Puckered and JNK signaling in pioneer neurons coordinates the motor activity of the Drosophila embryo

Central nervous system organogenesis is a complex process that obeys precise architectural rules. The impact that nervous system architecture may have on its functionality remains, however, relatively unexplored. To clarify this problem, we analyze the development of the Drosophila embryonic Ventral Nerve Cord (VNC). VNC morphogenesis requires the tight control of Jun kinase (JNK) signaling in a subset of pioneer neurons, exerted in part via a negative feedback loop mediated by the dual specificity phosphatase Puckered. Here we show that the JNK pathway autonomously regulates neuronal electrophysiological properties without affecting synaptic vesicle transport. Manipulating JNK signaling activity in pioneer neurons during early embryogenesis directly influences their function as organizers of VNC architecture and, moreover, uncovers a role in the coordination of the embryonic motor circuitry that is required for hatching. Together, our data reveal critical links, mediated by the control of the JNK signaling cascade by Puckered, between the structural organization of the VNC and its functional optimization.

Phosphorylation of MAP kinase in corneal epithelial cells during wound healing

PURPOSE

To investigate the role of mitogen-activated protein kinase (MAPK), such as p44/42 MAPK, p38 MAPK and stress-activated protein kinase (SAPK), in corneal epithelial cells during the wound healing process.

METHODS

A single non-penetrating incision was produced on rat cornea. Then the corneal wound healing process was observed with an immunocytochemical technique using specific antibodies reacting only with phosphorylated p44/42 MAPK, p38 MAPK or SAPK. Cell lysates of corneal epithelial cells in rabbits stimulated with keratinocyte growth factor (KGF) and hepatocyte growth factor (HGF) were processed for Western blot using antibodies to phosphorylated p44/42 MAPK.

RESULTS

Maximum activation of p44/42 MAPK was observed in wing and basal cells at wounded regions in rat cornea at 1 hour after the incision. Activation of p44/42 MAPK was still detected in all basal and wing cells at wounded regions at up to 24 hours when the incisions were completely closed, and then receded to normal intensity after 7 days. Neither p38 MAPK nor SAPK were activated during the wound healing process. Western blot analysis of cultured corneal epithelial cells in rabbits showed phosphorylation of p44/42 MAPK after 30 minutes in response to KGF and HGF, whereas non-activated p44/42 MAPK was ordinarily detected even at the absence of KGF or HGF.

CONCLUSIONS

These results demonstrate that p44/42 MAPK is activated during the corneal wound healing process and suggest that KGF and HGF play an important role in initiation of cell migration and proliferation in the initial wound healing process by activating p44/42 MAPK.

Distinct roles for JNK1 and JNK2 in regulating JNK activity and c-Jun-dependent cell proliferation

Different c-Jun N-terminal kinases (JNKs) are activated by a plethora of signals and phosphorylate substrates such as c-Jun, which is required for efficient cell cycle progression. Although JNK1 and JNK2 were shown to differentially regulate fibroblast proliferation, the underlying mechanistic basis remains unclear. We found that Jnk2-/- fibroblasts exit G1 and enter S phase earlier than wild-type counterparts, while Jnk1-/- cells show the inverse phenotype. Moreover, Jnk2-/- erythroblasts also exhibit a proliferative advantage. JNK2 deficiency results in elevated c-Jun phosphorylation and stability, whereas the absence of JNK1 reduces c-Jun phosphorylation and stability. Re-expression of JNK2 in Jnk2-/- cells reverses the JNK2 null phenotype, whereas ectopic expression of JNK1 augments it. JNK2 is preferentially bound to c-Jun in unstimulated cells, thereby contributing to c-Jun degradation. In contrast, JNK1 becomes the major c-Jun interacting kinase after cell stimulation. These data provide mechanistic insights into the distinct roles of different JNK isoforms.

Signal pathway involved in increased expression of neutral endopeptidase 24.11 by gonadotropin releasing hormone in choriocarcinoma cells

Neutral endopeptidase 24.11 (NEP) is known to regulate cellular functions by degrading several bioactive peptides, such as gonadotropin-releasing hormone (GnRH). The present study was performed to clarify the mechanisms of NEP expression by GnRH in human choriocarcinoma (BeWo) cells. GnRH increased NEP expression and enzyme activity in a dose- and time-dependent manner in BeWo cells. The phosphorylation levels of protein kinase C (PKC) delta, p38 mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (JNK1 and 2) were enhanced after 10 min exposure of 10(-6)m GnRH. The effect of GnRH on both NEP expression and enzyme activity was completely inhibited by inhibitors of PKC, PKC delta, and p38MAPK. Cell number was reduced by 54.4 per cent of the control by culture with 10(-6)m GnRH for 24 h. However, phosphoramidon, a NEP specific inhibitor, inhibited antiproliferative effect of GnRH and reverted to the control level. In conclusion, GnRH induces NEP expression by PKC delta and p38MAPK, and increased NEP expression may be involved in antiproliferative effect in BeWo cells.

GM1-ganglioside-mediated activation of the unfolded protein response causes neuronal death in a neurodegenerative gangliosidosis

GM1-ganglioside (GM1) is a major sialoglycolipid of neuronal membranes that, among other functions, modulates calcium homeostasis. Excessive accumulation of GM1 due to deficiency of lysosomal beta-galactosidase (beta-gal) characterizes the neurodegenerative disease GM1-gangliosidosis, but whether the accumulation of GM1 is directly responsible for CNS pathogenesis was unknown. Here we demonstrate that activation of an unfolded protein response (UPR) associated with the upregulation of BiP and CHOP and the activation of JNK2 and caspase-12 leads to neuronal apoptosis in the mouse model of GM1-gangliosidosis. GM1 loading of wild-type neurospheres recapitulated the phenotype of beta-gal-/- cells and activated this pathway by depleting ER calcium stores, which ultimately culminated in apoptosis. Activation of UPR pathways did not occur in mice double deficient for beta-gal and ganglioside synthase, beta-gal-/-/GalNAcT-/-, which do not accumulate GM1. These findings suggest that the UPR can be induced by accumulation of the sialoglycolipid GM1 and this causes a novel mechanism of neuronal apoptosis.

Jun turnover is controlled through JNK-dependent phosphorylation of the E3 ligase Itch

The turnover of Jun proteins, like that of other transcription factors, is regulated through ubiquitin-dependent proteolysis. Usually, such processes are regulated by extracellular stimuli through phosphorylation of the target protein, which allows recognition by F box-containing E3 ubiquitin ligases. In the case of c-Jun and JunB, we found that extracellular stimuli also modulate protein turnover by regulating the activity of an E3 ligase by means of its phosphorylation. Activation of the Jun amino-terminal kinase (JNK) mitogen-activated protein kinase cascade after T cell stimulation accelerated degradation of c-Jun and JunB through phosphorylation-dependent activation of the E3 ligase Itch. This pathway modulates cytokine production by effector T cells.

JNKing Revealed

In a recent issue of Molecular Cell, Sabapathy et al. (2004) demonstrate that JNK2 destabilizes c-Jun under nonstimulating conditions, whereas after stress, activated JNK1 phosphorylates c-Jun, resulting in its activation and stabilization, thereby highlighting functional differences between JNK1 and JNK2.

Nuclear factor of activated T cells balances angiogenesis activation and inhibition

It has been demonstrated that vascular endothelial cell growth factor (VEGF) induction of angiogenesis requires activation of the nuclear factor of activated T cells (NFAT). We show that NFATc2 is also activated by basic fibroblast growth factor and blocked by the inhibitor of angiogenesis pigment epithelial–derived factor (PEDF). This suggests a pivotal role for this transcription factor as a convergence point between stimulatory and inhibitory signals in the regulation of angiogenesis.

We identified c-Jun NH₂-terminal kinases (JNKs) as essential upstream regulators of NFAT activity in angiogenesis. We distinguished JNK-2 as responsible for NFATc2 cytoplasmic retention by PEDF and JNK-1 and JNK-2 as mediators of PEDF-driven NFAT nuclear export.

We identified a novel NFAT target, caspase-8 inhibitor cellular Fas-associated death domain–like interleukin 1β–converting enzyme inhibitory protein (c-FLIP), whose expression was coregulated by VEGF and PEDF. Chromatin immunoprecipitation showed VEGF-dependent increase of NFATc2 binding to the c-FLIP promoter in vivo, which was attenuated by PEDF. We propose that one possible mechanism of concerted angiogenesis regulation by activators and inhibitors may be modulation of the endothelial cell apoptosis via c-FLIP controlled by NFAT and its upstream regulator JNK.

Gastrodia elata prevents rat pheochromocytoma cells from serum-deprived apoptosis: the role of the MAPK family

Gastrodia elata (G. elata) is a traditional Chinese herbal medicine for treating headaches, dizziness, tetanus, and epilepsy. In this study, differential methanol (MeOH) extracts of G. elata were found to prevent serum-deprived rat pheochromocytoma (PC12) cell apoptosis by the MTT assay and Hoechst staining. A serine/threonine kinase inhibitor attenuated this protection. G. elata resulted in phosphorylation and dephosphorylation of ERK1/2 and JNK1/2-p38 MAPKs (members of the serine/threonine kinase family), respectively, as revealed by Western blot analysis. An upstream ERK inhibitor attenuated G. elata-induced ERK phosphorylation but not protective effect. Although JNK and p38 inhibitors attenuated their related enzyme activities during serum deprivation, only JNK inhibitor prevented serum-deprived apoptosis. Thus, G. elata prevents serum-deprived apoptosis through activation of the serine/threonine kinase-dependent pathway and suppression of JNK activity.

Deoxynivalenol-induced mitogen-activated protein kinase phosphorylation and IL-6 expression in mice suppressed by fish oil

The trichothecene mycotoxin deoxynivalenol (DON) induces IgA hyperelevation and mesangial IgA deposition in mice that mimics the early stages of human IgA nephropathy (IgAN). Among potential mediators of this disease, interleukin-6 (IL-6) is likely to play a particularly critical role in IgA elevation and disease exacerbation. Based on previous findings that dietary fish oil (FO) suppresses DON-induced IgAN, we hypothesized that FO inhibits the induction of IL-6 expression by this mycotoxin in vivo and in vitro. Mice were fed modified AIN 93G diet amended with 7% corn oil (CO) or with 1% corn oil plus 6% menhaden fish oil (FO) for up to 8 weeks and then exposed acutely to DON by oral gavage. DON-induced plasma IL-6 and splenic mRNA elevation in FO-fed mice were significantly suppressed after 8 weeks when compared to the CO-fed group. The effects of FO on phosphorylation of mitogen-activated protein kinases (MAPKs), critical upstream transducers of IL-6 up-regulation, were also assessed. DON-induced phosphorylation of extracellular signal regulated protein kinases 1 and 2 (ERK1/2) and c-Jun N-terminal kinases 1 and 2 (JNK1/2) was significantly suppressed in spleens of mice fed with FO, whereas p38 was not. Splenic COX-2 mRNA expression, which has been previously shown to enhance DON-induced IL-6, was also significantly decreased by FO, whereas plasma levels of the COX-2 metabolite, prostaglandin E2, were not affected. To confirm in vivo findings, the effects of pretreatment with the two primary n-3 PUFAs in FO, eicosapentaenoic acid (20:5[n-3]; EPA) and docosahexaenoic acid, (22:6[n-3]; DHA), on DON-induced IL-6 expression were assessed in LPS-treated RAW 264.7 macrophage cells. Consistent with the in vivo findings, both EPA and DHA significantly suppressed IL-6 superinduction by DON, as well as impaired DON-induced ERK1/2 and JNK1/2 phosphorylation. In contrast, the n-6 PUFA arachidonic acid (20:4[n-3]) had markedly less effects on these MAPKs. Taken together, the capacity of FO and its component n-3 PUFAs to suppress IL-6 expression as well as ERK 1/2 and JNK 1/2 activation might explain, in part, the reported suppressive effects of these lipids on DON-induced IgA nephropathy.

Inhibition of JNK2 disrupts anaphase and produces aneuploidy in mammalian cells

The JNK family members JNK1 and JNK2 regulate tumor growth and are essential for transformation by oncogenes such as constitutively activated Ras. The mechanisms downstream of JNK that regulate cell cycle progression and transformation are unclear. Here we show that inhibition of JNK2, but not JNK1, with either a dominant-negative mutant, a pharmacological inhibitor, or RNA interference caused an accumulation of mammalian cells with 4N DNA content. When observed by immunofluorescence, these cells progressed to metaphase without apparent defects in spindle formation or chromosome alignment to the metaphase plate, suggesting that the 4N accumulation is a result of postmetaphase defects. Consistent with this prediction, when JNK activity was suppressed, we observed defects in central spindle formation and chromosome segregation during anaphase. In contrast, cyclin-dependent kinase 1 activity, cyclin B1 protein, and Polo-like kinase 1 protein turnover remained intact when JNK was inhibited. In addition, continued inhibition of JNK activity did not block reentry into subsequent cell cycles but instead resulted in polyploidy. This evidence suggests that JNK2 functions in maintaining the genomic stability of mammalian cells by signaling that is independent of cyclin-dependent kinase 1/cyclin B1 down-regulation.

Phosphorylation of microtubule-associated protein tau by isoforms of c-Jun N-terminal kinase (JNK)

Microtubule-associated protein tau in a hyperphosphorylated state is the major component of the filamentous lesions that define a number of neurodegenerative diseases commonly referred to as tauopathies. Hyperphosphorylation of tau at most sites appears to precede filament assembly. Many of the hyperphosphorylated sites are serine/threonine-proline sequences. Here we show that c-Jun N-terminal kinases JNK1, JNK2 and JNK3 phosphorylate tau at many serine/threonine-prolines, as assessed by the generation of the epitopes of phosphorylation-dependent anti-tau antibodies. Of the three protein kinases, JNK2 phosphorylated the most sites in tau, followed by JNK3 and JNK1. Phosphorylation by JNK isoforms resulted in a greatly reduced ability of tau to promote microtubule assembly. These findings extend the number of candidate protein kinases for the hyperphosphorylation of tau in Alzheimer's disease and other neurodegenerative disorders.

Mitogen-activated protein kinases in apoptosis regulation

Cells are continuously exposed to a variety of environmental stresses and have to decide 'to be or not to be' depending on the types and strength of stress. Among the many signaling pathways that respond to stress, mitogen-activated protein kinase (MAPK) family members are crucial for the maintenance of cells. Three subfamilies of MAPKs have been identified: extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs), and p38-MAPKs. It has been originally shown that ERKs are important for cell survival, whereas JNKs and p38-MAPKs were deemed stress responsive and thus involved in apoptosis. However, the regulation of apoptosis by MAPKs is more complex than initially thought and often controversial. In this review, we discuss MAPKs in apoptosis regulation with attention to mouse genetic models and critically point out the multiple roles of MAPKs.

Activation and involvement of JNK1/2 in hydrogen peroxide-induced neurotoxicity in cultured rat cortical neurons

AIM

To investigate the role of c-Jun N-terminal protein kinase 1 and 2 (JNK1/2) and the main signal pathway for its activation in hydrogen peroxide (H(2)O(2)) induced apoptotic-like cortical cell death.

METHODS

Using the model of oxidative stress induced by H(2)O(2), the expression and diphosphorylation of JNK1/2 was examined by immunoblotting analysis, and neuronal apoptotic like cell death was determined by 4',6-diamidino-2-phenylindole (DAPI) staining.

RESULTS

The elevation in diphosphorylation level of JNK1/2 (4.40-/5.61-fold vs sham control) was associated with the concentration of H(2)O(2) (0-100 micromol/L) and the development of apoptotic-like cell death (11.04 %-81.01 %). There was no alteration of JNK1/2 protein expression following H(2)O(2) treatment and recovery at different time points. Administration with JNK1/2 antisense oligonucleotides not only significantly decreased JNK1/2 protein expression and activation level, but also significantly reduced cortical cell death induced by H(2)O(2) exposure. Furthermore, both JNK1/2 diphosphorylation and apoptotic-like cell death were largely prevented by pretreatment with (5S,10R)-(-)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801) or omission of Ca(2+) in incubation medium with ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA).

CONCLUSION

JNK1/2 is activated and participates in H(2)O(2)-induced apoptotic-like death in cultured rat cortical neurons mainly via N-methyl-D-aspartate (NMDA) receptor-mediated influx of extracellular Ca(2+).

Regulation of c-Jun N-terminal kinase activation in hydrogen peroxide induced neurotoxicity

C-Jun N-terminal kinase 1 and 2 (JNK1/2) have been shown to be transiently activated and involved in neurotoxicity. We searched for possible upstream molecules, which are responsible for the regulation of hydrogen peroxide-(H2O2) induced JNK1/2 activation and JNK1/2-mediated apoptotic-like cell death in cultured rat cortical neurons. The results showed that JNK1/2 activation (monitored by anti-diphosphorylated JNK1/2 antibody) was largely prevented by elimination of extracellular Ca2+ or blockage of NMDA-receptors (NMDA-R), and was weakly but significantly decreased by blockage of L-type voltage-gated calcium channel (L-VGCC); furthermore, JNK1/2 activation was largely prevented by inhibition of Ca2+/calmodulin-dependent protein kinase-II (CaMKII) and protein-tyrosine kinases (PTK). We also found that H2O2-induced apoptotic-like cell death was partially prevented by elimination of extracellular Ca2+, or by inhibition of NMDA-R, L-VGCC, PTK and CaMKII, respectively. The above results suggest that in H2O2-induced neurotoxicity, JNK1/2 activation is mainly mediated by NMDA-R and L-VGCC. Consequently, PTK and CaMKII are critical intermediaries in JNK1/2 activation and are mainly responsible for JNK1/2-mediated apoptotic-like cell death.

Overexpression or ablation of JNK in skeletal muscle has no effect on glycogen synthase activity

c-Jun NH(2)-terminal kinase (JNK) is highly expressed in skeletal muscle and is robustly activated in response to muscle contraction. Little is known about the biological functions of JNK signaling in terminally differentiated muscle cells, although this protein has been proposed to regulate insulin-stimulated glycogen synthase activity in mouse skeletal muscle. To determine whether JNK signaling regulates contraction-stimulated glycogen synthase activation, we applied an electroporation technique to induce JNK overexpression (O/E) in mouse skeletal muscle. Ten days after electroporation, in situ muscle contraction increased JNK activity 2.6-fold in control muscles and 15-fold in the JNK O/E muscles. Despite the enormous activation of JNK activity in JNK O/E muscles, contraction resulted in similar increases in glycogen synthase activity in control and JNK O/E muscles. Consistent with these findings, basal and contraction-induced glycogen synthase activity was normal in muscles of both JNK1- and JNK2-deficient mice. JNK overexpression in muscle resulted in significant alterations in the basal phosphorylation state of several signaling proteins, such as extracellular signal-regulated kinase 1/2, p90 S6 kinase, glycogen synthase kinase 3, protein kinase B/Akt, and p70 S6 kinase, in the absence of changes in the expression of these proteins. These data suggest that JNK signaling regulates the phosphorylation state of several kinases in skeletal muscle. JNK activation is unlikely to be the major mechanism by which contractile activity increases glycogen synthase activity in skeletal muscle.

HSP25 overexpression attenuates oxidative stress-induced apoptosis: roles of ERK1/2 signaling and manganese superoxide dismutase

HSP25 has been shown to induce resistance to radiation and oxidative stress; however, its exact mechanisms remain unclear. In the present study, a high concentration of H2O2 was found to induce DNA fragmentation in L929 mouse fibroblast cells, and HSP25 overexpression attenuated this phenomenon. To elucidate the mechanisms of H2O2-mediated cell death, ERK1/2, p38 MAPK, and JNK1/2 phosphorylation in the cells after treatment with H2O2 were examined. ERK1/2 and JNK1/2 were activated by H2O2; ERK1/2 activation was inhibited in HSP25-overexpressed cells, while JNK1/2 was indifferent. Inhibition of ERK1/2 activation by treatment of the cells with PD98059 or dominant-negative ERK2 transfection blocked H2O2-induced cell death; similarly treated HSP25-overexpressed cells were not at all affected. Moreover, inhibition of JNK1/2 by dominant-negative JNK1 or JNK2 transfection did not affect H2O2-mediated cell death in control cells. Dominant-negative Ras or Raf transfection inhibited H2O2-mediated ERK1/2 activation and cell death in control cells. On the contrary, HSP25-overexpressed cells did not show any differences. Upstream pathways of H2O2-mediated ERK1/2 activation and cell death involved both tyrosine kinase (PDGFbeta receptor and Src) and PKCdelta, while in HSP25-overexpressed cells these kinases did not respond to H2O2 treatment. Since HSP25 overexpression reduced reactive oxygen species (ROS), increased manganese superoxide dismutase (MnSOD) gene expression, and increased enzyme activity, involvement of MnSOD in HSP25-mediated attenuation of H2O2-mediated ERK1/2 activation and cell death was examined. Blockage of MnSOD with antisense oligonucleotides prevented DNA fragmentation and returned the ERK1/2 activation to the control level. Indeed, when MnSOD was overexpressed in L929 cells, similar to in HSP25-overexpressed cells, DNA fragmentation and ERK1/2 activation were reduced. From the above results, we suggest for the first time that reduced oxidative damage by HSP25 was due to MnSOD-mediated downregulation of ERK1/2.

Multifaceted roles of TNF-alpha in myoblast destruction: a multitude of signal transduction pathways

In catabolic conditions, such as cancer cachexia, a balance favouring a cytokine environment culminates in muscle destruction. Utilising an in vitro model to mimic muscle wasting, we elucidate here the multifaceted roles that one such cytokine, TNF-alpha, invokes in the degeneration process. Treatment of C2 skeletal myoblasts with TNF-alpha not only suppresses morphological and biochemical differentiation, but following an initial wave of proliferation, and of survival (24 h), induces apoptosis. Investigating the mechanisms underlying these diverse actions of TNF-alpha, we demonstrate that cell replication is dependent on rapid and sustained activation of MAP kinase. Map kinase is not, however, central to the death process, which is associated with a progressive rise in caspase-8 activity, and is accompanied by sustained activation of JNK1 and transient activation of JNK2. Caspase inhibition caused a dose responsive reduction in cell death, while inhibition of the JNKs caused a significant increase in apoptosis. We further report that PI3 kinase is not involved in conferring early protection against TNF-alpha-induced death. By contrast, inhibition of NF-kappaB in the presence of TNF-alpha culminates in increased cell cycle progression, decreased gadd45beta expression and significant and precociously increased cell death, when compared with TNF-alpha alone. Our results begin to characterise the mechanisms underlying the acute mitogenic and anti-apoptotic roles of TNF-alpha, which appear to be defined by a balance between MAP kinase, Jun kinase (JNK), NF-kappaB and gadd45beta. They establish that inhibition of any one of these molecules, as may occur following caspase activation, could eliminate vital stem cells required for skeletal muscle regeneration during chronic catabolic conditions.

Intraluminal pressure is a stimulus for NFATc3 nuclear accumulation: role of calcium, endothelium-derived nitric oxide, and cGMP-dependent protein kinase

The transcription factor NFAT (nuclear factor of activated T-cells) is implicated in cardiac hypertrophy and vasculogenesis. NFAT activation, reflecting dephosphorylation by the calcium-dependent phosphatase, calcineurin, and subsequent nuclear localization, is generally thought to require a sustained increase in intracellular calcium. However, in smooth muscle we have found that elevation of calcium by membrane depolarization fails to induce an increase in nuclear localization of the NFATc3 isoform. Here, we demonstrate that physiological intravascular pressure (100 mm Hg) induces an increase in NFATc3 nuclear localization in mouse cerebral arteries. Pressure-induced NFATc3 nuclear accumulation is abrogated by endothelial denudation and by nitric-oxide synthase, cGMP-dependent kinase (PKG), and voltage-dependent calcium channels inhibition. We further show that exogenous nitric oxide, in combination with an elevation in calcium, is an effective stimulus for NFATc3 nuclear accumulation. c-Jun terminal kinase 2 (JNK) activity, which has been shown to regulate NFATc3 nuclear export, is also reduced by pressure, an effect that is prevented by pretreatment with a PKG inhibitor. Consistent with this, pressure-induced NFATc3 nuclear accumulation is independent of PKG in arteries from JNK2(-/-) mice. Collectively, our results indicate that both activation of the NO/PKG pathway and elevation of smooth muscle calcium are required for NFATc3 nuclear accumulation and that PKG inhibits JNK2 to decrease NFAT nuclear export. Our findings suggest that at physiological intravascular pressures NFATc3 is localized to the nucleus in smooth muscle cells of intact arteries and indicate a novel and unexpected role for nitric oxide/PKG in NFAT activation.

Expression and activity of the signaling molecules for mitogen-activated protein kinase pathways in human, bovine, and rat lenses

PURPOSE

The mitogen-activated protein kinase (MAPK) pathways play distinct roles in the lens. However, the expression patterns and activity levels of various components for these pathways have not been well-documented in vertebrate lenses, especially human lens. In the present study, the expressions and activities of extracellular signal-regulated kinase (ERK)-1/2/3, c-Jun NH2-terminal kinase (JNK)-1/2, p38 kinase, mitogen-activated protein kinase kinase (MEK)-1/2, and RAF1 were recorded in human, bovine, and rat lenses.

METHODS

Human, bovine, and rat lenses were isolated from intact eyes. The epithelia and different layers of fiber cells were isolated from these lenses. Total proteins extracted from these samples were subject to analysis of the expression patterns and activity levels of the MAPKs and the activating kinases of ERK1/2.

RESULTS

ERK1 and ERK2 were the most abundant MAPKs in terms of both protein and activity levels in all lenses. JNK1 and JNK2 were highly expressed in bovine lens, which differed from the pattern shared by human and rat lenses. p38 kinase was similarly expressed in bovine and rat lenses, but different from that in human lens. However, p38 kinase activity was exclusively detected in the epithelia. All lenses had MEK1/2 activity in their epithelia but the expression patterns of MEK1 and MEK2 differed in these lenses. RAF1 was expressed in the epithelia of all lenses, but its activity was detected only in rat lens.

CONCLUSIONS

ERK1 and ERK2 are the most abundant MAPKs in the ocular lens, providing the basis for their multiple functions in lens development and pathogenesis. The dominant epithelial distribution of JNK1/2 and p38 kinase suggests that the lens epithelium is a major site for stress response. ERK1, p38 kinase, and PKCalpha can be used as molecular markers for aging.

CLIP identifies Nova-regulated RNA networks in the brain

Nova proteins are neuron-specific antigens targeted in paraneoplastic opsoclonus myoclonus ataxia (POMA), an autoimmune neurologic disease characterized by abnormal motor inhibition. Nova proteins regulate neuronal pre-messenger RNA splicing by directly binding to RNA. To identify Nova RNA targets, we developed a method to purify protein-RNA complexes from mouse brain with the use of ultraviolet cross-linking and immunoprecipitation (CLIP).Thirty-four transcripts were identified multiple times by Nova CLIP.Three-quarters of these encode proteins that function at the neuronal synapse, and one-third are involved in neuronal inhibition.Splicing targets confirmed in Nova-/- mice include c-Jun N-terminal kinase 2, neogenin, and gephyrin; the latter encodes a protein that clusters inhibitory gamma-aminobutyric acid and glycine receptors, two previously identified Nova splicing targets.Thus, CLIP reveals that Nova coordinately regulates a biologically coherent set of RNAs encoding multiple components of the inhibitory synapse, an observation that may relate to the cause of abnormal motor inhibition in POMA.

Development of a 1-microl scale assay for mitogen-activated kinase kinase 7 using 2-D fluorescence intensity distribution analysis anisotropy

This paper describes the development of a robust, miniaturizable, and quantitative fluorescence-based assay for mitogen-activated protein kinase kinase 7 (MKK7). As a first step, the basic steady-state kinetics of the MKK7-catalyzed phosphorylation of c-Jun N-terminal kinases (JNKs) 1, 2, and 3 were defined using standard radiometric methods. Subsequently, the authors found that in addition to the holo JNKs, a series of novel small peptides (based on the region around the JNK phosphorylation site) are also substrates, provided that these were prephosphorylated on the Y residue of the TPY motif. One of these peptide substrates was used in the development of a fluorescence polarization-based assay using an antibody as a sensor. The assay was successfully miniaturized for use with conventional fluorescence polarization (FP) reader technology in 8.5 microl and on the single microl scale using Evotec proprietary 2-dimensional fluorescence intensity distribution analysis (2D-FIDA) anisotropy and liquid handling technology. The steady-state kinetic parameters derived using the FP or 2D-FIDA anisotropy format assays correlated well with those generated using a radiometric assay. Moreover, the quantitative sensitivity to known inhibitors was maintained independent of the format and assay volume. In addition, the authors found that the 2D-FIDA anisotropy assay exhibited superior performance statistics (typical Z' = approximately 0.5) relative to conventional FP (typical Z' = 0.3) and yielded the additional benefit of order-of-magnitude savings in terms of reagent costs. The 2D-FIDA anisotropy assay was used to carry out a successful high-throughput screening in 1-microl final volume against company file compounds.

Constitutively elevated nuclear export activity opposes Ca2+-dependent NFATc3 nuclear accumulation in vascular smooth muscle: role of JNK2 and Crm-1

The transcription factor NFAT (nuclear factor of activated T-cells) is a cytosolic phosphoprotein that accumulates in the nucleus following dephosphorylation by the calcium (Ca2+)/calmodulin-dependent phosphatase, calcineurin. A defining feature of stimuli that induce NFAT nuclear accumulation/activation is a sustained increase in global intracellular Ca2+. Contrary to expectations, we have found that a sustained elevation of intracellular Ca2+, induced by membrane potential depolarization and mediated by voltage-dependent Ca2+ channels, does not result in nuclear localization of the NFATc3 isoform in smooth muscle. However, vasoconstrictors (e.g. uridine triphosphate (UTP)) and growth factors, which elevate intracellular Ca2+ and engage multiple intracellular signaling pathways, induce a robust increase in smooth muscle nuclear NFATc3. Here we show that depolarizing stimuli that normally fail to induce NFATc3 nuclear accumulation in arterial smooth muscle effectively induce nuclear accumulation under conditions in which Crm-1-dependent or JNK2-mediated nuclear export processes are disrupted. Consistent with an important regulatory role for JNK, UTP exerts a suppressive effect on JNK activity in smooth muscle. Export of nuclear NFATc3 following UTP-induced nuclear accumulation is dramatically slowed in cerebral arteries from JNK2-/- animals. These data indicate that in smooth muscle, stimulation of Ca2+-dependent, calcineurin-mediated nuclear import and suppression of Crm-1/JNK-dependent nuclear export are both required for induction of NFATc3 nuclear accumulation. These results highlight the dynamic interplay between influences that promote and oppose NFAT nuclear accumulation and suggest that in arterial smooth muscle suppression of constitutive nuclear export activity is an important property of NFAT-activating stimuli.

JNK-dependent phosphorylation of c-Jun on serine 63 mediates nitric oxide-induced apoptosis of neuroblastoma cells

c-Jun NH2-terminal kinases (JNKs) potentiate transcriptional activity of c-Jun by phosphorylating serines 63 and 73. Moreover, JNK and c-Jun can modulate apoptosis. However, an involvement of nitric oxide (NO)-induced phosphorylation of c-Jun on Ser-63 and Ser-73 in apoptosis has not been explored. We report that in SH-Sy5y neuroblastoma cells, NO induced apoptosis following JNK activation and phosphorylation of c-Jun almost exclusively on Ser-63. Importantly, NO-induced apoptosis and caspase-3 activity were inhibited in cells stably transformed with dominant-negative c-Jun in which Ser-63 is mutated to alanine (S63A), but not in cells transformed with dominant-negative c-Jun (S73A). Ser-63 of c-Jun (but not Ser-73) was required for NO-induced, c-Jun-dependent transcriptional activity. NO-induced apoptosis, Ser-63 phosphorylation of c-Jun, and caspase-3 activity were all inhibited in SH-Sy5y cells transformed with dominant-negative jnk. A caspase-3 inhibitor prevented apoptosis but not c-Jun phosphorylation. In a different neuroblastoma cell line, NO-induced Ser-63 phosphorylation of c-Jun and apoptosis were blocked by a specific JNK inhibitor. We conclude that NO-inducible apoptosis is mediated by JNK-dependent Ser-63 phosphorylation of c-Jun upstream of caspase-3 activation in neuroblastoma cells.

Determination of onset of apoptosis in granulosa cells of the preovulatory follicles in the bonnet monkey (Macaca radiata): correlation with mitogen-activated protein kinase activities

During reproductive life, only a selected few ovarian follicles mature and ovulate, while the vast majority of follicles undergo a degenerative process called atresia. Recent studies have indicated that follicular atresia is mediated through apoptosis of follicular granulosa cells. The objectives of the present study were to determine the time of onset of apoptosis in granulosa cells of preovulatory follicles and to evaluate the consequences of gonadotropin withdrawal on mitogen-activated protein (MAP) kinase activities. Bonnet monkeys (Macaca radiata) undergoing controlled ovarian stimulation cycles were utilized for stimulation of multiple follicles, and granulosa cells were retrieved from preovulatory follicles at 24, 48, 72, and 96 h after stopping gonadotropin treatment. Serum and follicular fluid estradiol concentrations were highest at 24 h but declined precipitously (P < 0.05) to reach the lowest concentrations at 96 h; however, progesterone concentrations during this period did not increase, indicating the absence of luteinization. Quantitative analysis of genomic DNA by 3'-end labeling revealed the presence of low-molecular-weight fragments from 48 h onward, but by agarose gel electrophoresis, DNA laddering could be visualized only after 72 h. Messenger RNA expression for Bax, caspase-2, and caspase-3 increased with the onset of apoptosis. Immunoblot analysis of MAP kinases in lysates of granulosa cells (48-72 h) indicated increased (P < 0.05) levels of phosphorylated extracellular response kinase-1 and -2, Jun N-terminal kinase (JNK)-1 and -2, and p38. However, in vitro kinase assay data indicated that only phospho-JNK and -p38 activities were higher at 72 h compared to 24 h. These results demonstrate that granulosa cells of preovulatory follicles undergo apoptosis and that increased activities of phospho-JNK and -p38 are correlated with apoptosis in the primate.

Suppression of inflammatory cytokine production by carbon monoxide involves the JNK pathway and AP-1

The stress-inducible protein heme oxygenase-1 provides protection against oxidative stress and modulates pro-inflammatory cytokines. As the sepsis syndrome results from the release of pro-inflammatory mediators, we postulated that heme oxygenase-1 and its enzymatic product CO would protect against lethality in a murine model of sepsis. Mice treated with a lethal dose of lipopolysaccharide (LPS) and subsequently exposed to inhaled CO had significantly better survival and lower serum interleukin (IL)-6 and IL-1beta levels than their untreated counterparts. In vitro, mouse macrophages exposed to LPS and CO had significantly attenuated IL-6 production; this effect was concentration-dependent and occurred at a transcriptional level. The same effect was seen with increased endogenous CO production through overexpression of heme oxygenase-1. Mutation within the AP-1-binding site in the IL-6 promoter diminished the effect of CO on promoter activity, and treatment of macrophages with CO decreased AP-1 binding in an electrophoretic mobility shift assay. Electrophoretic mobility supershift assay indicated that the JunB, JunD, and c-Fos components of AP-1 were particularly affected. Upstream of AP-1, CO decreased JNK phosphorylation in murine macrophages and lung endothelial cells. Mice deficient in the JNK pathway had decreased serum levels of IL-6 and IL-1beta in response to LPS compared with control mice, and no effect of CO on these cytokine levels was seen in Jnk1 or Jnk2 genedeleted mice. In summary, these results suggest that CO provides protection in a murine model of sepsis through modulation of inflammatory cytokine production. For the first time, the effect of CO is shown to be mediated via the JNK signaling pathway and the transcription factor AP-1.

Inhibition of JNK signaling diminishes early but not late cellular stress-induced apoptosis

The human leukemic T-cell line Jurkat was used to define the role of the cellular stress pathway with its key player kinase JNK in cancer therapy-induced apoptosis. JNK activity was inhibited by stable transfection with a dominant negative mutant of the upstream kinase JNKK/MKK4 or with the novel, potent and selective JNK1, -2 and -3 inhibitor SP600125. Inhibition of JNK activity delayed the onset of apoptosis induced by cisplatin, doxorubicin, gamma-irradiation and CD95-L but did not prevent apoptosis per se. Early events during apoptosis such as induction of CD95-L, activation of caspase-8 and exposure of phosphatidylserine on the cell surface were strongly inhibited. Also, at early time points of apoptosis, loss of the mitochondrial membrane potential and release of cytochrome c were markedly impaired. However, late signaling events during apoptosis such as cleavage of PARP and DNA fragmentation apoptosis were only marginally affected. These findings are in accordance with the activity of initiator and effector caspases. Whereas activity of the initiator caspase-8 was strongly inhibited early and late after induction, an inhibition of caspase-3 activity was only observed early after induction of apoptosis. We therefore suggest that cellular stress signaling contributes to the initiation of apoptosis, whereas it might be dispensable for the progression of apoptosis. Dysfunction of this pathway under pathological conditions might contribute to therapy resistance of cancer cells.

The KDEL receptor modulates the endoplasmic reticulum stress response through mitogen-activated protein kinase signaling cascades

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) evokes the ER stress response. The resultant outcomes are cytoprotective but also proapoptotic. ER chaperones and misfolded proteins exit to the secretory pathway and are retrieved to the ER, during which process the KDEL receptor plays a significant role. Using an expression of a mutant KDEL receptor that lacks the ability for ligand recognition, we show that the impairment of retrieval by the KDEL receptor led to a mis-sorting of the immunoglobulin-binding protein BiP, an ER chaperone that has a retrieval signal from the early secretory pathway, which induced intense ER stress response and an increase in susceptibility to ER stress in HeLa cells. Furthermore, we show that the ER stress response accompanied the activation of p38 mitogen-activated protein (MAP) kinases and c-Jun amino-terminal kinases (JNKs) and that the expression of the mutant KDEL receptor suppressed the activation of p38 and JNK1 but not JNK2. The effect of the expression of the mutant KDEL receptor was consistent with the effect of a specific inhibitor for p38 MAP kinases, because the inhibitor sensitized HeLa cells to ER stress. We also found that activation of the KDEL receptor by the ligand induced the phosphorylation of p38 MAP kinases. These results indicate that the KDEL receptor participates in the ER stress response not only by its retrieval ability but also by modulating MAP kinase signaling, which may affect the outcomes of the mammalian ER stress response.

Association of gp91phox homolog Nox1 with anchorage-independent growth and MAP kinase-activation of transformed human keratinocytes

Among five members of the NADPH oxidase (Nox) family, Nox1 confers mitogenic properties and is implicated to participate in the process of cell transformation. We have established two phenotypes of carcinogenesis model by ethanol treatment of human gingival keratinocytes immortalized with E6/E7 oncogenes of human papillomavirus type16: immortalized (EPI) nontransformed cells with epithelium-like morphology and more advanced transformed (FIB) cells with spindle fibroblastic-shape morphology. FIB membranes possessed a 63-kDa Nox1 protein at higher levels and exhibited 2.8-fold higher capability for superoxide and hydroxyl radical generation, compared with EPI membranes. Both EPI and FIB cells expressed more abundant Nox1 protein at a proliferating stage than that at a quiescent confluent phase. Immunofluorescence staining with an anti-Nox1 antibody showed that immunoreactive materials were distributed in the whole interior of both types of cells, while they were preferentially localized in the nuclei of FIB cells. Nuclei isolated from EPI and FIB cells contained a 63 kDa-Nox1 protein. Compared with EPI cells, FIB cells expressed elevated levels of Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase proteins. Furthermore, JNK2 was constitutively phosphorylated in FIB cells. Together, our data strongly implicate Nox1 in redox-mediated signaling related to cellular activation of human keratinocytes at a more advanced stage of transformation.

5-fluorouracil blocks transforming growth factor-beta-induced alpha 2 type I collagen gene (COL1A2) expression in human fibroblasts via c-Jun NH2-terminal kinase/activator protein-1 activation

5-Fluorouracil (5-FU), a pyrimidine analog widely used in cancer chemotherapy and in glaucoma surgery, has recently shown some efficacy in the treatment of keloids, scars that overgrow the boundaries of original wounds. Given the physiopathological importance of transforming growth factor-beta (TGF-beta) in keloid and scar formation, we have examined whether the clinical benefits from 5-FU treatment may result from its capacity to interfere with TGF-beta signaling and resulting activation of type I collagen gene expression. Using various molecular approaches to study the mechanisms underlying 5-FU effects, we have demonstrated that 5-FU antagonizes TGF-beta-driven COL1A2 transcription and associated type I collagen production by dermal fibroblasts. In addition, 5-FU inhibits both SMAD3/4-specific transcription and formation of SMAD/DNA complexes induced by TGF-beta. 5-FU induces c-Jun phosphorylation and activates both AP-1-specific transcription and DNA binding. Overexpression of an antisense c-jun expression vector, or that of a dominant-negative form of MKK4 that interferes with c-Jun N-terminal kinase (JNK) activation, blocks the inhibitory activity of 5-FU on TGF-beta-induced COL1A2 transcription. Furthermore, in a cellular context devoid of JNK activity (i.e., JNK-/- fibroblasts), 5-FU inhibits neither formation of SMAD/DNA complexes nor SMAD-driven COL1A2 transcription in response to TGF-beta. Together, these results identify 5-FU as a potent inhibitor of TGF-beta/SMAD signaling, capable of blocking TGF-beta-induced, SMAD-driven up-regulation of COL1A2 gene expression in a JNK-dependent manner. We thus provide a molecular explanation to the observed clinical benefits of 5-FU in the treatment of keloids and hypertrophic scars.

A docking site in MKK4 mediates high affinity binding to JNK MAPKs and competes with similar docking sites in JNK substrates

Specific docking interactions between MAPKs and their activating MAPK kinases (MKKs or MEKs) are crucial for efficient and accurate signal transmission. Here, we report the identification of a MAPK-docking site, or "D-site," in the N terminus of human MKK4/JNKK1. This docking site conforms to the consensus sequence for known D-sites in other MKKs and contains the first of the two cleavage sites for anthrax lethal factor protease that have been found in the N terminus of MKK4. This docking site was both necessary and sufficient for the high affinity binding of the MAPKs JNK1, JNK2, JNK3, p38 alpha, and p38 beta to MKK4. Mutations that altered conserved residues in this docking site reduced JNK/p38 binding. In addition, a peptide version of this docking site, as well as a peptide version of the JNK-binding site of the JIP-1 scaffold protein, inhibited both MKK4/JNK binding and MKK4-mediated phosphorylation of JNK1. These same peptides also inhibited JNK2-mediated phosphorylation of c-Jun and ATF2, suggesting that transcription factors, MKK4, and the JIP scaffold compete for docking to JNK. Finally, the selectivity of the MKK4, MEK1, and MEK2 D-sites for JNK versus ERK was quantified. The MEK1 and MEK2 D-sites displayed a strong selectivity for their cognate MAPK (ERK2) versus a non-cognate MAPK (JNK). In contrast, the MKK4 D-site exhibited only limited selectivity for JNK versus ERK.

A neuron-specific EGF family protein, NELL2, promotes survival of neurons through mitogen-activated protein kinases

NELL2 is a neuron-specific thrombospondin-1-like extracellular protein containing six epidermal growth factor-like domains. NELL2 is highly expressed in the hippocampus and cerebral cortex. Although the involvement of NELL2 in neural functions has been inferred from its expression and biochemical profiles, biological roles of NELL2 remain uncertain. We evaluated the survival effect of NELL2 using primary cultured neurons from fetal rat brain following treatment with a recombinant NELL2 protein. NELL2 increased survival of neurons from the hippocampus and cerebral cortex. We further examined the protective effect of NELL2 from oxygen-glucose deprivation- and beta-amyloid-induced neuronal death, and found that NELL2 did not protect neurons from these insults. To understand signaling properties underlying the survival effect, we studied activation of mitogen-activated protein kinases (MAPKs) by NELL2. Treatment of primary cultured cells from the hippocampus with NELL2 enhanced phosphorylation of c-jun N-terminal kinase (JNK), whereas phosphorylation of extracellular signal-regulated kinase (ERK) was decreased by NELL2 treatment. NELL2-enhanced survival of hippocampal neurons was completely blocked by SP600125, an anthrapyrazolone inhibitor of JNK, while treatment of MEK (MAPK/ERK kinase) inhibitors per se enhanced survival of neurons similar to NELL2 treatment. These results suggest that NELL2 promotes survival of neurons by modulating MAPK activities.

Dopamine induces autophagic cell death and alpha-synuclein increase in human neuroblastoma SH-SY5Y cells

Free cytoplasmic dopamine may be involved in the genesis of neuronal degeneration in Parkinson's disease and other such diseases. We used SH-SY5Y human neuroblastoma cells to study the effect of dopamine on cell death, activation of stress-induced pathways, and expression of alpha-synuclein, the characteristic protein accumulated in Lewy bodies. We show that 100 and 500 microM dopamine causes a 40% and 60% decrease of viability, respectively, and triggers autophagy after 24 hr of exposure, characterized by the presence of numerous cytoplasmic vacuoles with inclusions. Dopamine causes mitochondrial aggregation in adherent cells prior to the loss of functionality. Plasma membrane and nucleus also maintain their integrity. Cell viability is protected by the dopamine transporter blocker nomifensine and the antioxidants N-acetylcysteine and ascorbic acid. Dopamine activates the stress-response kinases, SAPK/JNK and p38, but not ERK/MAPK or MEK, and increases alpha-synuclein expression. Both cell viability and the increase in alpha-synuclein expression are prevented by antioxidants; by the specific inhibitors of p38 and SAPK/JNK, SB203580 and SP600125, respectively; and by the inhibitor of autophagy 3-methyladenine. This indicates that oxidative stress, stress-activated kinases, and factors involved in autophagy up-regulate alpha-synuclein content. The results show that nonapoptotic death pathways are triggered by dopamine, leading to autophagy. These findings should be taken into account in the search for strategies to protect dopaminergic neurons from degeneration.

Shear-induced cyclooxygenase-2 via a JNK2/c-Jun-dependent pathway regulates prostaglandin receptor expression in chondrocytic cells

Using cDNA microarrays coupled with bioinformatics tools, we elucidated a signaling cascade regulating cyclooxygenase-2 (COX-2), a pivotal pro-inflammatory enzyme expressed in rheumatic and osteoarthritic, but not normal, cartilage. Exposure of T/C-28a2 chondrocytic cells to fluid shear results in co-regulation of c-Jun N-terminal kinase2 (JNK2), c-Jun, and COX-2 as well as concomitant downstream expression of prostaglandin receptors EP2 and EP3a1. JNK2 transcript inhibition abrogated shear-induced COX-2, EP2, and EP3a1 mRNA up-regulation as well as c-Jun phosphorylation. Functional knock-out experiments using an antisense c-Jun oligonucleotide revealed the abolition of shear-induced COX-2, EP2, and EP3a1, but not JNK2, transcripts. Moreover, inhibition of COX-2 activity eliminated mRNA upregulation of EP2 and EP3a1 induced by shear. Hence, a biochemical pathway exists wherein fluid shear activates COX-2, via a JNK2/c-Jun-dependent pathway, which in turn elicits downstream EP2 and EP3a1 mRNA synthesis.

Antioxidants attenuate myocyte apoptosis and improve cardiac function in CHF: association with changes in MAPK pathways

Antioxidant vitamins reduce cardiac oxidative stress and cardiomyocyte apoptosis produced by exogenous norepinephrine (NE) and attenuate cardiac dysfunction in animals with pacing-induced congestive heart failure (CHF). This study was carried out to determine whether the mitogen-activated protein kinase (MAPK) signal transduction pathways are involved in oxidative stress-induced myocyte apoptosis. Rabbits with rapid pacing-induced CHF and sham operation were randomized to receive either a combination of antioxidant vitamins (beta-carotene, ascorbic acid, and alpha-tocopherol), alpha-tocopherol alone, or placebo for 8 wk. Compared with sham-operated animals, CHF animals exhibited increased oxidative stress as evidenced by decreased myocardial reduced-to-oxidized glutathione (GSH/GSSG) ratio (27 +/- 7 vs. 143 +/- 24, P < 0.05), myocyte apoptosis (77 +/- 18 vs. 17 +/- 4 apoptotic nuclei/10,000 cardiomyocytes, P < 0.05), increased total and phosphorylated c-Jun NH2-terminal protein kinase (p-JNK; 1.95 +/- 0.14 vs. 1.04 +/- 0.04 arbitrary units, P < 0.05) and phosphorylated p38 kinase (p-p38), and decreased phosphorylated extracellular signal-regulated kinase (p-ERK). Administration of antioxidant vitamins and alpha-tocopherol attenuated oxidative stress, myocyte apoptosis, and cardiac dysfunction, with reversal of the changes of total JNK, p-JNK, and p-ERK in CHF. Furthermore, because NE infusion produced changes of JNK, p-p38, and p-ERK similar to those in CHF, we conclude that NE may play an important role in the production of oxidative stress, MAPK activation, and myocyte apoptosis in CHF.

Oxidative stress is a critical mediator of the angiotensin II signal in human neutrophils: involvement of mitogen-activated protein kinase, calcineurin, and the transcription factor NF-kappaB

Neutrophils are mobilized to the vascular wall during vessel inflammation. Published data are conflicting on phagocytic nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase activation during the hypertensive state, and the capacity of angiotensin II (Ang II) to modulate the intracellular redox status has not been analyzed in neutrophils. We here describe that Ang II highly stimulates endogenous and extracellular O2- production in these cells, consistent with the translocation to the cell membrane of the cytosolic components of NADPH oxidase, p47phox, and p67phox. The Ang II-dependent O2- production was suppressed by specific inhibitors of AT1 receptors, of the p38MAPK and ERK1/2 pathways, and of flavin oxidases. Furthermore, Ang II induced a robust phosphorylation of p38MAPK, ERK1/2, and JNK1/2 (particularly JNK2), which was hindered by inhibitors of NADPH oxidase, tyrosine kinases, and ROS scavengers. Ang II increased cytosolic Ca2+ levels-released mainly from calcium stores-enhanced the synthesis de novo and activity of calcineurin, and stimulated the DNA-binding activity of the transcription factor NF-kappaB in cultured human neutrophils. Present data demonstrate for the first time a stimulatory role of Ang II in the activation of phagocytic cells, underscore the relevant role of ROS as mediators in this process, and uncover a variety of signaling pathways by which Ang II operates in human neutrophils.

Role of the phosphatidylinositol 3 kinase-Akt pathway in the regulation of IL-10 and IL-12 by Porphyromonas gingivalis lipopolysaccharide

Stimulation of the APC by Porphyromonas gingivalis LPS has been shown to result in the production of certain pro- and anti-inflammatory cytokines. However, the signaling pathways that regulate these processes are currently unknown. In the present study, the role of the phosphatidylinositol 3 kinase (PI3K)-Akt pathway in regulating P. gingivalis LPS-induced production of IL-10, IL-12 p40, and IL-12 p70 by human monocytes was investigated. P. gingivalis LPS selectively activates the PI3K-Akt pathway via Toll-like receptor 2, and inhibition of this pathway results in an abrogation of extracellular signal-regulated kinase 1/2 phosphorylation, whereas the activation of p38 and c-Jun N-terminal kinase 1/2 kinases were unaffected. Analysis of cytokine production following stimulation of monocytes with P. gingivalis LPS revealed that inhibition of the PI3K pathway differentially regulated IL-10 and IL-12 synthesis. IL-10 production was suppressed, whereas IL-12 levels were enhanced. Inhibition of P. gingivalis LPS-mediated activation of the PI3K-Akt pathway resulted in a pronounced augmentation of NF-kappaB p65 that was independent of IkappaB-alpha degradation. Furthermore, the ability of the PI3K-Akt pathway to modulate IL-10 and IL-12 production appears to be mediated by the selective suppression of extracellular signal-regulated kinase 1/2 activity, as the MEK1 inhibitor PD98059 closely mimicked the effects of wortmannin and LY294002 to differentially regulate IL-10 and IL-12 production by P. gingivalis LPS-stimulated monocytes. These studies provide new insight into how engagement of the PI3K-Akt pathway by P. gingivalis LPS affects the induction of key immunoregulatory cytokines that control both qualitative and quantitative aspects of innate and adaptive immunity.

c-Jun N-terminal kinase negatively regulates lipopolysaccharide-induced IL-12 production in human macrophages: role of mitogen-activated protein kinase in glutathione redox regulation of IL-12 production

Although c-Jun N-terminal kinase (JNK) plays an important role in cytokine expression, its function in IL-12 production is obscure. The present study uses human macrophages to examine whether the JNK pathway is required for LPS-induced IL-12 production and defines how JNK is involved in the regulation of IL-12 production by glutathione redox, which is the balance between intracellular reduced (GSH) and oxidized glutathione (GSSG). We found that LPS induced IL-12 p40 protein and mRNA in a time- and concentration-dependent manner in PMA-treated THP-1 macrophages, and that LPS activated JNK and p38 mitogen-activated protein (MAP) kinase, but not extracellular signal-regulated kinase, in PMA-treated THP-1 cells. Inhibition of p38 MAP kinase activation using SB203580 dose dependently repressed LPS-induced IL-12 p40 production, as described. Conversely, inhibition of JNK activation using SP600125 dose dependently enhanced both LPS-induced IL-12 p40 production from THP-1 cells and p70 production from human monocytes. Furthermore, JNK antisense oligonucleotides attenuated cellular levels of JNK protein and LPS-induced JNK activation, but augmented IL-12 p40 protein production and mRNA expression. Finally, the increase in the ratio of GSH/GSSG induced by glutathione reduced form ethyl ester (GSH-OEt) dose dependently enhanced LPS-induced IL-12 p40 production in PMA-treated THP-1 cells. GSH-OEt augmented p38 MAP kinase activation, but suppressed the JNK activation induced by LPS. Our findings indicate that JNK negatively affects LPS-induced IL-12 production from human macrophages, and that glutathione redox regulates LPS-induced IL-12 production through the opposite control of JNK and p38 MAP kinase activation.

Caspase-mediated cleavage of JNK during stress-induced apoptosis

The c-Jun N-terminal kinases (JNKs) are a subfamily of the mitogen-activated protein kinases (MAPKs). The JNKs are encoded by three separate genes (jnk1, jnk2, and jnk3), which are spliced alternatively to create 10 JNK isoforms that are either p46 or p54 in size. In this study, we found that the p52 form of JNK emerged in human leukemia MOLT-4 or U937 cells following X-irradiation or heat treatment. The accumulation of p52 coincided with the reduction of p54 JNK. On the other hand, the amounts of p46 JNK did not change by X-irradiation. Induction of the p52 form of JNK also paralleled the appearance of the active form of caspase-3 and was suppressed by a caspase-specific inhibitor, Ac-DEVD-CHO, but not by Ac-YVAD-CHO. In vitro cleavage assays indicated that recombinant human JNK1beta2 and JNK2beta2 were cleaved by caspase-3, and that the mutation of aspartic acid at position 413 of JNK1beta2 or 410 of JNK2beta2 to alanine abolished the cleavage. Altogether, our results demonstrated that p54 JNKs, at least JNK1beta2 and JNK2beta2, were new selective targets of caspases in JNK splicing variants, and suggested that the p52 form could serve as a marker of apoptosis.

c-Jun N-terminal kinase contributes to apoptotic synergy induced by tumor necrosis factor-related apoptosis-inducing ligand plus DNA damage in chemoresistant, p53 inactive mesothelioma cells

Apoptotic resistance of cancer cells may be overcome by the combination of treatments that activate the two major apoptotic pathways: (i) the death receptor pathway activated by death ligands and (ii) the DNA damage pathway activated by chemotherapy. We have previously shown that mesothelioma cells, resistant to most treatments, are sensitive to the combination of the death ligand tumor necrosis factor-related apoptosis inducing ligand (TRAIL/Apo2L) plus chemotherapy. We investigated a possible role for c-Jun N-terminal kinase (JNK) in the synergistic effect, knowing that JNK can be activated separately by TRAIL and by DNA damage. We chose to study the M28 and REN human mesothelioma cell lines, which are p53-inactivated, to avoid an interaction between p53 and JNK. We showed that JNK was activated by TRAIL and by etoposide and that the activation was enhanced by the combination of the two treatments. We found this activation to be caspase-independent. To inhibit the JNK pathway, we used either dominant-negative constructs of JNK1 and JNK2 (compared with dominant-negative caspase 9) or a chemical inhibitor of the JNK pathway (SP600125). In cells treated with TRAIL plus etoposide, JNK inhibition increased cell survival and decreased apoptosis significantly. In transfected M28 cells, the effect of JNK inhibition was as great as that of the dominant-negative caspase 9 construct. We conclude that JNK contributes to the synergistic effect of TRAIL combined with DNA damage by mediating signals independent of p53 leading to apoptosis.

Upregulation of the Rac1/JNK signaling pathway in primary human schwannoma cells

Schwann cells lacking the tumor-suppressor-protein merlin tend in man to build benign tumors (schwannoma). We observed that characteristic features of these cells which are relevant to tumorigenicity resemble those described in cells with high Rac activity. Moreover this small GTPase also phosphorylates merlin via PAK activation. We hypothesized that merlin deficiency might cause an activation of Rac and its dependent signaling pathways, in particular the pro-tumorigenic JNK pathway. We show an enhanced activation of Rac1 in primary human schwannoma cells, find both Rac and its effector PAK at the membrane where they colocalize, and describe increased levels of phosphorylated JNK in the nucleus of these cells. Further we describe regulation at post-transcriptional level with upregulated protein, but not mRNA levels for Rac1, and JNK1/2. We conclude that merlin regulates Rac activation, and suggest that this is important for human schwannoma cell dedifferentiation.

C-Jun-NH2-terminal kinase mediates expression of connective tissue growth factor induced by transforming growth factor-beta1 in human lung fibroblasts

Many of the fibrogenic effects of transforming growth factor-beta (TGF-beta) might be mediated by connective tissue growth factor (CTGF). The present study investigates the role of mitogen-activated protein (MAP) kinase in the expression of CTGF mRNA in the human lung fibroblast line, HFL-1. TGF-beta1 enhanced CTGF mRNA levels in a time- and concentration-dependent manner, and this enhancement was also dependent upon transcription. Inhibition of p38 MAP kinase or extracellular signal-regulated kinase (ERK) activation did not affect TGF-beta1-induced CTGF expression. On the other hand, specific inhibitors of phosphatidylinositol 3-kinase (PI3K) suppressed TGF-beta1-induced CTGF expression in a concentration-dependent manner. TGF-beta1 activated c-Jun NH2-terminal kinase (JNK) and p38 MAP kinase, but not ERK in HFL-1 cells. PI3K inhibitors dose-dependently suppressed TGF-beta1-induced JNK, but not p38 MAP kinase activation. Finally, JNK1 and JNK2 antisense oligonucleotides attenuated cellular levels of JNK1 and JNK2 protein, respectively, and repressed TGF-beta1-induced CTGF expression. These results suggest that TGF-beta1-induced CTGF mRNA expression is mediated through the JNK-dependent pathway, whereas p38 MAP kinase and ERK pathways minimally contribute.

A role for c-Jun N-terminal kinase 1 (JNK1), but not JNK2, in the beta-amyloid-mediated stabilization of protein p53 and induction of the apoptotic cascade in cultured cortical neurons

beta-Amyloid (A beta) peptide has been shown to induce neuronal apoptosis; however, the mechanisms underlying A beta-induced neuronal cell death remain to be fully elucidated. The stress-activated protein kinase, c-Jun N-terminal kinase (JNK), is activated in response to cellular stress and has been identified as a proximal mediator of cell death. In the present study, expression of active JNK was increased in the nucleus and cytoplasm of A beta-treated cells. Evaluation of the nature of the JNK isoforms activated by A beta revealed a transient increase in JNK1 activity that reached its peak at 1 h and a later activation (at 24 h) of JNK2. The tumour suppressor protein, p53, is a substrate for JNK and can serve as a signalling molecule in apoptosis. In cultured cortical neurons, we found that A beta increased p53 protein expression and phosphorylation of p53 at Ser(15). Thus it appears that A beta increases p53 expression via phosphorylation-mediated stabilization of the protein. Given the lack of availability of a JNK inhibitor that can distinguish between JNK1- and JNK2-mediated effects, we employed antisense technology to deplete cells of JNK1 or JNK2 selectively. Using this strategy, the respective roles of JNK1 and JNK2 on the A beta-mediated activation of the apoptotic cascade (i.e. p53 stabilization, caspase 3 activation and DNA fragmentation) were examined. The results obtained demonstrate a role for JNK1 in the A beta-induced stabilization of p53, activation of caspase 3 and DNA fragmentation. In contrast, depletion of JNK2 had no effect on the proclivity of A beta to activate capase 3 or induce DNA fragmentation. These results demonstrate a significant role for JNK1 in A beta-mediated induction of the apoptotic cascade in cultured cortical neurons.

Bile acid regulation of C/EBPbeta, CREB, and c-Jun function, via the extracellular signal-regulated kinase and c-Jun NH2-terminal kinase pathways, modulates the apoptotic response of hepatocytes

Previously, we have demonstrated that deoxycholic acid (DCA)-induced signaling of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in primary hepatocytes is a protective response. In the present study, we examined the roles of the ERK and c-Jun NH(2)-terminal kinase (JNK) pathways, and downstream transcription factors, in the survival response of hepatocytes. DCA caused activation of the ERK1/2 and JNK1/2 pathways. Inhibition of either DCA-induced ERK1/2 or DCA-induced JNK1/2 signaling enhanced the apoptotic response of hepatocytes. Further analyses demonstrated that DCA-induced JNK2 signaling was cytoprotective whereas DCA-induced JNK1 signaling was cytotoxic. DCA-induced ERK1/2 activation was responsible for increased DNA binding of C/EBPbeta, CREB, and c-Jun/AP-1. Inhibition of C/EBPbeta, CREB, and c-Jun function promoted apoptosis following DCA treatment, and the level of apoptosis was further increased in the case of CREB and c-Jun, but not C/EBPbeta, by inhibition of MEK1/2. The combined loss of CREB and c-Jun function or of C/EBPbeta and c-Jun function enhanced DCA-induced apoptosis above the levels resulting from the loss of either factor individually; however, these effects were less than additive. Loss of c-Jun or CREB function correlated with increased expression of FAS death receptor and PUMA and decreased expression of c-FLIP-(L) and c-FLIP-(S), proteins previously implicated in the modulation of the cellular apoptotic response. Collectively, these data demonstrate that multiple DCA-induced signaling pathways and transcription factors control hepatocyte survival.

Regulation of hairy-cell survival through constitutive activation of mitogen-activated protein kinase pathways

The hairy cells (HCs) of hairy-cell leukemia are intrinsically activated mature clonal B cells. The aims of this study were to gain further insights into the nature of this activation and to assess its importance for the prolonged HC survival in this chronic disease. We show that HCs contain phosphorylated/activated p38 MAPK, JNK and ERK1/ERK2 (ERK1/2). PKC inhibitors increased the activation of p38 and JNK, but reduced the phosphorylation of ERK1/2. Moreover, PKC inhibition resulted in cell death; cell death was also observed when the activation of ERK1/2 in HCs was abrogated with an inhibitor of MEK1/2 activation. In addition to PKC, active Src kinase was also shown to be involved in the maintenance of Raf-independent ERK activation in HCs. During cell culture on a nonadherent surface, ERK phosphorylation was sustained, while phosphorylation of p38 and JNK decreased. This decrease was not observed in HCs cultured on vitronectin (VN), indicating that p38/JNK activation is probably a consequence of in vivo HC interaction with VN present in abundance in the red pulp of the spleen. Taken together, these results suggest that active p38/JNK make HCs susceptible to apoptosis, but the cells are effectively rescued by ERK activation involving constitutively active PKC and Src. These findings are relevant for the understanding of the prolonged cell survival of HCs and their selective sensitivity to some chemotherapeutic agents.

c-Jun NH(2)-terminal kinase is essential for the regulation of AP-1 by tumor necrosis factor

The c-Jun NH(2)-terminal kinase (JNK) is activated by the cytokine tumor necrosis factor (TNF). This pathway is implicated in the regulation of AP-1-dependent gene expression by TNF. To examine the role of the JNK signaling pathway, we compared the effects of TNF on wild-type and Jnk1(-/-) Jnk2(-/-) murine embryo fibroblasts. We show that JNK is required for the normal regulation of AP-1 by TNF. The JNK-deficient cells exhibited decreased expression of c-Jun, JunD, c-Fos, Fra1, and Fra2; decreased phosphorylation of c-Jun and JunD; and decreased AP-1 DNA binding activity. The JNK-deficient cells also exhibited defects in the regulation of the AP-1-related transcription factor ATF2. These changes were associated with marked defects in TNF-regulated gene expression. The JNK signal transduction pathway is therefore essential for AP-1 transcription factor regulation in cells exposed to TNF.

Mitogen-activated protein kinase (MAPK) pathway activation: effects of age and acute exercise on human skeletal muscle

The purpose of this investigation was to examine the activation (phosphorylation) and total protein content of MAPK signalling cascade proteins (ERK 1/2, p90RSK, Mnk 1, eIF4E, p38 MAPK, JNK/SAPK, MKP 1) at rest and following exercise, in sedentary young and old men. Eight young (22 +/- 1 years; YM) and eight old (79 +/- 3 years; OM) men underwent a resting muscle biopsy of the vastus lateralis; they then performed a knee extensor resistance exercise session (29 contractions at approximately 70 % of max), followed by a post-exercise biopsy. Western immunoblot analysis demonstrated that the OM had higher resting phosphorylation of ERK 1/2, p90RSK, Mnk 1, p38 MAPK and JNK/SAPK proteins versus YM (P < 0.05). The resistance exercise bout caused an increase in phosphorylation of the ERK 1/2, p90RSK and Mnk 1 proteins (P < 0.05) in the YM. Conversely, the OM had a decrease in ERK 1/2, p90RSK, Mnk 1, p38 MAPK and JNK/SAPK phosphorylation (P < 0.05) after the exercise bout. Neither group showed a change in eIF4E phosphorylation. The total amount of protein expression of the MAPK signalling proteins was not different between the YM and OM, except that there was a higher (P < 0.05) MKP 1 protein content in the OM. This investigation is the first to provide evidence that MAPK proteins are differentially activated at rest and in response to a bout of resistance exercise in skeletal muscle of young and old men. These findings may have implications for other processes (e.g. transcription and translation) involved in skeletal muscle type and growth, when examining the changes occurring with ageing muscle before and after resistance exercise/training.

Evidence for a role of p38 kinase in hypoxia-inducible factor 1-independent induction of vascular endothelial growth factor expression by sodium arsenite

Recently we have demonstrated that sodium arsenite induces the expression of hypoxia-inducible factor 1alpha (HIF-1alpha) protein and vascular endothelial growth factor (VEGF) in OVCAR-3 human ovarian cancer cells. We now show that arsenic trioxide, an experimental anticancer drug, exerts the same effects. The involvement of phosphatidylinositol 3-kinase and mitogen-activated protein kinase (MAPK) pathways in the effects of sodium arsenite was investigated. By using kinase inhibitors in OVCAR-3 cells, both effects of sodium arsenite were found to be independent of phosphatidylinositol 3-kinase and p44/p42 MAPKS but were attenuated by inhibition of p38 MAPK. A role for p38 in the regulation of HIF-1alpha and VEGF expression was supported further by analysis of activation kinetics. Experiments in mouse fibroblast cell lines, lacking expression of c-Jun N-terminal kinases 1 and 2, suggested that these kinases are not required for induction of HIF-1alpha protein and VEGF mRNA. Unexpectedly, sodium arsenite did not activate a HIF-1-dependent reporter gene in OVCAR-3 cells, indicating that functional HIF-1 was not induced. In agreement with this hypothesis, up-regulation of VEGF mRNA was not reduced in HIF-1alpha(-/-) mouse fibroblast cell lines. Altogether, these data suggest that not HIF-1, but rather p38, mediates induction of VEGF mRNA expression by sodium arsenite.

c-Jun N-terminal kinase (JNK) mediates feedback inhibition of the insulin signaling cascade

Activation of the c-Jun N-terminal kinase (JNK) by proinflammatory cytokines inhibits insulin signaling, at least in part, by stimulating phosphorylation of rat/mouse insulin receptor substrate 1 (Irs1) at Ser(307) (Ser(312) in human IRS1). Here we show that JNK mediated feedback inhibition of the insulin signal in mouse embryo fibroblasts, 3T3-L1 adipocytes, and 32D(IR) cells. Insulin stimulation of JNK activity required phosphatidylinositol 3-kinase and Grb2 signaling. Moreover, activation of JNK by insulin was inhibited by a cell-permeable peptide that disrupted the interaction of JNK with cellular proteins. However, the direct binding of JNK to Irs1 was not required for its activation by insulin, whereas direct binding was required for Ser(307) phosphorylation of Irs1. Insulin-stimulated Ser(307) phosphorylation was reduced 80% in cells lacking JNK1 and JNK2 or in cells expressing a mutant Irs1 protein lacking the JNK binding site. Reduced Ser(307) phosphorylation was directly related to increased insulin-stimulated tyrosine phosphorylation, Akt phosphorylation, and glucose uptake. These results support the hypothesis that JNK is a negative feedback regulator of insulin action by phosphorylating Ser(307) in Irs1.

Gene expression profiles at different stages of human esophageal squamous cell carcinoma

AIM: To characterize the gene expression profiles in different stages of carcinogenesis of esophageal epithelium.

METHODS: A microarray containing 588 cancer related genes was employed to study the gene expression profile at different stages of esophageal squamous cell carcinoma including basal cell hyperplasia, high-grade dysplasia, carcinoma in situ, early and late cancer. Principle component analysis was performed to search the genes which were important in carcinogenesis.

RESULTS: More than 100 genes were up or down regulated in esophageal epithelial cells during the stages of basal cell hyperplasia, high-grade dysplasia, carcinoma in situ, early and late cancer. Principle component analysis identified a set of genes which may play important roles in the tumor development. Comparison of expression profiles between these stages showed that some genes, such as P160ROCK, JNK2, were activated and may play an important role in early stages of carcinogenesis.

CONCLUSION: These findings provided an esophageal cancer-specific and stage-specific expression profiles, showing that complex alterations of gene expression underlie the development of malignant phenotype of esophageal cancer cells.