Parallel signal processing among mammalian MAPKs

Novel targeted therapies in epithelial ovarian cancer: from basic research to the clinic

The development of new molecularly targeted therapies represents a high priority for the treatment of epithelial ovarian cancer. P-glycoprotein overexpression has been associated with multidrug resistance, and the use of multidrug resistance modulators, such as valspodar, is being explored in combination with chemotherapy. Human epidermal receptor (HER) family members are attractive targets for biological therapies. The addition of erlotinib or cetuximab to first-line paclitaxel- plus carboplatin-based chemotherapy is feasible and well tolerated. Gefitinib is able to inhibit the proliferation of ovarian clear-cell carcinoma in in vitro and in vivo experimental models. Single-agent trastuzumab has a limited value for recurrent epithelial ovarian cancer owing to the low frequency of HER2 overexpression and the low rate of objective responses among HER2-overexpressing patients. A Gynecologic Oncology Group Phase II trial of the proteasome inhibitor bortezomib in recurrent epithelial ovarian cancer is currently ongoing, and the combination of bortezomib and chemotherapeutic agents should be assessed. The mammalian target of rapamycin (mTOR) plays an important role in stimulating the translation of mRNAs encoding key proteins for cell growth and angiogenesis, and mTOR inhibitors, such as AP-23573 (ARIAD), deserve to be tested in selected epithelial ovarian cancer patients. The addition of intraperitoneal treatment with adenovirus containing human wild-type p53 to standard paclitaxel- plus carboplatin-based chemotherapy failed to improve the clinical outcome of patients with mutated p53 epithelial ovarian cancer. The Gynecologic Oncology Group is conducting a Phase II trial of single-agent bevacizumab (antivascular endothelial growth factor monoclonal antibody) in platinum-resistant disease. In conclusion, emerging drugs for epithelial ovarian cancer include agents designed to overcome chemoresistance, HER-targeting agents, proteasome inhibitors, mTOR inhibitors and angiogenesis inhibitors. A new paradigm of treatment could consist of chemotherapy combined with a biological agent for six cycles, and followed by chronic maintenance therapy with the biological agent alone. Advances in genomics and proteomics will elucidate the molecular mechanisms of ovarian carcinogenesis, which will hopefully lead to individualized molecular medicine in the next years.

Increased expression of SKP2 and phospho-MAPK/ERK1/2 and decreased expression of p27 during tumor progression of cervical neoplasms

OBJECTIVE

The objective of this study was to investigate whether the expression of SKP2, p27 and phospho-MAPK/ERK1/2 is associated with the progression of human cervical neoplasia.

METHODS

We performed immunohistochemical detection to stain formalin-fixed paraffin-embedded cervical tissues with anti-SKP2 and anti-p27 monoclonal antibodies and anti-phospho-p42/44 MAPK antibody. The study sample included 23 normal cervical epithelium, 25 low-grade squamous intraepithelial lesion (LSIL), 19 high-grade squamous intraepithelial lesion (HSIL), and 31 squamous cell carcinomas (SCC). In addition, 14 frozen cervical biopsies, including 1 normal, 6 HSIL, 2 adenocarcinoma and 5 SCC, and a human cervical cancer cell line (HeLa), were analyzed the expression levels of mRNA and protein of SKP2 and p27 by RT-PCR and Western blot analysis, respectively.

RESULTS

The expression of SKP2, p27 and phospho-MAPK/ERK1/2 were strongly associated with cervical neoplastic progression (P<0.0001, P=0.006, P=0.003, respectively; Fisher's Exact Test). In addition, SKP2 expression was positively correlated with phospho-MAPK/ERK1/2 expression (Spearman correlation coefficient=0.480, P=0.0002). The association between SKP2 and phospho-MAPK/ERK1/2 was significant after controlling for the four histologic grades (P=0.038, Mantel-Haenszel test).

CONCLUSIONS

These results suggest that expression levels of SKP2, p27 and phospho-MAPK/ERK1/2 may serve as markers for progression in human cervical carcinoma and may also play roles in cervical carcinoma progression and cervical carcinogenesis.

The regulation of ATF3 gene expression by mitogen-activated protein kinases

ATF3 (activating transcription factor 3) gene encodes a member of the ATF/CREB (cAMP-response-element-binding protein) family of transcription factors. Its expression is induced by a wide range of signals, including stress signals and signals that promote cell proliferation and motility. Thus the ATF3 gene can be characterized as an 'adaptive response' gene for the cells to cope with extra- and/or intra-cellular changes. In the present study, we demonstrate that the p38 signalling pathway is involved in the induction of ATF3 by stress signals. Ectopic expression of CA (constitutively active) MKK6 [MAPK (mitogen-activated protein kinase) kinase 6], a kinase upstream of p38, indicated that activation of the p38 pathway is sufficient to induce the expression of the ATF3 gene. Inhibition of the pathway indicated that the p38 pathway is necessary for various signals to induce ATF3, including anisomycin, IL-1beta (interleukin 1beta), TNFalpha (tumour necrosis factor alpha) and H2O2. Analysis of the endogenous ATF3 gene indicates that the regulation is at least in part at the transcription level. Specifically, CREB, a transcription factor known to be phosphorylated by p38, plays a role in this induction. Interestingly, the ERK (extracellular-signal-regulated kinase) and JNK (c-Jun N-terminal kinase)/SAPK (stress-activated protein kinase) signalling pathways are neither necessary nor sufficient to induce ATF3 in the anisomycin stress paradigm. Furthermore, analysis of caspase 3 activation indicated that knocking down ATF3 reduced the ability of MKK6(CA) to exert its pro-apoptotic effect. Taken together, our results indicate that a major signalling pathway, the p38 pathway, plays a critical role in the induction of ATF3 by stress signals, and that ATF3 is functionally important to mediate the pro-apoptotic effects of p38.

Structures of p38α Active Mutants Reveal Conformational Changes in L16 Loop that Induce Autophosphorylation and Activation

p38 mitogen-activated protein (MAP) kinases function in numerous signaling processes and are crucial for normal functions of cells and organisms. Abnormal p38 activity is associated with inflammatory diseases and cancers making the understanding of its activation mechanisms highly important. p38s are commonly activated by phosphorylation, catalyzed by MAP kinase kinases (MKKs). Moreover, it was recently revealed that the p38alpha is also activated via alternative pathways, which are MKK independent. The structural basis of p38 activation, especially in the alternative pathways, is mostly unknown. This lack of structural data hinders the study of p38's biology as well as the development of novel strategies for p38 inhibition. We have recently discovered and optimized a novel set of intrinsically active p38 mutants whose activities are independent of any upstream activation. The high-resolution crystal structures of the intrinsically active p38alpha mutants reveal that local alterations in the L16 loop region promote kinase activation. The L16 loop can be thus regarded as a molecular switch that upon conformational changes promotes activation. We suggest that similar conformational changes in L16 loop also occur in natural activation mechanisms of p38alpha in T-cells. Our biochemical studies reveal novel mechanistic insights into the activation process of p38. In this regard, the results indicate that the activation mechanism of the mutants involves dimerization and subsequent trans autophosphorylation on Thr180 (on the phosphorylation lip). Finally, we suggest a model of in vivo p38alpha activation induced by the L16 switch with auto regulatory characteristics.

Divergent effects of the MEKK-1/JNK pathway on NB2a/d1 differentiation: Some activity is required for outgrowth and stabilization of neurites but overactivation inhibits both phenomena

c-Jun N-terminal kinase (JNK), along with its upstream activator MEKK-1, is typically thought of as a stress-activated kinase that mediates apoptosis. However, additional studies indicate that the MEKK-1/JNK pathway mediates critical aspects of neuronal survival and differentiation. Herein, we demonstrate that transfection of differentiated NB2a/d1 cells with a construct expression constitutively activated (ca) MEKK-1 increases levels of phospho-dependent neurofilament (NF) immunoreactivity within perikarya, while expression of a dominant-negative (dn) form of MEKK-1 decreases it. Steady-state levels of perikaryal phospho-NF immunoreactivity are reduced and the increase resulting from expression of caMEKK-1 is prevented, by the JNK inhibitor SP600125, suggesting that JNK is a major downstream effector of MEKK-1 on NF phosphorylation. Unexpectedly, both caMEKK-1 and dnMEKK-1 inhibited neuritogenesis as well as translocation of NFs into newly elaborated neurites. The JNK inhibitor SP600125 also inhibited NF transport in a dose-dependent manner. caMEKK-1 also prevented the increase in NF transport otherwise mediated by MAP kinase. Finally, both caMEKK-1 and dnMEKK-1 prevented initial neuritogenesis. These findings indicate that the MEKK-1/JNK pathway regulates critical aspects of initial outgrowth, and subsequent stabilization of axonal neurites.

MAP kinases: Differential activation following in vivo and ex vivo irradiation

Mitogen activated protein kinases (MAPK) play a critical role in controlling cell survival and repopulation following exposure to ionising radiation. Most investigations on these pathways have been done using cultured cells or by ex vivo treatments. The present study was carried out to determine whether the response of MAPKs in mouse lymphocytes differs following in vivo and ex vivo irradiation with 60Co gamma-rays. We observed that ex vivo treatment resulted in a very significant decrease in the activated p44/42 and p38 MAPK as compared to in vivo. However, stress activated protein kinase (SAPK) response showed no significant difference between in vivo and ex vivo treatments. These observations point towards the differences in response elicited when the treatment is given in vivo as compared to in vitro. Therefore the findings reported from in vitro or ex vivo treatments should be treated with caution especially if it has to be clinically applied.

MgHog1 regulates dimorphism and pathogenicity in the fungal wheat pathogen Mycosphaerella graminicola

The dimorphic ascomycete pathogen Mycosphaerella graminicola switches from a yeastlike form to an infectious filamentous form that penetrates the host foliage through stomata. We examined the biological function of the mitogen-activated protein kinase-encoding gene MgHog1 in M. graminicola. Interestingly, MgHog1 mutants were unable to switch to filamentous growth on water agar that mimics the nutritionally poor conditions on the foliar surface and, hence, exclusively developed by a yeastlike budding process. Consequently, due to impaired initiation of infectious germ tubes, as revealed by detailed in planta cytological analyses, the MgHog1 mutants failed to infect wheat leaves. We, therefore, conclude that MgHog1 is a new pathogenicity factor involved in the regulation of dimorphism in M. graminicola. Furthermore, MgHog1 mutants are osmosensitive, resistant to phenylpyrrole and dicarboximide fungicides, and do not melanize.

Nucleotide receptors stimulation by extracellular ATP controls Hsp90 expression through APE1/Ref-1 in thyroid cancer cells: a novel tumorigenic pathway

Nucleotide receptors signaling affects cell proliferation, with possible implications on tumorigenic processes. However, molecular targets and action mechanisms of the extracellular nucleotides are still poorly elucidated. We have previously shown in ARO cells that APE1/Ref-1, a transcriptional coactivator responsible for the maintenance of the cellular proliferative rate, is functionally controlled by P2-mediated signaling. Here, we demonstrate that extracellular ATP has a mitogenic effect on ARO cells, increasing ERK phosphorylation, AP1 activation, and cyclin D1 expression. Using the ATP/ADPase apyrase and the P2 receptor antagonist suramin, we show that the extracellular ATP, physiologically released by ARO cells, exerts mitogenic effects. A differential proteomic approach was used to identify molecular events associated with the ATP-induced cell proliferation. Among other proteins, Hsp90 was found upregulated upon ATP stimulation. Pretreatment with suramin completely blocked the ATP-induced Hsp90 activation, confirming the involvement of cell-surface P2 nucleotide receptors in the ATP-mediated activation of ARO cells. Treatment of proliferating ARO cells with suramin and apyrase significantly reduced the intracellular levels of Hsp90, suggesting an autocrine/paracrine mechanism of control on Hsp90 expression by extracellular ATP. The influence of Hsp90 on ATP-induced cell proliferation was also demonstrated by its specific inhibition with 17-AAG. The molecular pathway by which ATP stimulates cell proliferation was further investigated by siRNA strategies showing that Hsp90 is a target of APE1/Ref-1 functional activation. Stimulation of ARO cells with specific nucleotide receptors agonists evidenced a major involvement of P2Y1 and P2Y2 receptors in controlling the Hsp90 activation. Accordingly, these two receptors resulted significantly upregulated in sample biopsies from different thyroid tumors.

Nitric oxide inhibits an interaction between JNK1 and c-Jun through nitrosylation

Nitric oxide (NO) has been shown to negatively regulate c-Jun N-terminal kinase (JNK) through S-nitrosylation. Here, we show that disruption of an interaction between JNK and its substrate c-Jun is an important mechanism underlying the NO-mediated inhibition of JNK signaling. Endogenous NO, which was generated by interferon-gamma treatment, suppressed anisomycin-stimulated JNK activity in microglial BV-2 cells. The interferon-gamma-induced suppression of JNK1 activation in BV-2 cells was prevented completely by treatment with N(G)-nitro-l-arginine, an inhibitor of NO synthase. A NO donor S-nitro-N-acetyl-dl-penicillamine (SNAP) inhibited JNK activity in vitro, and this inhibition was reversed by a thiol-reducing agent, dithiothreitol. Nitric oxide disrupts a physical interaction between JNK and its substrate c-Jun both in vitro and in intact cells without affecting an interaction between SEK1 and JNK. Collectively, our results suggest that the inhibition of the interaction between JNK and c-Jun may be an integral part of the mechanism underlying the negative regulation of the JNK signaling pathway by NO.

Involvement of p38alpha mitogen-activated protein kinase in lung metastasis of tumor cells

To study the role of p38 mitogen-activated protein kinase (p38) activity during the process of metastasis, p38alpha(+/-) mice were subjected to an in vivo metastasis assay. The number of lung colonies of tumor cells intravenously injected in p38alpha(+/-) mice was markedly decreased compared with that in wild-type (WT) mice. On the other hand, the time-dependent increase in tumor volume after subcutaneous tumor cells transplantation was comparable between WT and p38alpha(+/-) mice. Platelets of p38alpha(+/-) mice were poorly bound to tumor cells in vitro and in vivo compared with those of WT mice. E- and P-selectin mRNAs were markedly induced in the lung after intravenous injection of tumor cells. However, the induction of these selectin mRNAs in p38alpha(+/-) mice was weaker than that in WT mice. Furthermore, the resting expression levels of E-selectin in lung endothelial cells and P-selectin in platelets of p38alpha(+/-) mice were suppressed compared with those of WT mice. The number of tumor cells attached on lung endothelial cells of p38alpha(+/-) mice was significantly reduced compared with that of WT mice. The transmigrating activity of tumor cells through lung endothelial cells of p38alpha(+/-) mice was similar to that of WT mice. These results suggest that p38alpha plays an important role in extravasation of tumor cells, possibly through regulating the formation of tumor-platelet aggregates and their interaction with the endothelium involved in a step of hematogenous metastasis.

Reactive oxygen species-induced activation of the MAP kinase signaling pathways

An abundance of scientific literature exists demonstrating that oxidative stress influences the MAPK signaling pathways. This review summarizes these findings for the ERK, JNK, p38, and BMK1 pathways. For each of these different MAPK signaling pathways, the following is reviewed: the proteins involved in the signaling pathways, how oxidative stress can activate cellular signaling via these pathways, the types of oxidative stress that are known to induce activation of the different pathways, and the specific cell types in which oxidants induce MAPK responses. In addition, the functional outcome of oxidative stress-induced activation of these pathways is discussed. The purpose of this review is to provide the reader with an overall understanding and appreciation of oxidative stress-induced MAPK signaling.

MAP kinases p38 and JNK are activated by the steroid hormone 1alpha,25(OH)2-vitamin D3 in the C2C12 muscle cell line

In chick skeletal muscle cell primary cultures, we previously demonstrated that 1alpha,25(OH)2-vitamin D3 [1alpha,25(OH)2D3], the hormonally active form of vitamin D, increases the phosphorylation and activity of the extracellular signal-regulated mitogen-activated protein (MAP) kinase isoforms ERK1 and ERK2, their subsequent translocation to the nucleus and involvement in DNA synthesis stimulation. In this study, we show that other members of the MAP kinase superfamily are also activated by the hormone. Using the muscle cell line C2C12 we found that 1alpha,25(OH)2D3 within 1 min phosphorylates and increases the activity of p38 MAPK. The immediately upstream mitogen-activated protein kinase kinases 3/6 (MKK3/MKK6) were also phosphorylated by the hormone suggesting their participation in p38 activation. 1Alpha,25(OH)2D3 was able to dephosphorylate/activate the ubiquitous cytosolic tyrosine kinase c-Src in C2C12 cells and studies with specific inhibitors imply that Src participates in hormone induced-p38 activation. Of relevance, 1alpha,25(OH)2D3 induced in the C2C12 line the stimulation of mitogen-activated protein kinase activating protein kinase 2 (MAPKAP-kinase 2) and subsequent phosphorylation of heat shock protein 27 (HSP27) in a p38 kinase activation-dependent manner. Treatment with the p38 inhibitor, SB203580, blocked p38 phosphorylation caused by the hormone and inhibited the phosphorylation of its downstrean substrates. 1Alpha,25(OH)2D3 also promotes the phosphorylation of c-jun N-terminal protein kinases (JNK 1/2), the response is fast (0.5-1 min) and maximal phosphorylation of the enzyme is observed at physiological doses of 1alpha,25(OH)2D3 (1 nM). The relative contribution of ERK-1/2, p38, and JNK-1/2 and their interrelationships in hormonal regulation of muscle cell proliferation and differentiation remain to be established.

Requirement for Map2k1 (Mek1) in extra-embryonic ectoderm during placentogenesis

Map2k1(-/-) embryos die at mid-gestation from abnormal development and hypovascularization of the placenta. We now show that this phenotype is associated with a decreased labyrinth cell proliferation and an augmented cell apoptosis. Although the activation of MAP2K1 and MAP2K2 is widespread in the labyrinthine region, MAPK1 and MAPK3 activation is restricted to the cells lining the maternal sinuses, suggesting an important role for the ERK/MAPK cascade in these cells. In Map2k1(-/-) placenta, ERK/MAPK cascade activation is perturbed. Abnormal localization of the syncytiotrophoblasts is also observed in Map2k1(-/-) placenta, even though this cell lineage is specified at the correct time during placentogenesis. The placental phenotype can be rescued in tetraploid experiments. In addition, Map2k1-specific deletion in the embryo leads to normal embryo development and to the birth of viable Map2k1(-/-) mice. Altogether, these data enlighten the essential role of Map2k1 in extra-embryonic ectoderm during placentogenesis. In the embryo, the Map2k1 gene function appears dispensable.

Hog1 mitogen-activated protein kinase plays conserved and distinct roles in the osmotolerant yeast Torulaspora delbrueckii

Torulaspora delbrueckii has emerged during evolution as one of the most osmotolerant yeasts. However, the molecular mechanisms underlying this unusual stress resistance are poorly understood. In this study, we have characterized the functional role of the high-osmolarity glycerol (HOG) mitogen-activated protein kinase pathway in mediating the osmotic stress response, among others, in T. delbrueckii. We show that the T. delbrueckii Hog1p homologue TdHog1p is phosphorylated after cell transfer to NaCl- or sorbitol-containing medium. However, TdHog1p plays a minor role in tolerance to conditions of moderate osmotic stress, a trait related mainly with the osmotic balance. In consonance with this, the absence of TdHog1p produced only a weak defect in the timing of the osmostress-induced glycerol and GPD1 mRNA overaccumulation. Tdhog1Delta mutants also failed to display aberrant morphology changes in response to osmotic stress. Furthermore, our data indicate that the T. delbrueckii HOG pathway has evolved to respond to specific environmental conditions and to play a pivotal role in the stress cross-protection mechanism.

Staurosporine modulates radiosensitivity and radiation-induced apoptosis in U937 cells

PURPOSE

The present study aims at investigating the involvement of several genes in the cell cycle distribution and apoptosis in U937 cells, a cell line lacking functional p53 protein, after combined treatment with staurosporine and irradiation.

MATERIALS AND METHODS

Using a DNA fragmentation assay, flow cytometry and western blot analysis, the molecular basis for the effects of staurosporine in combination with the irradiation of leukemia cells was investigated.

RESULTS

Our results indicated that combined treatment led to an increased apoptotic cell death in U937 cells, which is correlated with the phosphorylation of the V-Jun sarcoma virus 17 oncogene homolog (c-JUN) NH(2)-terminal kinase protein (JNK), the activation of caspases, the increase in B cell leukemia/lymphoma 2 (Bcl-2) associated X protein (Bax), the decrease in Bcl xL protein (Bcl-XL) levels, the loss of mitochondria membrane potential and the release of cytochrome c.

CONCLUSIONS

Abrogation of the G2 checkpoint should be an effective strategy against p53-deficient leukemia cells to irradiation-induced cell killing.

Benzo[a]pyrene-induced cell cycle progression is through ERKs/cyclin D1 pathway and requires the activation of JNKs and p38 mapk in human diploid lung fibroblasts

Treatment of cells with carcinogen Benzo[a]pyrene (B[a]P) allows cells to evade G1 arrest and induces cells abnormal proliferation. However, the mechanisms of its action at cellular level are not well understood. To address this question, normal human embryo lung diploid fibroblasts (HELF) were selected in the present study. We found that exposure of cells with 2.5 microM of B[a]P for 24 h resulted in a decrease of G1 population by 11.9% (P < 0.05) and a increase of S population by 17.2% (P < 0.05). Treatment of cells with B[a]P also caused dose-related activation of MAPK and induction of cyclin D1 protein expression, whereas the CDK4 protein levels were not significantly affected by B[a]P. Overexpression of cyclin D1 protein stimulated by B[a]P was significantly inhibited by 50 microM AG126 (an inhibitor of ERK1/2), but not by 25 microM SP600125 (an inhibitor of JNK1/2) or 5 microM SB203580 (an inhibitor of p38 mapk), suggesting that B[a]P-induced cyclin D1 expression was only regulated by ERK1/2 pathway. However, AG126, SP600125 or SB203580 led to cell cycle significantly arrested in G1 phase, indicating that ERK1/2, JNK1/2 and p38 mapk pathways are all required for B[a]P-induced G1/S transition. In addition, HELF cells transfecting with antisense cyclin D1 cDNA or antisense CDK4 cDNA showed significantly G1 arrest after B[a]P stimulation. These results suggested that B[a]P exposure accelerated the G1-->S transition by activation of MAPK signaling pathways. Cyclin D1 and CDK4 are rate-limiting regulators of the G1-->S transition and expression of cyclin D1 is predominantly regulated by ERK1/2 pathway in HELF cells.

Regulation of the mitogen-activated protein kinase p44 ERK activity during anoxia/recovery in rainbow trout hypodermal fibroblasts

It is well known from various mammalian cells that anoxia has a major impact on the mitogen-activated protein kinase ERK, but a possible similar effect in fish cells has not been investigated. Here we characterise a p44ERK-like protein in the rainbow trout cell line RTHDF and study the effect of (i) serum stimulation, (ii) sodium azide (chemical anoxia) and removal of azide (recovery) and (iii) anoxia (PO2&lt;0.1%) and recovery. During both chemical and true anoxia p44ERK was inhibited and recovery resulted in robust reactivation of p44ERK activity, far above the initial level. The inhibition was secondary to activation of p38MAPK and the increase was MEK dependent, as SB203580 inhibited the dephosphorylation during anoxia and the presence of PD98059 inhibited phosphorylation of p44ERK during recovery. In addition, we demonstrated that the reactivation of p44ERK during recovery also was dependent on reactive oxygen species and a PP1/PP2A-like phosphatase.

Membrane accumulation of influenza A virus hemagglutinin triggers nuclear export of the viral genome via protein kinase Calpha-mediated activation of ERK signaling

Replication and transcription of the influenza virus genome takes place exclusively within the nucleus of the infected cells. The viral RNA genome, polymerase subunits, and nucleoprotein form ribonucleoprotein (RNP) complexes. Late in the infectious cycle RNPs have to be exported from the nucleus to be enwrapped into budding progeny virions at the cell membrane. This process requires viral activation of the cellular Raf/MEK/ERK (mitogen-activated protein kinase (MAPK)) signaling cascade that is activated late in the infection cycle. Accordingly, block of the cascade results in retardation of RNP export and reduced titers of progeny virus. In the present study we have analyzed the importance of cell-membrane association of the viral hemagglutinin glycoprotein for viral MAPK activation. We show that hemagglutinin membrane accumulation and its tight association with lipid-raft domains trigger activation of the MAPK cascade via protein kinase Calpha activation and induces RNP export. This may represent an auto-regulative mechanism that coordinates timing of RNP export to a point when all viral components are ready for virus budding.

N-methyl-D-aspartate (NMDA) and the regulation of mitogen-activated protein kinase (MAPK) signaling pathways: a revolving neurochemical axis for therapeutic intervention?

Excitatory synaptic transmission in the central nervous system (CNS) is mediated by the release of glutamate from presynaptic terminals onto postsynaptic channels gated by N-methyl-D-aspartate (NMDA) and non-NMDA (AMPA and KA) receptors. Extracellular signals control diverse neuronal functions and are responsible for mediating activity-dependent changes in synaptic strength and neuronal survival. Influx of extracellular calcium ([Ca(2+)](e)) through the NMDA receptor (NMDAR) is required for neuronal activity to change the strength of many synapses. At the molecular level, the NMDAR interacts with signaling modules, which, like the mitogen-activated protein kinase (MAPK) superfamily, transduce excitatory signals across neurons. Recent burgeoning evidence points to the fact that MAPKs play a crucial role in regulating the neurochemistry of NMDARs, their physiologic and biochemical/biophysical properties, and their potential role in pathophysiology. It is the purpose of this review to discuss: (i) the MAPKs and their role in a plethora of cellular functions; (ii) the role of MAPKs in regulating the biochemistry and physiology of NMDA receptors; (iii) the kinetics of MAPK-NMDA interactions and their biologic and neurochemical properties; (iv) how cellular signaling pathways, related cofactors and intracellular conditions affect NMDA-MAPK interactions and (v) the role of NMDA-MAPK pathways in pathophysiology and the evolution of disease conditions. Given the versatility of the NMDA-MAPK interactions, the NMDA-MAPK axis will likely form a neurochemical target for therapeutic interventions.

The signaling pathways linking to lysophosphatidic acid-promoted meiotic maturation in mice

The signaling pathways linking to lysophosphatidic acid-promoted meiotic maturation in mice were studied. When mouse oocyte-cumulus cells complexes were cultured with 10(-5) M lysophosphatidic acid (the LPA group), the rate of oocyte nuclear maturation was significantly increased. Additions of pertussis toxin, genistein, U73122, Ro320432, PD98059 or SB203580 significantly suppressed the increase in lysophosphatidic acid-stimulated nuclear maturation rate. These results suggested that Gi/o-coupled lysophosphatidic acid receptors activate phosphatidylinositol-specific phospholipase C, and result in ERK and MAP kinase activation, which is triggered by diacylglycerol-dependent protein kinase C. When intracellular cAMP concentrations of oocytes in the LPA and control groups were measured using the acetylation assay, the intracellular cAMP concentration of an oocyte in the LPA group was significantly lower than the control oocyte (0.117+/-0.04 fmol/oocyte vs. 0.176+/-0.036 fmol/oocyte, p<0.05). In conclusion, our results suggested that lysophosphatidic acid stimulates phospholipase C through a Gi-protein linked receptor on the surface of mouse cumulus cells and stimulates both extracellular signal-regulated kinase and p38 mitogen-activated kinase, resulting in the closure or loose of gap junctions between cumulus cells and the oocyte. The resultant early decrease of oocyte cAMP levels may promote nuclear maturation of mouse oocytes in vitro.

Voltage-gated sodium channel Nav1.6 is modulated by p38 mitogen-activated protein kinase

Nav1.6 is the major sodium channel isoform at nodes of Ranvier in myelinated axons and, additionally, is distributed along unmyelinated C-fibers of sensory neurons. Thus, modulation of the sodium current produced by Nav1.6 might significantly impact axonal conduction. Mitogen-activated protein kinases (MAPKs) are expressed in neurons and are activated after injury, for example, after sciatic nerve transection and hypoxia. Although the role of MAPK in signal transduction and in injury-induced regulation of gene expression is well established, the ability of these kinases to phosphorylate and modulate voltage-gated sodium channels has not been reported. Sequence analysis shows that Nav1.6 contains a putative MAP kinase-recognition module in the cytoplasmic loop (L1), which joins domains 1 and 2. We show in this study that sodium channels and p38 MAP kinase colocalize in rat brain tissue and that activated p38alpha phosphorylates L1 of Nav1.6, specifically at serine 553 (S553), in vitro. None of the other cytoplasmic loops and termini of the channel are phosphorylated by activated p38alpha in these assays. Activation of p38 in the neuronal ND7/23 cell line transfected with Nav1.6 leads to a significant reduction in the peak Nav1.6 current amplitude, without a detectable effect on gating properties. The substitution of S553 with alanine within L1 of the Nav1.6 channel prevents p38-mediated reduction of Nav1.6 current density. This is the first demonstration of MAPK phosphorylation and modulation of a voltage-gated sodium channel, and this modulation may represent an additional role for MAPK in regulating the neuronal response to injury.

Novel concepts of neuropeptide-based drug therapy: vasoactive intestinal polypeptide and its receptors

Chronic inflammatory airway diseases such as bronchial asthma or chronic obstructive pulmonary disease (COPD) are major contributors to the global burden of disease. Although inflammatory cells play the central role in the pathogenesis of the diseases, recent observations indicate that also resident respiratory cells represent important targets for pulmonary drug development. Especially targeting airway neuromediators offers a possible mechanism by which respiratory diseases may be treated in the future. Among numerous peptide mediators such as tachykinins, calcitonin gene-related peptide, neurotrophins or opioids, vasoactive intestinal polypeptide (VIP) is one of the most abundant molecules found in the respiratory tract. In human airways, it influences many respiratory functions via the receptors VPAC1, VPAC2 and PAC1. VIP-expressing nerve fibers are present in the tracheobronchial smooth muscle layer, submucosal glands and in the walls of pulmonary and bronchial arteries and veins. Next to its strong bronchodilator effects, VIP potently relaxes pulmonary vessels, and plays a pivotal role in the mediation of immune mechanisms. A therapy utilizing the respiratory effects of VIP would offer potential benefits in the treatment of obstructive and inflammatory diseases and long acting VIP-based synthetic non-peptide compounds may represent a novel target for drug development.

Activation of ERK1/2 and TNF-α production are mediated by calcium/calmodulin, and PKA signaling pathways during Mycobacterium bovis infection

Mycobacterium bovis bacillus Calmette-Guérin (BCG)-induced tumor necrosis factor (TNF)-alpha secretion via an extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase-dependent mechanism is an important host defence mechanism against Mycobacterium tuberculosis in human monocytes. We now define distinct signaling pathways that regulate induction of TNF-alpha and activation of ERK1/2 by intracellular signaling mechanisms during M. bovis infection. We determined that M. bovis BCG-induced ERK 1/2 activation occurs through a mechanism that requires intracellular calcium and likely involves a calmodulin-sensitive step. In contrast, M. bovis BCG can induce p38 mapk activation by a calcium (Ca2+)/calmodulin-independent mechanism. Interestingly, we present evidence that M. bovis BCG activates protein kinase A (PKA), since pretreatment of monocytes with H-89, a inhibitor of PKA activity, blocked the ability of M. bovis BCG to induce ERK1/2 activation. These results were further supported by the fact that treatment of cells with KT5720, another well-described inhibitor of PKA activity, significantly diminished the effect of M. bovis BCG on ERK1/2 activation. Furthermore, secretion of TNF-alpha in M. bovis-infected human monocytes was also dependent on Ca2+/calmodulin, and PKA pathways. Finally, addition of H-89 significantly diminished TNF-alpha mRNA expression in M. bovis-infected human monocytes. These results indicate that the Ca2+/calmodulin, and PKA pathways play important regulatory roles in monocyte signaling upon M. bovis infection.

Mechanistic insights into achievement of cardiac allograft long-term survival by treatment with immature dendritic cells and sub-dose sirolimus

BACKGROUND

Administration of immature dendritic cells (DC) prolongs but does not result in indefinite allograft survival. We attempted to achieve this goal by adding a sub-therapeutic dose of immunosuppression.

METHODS

DC propagated from B10 (H-2(b)) mouse bone marrow (BM) were transfected with nuclear factor-kappaB (NF-kappaB)-binding-site-specific oligodeoxyribonucleotide (ODN). The allostimulatory activity of transfected and normal DC were examined in mixed-lymphocyte reaction (MLR) and cytotoxic T-lymphocyte (CTL) assays in vitro, and their influence on allograft survival by systemic administration of DC in vivo.

RESULTS

Transfection of DC with NF-kappaB ODN resulted in complete abrogation of NF-kappaB activity and inhibition of co-stimulation. Allogeneic (C3H, H-2(k)) T cells stimulated by ODN DC demonstrated impairment in MLR and CTL activity. Administration of ODN DC significantly prolonged B10 allograft survival. In contrast to cyclosporine, which failed to enhance the effect of ODN DC, a combination of ODN DC with sirolimus at 6 mg/kg/day for 6 days achieved long-term survival in all allografts. This was associated with low CTL activity of either graft-infiltrating cells or splenic T cells and increased TUNEL-positive cells in T-cell areas of recipient mesenteric lymph nodes. Analysis of transcription factor nuclear translocation with Cellomics indicated that stimulation with ODN DC showed inhibited T-cell nuclear translocation of signal transducer and activator of transcription (Stat)1 and Stat3, extracellular signal-related kinase (ERK) and activating transcription factor (ATF)-2, but not NF-kappaB and P38, compared with mature DC. The selective inhibition was enhanced by sirolimus, but not cyclosporine.

CONCLUSIONS

Sirolimus enhances immature DC tolerogenicity by induction of T-cell apoptosis, and promotes immature DC-induced inhibition of Stat1, ERK and ATF-2 activation.

Free radicals, metals and antioxidants in oxidative stress-induced cancer

Oxygen-free radicals, more generally known as reactive oxygen species (ROS) along with reactive nitrogen species (RNS) are well recognised for playing a dual role as both deleterious and beneficial species. The "two-faced" character of ROS is substantiated by growing body of evidence that ROS within cells act as secondary messengers in intracellular signalling cascades, which induce and maintain the oncogenic phenotype of cancer cells, however, ROS can also induce cellular senescence and apoptosis and can therefore function as anti-tumourigenic species. The cumulative production of ROS/RNS through either endogenous or exogenous insults is termed oxidative stress and is common for many types of cancer cell that are linked with altered redox regulation of cellular signalling pathways. Oxidative stress induces a cellular redox imbalance which has been found to be present in various cancer cells compared with normal cells; the redox imbalance thus may be related to oncogenic stimulation. DNA mutation is a critical step in carcinogenesis and elevated levels of oxidative DNA lesions (8-OH-G) have been noted in various tumours, strongly implicating such damage in the etiology of cancer. It appears that the DNA damage is predominantly linked with the initiation process. This review examines the evidence for involvement of the oxidative stress in the carcinogenesis process. Attention is focused on structural, chemical and biochemical aspects of free radicals, the endogenous and exogenous sources of their generation, the metal (iron, copper, chromium, cobalt, vanadium, cadmium, arsenic, nickel)-mediated formation of free radicals (e.g. Fenton chemistry), the DNA damage (both mitochondrial and nuclear), the damage to lipids and proteins by free radicals, the phenomenon of oxidative stress, cancer and the redox environment of a cell, the mechanisms of carcinogenesis and the role of signalling cascades by ROS; in particular, ROS activation of AP-1 (activator protein) and NF-kappaB (nuclear factor kappa B) signal transduction pathways, which in turn lead to the transcription of genes involved in cell growth regulatory pathways. The role of enzymatic (superoxide dismutase (Cu, Zn-SOD, Mn-SOD), catalase, glutathione peroxidase) and non-enzymatic antioxidants (Vitamin C, Vitamin E, carotenoids, thiol antioxidants (glutathione, thioredoxin and lipoic acid), flavonoids, selenium and others) in the process of carcinogenesis as well as the antioxidant interactions with various regulatory factors, including Ref-1, NF-kappaB, AP-1 are also reviewed.

Betaine suppresses proinflammatory signaling during aging: the involvement of nuclear factor-kappaB via nuclear factor-inducing kinase/IkappaB kinase and mitogen-activated protein kinases

Betaine is an important human nutrient obtained from various foods. In the present study, we assessed the anti-inflammatory effect of betaine on nuclear factor-kappaB (NF-kappaB) during aging. Sprague-Dawley (SD) rats, ages 7 and 21 months, were used in this study. The older rats were fed betaine. To elucidate the effect of betaine on oxidative stress-induced NF-kappaB and its signaling pathway at molecular levels, YPEN-1 cells were used. Results showed that betaine suppressed NF-kappaB and its related gene expressions of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), vascular cell adhesion molecule-1 (VCAM-1), and intracellular cell adhesion molecule-1 (ICAM-1) in aged kidney. Furthermore, betaine attenuated oxidative stress-induced NF-kappaB via nuclear factor-inducing kinase/IkappaB kinase (NIK/IKK) and mitogen-activated protein kinases (MAPKs) in the YPEN-1 cells. On the basis of these results, we concluded that betaine suppressed the age-related NF-kappaB activities associated with upregulated NIK/IKK and MAPKs that were induced by oxidative stress. Thus, betaine might be useful as a preventive agent against the activation of NF-kappaB induced during inflammation and aging.

1α,25(OH)2-Vitamin D3 stimulates intestinal cell p38 MAPK activity and increases c-Fos expression

In intestinal cells, as in other target cells, the steroid hormone 1alpha,25(OH)(2)-Vitamin D(3) (1alpha,25(OH)(2)D(3)) regulates gene expression via the specific intracellular Vitamin D receptor and induces fast non-transcriptional responses involving stimulation of transmembrane signal transduction pathways. We have previously shown that the hormone activates the extracellular signal-regulated mitogen-activated protein (MAP) kinase isoforms ERK1 and ERK2 in rat intestinal cells. In the present study, we have demonstrated that 1alpha,25(OH)(2)D(3) also induces the phosphorylation and activation of p38 MAPK in these cells. The hormone effects were time and dose-dependent, with maximal stimulation at 2min (+3-fold) and 1nM. 1alpha,25(OH)(2)D(3)-dependent p38 phosphorylation was suppressed by SB 203580, a selective inhibitor of p38 MAPK. Ca(2+) chelation with EGTA, inhibition of the c-Src-tyrosine kinase family with PP1 or protein kinase A (PKA) with Rp-cAMP, attenuated hormone activation of p38 MAPK. The physiological significance of 1alpha,25(OH)(2)D(3)-dependent activation of ERK1/2 and p38 MAP kinases was addressed by monitoring c-Fos expression. Incubation of intestinal cells with the hormone was followed by a rapid induction of c-Fos expression which was blocked by SB 203580 and partially suppressed by the ERK1/2 inhibitor PD 98059. Our results suggest that 1alpha,25(OH)(2)D(3) activates p38 MAPK, involving Ca(2+), c-Src and PKA as upstream regulators, and that p38 MAPK has a central role in hormone-induction of the oncoprotein c-Fos in rat intestinal cells.

A MAPK gene from Dead Sea fungus confers stress tolerance to lithium salt and freezing-thawing: Prospects for saline agriculture

The Dead Sea is one of the most saline lakes on earth ( approximately 340 g/liter salinity) and is approximately 10 times saltier than the oceans. Eurotium herbariorum, a common fungal species, was isolated from its water. EhHOG gene, encoding a mitogen-activated protein kinase (MAPK) that plays an essential role in the osmoregulatory pathway in yeast and many other eukaryotes, was isolated from E. herbariorum. The deduced amino acid sequences of EhHOG indicated high similarity with homologous genes from Aspergillus nidulans, Saccharomyces cerevisiae, and Schizosaccharomyces pombe and contained a TGY motif for phosphorylation by MAPK kinase. When EhHOG was expressed in S. cerevisiae hog1Delta mutant, the growth and aberrant morphology of hog1Delta mutant was restored under high osmotic stress condition. Moreover, intracellular glycerol content in the transformant increased to a much higher level than that in the mutant during salt-stress situations. hog1Delta mutant complemented by EhHOG outperformed the wild type or had higher genetic fitness under high Li(+) and freezing-thawing conditions. The present study revealed the putative presence of a high-osmolarity glycerol response (HOG) pathway in E. herbariorum and the significance of EhHOG in osmotic regulation, heat stress, freeze stress, and oxidative stress. The Dead Sea is becoming increasingly more saline while the fungi living in it evolutionarily adapt to its high-saline environment, particularly with the extraordinarily high Li(+) concentration. The Dead Sea is potentially an excellent model for studies of evolution under extreme environments and is an important gene pool for future agricultural genetic engineering prospects.

Inhibition of angiotensin II- and endothelin-1-stimulated proliferation by selective MEK inhibitor in cultured rabbit gingival fibroblasts+

We investigated the implication of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) in the proliferation stimulated by angiotensin II (Ang II) and endothelin-1 (ET-1) in cultured rabbit gingival fibroblasts (CRGF). Ang II stimulated activation of ERK1/2 and the activation was inhibited by CV-11974, an AT1 antagonist, and saralasin, an AT1/AT2 antagonist, but not by PD123,319, an AT2 antagonist in the CRGF. Ang II-stimulated proliferation was inhibited by PD98059 or U0126, selective MEK inhibitors. Furthermore, ET-1 stimulated proliferation via G-protein-coupled ETA receptors, which were identified by Western blot analysis of membrane protein from the CRGF. ET-1 also stimulated activation of ERK1/2 and the activation was inhibited by BQ-123, an ETA inhibitor, and TAK044, an ETA/ETB inhibitor, but not by BQ-788, an ETB inhibitor. ET-1-stimulated proliferation was inhibited by PD98059 or U0126. These findings suggest that ERK1/2 play a role in the signaling process leading to proliferation stimulated by Ang II and ET-1 via G-protein-coupled receptors, AT1 and ETA in CRGF.

Suppressed MKP-1 is an independent predictor of outcome in patients with hepatocellular carcinoma

OBJECTIVE

An increase in the activity of mitogen-activated protein kinases (MAPKs) has been correlated with a more malignant phenotype in several tumor models in vivo. This study was designed to clarify the expression of MKP-1 in surgically resected hepatocellular carcinoma (HCC).

METHODS

We reviewed the cases of 77 patients who had undergone initial liver resection for HCC without preoperative treatment. Immunohistochemical analysis of MKP-1 was performed on paraffin-embedded tissues. The correlation between MKP-1 expression and clinical outcome was investigated.

RESULTS

Tumor cells were immunohistochemically stained for MKP-1 expression, and the same levels as in normal hepatocytes were detected in 66 (85%) of 77 HCC patients, being decreased in 11 (15%) HCCs. Decreased MKP-1 expression significantly correlated with serum alpha-fetoprotein levels and tumor size (p<0.05). The disease-free survival rates in MKP-1-negative and -positive patients were 0 and 31.0% at 5 years, respectively (p<0.01). The survival rates after a surgical resection in MKP-1-negative and -positive patients were 18.2 and 65.5% at 5 years, respectively (p<0.01).

CONCLUSIONS

The MKP-1 expression in HCC was an independent prognostic factor for outcome in HCC patients. In the future, it will be useful to explore whether the phosphatase expression might account for the response to HCC treatments targeting at MAPK activation.

Production of active recombinant mitogen-activated protein kinases through transient transfection of 293T cells

Mitogen-activated protein (MAP) kinases are a family of serine/threonine protein kinases that play an important role in a myriad of cellular processes, including cell proliferation, differentiation, and apoptosis. Abnormal activation of MAP kinases has been shown to participate in a variety of human diseases which include cancer, septic shock, rheumatoid arthritis, diabetes, and cardiovascular diseases. Active MAP kinase enzymes are not only valuable for basic biomedical research but are also critical for the development of pharmacological inhibitors as therapeutic drugs in the treatment of relevant human diseases. MAP kinases produced in a bacterial system are poorly active due to a lack of proper phosphorylation at their characteristic threonine and tyrosine residues. To overcome these limitations, we have developed a mammalian expression system for high level expression and one-step purification of enzymatically MAP kinases. We cloned JNK1, p38, and p38-regulated MAP kinase-activated protein kinase-2 into the mammalian expression vector pEBG, and expressed these protein kinases as glutathione S-transferase fusion proteins in human embryonic kidney 293T cells through transient transfection. The protein kinases were activated in vivo through treating the transfected cells with sodium arsenite and affinity-purified using glutathione-Sepharose beads. The enzymatic activities of these protein kinases were demonstrated by Western blot analysis and in vitro kinase assays. Our results indicate that this system is an extremely powerful tool for generating valuable reagents, and could be very valuable for proteomic studies.

Role of c-Jun NH2-terminal kinase in G-protein-coupled receptor agonist-induced cardiac plasminogen activator inhibitor-1 expression

Plasminogen activator inhibitor-1 (PAI-1) has been implicated as a contributing risk factor for cardiovascular disease. However, little is known about molecular mechanisms of cardiac PAI-1 gene expression. To elucidate these mechanisms, dominant negative mutants of c-Jun NH(2)-terminal kinase (JNK), p38MAPK, apoptosis signal-regulating kinase-1 (ASK-1) and c-Jun were overexpressed in rat neonatal ventricular cardiac myocytes and fibroblasts by adenovirus vector to abrogate the activation of the corresponding endogenous proteins. One hundred nmol/l of angiotensin II significantly enhanced the JNK and p38MAPK activities of cardiomyocytes (2.3-fold and 1.9-fold, P < 0.05) and fibroblasts (3.2-fold and 2.5-fold, P < 0.05). At 3 h after stimulation, angiotensin II was found to have significantly increased PAI-1 mRNA, by 5.2-fold in cardiomyocytes and by 9.7-fold in fibroblasts. Dominant negative mutants of JNK, ASK-1 and c-Jun significantly inhibited PAI-1 mRNA expression and protein synthesis in both cardiomyocytes and fibroblasts, whereas a dominant negative mutant of p38MAPK did not change this expression. Moreover, a dominant negative mutant of JNK also significantly prevented the induction of PAI-1 mRNA expression by 100 nmol/l endothelin-1 and 10 micromol/l phenylephrine. In conclusion, G-protein-coupled receptor agonist-induced PAI-1 expression is partially mediated through JNK activation.

Modulation of tyrosine phosphorylation signalling pathways by 1alpha,25(OH)2-vitamin D3

Hormonally active vitamin D(3), 1alpha,25(OH)(2)D(3), interacts with the classic vitamin D nuclear receptor that regulates gene transcription and with a putative cell membrane receptor that mediates rapid biological responses. 1alpha,25(OH)(2)D(3) actions on target tissues regulate: mineral metabolism and intracellular Ca(2+); protein kinase cascades leading to cell proliferation, differentiation and apoptosis; muscle growth and contractility; and the immune system. There is evidence for underlying 1alpha,25(OH)(2)D(3)-mediated protein tyrosine phosphorylation signalling in bone, intestine, muscle, epidermal and cancer cells. Extracellular-signal-regulated kinases-1/2, p38 and/or c-jun N-terminal kinase pathways play important roles in mediating 1alpha,25(OH)(2)D(3) actions. Studies to elucidate key regulatory metabolic steps and crosstalk sites in these pathways would enhance our understanding of the significance of tyrosine phosphorylation cascades in normal 1alpha,25(OH)(2)D(3) physiology, pathophysiology and pharmacology.

Leptin activates STAT and ERK2 pathways and induces gastric cancer cell proliferation

Although leptin is known to induce proliferative response in gastric cancer cells, the mechanism(s) underlying this action remains poorly understood. Here, we provide evidence that leptin-induced gastric cancer cell proliferation involves activation of STAT and ERK2 signaling pathways. Leptin-induced STAT3 phosphorylation is independent of ERK2 activation. Leptin increases SHP2 phosphorylation and enhances binding of Grb2 to SHP2. Inhibition of SHP2 expression with siRNA but not SHP2 phosphatase activity abolished leptin-induced ERK2 activation. While JAK inhibition with AG490 significantly reduced leptin-induced ERK2, STAT3 phosphorylation, and cell proliferation, SHP2 inhibition only partially reduced cancer cell proliferation. Immunostaining of gastric cancer tissues displayed local overexpression of leptin and its receptor indicating that leptin might be produced and act locally in a paracrine or autocrine manner. These findings indicate that leptin promotes cancer growth by activating multiple signaling pathways and therefore blocking its action at the receptor level could be a rational therapeutic strategy.

Inhibition of activator protein-1, NF-kappaB, and MAPKs and induction of phase 2 detoxifying enzyme activity by chlorogenic acid

Chlorogenic acid, the ester of caffeic acid with quinic acid, is one of the most abundant polyphenols in the human diet. The antioxidant and anticarcinogenic properties of chlorogenic acid have been established in animal studies. However, little is known about the molecular mechanisms through which chlorogenic acid inhibits carcinogenesis. In this study, we found that chlorogenic acid inhibited the proliferation of A549 human cancer cells in vitro. The results of the soft agar assay indicated that chlorogenic acid suppressed 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced neoplastic transformation of JB6 P+ cells in a dose-dependent manner. Pretreatment of JB6 cells with chlorogenic acid blocked UVB- or TPA-induced transactivation of AP-1 and NF-kappaB over the same dose range. At low concentrations, chlorogenic acid decreased the phosphorylation of c-Jun NH2-terminal kinases, p38 kinase, and MAPK kinase 4 induced by UVB/12-O-tetradecanoylphorbol-13-acetate, yet higher doses were required to inhibit extracellular signal-regulated kinases. Chlorogenic acid also increased the enzymatic activities of glutathione S-transferases (GST) and NAD(P)H: quinone oxidoreductase. Further studies indicated that chlorogenic acid could stimulate the nuclear translocation of Nrf2 (NF-E2-related factor) as well as subsequent induction of GSTA1 antioxidant response element (ARE)-mediated GST activity. The phosphatidylinositol 3-kinase pathway might be involved in the activation of Nrf2 translocation. These results provide the first evidence that chlorogenic acid could protect against environmental carcinogen-induced carcinogenesis and suggest that the chemopreventive effects of chlorogenic acid may be through its up-regulation of cellular antioxidant enzymes and suppression of ROS-mediated NF-kappaB, AP-1, and MAPK activation.

Dehydroepiandrosterone negatively regulates the p38 mitogen-activated protein kinase pathway by a novel mitogen-activated protein kinase phosphatase

Dehydroepiandrosterone-sulfate, the sulfated form of dehydroepiandrosterone, is the most abundant steroid in young adults, but gradually declines with aging. In humans, the clinical application of dehydroepiandrosterone targeting some collagen diseases, such as systemic lupus erythematosus, as an adjunctive treatment has been applied in clinical trial. Here, we report that dehydroepiandrosterone may negatively regulate the mitogen-activated protein kinase pathway in humans via a novel dual specificity protein phosphatase, DDSP (dehydroepiandrosterone-enhanced dual specificity protein phosphatase). DDSP is highly homologous to LCPTP/HePTP, a tissue-specific protein tyrosine phosphatase (PTP) which negatively regulates both ERK and p38-mitogen-activated protein kinase, and is transcribed from the PTPN7 locus by alternative splicing. Although previous reports have shown that the mRNA expression of the LCPTP/HePTP gene was inducible by extracellular signals such as T-cell antigen receptor stimulation, reverse transcribed (RT)-PCR experiments using specific sets of primers suggested that the expression of LCPTP/HePTP was constitutive while the actual inducible sequence was that of DDSP. Furthermore DDSP was widely distributed among different types of human tissues and specifically interacted with p38-mitogen-activated protein kinase. This inducible negative regulation of the p38-mitogen-activated protein kinase-dependent pathway may help to clarify the broad range of dehydroepiandrosterone actions, thereby aiding the development of new preventive or adjunctive applications for human diseases.

Changes in gene expression within the nucleus accumbens and striatum following sexual experience

Sexual experience, like repeated drug use, produces long-term changes including sensitization in the nucleus accumbens and dorsal striatum. To better understand the molecular mechanisms underlying the neuroadaptations following sexual experience, we employed a DNA microarray approach to identify genes differentially expressed between sexually experienced and sexually naive female hamsters within the nucleus accumbens and dorsal striatum. For 6 weeks, a stimulus male was placed in the home cage of one-half of the hormonally primed, ovariectomized female hamsters. On the seventh week, the two experimental groups were subdivided, with one half paired with a stimulus male. In comparison with sexually naive animals, sexually experienced hamsters receiving a stimulus male on week 7 exhibited an increase in a large number of genes. Conversely, sexually experienced female hamsters not receiving a stimulus male on week 7 exhibited a reduction in the expression of many genes. For directional changes and the categories of genes regulated by the experimental conditions, data were consistent across the nucleus accumbens and dorsal striatum. However, the specific genes exhibiting changes in expression were disparate. These experiments, among the first to profile genes regulated by female sexual behavior, will provide insight into the mechanisms by which both motivated behaviors and drugs of abuse induce long-term changes in the mesolimbic and nigrostriatal dopamine pathways.

Regulation of the cyclooxygenase-2 system by interleukin-1beta through mitogen-activated protein kinase signaling pathways: a comparative study of human neuroglioma and neuroblastoma cells

Glial activation and inflammation following brain injury may initiate and maintain the process of neurodegeneration. Both glia and neurons synthesize proinflammatory mediators such as interleukin 1 beta (IL-1beta), cytosolic phospholipase A2 (cPLA2), cyclooxygenase-2 (COX-2), and prostaglandins. The molecular mechanisms by which IL-1beta regulates inflammatory genes such as cPLA2 and COX-2 in glial and neuronal cells are poorly understood. We have studied IL-1beta-mediated gene regulation in an established glial and neuronal human cell lines. We report that IL-1beta induced cPLA2 and COX-2 mRNA and protein expression and subsequent prostaglandin E2 (PGE2) release in a time-dependent manner in H4 neuroglioma cells. Both SB203580 and PD98059 [p38 and p42/44 mitogen-activated protein kinase (MAPKs) inhibitors, respectively] reduced IL-1beta-induced PGE2 production, while only SB203580 reduced both cPLA2 and COX-2 expression. Similarly, in SKNSH neuroblastoma cells, both SB203580 and PD98059 reduced IL-1beta-induced PGE2 release, with no detectable COX-2 and cPLA2 protein expression in these cells. Our results indicate that the signaling mechanisms of p38 and p42/44 MAPKs play a role in IL-1beta-mediated PGE2 release in both of these cell lines, with differences upstream at the level of cPLA(2)/COX-2 expression. IL-1beta-induced cPLA2 and COX-2 gene expression is modulated through the p38 MAPK pathway in both neuroglioma and neuroblastoma cells. Understanding the signaling mechanisms involved in IL-1beta-mediated inflammatory processes in both glia and neuronal cells may provide potential targets for therapeutic intervention for neurological disorders.

The induction of sexual development and virulence in the smut fungus Ustilago maydis depends on Crk1, a novel MAPK protein

MAP kinases (mitogen-activated protein kinases) are activated by dual phosphorylation on specific threonine and specific tyrosine residues that are separated by a single residue, and the TXY activation motif is a hallmark of MAP kinases. In the fungus Ustilago maydis, which causes corn smut disease, the Crk1 protein, a kinase previously described to have roles in morphogenesis, carries a TXY motif that aligns with the TXY of MAP kinases. In this work, we demonstrate that Crk1 is activated through a mechanism that requires the phosphorylation of this motif. Our data show that Fuz7, a MAPK kinase involved in mating and pathogenesis in U. maydis, is required to activate Crk1, most likely through phosphorylation of the TXY motif. Consistently, we found that Crk1 is also required for mating and virulence. We investigated the reasons for sterility and avirulence of crk1-deficient cells, and we found that Crk1 is required for transcription of prf1, a central regulator of mating and pathogenicity in U. maydis. Crk1 belongs to a wide conserved protein group, whose members have not been previously defined as MAP kinases, although they carry TXY motifs. On the basis of our data, we propose that all of these proteins constitute a new family of MAP kinases.

Hypoxia and the regulation of mitogen-activated protein kinases: gene transcription and the assessment of potential pharmacologic therapeutic interventions

Oxygen is an environmental/developmental signal that regulates cellular energetics, growth, and differentiation processes. Despite its central role in nearly all higher life processes, the molecular mechanisms for sensing oxygen levels and the pathways involved in transducing this information are still being elucidated. Altering gene expression is the most fundamental and effective way for a cell to respond to extracellular signals and/or changes in its microenvironment. During development, the expression of specific sets of genes is regulated spatially (by position/morphogenetic gradients) and temporally, presumably via the sensing of molecular oxygen available within the microenvironment. Regulation of signaling responses is governed by transcription factors that bind to control regions (consensus sequences) of target genes and alter their expression in response to specific signals. Complex signal transduction during hypoxia (deficiency of oxygen in inspired gases or in arterial blood and/or in tissues) involves the coupling of ligand-receptor interactions to many intracellular events. These events basically include phosphorylations by tyrosine kinases and/or serine/threonine kinases, such as those of mitogen-activated protein kinases (MAPKs), a superfamily of kinases responsive to stress nonhomeostatic conditions. Protein phosphorylations imposed during hypoxia change enzyme activities and protein conformations, and the eventual outcome is rather complex, comprising of an alteration in cellular activity and changes in the programming of genes expressed within the responding cells. These molecular changes serve as signals that are crucial for cell survival under contingent conditions imposed during hypoxia. This review correlates current concepts of hypoxic sensing pathways with hypoxia-related phosphorylation mechanisms mediated by MAPKs via the genetic and pharmacologic regulation/manipulation of specific transcription factors and related cofactors.

The p38 MAP kinase pathway and its biological function

p38 is a mitogen-activated protein (MAP) kinase with structural and functional characteristics that distinguish it from JNK and ERK MAP kinases. p38 activity is upregulated when cells are exposed to a variety of stimuli including bacterial pathogens, proinflammatory cytokines, certain growth factors, and other forms of environmental stress. By regulating downstream substrates that include protein kinases and transcription factors, p38 participates in transmission, amplification, and diversification of the extracellular signal, initiating several different cellular responses. Studies have revealed that activation of p38 pathway is related to many pathological changes that occur in the course of inflammatory/immunologic and cardiovascular diseases.

Lipid peroxidation triggers both c-Jun N-terminal kinase (JNK) and extracellular-regulated kinase (ERK) activation and neointimal hyperplasia induced by cessation of blood flow in the mouse carotid artery

We investigated whether lipid peroxidation might influence activation of the mitogen activated protein kinase (MAPK) extracellular regulated kinase (ERK1/2) and c-Jun N-terminal kinase (JNK) in neointimal hyperplasia induced by flow interruption of carotid artery in mice. C57/BL6 mice were subjected to a complete ligation of the left common carotid artery or to a sham ligation. Animals were randomized to receive either IRFI-042, a Vitamin E-like inhibitor of lipid peroxidation (20 mg/kg/i.p., immediately after artery occlusion) or its vehicle (1 ml/kg of a NaCl-DMSO solution). The extent of lipid peroxidation (investigated by the means of conjugated dienes levels) and JNK and ERK activation were evaluated by Western blot analysis after blood flow interruption. ICAM-1 expression in injured arteries was investigated 4 days after artery ligation by the means of reverse transcriptase polymerase chain reaction (RT-PCR) and quantification of the ICAM-1 protein levels. Morphometric analysis of the structural alteration caused by the disruption of the arterial blood flow was performed 4 weeks after surgery. Flow interruption in the carotid artery resulted at 10 min, following occlusion in a marked increase in conjugated dienes tissue levels (5.8+/-0.44 DeltaABS/mg protein), caused at 30 min after occlusion peak increase in both ERK1/2 (45+/-8 integrated intensity) and JNK (38+/-6 integrated intensity) activities, enhanced ICAM-1 expression (1.5+/-0.45 relative amount of ICAM-1 mRNA) and ICAM-1 protein levels (55+/-12 pg/mg protein) and produced a marked neointimal hyperplasia (mean intimal area=101+/-14 microm2). Injured arteries harvested from IRFI-042-treated mice had reduced conjugated dienes tissue levels (2.9+/-0.5 DeltaABS/mg protein), attenuated ERK1/2 (19+/-6 integrated intensity) and JNK (2.9+/-0.5 integrated intensity) activities, blunted ICAM-1 expression (0.38+/-0.1 relative amount of ICAM-1 mRNA) and protein levels (26+/-8 pg/mg protein) and decreased neointimal hyperplasia (mean intimal area=4.5+/-1.5 microm2). Our data indicate that ERK1/2 and JNK kinases play a crucial role in neointimal hyperplasia induced by flow cessation in the mouse carotid artery. Furthermore, the present data suggest that lipid peroxidation triggers ERK and JNK activation.

Upregulation of FasL by LPA on ovarian cancer cell surface leads to apoptosis of activated lymphocytes

OBJECTIVE

Constitutive expression and upregulation of FasL by malignant epithelial cells counterattack infiltrating natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) and induce apoptosis of normal cells within the tumor, which may induce metastasis. As little is known about the mechanisms that regulate expression of Fas ligand and the subsequent release of FasL in epithelial ovarian cancer cells (EOC), we investigated the effects of lysophosphatidic acid (LPA) on FasL expression and associated signaling pathways.

METHODS

We used established EOC cell lines that were incubated with or without LPA and FasL expression was detected by flow cytometry. Cells were additionally lysed and detected for total protein expression. Activated CD4+ T cells, after coculture with or without EOC, were collected for apoptosis staining and analysis by flow cytometry.

RESULTS

Flow cytometry showed that LPA strongly upregulated FasL expression on the OVCAR3 cell surface (P < 0.01), yet in Dov13 cells, LPA significantly upregulated FasL expression only in the presence of the general matrix metalloproteinase (MMP) inhibitors GM6001 and MMP inhibitor II (P < 0.01). The MEK/ERK1/2 kinase cascade is required for FasL upregulation, since the MEK inhibitor PD98059 significantly inhibited FasL upregulation induced by LPA (P < 0.01). Type II secretory phospholipase A2 (sPLA2-II), which promotes protein exocytosis from secretory vesicles and gelatinase granules, affects FasL translocation from intracellular to the cell surface. Pretreatment of Dov13 cells with LPA increased activated T cell apoptosis in cocultures.

CONCLUSIONS

These data suggest that upregulation of FasL by LPA provides EOC immune-privilege and leads to apoptosis of activated T lymphocytes.

Estrogen and insulin/IGF-1 cooperatively stimulate cell cycle progression in MCF-7 breast cancer cells through differential regulation of c-Myc and cyclin D1

Estrogen and insulin/insulin-like growth factor-I (IGF-I) are major mitogens for breast epithelial cells and when co-administered, synergistically induce G(1)-S phase cell cycle progression. We investigated this cooperativity by evaluating if the key cell cycle regulators, c-Myc and cyclin D1, represent points of convergence in the action of these mitogens in MCF-7 breast cancer cells. These studies demonstrated that estrogen significantly increased both c-Myc and cyclin D1 protein, while insulin predominantly increased cyclin D1 levels. This cumulative increase in c-Myc and cyclin D1 contributes to the cooperativity of these mitogens, since ectopic expression of c-Myc or cyclin D1 cooperates with either the estrogen or insulin signaling pathways to increase cell cycle progression. Inhibition of the MAPK or PI3-kinase pathways significantly reduced c-Myc and cyclin D1 protein levels and cell cycle progression. Ectopic expression of cyclin D1 partially overcame this inhibition, while ectopic expression of c-Myc partially overcame MAPK but not PI3-kinase inhibition. Therefore, estrogen and insulin/IGF-1 differentially regulate c-Myc and cyclin D1 to cooperatively stimulate breast cancer cell proliferation.

Exposure to toxic concentrations of aluminum activates a MAPK-like protein in cell suspension cultures of Coffea arabica

Addition of a toxic concentration of aluminum (Al) to cell suspension cultures of Coffea arabica L. induced the rapid and transient activation of a protein kinase that phosphorylates myelin basic protein (MBP), as revealed by in-gel kinase assays. This enzyme with an apparent molecular mass of 58 kDa was activated shortly after cells were exposed to 50 microM AlCl(3), a concentration previously shown to produce toxicity in plant cells in vitro. The activity of this kinase dropped to basal levels after 20 min of Al addition; this activity is specific for MBP as it could not be detected when casein or histone H1 were used as substrates. Analysis of the same cell extracts with antibodies that specifically recognize bis-phosphorylated (active) mitogen-activated protein kinases (MAP kinases), revealed the presence of a phosphoprotein with an apparent molecular mass of 58 kDa, which showed the same response to Al as the protein kinase revealed by the in-gel kinase assays. Furthermore, immunoprecipitation with an antibody directed against mammalian MAP kinases depleted both the enzymatic activity and the phosphoprotein from the cell extracts, suggesting that the 58 kDa kinase and the 58 kDa phosphoprotein from C. arabica cells are the same protein, and that it can be actually a member of the MAP kinase family of protein kinases. Since its activity is enhanced dramatically after addition of AlCl(3) to the medium, we can speculate that Al toxicity in plants could be perceived through the MAP kinase signal transduction pathway.

Mitogen-activated protein kinase phosphatase-1 is overexpressed in non-small cell lung cancer and is an independent predictor of outcome in patients

PURPOSE

An increase in the activity of the mitogen-activated protein kinases (MAPKs) has been correlated with a more malignant phenotype in several tumor models in vitro and in vivo. A key regulatory mechanism of the MAPKs [extracellular signal-regulated kinase (ERK); c-jun NH(2)-terminal kinase (JNK); and p38] is the dual specificity phosphatase CL100, also called MAPK phosphatase-1 (MKP-1). This study was designed to examine the involvement of CL100/MKP-1 and stress-related MAPKs in lung cancer.

EXPERIMENTAL DESIGN

We assessed the expression of CL100/MKP-1 and the activation of the MAPKs in a panel of 18 human cell lines [1 primary normal bronchial epithelium, 8 non-small cell lung cancer (NSCLC), 7 small cell lung cancer (SCLC), and 2 carcinoids] and in 108 NSCLC surgical specimens.

RESULTS

In the cell lines, CL100/MKP-1 expression was substantially higher in NSCLC than in SCLC. P-ERK, P-JNK, and P-p38 were activated in SCLC and NSCLC, but the degree of their activation was variable. Immunohistochemistry in NSCLC resection specimens showed high levels of CL100/MKP-1 and activation of the three MAPK compared with normal lung. In univariate analysis, no relationship was found among CL100/MKP-1 expression and P-ERK, P-JNK, or P-p38. Interestingly, high CL100/MKP-1 expression levels independently predicted improved survival in multivariate analysis. JNK activation associated with T(1-2) and early stage, whereas ERK activation correlated with late stages and higher T and N. Neither JNK nor ERK activation were independent prognostic factors when studied for patient survival.

CONCLUSIONS

Our data indicate the relevance of MAPKs and CL100/MKP-1 in lung cancer and point at CL100/MKP-1 as a potential positive prognostic factor in NSCLC. Finally, our study supports the search of new molecular targets for lung cancer therapy within the MAPK signaling pathway.

Structure and regulation of MAPK phosphatases

MAP kinases (MAPKs), which control mitogenic signal transduction in all eukaryotic organisms, are inactivated by dual specificity MAPK phosphatases (DS-MKPs). Recent studies reveal that substrate specificity and enzymatic activity of MKPs are tightly controlled not only by the conserved C-terminal phosphatase domain but also by an N-terminal (NT) kinase-binding domain. Notably, MKPs that consist of a kinase-binding domain and a phosphatase domain exhibit little phosphatase activity in the absence of their physiological substrates. MKP binding to a specific MAPK results in enzymatic activation of the phosphatase in a substrate-induced activation mechanism. This direct coupling of inactivation of an MAPK to activation of an MKP provides a tightly controlled regulation that enables these two key enzymes to keep each other in check, thus guaranteeing the fidelity of signal transduction. This review discusses the recent understanding of structure and regulation of the large family of dual specificity MKPs, which can be divided into four subgroups according to their functional domains and mechanism of substrate recognition and enzymatic regulation. Moreover, detailed comparison of the structural basis between this unique substrate-induced activation mechanism and the common auto-inhibition mechanism is provided.

Protective effects of SP600125 a new inhibitor of c-jun N-terminal kinase (JNK) and extracellular-regulated kinase (ERK1/2) in an experimental model of cerulein-induced pancreatitis

Extracellular regulated kinases (ERK1/2) and c-Jun N-terminal Kinases (JNK), are generally considered to play a key role in signal transduction pathways activated by a wide range of stimuli. We studied the effects of SP600125, a novel inhibitor of both JNK and ERK1/2, in male C57/BL6 mice given with an hyper-stimulating dose of cerulein (50 microg/kg for each of four injections at hourly intervals) to elicit secretagogue-induced pancreatitis. A control group received four intra-peritoneal injections of 0.9% saline at hourly intervals. Animals were randomized to receive either SP600125 (15 mg/kg i.p. administered 2 h before and 30 min after the first injection of cerulein) or its vehicle (1 ml/kg of a 10% DMSO/NaCl solution). A group of animals was killed 30 minutes after the last cerulein injection to evaluate pancreatic JNK and ERK1/2 activation by Western Blot analysis. Another group was sacrificed 2 hours after the last cerulein injection to evaluate serum lipase and amylase levels, pancreas oedema, pancreatic content of Tumor Necrosis Factor-alpha (TNF-alpha) and Intercellular adhesion molecule-1 (ICAM-1) and the histological alterations. SP600125 inhibited almost totally JNK activation (90%) and partially ERK1/2 activation (45%), reduced the serum lipase and amylase levels and the degree of oedema, blunted the increased pancreatic content of TNF-alpha and ICAM-1 and protected against the histological damage. Our data confirm that both JNK and ERK1/2 activation plays a key role in acute pancreatitis and that SP600125 may represent a potential therapeutic approach to the treatment of patients at high risk of developing this life-threatening condition.

Furosin, an ellagitannin, suppresses RANKL-induced osteoclast differentiation and function through inhibition of MAP kinase activation and actin ring formation

Phenolic compounds including tannins and flavonoids have been implicated in suppression of osteoclast differentiation/function and prevention of bone diseases. However, the effects of hydrolysable tannins on bone metabolism remain to be elucidated. In this study, we found that furosin, a hydrolysable tannin, markedly decreased the differentiation of both murine bone marrow mononuclear cells and Raw264.7 cells into osteoclasts, as revealed by the reduced number of tartrate resistant acid phosphatase (TRAP)-positive multinucleated cells and decreased TRAP activity. Furosin appears to target at the early stage of osteoclastic differentiation while having no cytotoxic effect on osteoclast precursors. Analysis of the inhibitory mechanisms of furosin revealed that it inhibited the receptor activator of nuclear factor-kappaB ligand (RANKL)-induced activation of p38 mitogen-activated protein kinase (p38MAPK) and c-Jun N-terminal kinase (JNK)/activating protein-1 (AP-1). Furthermore, furosin reduced resorption pit formation in osteoclasts, which was accompanied by disruption of the actin rings. Taken together, these results demonstrate that naturally occurring furosin has an inhibitory activity on both osteoclast differentiation and function through mechanisms involving inhibition of the RANKL-induced p38MAPK and JNK/AP-1 activation as well as actin ring formation.

Oxidative stress activates FUS1 and RLM1 transcription in the yeast Saccharomyces cerevisiae in an oxidant-dependent Manner

Mating in haploid Saccharomyces cerevisiae occurs after activation of the pheromone response pathway. Biochemical components of this pathway are involved in other yeast signal transduction networks. To understand more about the coordination between signaling pathways, we used a "chemical genetic" approach, searching for compounds that would activate the pheromone-responsive gene FUS1 and RLM1, a reporter for the cell integrity pathway. We found that catecholamines (l-3,4-hydroxyphenylalanine [l-dopa], dopamine, adrenaline, and noradrenaline) elevate FUS1 and RLM1 transcription. N-Acetyl-cysteine, a powerful antioxidant in yeast, completely reversed this effect, suggesting that FUS1 and RLM1 activation in response to catecholamines is a result of oxidative stress. The oxidant hydrogen peroxide also was found to activate transcription of an RLM1 reporter. Further genetic analysis combined with immunoblotting revealed that Kss1, one of the mating mitogen-activated protein kinases (MAPKs), and Mpk1, an MAPK of the cell integrity pathway, participated in l-dopa-induced stimulation of FUS1 and RLM1 transcription. We also report that Mpk1 and Hog1, the high osmolarity MAPK, were phosphorylated upon induction by hydrogen peroxide. Together, our results demonstrate that cells respond to oxidative stress via different signal transduction machinery dependent upon the nature of the oxidant.