream of p38 during global cardiac ischaemia. Ischaemia strongly activated p38α but not the JNK pathway. The MAPKKs, MKK3, MKK4 and MKK6 have previously been identified as potential upstream activators of p38; however, in the ischaemic perfused heart, we saw activation of MKK3 and MKK6 but not MKK4. MKK3 and MKK6 showed different temporal patterns of activity, indicating distinct modes of activation and physiological function. Consistent with a lack of JNK activation, we saw no activation of MKK4 or MKK7 at any time point during ischaemia. A lack of MKK4 activation indicates, at least in the ischaemic heart, that MKK4 is not a physiologically relevant activator of p38. The MAPKKK, ASK1, was strongly activated late during ischaemia, with a similar time course to that of MKK6 and in ischaemic neonatal cardiac myocytes ASK1 expression preferentially activated MKK6 rather than MKK3. These observations suggest that during ischaemia ASK1 is coupled to p38 activation primarily via MKK6. Potent activation of ASK1 during ischaemia without JNK activation shows that during cardiac ischaemia, ASK1 preferentially activates the p38 pathway. These results demonstrate a specificity of responses seldom seen in previous studies and illustrate the benefits of using direct assays in intact tissues responding to physiologically relevant stimuli to unravel the complexities of MAPK signalling.

Signal Transduction Pathways Leading to Heat Shock Transcription

Heat shock proteins (HSP) are essential for intracellular protein folding during stress and protect cells from denaturation and aggregation cascades that can lead to cell death. HSP genes are regulated at the transcriptional level by heat shock transcription factor 1 (HSF1) that is activated by stress and binds to heat shock elements in HSP genes. The activation of HSF1 during heat shock involves conversion from an inert monomer to a DNA binding trimer through a series of intramolecular folding rearrangements. However, the trigger for HSF1 at the molecular level is unclear and hypotheses for this process include reversal of feedback inhibition of HSF1 by molecular chaperones and heat-induced binding to large non-coding RNAs. Heat shock also causes a profound modulation in cell signaling pathways that lead to protein kinase activation and phosphorylation of HSF1 at a number of regulatory serine residues. HSP genes themselves exist in an accessible chromatin conformation already bound to RNA polymerase II. The RNA polymerase II is paused on HSP promoters after transcribing a short RNA sequence proximal to the promoter. Activation by heat shock involves HSF1 binding to the promoter and release of the paused RNA polymerase II followed by further rounds of transcriptional initiation and elongation. HSF1 is thus involved in both initiation and elongation of HSP RNA transcripts. Recent studies indicate important roles for histone modifications on HSP genes during heat shock. Histone modification occurs rapidly after stress and may be involved in promoting nucleosome remodeling on HSP promoters and in the open reading frames of HSP genes. Understanding these processes may be key to evaluating mechanisms of deregulated HSP expression that plays a key role in neurodegeneration and cancer.

Cytosolic Hsp60 is involved in the NF-kappaB-dependent survival of cancer cells via IKK regulation

Cytoplasmic presence of Hsp60, which is principally a nuclear gene-encoded mitochondrial chaperonin, has frequently been stated, but its role in intracellular signaling is largely unknown. In this study, we demonstrate that the cytosolic Hsp60 promotes the TNF-alpha-mediated activation of the IKK/NF-kappaB survival pathway via direct interaction with IKKalpha/beta in the cytoplasm. Selective loss or blockade of cytosolic Hsp60 by specific antisense oligonucleotide or neutralizing antibody diminished the IKK/NF-kappaB activation and the expression of NF-kappaB target genes, such as Bfl-1/A1 and MnSOD, which thus augmented intracellular ROS production and ASK1-dependent cell death, in response to TNF-alpha. Conversely, the ectopic expression of cytosol-targeted Hsp60 enhanced IKK/NF-kappaB activation. Mechanistically, the cytosolic Hsp60 enhanced IKK activation via upregulating the activation-dependent serine phosphorylation in a chaperone-independent manner. Furthermore, transgenic mouse study showed that the cytosolic Hsp60 suppressed hepatic cell death induced by diethylnitrosamine in vivo. The cytosolic Hsp60 is likely to be a regulatory component of IKK complex and it implicates the first mitochondrial factor that regulates cell survival via NF-kappaB pathway.

A kinematic model coupling stress fiber dynamics with JNK activation in response to matrix stretching

The role of the actin cytoskeleton in regulating mechanotransduction in response to external forces is complex and incompletely understood. Here, we develop a mathematical model coupling the dynamic disassembly and reassembly of actin stress fibers and associated focal adhesions to the activation of c-jun N-terminal kinase (JNK) in cells attached to deformable matrices. The model is based on the assumptions that stress fibers are pre-extended to a preferred level under static conditions and that perturbations from this preferred level destabilize the stress fibers. The subsequent reassembly of fibers upregulates the rate of JNK activation as a result of the formation of new integrin bonds within the associated focal adhesions. Numerical solutions of the model equations predict that different patterns of matrix stretch result in distinct temporal patterns in JNK activation that compare well with published experimental results. In the case of cyclic uniaxial stretching, stretch-induced JNK activation slowly subsides as stress fibers gradually reorient perpendicular to the stretch direction. In contrast, JNK activation is chronically elevated in response to cyclic equibiaxial stretch. A step change in either uniaxial or equibiaxial stretch results in a short, transient upregulation in JNK that quickly returns to the basal level as overly stretched stress fibers disassemble and are replaced by fibers assembled at the preferred level of stretch. In summary, the model describes a mechanism by which the dynamic properties of the actin cytoskeleton allow cells to adapt to applied forces through turnover and reorganization to modulate intracellular signaling.

The C-terminal domain of Mnk1a plays a dual role in tightly regulating its activity

The human family of MAPK (mitogen-activated protein kinase) signal-integrating kinases (Mnks) comprises four related proteins derived from two genes by alternative splicing. The MNK1 gene gives rise to two proteins, Mnk1a and Mnk1b, which possess distinct C-termini and properties. Despite lacking the C-terminal MAPK-binding site, Mnk1b shows higher basal activity than Mnk1a. In contrast, the activity of Mnk1a is tightly regulated by signalling through ERK (extracellular-signal-regulated kinase) and p38 MAPK. We show that the short C-terminus of Mnk1b confers on it a 'default' behaviour of substantial, but unregulated, activity. In contrast, the longer C-terminus of Mnk1a represses the basal activity and T (activation)-loop phosphorylation of this isoenzyme while allowing both properties to be stimulated by upstream MAPK signalling. Two features of the C-terminus of Mnk1a appear to account for this behaviour: the known MAPK-binding site and a region (predicted to be alpha-helical) which occludes access to the catalytic domain and the T-loop. The activation of Mnk1a results in a marked conformational change leading to a more 'open' structure. We also identified a conserved phenylalanine residue in an Mnk-specific insert as playing a key role in governing the ease with which Mnk1a can be phosphorylated. These studies help to identify the features that give rise to the diverse properties of human Mnk isoforms.

Androgen via p21 inhibits tumor necrosis factor alpha-induced JNK activation and apoptosis

The male hormone androgen is a growth/survival factor for its target tissues or organs. Yet, the underlying mechanism is incompletely understood. Here, we report that androgen via p21 inhibits tumor necrosis factor alpha-induced JNK activation and apoptosis. Inhibition by androgen requires the transcription activity of androgen receptor (AR) and de novo protein synthesis. Androgen.AR induces expression of p21 that in turn inhibits tumor necrosis factor alpha-induced JNK and apoptosis. Furthermore, genetic interruption of p21 alleles abolishes the inhibition by androgen. Our results reveal a novel cross-talk between androgen x AR and JNK, thereby providing a molecular mechanism underlying the survival function of androgen.

Activation of JNK and PAK2 is essential for citrinin-induced apoptosis in a human osteoblast cell line

The mycotoxin citrinin (CTN), a natural contaminant in foodstuffs and animal feeds, exerts cytotoxic and genotoxic effects on various mammalian cells. CTN causes cell injury, including apoptosis. Previous studies by our group showed that CTN triggers apoptosis in mouse embryonic stem cells, as well as embryonic developmental injury. Here, we investigated the precise mechanisms governing this apoptotic effect in osteoblasts. CTN induced apoptotic biochemical changes in a human osteoblast cell line, including activation of c-Jun N-terminal kinase (JNK), loss of mitochondrial membrane potential, and caspase-3 and p21-activated protein kinase 2 (PAK2) activation. Experiments using a JNK-specific inhibitor, SP600125, and antisense oligonucleotides against JNK reduced CTN-induced activation of both JNK and caspase-3 in osteoblasts, indicating that JNK is required for caspase activation in this apoptotic pathway. Experiments using caspase-3 inhibitors and antisense oligonucleotides against PAK2 revealed that active caspase-3 is essential for PAK2 activation. Moreover, both caspase-3 and PAK2 require activation for CTN-induced apoptosis of osteoblasts. Interestingly, CTN stimulates two-stage activation of JNK in human osteoblasts. Early-stage JNK activation is solely ROS-dependent, whereas late-stage activation is dependent on ROS-mediated caspase activity, and regulated by caspase-induced activation of PAK2. On the basis of these results, we propose a signaling cascade model for CTN-induced apoptosis in human osteoblasts involving ROS, JNK, caspases, and PAK2.

The pathology and genetics of metastatic pancreatic cancer

CONTEXT

Metastatic disease is the most critical determinant of resectability of pancreatic cancer and accounts for the poor outcome of patients with this disease. Thus, a better understanding of metastatic pancreatic cancer will afford new opportunities for therapeutic intervention.

OBJECTIVE

To summarize and discuss the current understanding of the clinical and molecular features of metastatic pancreatic cancer.

DATA SOURCES

Published literature on advanced stage pancreatic cancer, pancreatic cancer metastasis, and autopsy findings in patients with pancreatic cancer.

CONCLUSIONS

In the clinical setting, it can be difficult to distinguish a metastatic pancreatic carcinoma from primary neoplasms in the liver, lung, or ovary. However, immunolabeling for DPC4 protein as part of a diagnostic panel is useful for making this distinction. Emerging data from a variety of investigators now indicate that overexpression of EphA2, loss of DPC4 and MKK4, and aberrant activation of the Hedgehog signaling pathway are associated with metastatic propensity of pancreatic cancers, providing novel therapeutic targets for the most lethal stage of this disease.

DAZAP1 interacts via its RNA-recognition motifs with the C-termini of other RNA-binding proteins

The turnover and translation of many human mRNAs is regulated by AU-rich elements present in their 3?untranslated region, which bind various trans acting factors. We previously identified a trans acting factor that interacts with these cis elements as DAZAP1 (deleted in Azoospermia (DAZ)-Associated Protein 1), whose interaction with the germ cell-specific protein DAZ was disrupted by the phosphorylation of DAZAP1. Here we have identified several other RNA-binding proteins as binding partners for DAZAP1 in non-germinal cells. Unlike DAZ, these interactions occur between the RNA recognition motifs of DAZAP1 and the C-termini of the binding partners and in a phosphorylation-independent manner. The results suggest that DAZAP1 is a component of complexes that are crucial for the degradation and silencing of mRNA.

JNK1 regulates histone acetylation in trigeminal neurons following chemical stimulation

Trigeminal nerve fibers in nasal and oral cavities are sensitive to various environmental hazardous stimuli, which trigger many neurotoxic problems such as chronic migraine headache and trigeminal irritated disorders. However, the role of JNK kinase cascade and its epigenetic modulation of histone remodeling in trigeminal ganglion (TG) neurons activated by environmental neurotoxins remains unknown. Here we investigated the role of JNK/c-Jun cascade in the regulation of acetylation of H3 histone in TG neurons following in vitro stimulation by a neuro-inflammatory agent, mustard oil (MO). We found that MO stimulation elicited JNK/c-Jun pathway significantly by enhancing phospho-JNK1, phospho-c-Jun expression, and c-Jun activity, which were correlated with an elevated acetylated H3 histone in TG neurons. However, increases in phospho-c-Jun and c-Jun activity were significantly blocked by a JNK inhibitor, SP600125. We also found that altered H3 histone remodeling, assessed by H3 acetylation in triggered TG neurons, was reduced by SP600125. The study suggests that the activated JNK signaling in regulation of histone remodeling may contribute to neuro-epigentic changes in peripheral sensory neurons following environmental neurotoxic exposure.

Prostaglandin F2alpha inhibits SERCA2 gene transcription through an induction of Egr-1 in cultured neonatal rat cardiac myocytes

Prostaglandin F(2alpha) (PGF(2alpha)) stimulates hypertrophic growth of neonatal rat cardiac myocytes, a feature of which includes downregulation of the Ca(2+)-ATPase (SERCA2), a major Ca(2+) transport protein in SR. The molecular mechanisms by which PGF(2alpha) inhibits SERCA2 gene expression remain unknown. We determined the cis-regulatory elements responsible for the regulation of the SERCA2 gene expression in cultured neonatal rat cardiac myocytes exposed to PGF(2alpha). The role of Egr-1 was evaluated by transient transfection of its expression vector and antisense oligonucleotide. Signaling pathways were determined by using the pharmacological inhibitors or cDNA expression plasmids coding for dominant negative forms of Ras and Rac. PGF(2alpha) reduced the SERCA2 mRNA levels in a time- and dose-dependent manner in cultured rat cardiac myocytes. Transient transfection analyses showed that PGF(2alpha) -responsive elements are located between -284 and -72 of the SERCA2 promoter, which contains G+C-rich sequences homologous to Sp1, Egr-1 and AP2-binding sites. PGF(2alpha) significantly increased Egr-1 expression, and overexpression of Egr-1 largely reduced the transcription of the SERCA2 gene. Egr-1 antisense oligonucleotides blocked the PGF(2alpha) -mediated decrease in SERCA2 mRNA expression. Furthermore, inhibitors for either genistein-sensitive tyrosine kinase or p38 MAPK, and dominant negative forms of either Ras or Rac, prevented PGF(2alpha) -induced repression of SERCA2 mRNA levels. These results suggest that Egr-1, as well as Ras, Rac, and p38 MAPK, plays a crucial role in the repression of SERCA2 gene expression during PGF(2alpha) -induced cardiac hypertrophy.

Are MAP kinases drug targets? Yes, but difficult ones

Pharmaceutical companies are facing an increasing interest in new target identification and validation. In particular, extensive efforts are being made in the field of protein kinase inhibitors research and development, and the past ten years of effort in this field have altered our perception of the potential of kinases as drug targets. Therefore, in the drug discovery process, the selection of relevant, susceptible protein kinase targets combined with searches for leads and candidates have become a crucial approach. The success of recent launches of protein kinase inhibitors (Gleevec, Imatinib, Sutent, Iressa, Nexavar, Sprycel) gave another push to this field. Numerous other kinase inhibitors are currently undergoing clinical trials or clinical development. Some questions are nevertheless unanswered, mostly related to the great number of known kinases in the human genome, to their similarity with each other, to the existence of functionally redundant kinases for specific pathways, and also because the connection between particular pathways and diseases is not always clear. The review is leading the reader through a panoramic view of protein kinase inhibition with a major focus on MAPK, successful examples and clinical candidates.

Mitogen-activated protein kinase kinase 4/c-Jun NH2-terminal kinase kinase 1 protein expression is subject to translational regulation in prostate cancer cell lines

Mitogen-activated protein kinase kinase 4/c-Jun NH(2)-terminal kinase kinase 1 (MKK4/JNKK1; hereafter referred to as MKK4) is a dual-specificity kinase with a critical role in regulating the activity of c-Jun NH(2)-terminal kinase and p38 kinases. We identified a novel biological function for MKK4 in the regulation of growth of ovarian and prostate cancer metastases. Clinical correlative studies showed that MKK4 protein levels were reduced in high-grade prostate cancer and prostate and ovarian cancer metastases compared with normal tissue, which prompted investigation into the mechanism(s) responsible for down-regulation of MKK4 in a panel of cancer cell lines. Initial studies found that low levels of MKK4 protein did not correlate with either exon deletion or decreased levels of MKK4 mRNA, suggesting that MKK4 protein levels were regulated posttranscriptionally by either reduced translation or reduced protein stability. Endogenous MKK4 was highly stable and not subject to altered proteolysis. Instead, MKK4 biosynthesis seemed to be regulated by altered translation. In support of this assertion, we found that cytosolic MKK4 mRNA was shifted toward active polysomes in cells with higher levels of MKK4 protein, suggesting that MKK4 mRNA was translated more efficiently in these cells. This study supports a novel mechanism for the regulation of MKK4 protein levels. Further, these findings have potential therapeutic implications for modulating the expression of a signaling kinase involved in the regulation of metastatic growth.

Citrinin induces apoptosis in mouse embryonic stem cells

The mycotoxin citrinin (CTN) is a natural contaminant in foodstuffs and animal feeds, and exerts cytotoxic and genotoxic effects on various mammalian cells. CTN causes cell injury, including apoptosis. However, its precise regulatory mechanisms of action, particularly in stem cells and embryos, are currently unclear. Recent studies show that CTN has cytotoxic effects on mouse embryonic stem cells and blastocysts, and is associated with defects in their subsequent development, both in vitro and in vivo. Experiments with the embryonic stem cell line, ESC-B5, disclose that CTN induces apoptosis via several mechanisms, including ROS generation, increased cytoplasmic free calcium levels, intracellular nitric oxide production, enhanced Bax/Bcl-2 ratio, loss of mitochondrial membrane potential, cytochrome c release, activation of caspase-9 and caspase-3, and p21-activated protein kinase 2 and c-Jun N-terminal protein kinase activation. Additional studies show that CTN promotes cell death via inactivation of the HSP90/multi-chaperone complex and subsequent degradation of Ras and Raf-1, further inhibiting anti-apoptotic processes such as the Ras-->ERK signal transduction pathway. On the basis of these findings, we propose a model for CTN-induced cell injury signalling cascades in embryonic stem cells and blastocysts.

All JNKs can kill, but nuclear localization is critical for neuronal death

JNKs are implicated in a range of brain pathologies and receive considerable attention as potential therapeutic targets. However, JNKs also regulate physiological and homeostatic processes. An attractive hypothesis from the drug development perspective is that distinct JNK isoforms mediate "physiological" and "pathological" responses. However, this lacks experimental evaluation. Here we investigate the isoforms, subcellular pools, and c-Jun/ATF2 targets of JNK in death of central nervous system neurons following withdrawal of trophic support. We use gene knockouts, gene silencing, subcellularly targeted dominant negative constructs, and pharmacological inhibitors. Combined small interfering RNA knockdown of all JNKs 1, 2, and 3, provides substantial neuroprotection. In contrast, knockdown or knock-out of individual JNKs or two JNKs together does not protect. This explains why the evidence for JNK in neuronal death has to date been largely pharmacological. Complete knockdown of c-Jun and ATF2 using small interfering RNA also fails to protect, casting doubt on c-Jun as a critical effector of JNK in neuronal death. Nonetheless, the death requires nuclear but not cytosolic JNK activity as nuclear dominant negative inhibitors of JNK protect, whereas cytosolic inhibitors only block physiological JNK function. Thus any one of the three JNKs is capable of mediating apoptosis and inhibition of nuclear JNK is protective.

Gene expression in human NAFLD

Despite the high prevalence of nonalcoholic fatty liver disease (NAFLD), little is known of its pathogenesis based on study of human liver samples. By the use of Affymetrix GeneChips (17,601 genes), we investigated gene expression in the human liver of subjects with extreme steatosis due to NAFLD without histological signs of inflammation (liver fat 66.0 +/- 6.8%) and in subjects with low liver fat content (6.4 +/- 2.7%). The data were analyzed by using sequence-based reannotation of Affymetrix probes and a robust model-based normalization method. We identified genes involved in hepatic glucose and lipid metabolism, insulin signaling, inflammation, coagulation, and cell adhesion to be significantly associated with liver fat content. In addition, genes involved in ceramide signaling (MAP2K4) and metabolism (UGCG) were found to be positively associated with liver fat content. Genes involved in lipid metabolism (PLIN, ACADM), fatty acid transport (FABP4, CD36), amino acid catabolism (BCAT1), and inflammation (CCL2) were validated by real-time PCR and were found to be upregulated in subjects with high liver fat content. The data show that multiple changes in gene expression characterize simple steatosis.

The detection of MAPK signaling

Mitogen-activated protein kinase (MAPK) cascades are central pathways that participate in the intracellular transmission of extracellular signals. Each of the MAPK signaling cascades seems to consist of three to five tiers of protein kinases that sequentially activate each other by phosphorylation. Since the majority of MAPK cascade components are kinases, the methods used to detect their activation involve determining phosphorylation state and protein kinase activities. The primary method describes the use of immunoblotting with specific anti-phospho antibody to detect activation of MAPK components. Alternative methods described are immunoprecipitation of desired protein kinases followed by phosphorylation of specific substrates and the use of an in-gel kinase assay. These methods have proven useful in the study of the MAPK signaling cascades.

The detection of MAPK signaling

Mitogen-activated protein kinase (MAPK) cascades are central pathways that participate in the intracellular transmission of extracellular signals. Each of the MAPK signaling cascades seems to consist of three to five tiers of protein kinases that sequentially activate each other by phosphorylation. Since the majority of MAPK cascade components are kinases, the methods used to detect their activation involve determining phosphorylation state and protein kinase activities. The Basic Protocol describes the use of immunoblotting with specific anti-phospho antibody to detect activation of MAPK components. Alternative methods described are immunoprecipitation of desired protein kinases followed by phosphorylation of specific substrates and the use of an in-gel kinase assay. These methods have proven useful in the study of the MAPK signaling cascades.

ZNF418, a novel human KRAB/C2H2 zinc finger protein, suppresses MAPK signaling pathway

Cardiac differentiation involves a cascade of coordinated gene expression that regulates cell proliferation and matrix protein formation in a defined temporal-spatial manner. Zinc finger-containing transcription factors have been implicated as critical regulators of multiple cardiac-expressed genes, and are thought to be important for human heart development and diseases. Here, we have identified and characterized a novel zinc finger gene named ZNF418 from a human embryo heart cDNA library. The gene spans 13.5 kb on chromosome 19q13.43 encompassing six exons, and transcribes a 3.7-kb mRNA that encodes a protein with 676 amino acid residues. The predicted protein contains a KRAB-A box and 17 tandem C2H2 type zinc finger motifs. Northern blot analysis indicates that ZNF418 is expressed in multiple fetal and adult tissues, but is expressed at higher levels in the heart. Reporter gene assays show that ZNF418 is a transcriptional repressor, and the KRAB motif of ZNF418 represents the basal repressive domain. Overexpression of ZNF418 in COS-7 cells inhibits the transcriptional activity of SRE and AP-1 which may be silenced by siRNA. These results suggest that ZNF418 is a member of the zincfinger transcription factor family and may act as a negative regulator in MAPK signaling pathway.

AMP-activated protein kinase subunit interactions: beta1:gamma1 association requires beta1 Thr-263 and Tyr-267

AMP-activated protein kinase (AMPK) plays multiple roles in the body's overall metabolic balance and response to exercise, nutritional stress, hormonal stimulation, and the glucose-lowering drugs metformin and rosiglitazone. AMPK consists of a catalytic alpha subunit and two non-catalytic subunits, beta and gamma, each with multiple isoforms that form active 1:1:1 heterotrimers. Here we show that recombinant human AMPK alpha1beta1gamma1 expressed in insect cells is monomeric and displays specific activity and AMP responsiveness similar to rat liver AMPK. The previously determined crystal structure of the core of mammalian alphabetagamma complex shows that beta binds alpha and gamma. Here we show that a beta1(186-270)gamma1 complex can form in the absence of detectable alpha subunit. Moreover, using alanine mutagenesis we show that beta1 Thr-263 and Tyr-267 are required for betagamma association but not alphabeta association.

Pyruvate kinase isozyme type M2 (PKM2) interacts and cooperates with Oct-4 in regulating transcription

The Oct-4 gene encodes a transcription factor that plays an important role in maintaining the pluripotent state of embryonic stem cells and may prevent expression of genes activated during differentiation. Although its role in maintaining embryonic stem cell pluripotency is well established, there is still little known about the binding partners that regulate its function. To identify proteins that control Oct-4 function, we used affinity chromatography on immobilized Oct-4 (POU) together with MALDI-TOF (matrix-assisted laser-desorption ionization-time-of-flight) MS (mass spectrometry) and isolated a novel Oct-4-interacting protein, pyruvate kinase type M2 (PKM2 or M2-PK). PKM2 is an isozyme of pyruvate kinase that is specifically expressed in proliferating cells, such as embryonic stem cells, embryonic carcinoma cells, as well as cancer cells. Oct-4 and PKM2 were co-affinity precipitated from cell extracts, and glutathione S-transferase pull-down assays revealed that the POU DNA binding domain of Oct-4 was required for interaction with PKM2. In addition, the C-terminal domain of PKM2 (amino acids 307-531) was involved in binding to Oct-4. Moreover, ectopic expression of the PKM2 enhanced Oct-4-mediated transcription. These observations indicate that the transactivation potential of the Oct-4 transcription factor is positively modulated by PKM2.

Programmed cell death and differential JNK, p38 and ERK response in a prenatal acute hypoxic hypoxia model

We previously found that prenatal hypoxia induces a significant increase in the levels of active Caspase 3 at 60 min post-hypoxia (p-h) and in the number of TUNEL-positive pyknotic cells, which peaks at 6h p-h. The aim of this work was to study alterations in MAPKs pathways and the effect of specific inhibitors of the JNK (SP600125) and p38 (SB203580) pathways following acute hypoxia in chick optic lobe at embryonic day (ED) 12. To this end, JNK, p38 and ERK1-2 protein kinase expression levels were determined by Western blot in both their active and inactive forms, evaluated at successive p-h times. At 10 and 30 min p-h the P-JNK/JNK ratio was 1.912+/-0.341 and 1.920+/-0.304, respectively. Concomitantly, at 0 min p-h the P-p38/p38 ratio was 1.657+/-0.203. Lastly, the P-ERK/ERK ratio proving non-significant throughout. When inhibitors for JNK and p38 were used, we observed a decrease in the values of active Caspase 3 at 60 min p-h, which correlated with the control values in the parameters of TUNEL-positive cells at 6h p-h. Analysis for P-ATF-2 demonstrated an increase in hypoxic embryos compared to control ones which was reverted in a dose-dependent manner with the use of both inhibitors. All these results indicate that at ED 12, acute hypoxia might be differentially activating JNK and p38 pathways, without affecting the ERK pathway, which in turn would be activating Caspase 3, thus leading to cell death by apoptosis. Furthermore, JNK and p38 activation precede in time the programmed cell death induced by hypoxia.

MLH1- and ATM-dependent MAPK signaling is activated through c-Abl in response to the alkylator N-methyl-N'-nitro-N'-nitrosoguanidine

N-Methyl-N'-nitro-N'-nitrosoguanidine (MNNG) is a DNA-methylating agent, and deficiency in mismatch repair (MMR) results in lack of sensitivity to this genotoxin (termed alkylation tolerance). A number of DNA damage response pathways are activated in a MMR-dependent manner following MNNG, and several also require ATM kinase activity. Here we show that activation of the transcription factor c-Jun is dependent upon both the MMR component MLH1 and ATM, but not ATR, in response to MNNG. In addition to c-Jun, the upstream MAPKs JNK and MKK4 are also activated in a MLH1- and ATM-dependent manner. We document that c-Jun activation is dependent on the MAPK kinase kinase MEKK1. Additionally, the tyrosine kinase c-Abl is required to activate this signaling cascade and forms a complex with MEKK1 and MLH1. This study indicates that an arm of DNA damage-activated MAPK signaling is activated in an MLH1- and ATM-dependent manner in response to MNNG and perhaps suggests that dysregulation of this signaling is responsible, in part, for alkylation tolerance.

Feedback regulation of p38 activity via ATF2 is essential for survival of embryonic liver cells

The ATF2 transcription factor is phosphorylated by the stress-activated mitogen-activated protein kinases (MAPKs) JNK and p38. We show that this phosphorylation is essential for ATF2 function in vivo, since a mouse carrying mutations in the critical phosphorylation sites has a strong phenotype identical to that seen upon deletion of the DNA-binding domain. In addition, combining this mutant with a knockout of the ATF2 homolog, ATF7, results in embryonic lethality with severe abnormalities in the developing liver and heart. The mutant fetal liver is characterized by high levels of apoptosis in developing hepatocytes and haematopoietic cells. Furthermore, we observe a significant increase in active p38 due to loss of a negative feedback loop involving the ATF2-dependent transcriptional activation of MAPK phosphatases. In embryonic liver cells, this increase drives apoptosis, since it can be suppressed by chemical inhibition of p38. Our findings demonstrate the importance of finely regulating the activities of MAPKs during development.

c-Jun NH2-terminal kinase 1 plays a critical role in intestinal homeostasis and tumor suppression

The c-Jun NH(2)-terminal kinase (JNK) signal transduction pathway plays important roles in cellular processes and stress. However, the role of JNK1 in intestinal homeostasis and tumorigenesis is unknown. Therefore, we used a JNK1 knockout mouse model to characterize intestinal cell maturation and tumorigenesis. In addition, colon cancer cell lines were used to validate the role of JNK1 and to elucidate the underlying molecular mechanisms in vitro. To our surprise, we found that mice with targeted inactivation of JNK1 spontaneously developed intestinal tumors. The normal mucosa in JNK1-deficient mice showed decreased cell differentiation and increased cell proliferation. This tumorigenesis was closely linked to the down-regulation of p21(WAF1/cip1), a cyclin-dependent kinase inhibitor, in intestinal epithelial cells. Immunohistochemical staining showed that JNK1 was highly expressed in the differentiation compartment of the intestinal mucosa and that the expression of JNK1 was significantly decreased in both human colonic and mouse intestinal tumors. In the colon cancer cell lines, JNK1 expression was up-regulated during spontaneous differentiation, corresponding to the up-regulation of p21(WAF1/cip1). Moreover, butyrate-induced p21 expression was linked to phosphorylation of JNK1. Reduced JNK1 expression by small interfering RNA suppressed butyrate-induced apoptosis. We concluded that JNK1 plays a critical role in the regulation of homeostasis and in the suppression of tumor formation in the intestine, which was linked to the altered expression of p21(WAF1/cip1).

Targeted Deletion of MKK4 Gene Potentiates TNF-Induced Apoptosis through the Down-Regulation of NF-κB Activation and NF-κB-Regulated Antiapoptotic Gene Products

MAPK kinase 4 (MKK4) is a dual-specificity kinase that activates both JNK and p38 MAPK. However, the mechanism by which MKK4 regulates TNF-induced apoptosis is not fully understood. Therefore, we used fibroblasts derived from MKK4 gene-deleted (MKK4-KO) mice to determine the role of this kinase in TNF signaling. We found that when compared with the wild-type cells, deletion of MKK4 gene enhanced TNF-induced apoptosis, and this correlated with down-regulation of TNF-induced cell-proliferative (COX-2 and cyclin D1) and antiapoptotic (survivin, IAP1, XIAP, Bcl-2, Bcl-x(L), and cFLIP) gene products, all regulated by NF-kappaB. Indeed we found that TNF-induced NF-kappaB activation was abrogated in MKK4 gene-deleted cells, as determined by DNA binding. Further investigation revealed that TNF-induced I kappaB alpha kinase activation, I kappaB alpha phosphorylation, I kappaB alpha degradation, and p65 nuclear translocation were all suppressed in MKK4-KO cells. NF-kappaB reporter assay revealed that NF-kappaB activation induced by TNF, TNFR1, TRADD, TRAF2, NIK, and I kappaB alpha kinase was modulated in gene-deleted cells. Overall, our results indicate that MKK4 plays a central role in TNF-induced apoptosis through the regulation of NF-kappaB-regulated gene products.

Gliotoxin causes apoptosis and necrosis of rat Kupffer cells in vitro and in vivo in the absence of oxidative stress: exacerbation by caspase and serine protease inhibition

BACKGROUND/AIMS

A potential application of gliotoxin therapy for liver fibrosis was suggested by its apoptotic effect on fibrogenic activated stellate cells. We investigated if gliotoxin exerts similar effects on hepatic macrophage Kupffer cells.

METHODS

Effects of gliotoxin on Kupffer cells isolated from the normal liver and in vivo following its administration to CCl(4)-induced cirrhotic rats were studied.

RESULTS

Gliotoxin caused apoptosis of cultured Kupffer cells, the effect being apparent at 0.3 microM concentration within 1h; longer incubation caused necrosis. This effect was associated with mitochondrial cytochrome c release, caspase-3 activation and ATP depletion. Interestingly, inhibition of caspase-3 and serine proteases accelerated and augmented gliotoxin-induced cell death via necrosis. Gliotoxin stimulated nuclear translocation of NFkappaB, and phosphorylation of p38, ERK1/2 and JNK MAP kinases, but these signaling molecules were not involved in gliotoxin-induced death of Kupffer cells. In vivo administration of gliotoxin to cirrhotic rats caused apoptosis of Kupffer cells, stellate cells and hepatocytes. In control rats, the effect was minimal on the nonparenchymal cells and not apparent on hepatocytes.

CONCLUSIONS

In the fibrotic liver, gliotoxin nonspecifically causes death of hepatic cell types. Modification of gliotoxin molecule may be necessary for selective targeting and elimination of activated stellate cells.

Wiring the cell signaling circuitry by the NF-kappa B and JNK1 crosstalk and its applications in human diseases

Integration of the cell signaling circuitry determines the ultimate response of a cell to extracellular stimuli. The transcription factor nuclear factor-kappa B (NF-kappaB) and mitogen-activated protein kinase JNK1 are major players in the cell signaling circuitry, regulating numerous cellular events and being implicated in the process of many human diseases and certain types of cancer. The interplay between NF-kappaB and JNK1 provides a paradigm that shows how the crosstalk between different signaling pathways decides the function of the cell signaling circuitry. Understanding the wiring of the cell signaling circuitry may hold the key for cell signaling-based therapy of human diseases.

Role of mitogen-activated protein kinase kinase 4 in cancer

Mitogen-activated protein (MAP) kinase kinase 4 (MKK4) is a component of stress activated MAP kinase signaling modules. It directly phosphorylates and activates the c-Jun N-terminal kinase (JNK) and p38 families of MAP kinases in response to environmental stress, pro-inflammatory cytokines and developmental cues. MKK4 is ubiquitously expressed and the targeted deletion of the Mkk4 gene in mice results in early embryonic lethality. Further studies in mice have indicated a role for MKK4 in liver formation, the immune system and cardiac hypertrophy. In humans, it is reported that loss of function mutations in the MKK4 gene are found in approximately 5% of tumors from a variety of tissues, suggesting it may have a tumor suppression function. Furthermore, MKK4 has been identified as a suppressor of metastasis of prostate and ovarian cancers. However, the role of MKK4 in cancer development appears complex as other studies support a pro-oncogenic role for MKK4 and JNK. Here we review the biochemical and functional properties of MKK4 and discuss the likely mechanisms by which it may regulate the steps leading to the formation of cancers.

Negative regulation of SEK1 signaling by serum- and glucocorticoid-inducible protein kinase 1

Serum- and glucocorticoid-inducible protein kinase 1 (SGK1) has been implicated in diverse cellular activities including the promotion of cell survival. The molecular mechanism of the role of SGK1 in protection against cellular stress has remained unclear, however. We have now shown that SGK1 inhibits the activation of SEK1 and thereby negatively regulates the JNK signaling pathway. SGK1 was found to physically associate with SEK1 in intact cells. Furthermore, activated SGK1 mediated the phosphorylation of SEK1 on serine 78, resulting in inhibition of the binding of SEK1 to JNK1, as well as to MEKK1. Replacement of serine 78 of SEK1 with alanine abolished SGK1-mediated SEK1 inhibition. Oxidative stress upregulated SGK1 expression, and depletion of SGK1 by RNA interference potentiated the activation of SEK1 induced by oxidative stress in Rat2 fibroblasts. Moreover, such SGK1 depletion prevented the dexamethasone-induced increase in SGK1 expression, as well as the inhibitory effects of dexamethasone on paclitaxel-induced SEK1-JNK signaling and apoptosis in MDA-MB-231 breast cancer cells. Together, our results suggest that SGK1 negatively regulates stress-activated signaling through inhibition of SEK1 function.

Deletion of the c-Jun N-terminal kinase 3 gene protects neonatal mice against cerebral hypoxic-ischaemic injury

c-Jun N-terminal kinase 3 (JNK3) is a member of the stress-activated group of mitogen-activated protein kinases. c-Jun N-terminal kinase 3 is a potent mediator of apoptosis and the use of JNK inhibitors or jnk3 gene deletion each protect against brain injury in adults. However, little is known about the role of JNK3 or its mechanism of action in neonatal brain injury. The aim of the present study was to compare the vulnerability of neonatal JNK3 knockout (JNK3 KO) mice and wild-type (WT) mice to cerebral hypoxic-ischaemic injury (HII) using unilateral-carotid occlusion combined with transient hypoxia. The degree of neural tissue loss in JNK3 KO mice was substantially reduced compared with WT mice (JNK3 KO 27.8%+/-2.8% versus WT 48.3%+/-2.0%, P<or=0.0001) after HII. Significant attenuation of injury was observed in the cerebral cortex, hippocampus, striatum, and thalamus of JNK3 KO compared with WT mice. Hypoxic-ischaemic injury increased JNK phosphorylation and activity, with JNK3 as the major isoform. Significantly, in JNK3 KO animals there was no difference in the activation of the upstream kinases mitogen-activated protein kinase kinase (MKK4) or MKK7. Downstream of JNK3, HII lead to increased phosphorylation of the transcription factors c-Jun and adenovirus transcription factor-2 (ATF-2), which was attenuated in JNK3 KO mice. c-Jun N-terminal kinase 3 deletion also decrease caspase-3 cleavage and Bim/PUMA expression, coupled with a upregulation of AKT/FOXO3a levels, linking JNK3 to apoptosis. These findings implicate JNK3 involvement in neural cell loss resulting from cerebral HII in the developing brain.

Different approaches to study mast cell functions

Mast cells have long been known to play a detrimental role in the pathogenesis of IgE-associated allergic disorders by their ability to release a wide variety of pro-inflammatory mediators. A number of studies, however, have demonstrated that mast cells play a beneficial role in innate host defense against bacterial infections. Since mast cells clearly play both physiological and pathophysiological functions in the body, it is important to learn about the components of mast cells that drive these responses. The functional roles of mast cell in vivo have been principally characterized by comparing the biological responses in mast cell-deficient mice (WBB6F(1)-W/W(v)), their normal wild-type littermates (WBB6F(1)-+/+) and mast cell deficient mice reconstituted locally or systemically with mast cells cultured from the bone marrow cells of WBB6F(1)-+/+ mice (WBB6F(1)-W/W(v)+MC). Recently investigators have demonstrated that mast cell-deficient mice (WBB6F(1)-W/W(v)) can be reconstituted with mast cells derived in vitro from the bone marrow cells of certain gene knock-out mice or genetically-manipulated embryonic stem cells. This novel approach of analyzing the biological consequences of gene mutations in mast cells will help us to better understand the role of individual gene products in mast cell responses. In this review, we discuss these new approaches to investigate the functions of mast cells in vivo.

Melphalan reduces the severity of experimental colitis in mice by blocking tumor necrosis factor-alpha signaling pathway

Melphalan is an alkylating agent, which is commonly used as an antineoplastic drug. Its cytostatic effect can be realized in humans in the dose range of 0.6-1.4 mg/kg body weight. However, previously it was shown that in the case of gradual dose decrease, the number of targets for alkylation was also reduced and the drug lost its cytostatic properties switching to cell growth modifier. It has been postulated that application of alkylating agents in such ultra-low concentrations (50- to 100-fold lower than cytostatic ones) may result in a beneficial effect in the therapy of diseases associated with mucosa inflammation. The aim of the article was to investigate the effect of ultra-low doses of melphalan in the murine experimental colitis induced by the replacement of drinking water with 5% solution of dextran sulphate sodium (DSS). Daily administration of melphalan (25 microg/kg body weight) markedly reduced the severity of DSS-colitis as determined by clinical and quantitative histological criteria. Both systemic and local anti-inflammatory effects of melphalan have been observed. The possible mechanisms of the beneficial effect of the drug have been discussed.

Hypotonicity stimulates renal epithelial sodium transport by activating JNK via receptor tyrosine kinases

We previously reported that hypotonic stress stimulated transepithelial Na(+) transport via a pathway dependent on protein tyrosine kinase (PTK; Niisato N, Van Driessche W, Liu M, Marunaka Y. J Membr Biol 175: 63-77, 2000). However, it is still unknown what type of PTK mediates this stimulation. In the present study, we investigated the role of receptor tyrosine kinase (RTK) in the hypotonic stimulation of Na(+) transport. In renal epithelial A6 cells, we observed inhibitory effects of AG1478 [an inhibitor of the EGF receptor (EGFR)] and AG1296 [an inhibitor of the PDGF receptor (PDGFR)] on both the hypotonic stress-induced stimulation of Na(+) transport and the hypotonic stress-induced ligand-independent activation of EGFR. We further studied whether hypotonic stress activates members of the MAP kinase family, ERK1/2, p38 MAPK, and JNK/SAPK, via an RTK-dependent pathway. The present study indicates that hypotonic stress induced phosphorylation of ERK1/2 and JNK/SAPK, but not p38 MAPK, that the hypotonic stress-induced phosphorylation of ERK1/2 and JNK/SAPK was diminished by coapplication of AG1478 and AG1296, and that only JNK/SAPK was involved in the hypotonic stimulation of Na(+) transport. A further study using cyclohexamide (a protein synthesis inhibitor) suggests that both RTK and JNK/SAPK contributed to the protein synthesis-independent early phase in hypotonic stress-induced Na(+) transport, but not to the protein synthesis-dependent late phase. The present study also suggests involvement of phosphatidylinositol 3-kinase (PI3-kinase) in RTK-JNK/SAPK cascade-mediated Na(+) transport. These observations indicate that 1) hypotonic stress activates JNK/SAPK via RTKs in a ligand-independent pathway, 2) the RTK-JNK/SAPK cascade acts as a mediator of hypotonic stress for stimulation of Na(+) transport, and 3) PI3-kinase is involved in the RTK-JNK/SAPK cascade for the hypotonic stress-induced stimulation of Na(+) transport.

c-Jun NH2-terminal kinase 2 is required for Ras transformation independently of activator protein 1

Active Ras oncogene is expressed in approximately 30% of human cancers. Yet, very little is known about the molecular mechanisms responsible for its transforming potential. Here, we show that H-Ras-mediated transformation requires isoform 2 of the c-Jun-NH(2)-terminal kinase (JNK). H-Ras-transduced JNK2-deficient (Jnk2-/-) murine embryonic fibroblasts (MEFs) were severely inhibited in colony formation and growth in soft agar in vitro as well as in tumor formation in immunodeficient mice as compared with corresponding Jnk1-/- and wild-type MEFs. Accordingly, the RNA interference-based depletion of JNK2 form wild-type MEFs also resulted in defective Ras transformation. The extra barrier against H-Ras transformation in Jnk2-/- MEFs was not due to their inability to inactivate p53 signaling because all JNK2-deficient MEF lines had lost p19(Arf). Furthermore, expression of the E6 protein of the human papilloma virus failed to overcome the transformation defect. It could, however, be overcome by coexpression of H-Ras with the SV40 large T antigen or c-Myc. Surprisingly, the H-Ras-transduced JNK2-deficient MEFs exhibited higher activity of activator protein-1 and higher levels of c-Jun expression compared with H-Ras-transduced JNK1-deficient or wild-type cells, indicating that the key target of JNK2 during Ras transformation was divergent from activator protein-1. These results clearly show that a single kinase, JNK2, could control Ras transformation and thus point out a vulnerable control point that may prove important for the tumor development in general.

Alternative pathway of transcriptional induction of p21WAF1/Cip1 by cyclosporine A in p53-deficient human glioblastoma cells

The cyclin-dependent kinase inhibitor p21WAF1/CIP1, a critical regulator of the cell cycle, is mainly regulated by p53 tumour suppressor at the transcriptional level. Restoration of p21WAF1/Cip1 expression in p53-deficient malignant cells suppress tumour growth. Cyclosporine A (CsA) affects proliferation and survival of cultured malignant glioma cells and impairs growth of experimental gliomas. CsA induced p21WAF1/Cip1 expression de novo in human glioblastoma cells with p53 deficiency. We demonstrate that transcriptional activation of p21WAF1/Cip1 expression correlated with induction of ERK1/2 and c-Jun phosphorylation in CsA-treated glioblastoma cells. Pre-treatment with ERK pathway inhibitors or overexpression of dominant-negative mutants MKK1, ERK2 and c-Jun reduced activation of the p21WAF1/Cip1 promoter. Overexpression of tethered AP-1 dimers containing c-Jun was sufficient to activate the truncated -200 bp p21WAF1/Cip1 promoter, which does not contain p53 binding sites. Chromatin immunoprecipitation revealed that P-c-Jun is bound to the proximal part of p21WAF1/Cip1 promoter in CsA-treated glioblastoma cells. It suggests that CsA activates p53-independent, transcriptional activation p21WAF1/Cip1 expression, mediated by ERK/c-Jun/AP-1 signaling pathway.

JNK1 is required for sulindac-mediated inhibition of cell proliferation and induction of apoptosis in vitro and in vivo

Our previous studies demonstrated that sulindac, a non-steroidal anti-inflammatory drug, suppressed intestinal tumor formation in mouse, which is linked to the induction of wild-type p53-activated fragment 1 (p21WAF1, or p21). Here we showed that sulindac also required c-Jun N-terminal Kinase 1 (JNK1) to inhibit cell proliferation and induce apoptosis in vitro and in vivo. First, sulindac inhibited cell proliferation and induced apoptosis in colon cancer cell lines HCT116 with wild-type p21 or null p21, which were p21-dependent and were also associated with the induction of p21 and phosphorylation of JNK1. Second, sulindac increased apoptosis in JNK1(+/+) and JNK1(-/-) mouse embryonic fibroblast (MEF) cells, but, the increase of apoptosis in JNK1(+/+) cells was more than that in JNK1(-/-) cells. More interestingly, sulindac significantly inhibited cell proliferation in JNK1(+/+) cells, but the inhibition in JNK1(-/-) cells markedly decreased. Further studies indicated that JNK1 was dramatically induced by sulindac in the JNK1(+/+) cells which correlated with the induction of p21. However, the induction of p21 in JNK1(-/-) cells was less than that in JNK1(+/+) cells. Finally, we determined the expression of JNK1 in the intestinal mucosa of Apc(+/-), p21(+/+) mice, and found that sulindac significantly induced JNK1 phosphorylation, corresponding to the induction of p21, both in mRNA and protein levels. Our data indicates that sulindac-mediated proliferation inhibition and apoptosis induction were not only p21-dependent, but also required JNK1.

Physiological roles of MKK4 and MKK7: insights from animal models

c-Jun NH2-terminal protein kinase (JNK) is a mitogen-activated protein kinase (MAPK) involved in the regulation of numerous physiological processes during development and in response to stress. Its activity is increased upon phosphorylation by the MAPK kinases, MKK4 and MKK7. Similar to the early embryonic death of mice caused by the targeted deletion of the jnk genes, mice lacking mkk4 or mkk7 die before birth. The inability of MKK4 and MKK7 to compensate for each other's functions in vivo is consistent with their synergistic effect in mediating JNK activation. However, the phenotypic analysis of the mutant mouse embryos indicates that MKK4 and MKK7 have specific roles that may be due to their selective regulation by extracellular stimuli and their distinct tissue distribution. MKK4 and MKK7 also have different biochemical properties. For example, whereas MKK4 can activate p38 MAPK, MKK7 functions as a specific activator of JNK. Here we summarize the studies that have shed light on the mechanism of activation of MKK4 and MKK7 and on their physiological functions.

A novel zinc-finger protein ZNF436 suppresses transcriptional activities of AP-1 and SRE

Mitogen-activated protein kinases (MAPKs) are evolutionary conserved enzymes in cell signal transduction connecting cell-surface receptors to critical regulatory targets within cells and control cell survival, adaptation, and proliferation. Previous studies revealed that zinc finger proteins are involved in the regulation of the MAPK signaling pathways. Here we report the identification and characterization of a novel human zinc finger protein, ZNF436. The cDNA of ZNF436 is 3.8 kb, encoding 470 amino acids in the nucleus. The protein is highly conserved in evolution across different vertebrate species from rat to human. RT-PCR indicates that ZNF436 is expressed in all the human fetal tissues examined, with a high level in brain and heart. Overexpression of pCMV-tag2A-ZNF436 in the COS-7 cells represses the transcriptional activities of SRE and AP-1. These results suggest that ZNF436 is a member of the zinc finger transcription factor family and may act as a negative regulator in gene transcription mediated by the MAPK signaling pathways.

Alkylating drugs applied in non-cytotoxic doses as a novel compounds targeting inflammatory signal pathway

Alkylating drugs (ADs) belonging to the nitrogen mustard family are commonly used as cytostatic and immunosuppressive agents. Our previous in vitro studies demonstrated that in the case of gradual dose decrease, the number of targets for alkylation in the cell is also reduced and the drug switches from brutal cytostatic to cell growth modifier. At doses of 0.3 microg/ml and lower, the effects of ADs are no longer associated with DNA damage or stress/MAPK pathways activation. Instead, the disruption of signal transduction by the IL-2beta and/or TNFalpha cell surface receptors is observed. As a result, ADs in the doses 100-fold lower than cytostatic ones are capable to modify lymphocyte activity including the activity of regulatory T cells. We hypothesized that ADs may have a beneficial effect in the treatment of inflammatory diseases. Indeed, the application of non-cytotoxic doses of an AD melphalan reduces the severity of murine experimental colitis. Daily administration of melphalan (25 microg/kg body weight) markedly reduced the severity of DSS-colitis as determined by clinical and histological criteria. Moreover, the beneficial effect of melphalan was also shown in asthmatic patients. In 60% of these patients histological and ultrastructural signs of bronchial epithelium regeneration were also revealed. Thus, ADs at non-cytotoxic concentrations exert beneficial effect both in acute and chronic inflammatory diseases. Such anti-inflammatory activity is thought to be due to blocking of signal transduction through various cell surface receptor including IL-2R and TNFR. Consequently different steps of inflammatory cascade turn out to be inhibited.

Active stress kinases in proliferating endothelial cells associated with cytoskeletal structures

It has become increasingly clear that stress-activated protein kinases have cytoplasmic substrates in addition to well-established transcription factor substrates in cell nuclei. The present study documented specific cytoplasmic locations of these enzymes in proliferating vascular cells. Immunofluorescent staining for active c-jun NH2-terminal kinase (JNK), the precipitation of JNK with microfilaments, and the loss of fiber-associated active JNK after cytochalasin treatment, but not nocodazole treatment, together indicate that active JNK is associated with stress fibers. The lack of complete scaffold colocalization and the total lack of immediate upsteam kinase colocalization along with the inability of JNK inhibitors to alter JNK-microfilament associations suggest that the microfilament association is not simply involved in enzyme activation. In addition, active p38 was found along with vinculin in focal adhesions. Although the p38 in focal adhesions could also be disrupted by cytochalasin treatment, it remained stable after nocodazole treatment. These results support the hypothesis that vascular cell stress kinase enzymes are important for signal transduction in the cytoplasm. The localization of active stress-activated protein kinases to specific cytoskeletal structures in proliferating cells suggests that subsets of these enzymes are involved in signal transduction to and/or from the cytoskeleton under conditions that include vascular cell proliferation.