Control of MAP kinase signaling to the nucleus

Extracellular signal-regulated protein kinase 5 modulates the spindle assembly to coordinate the oocyte meiotic maturation

Extracellular signal-regulated protein kinase 5 (Erk5), a member of the mitogen-activated protein kinase (MAPK) family, is ubiquitously expressed in all eukaryotic cells and is implicated in the various mitotic processes such as cell survival, proliferation, migration, and differentiation. However, the potential functional roles of Erk5 in oocyte meiosis have not been fully determined. In this study, we document that ERK5 participates in the meiotic maturation of mouse oocytes by regulating the spindle assembly to ensure the meiotic progression. We unexpectedly found that phosphorylated ERK5 was localized in the spindle pole region at metaphase I and II stages by immunostaining analysis. Inhibition of ERK5 activity using its specific inhibitor XMD8-92 dramatically reduced the incidence of first polar body extrusion. In addition, inhibition of ERK5 evoked the spindle assembly checkpoint to arrest oocytes at metaphase I stage by impairing the spindle assembly, chromosome alignment and kinetochore-microtubule attachment. Mechanically, over-strengthened microtubule stability was shown to disrupt the microtubule dynamics and thus compromise the spindle assembly in ERK5-inhibited oocytes. Conversely, overexpression of ERK5 caused decreased level of acetylated α-tubulin and spindle defects. Collectively, we conclude that ERK5 plays an important role in the oocyte meiotic maturation by regulating microtubule dynamics and spindle assembly.

ERK2 Is a Promoter of Cancer Cell Growth and Migration in Colon Adenocarcinoma

ERK1/2 phosphorylation is frequently downregulated in the early phase of colon tumorigenesis with subsequent activation of ERK5. In the current work, we studied the advantages of ERK1/2 downregulation for tumor growth by dissecting the individual functions of ERK1 and ERK2. The patient sample data demonstrated decreased ERK1/2 phosphorylation in the early phase of tumorigenesis followed by increased phosphorylation in late-stage colon adenocarcinomas with intratumoral invasion or metastasis. In vitro results indicated that SOD3-mediated coordination of small GTPase RAS regulatory genes inhibited RAS-ERK1/2 signaling. In vitro and in vivo studies suggested that ERK2 has a more prominent role in chemotactic invasion, collective migration, and cell proliferation than ERK1. Of note, simultaneous ERK1 and ERK2 expression inhibited collective cell migration and proliferation but tended to promote invasion, suggesting that ERK1 controls ERK2 function. According to the present data, phosphorylated ERK1/2 at the early phase of colon adenocarcinoma limits tumor mass expansion, whereas reactivation of the kinases at the later phase of colon carcinogenesis is associated with the initiation of metastasis. Additionally, our results suggest that ERK1 is a regulatory kinase that coordinates ERK2-promoted chemotactic invasion, collective migration, and cell proliferation. Our findings indicate that ROS, especially H2O2, are associated with the regulation of ERK1/2 phosphorylation in colon cancer by either increasing or decreasing kinase activity. These data suggest that ERK2 has a growth-promoting role and ERK1 has a regulatory role in colon tumorigenesis, which could lead to new avenues in the development of cancer therapy.

Neurodevelopmental disorders, like cancer, are connected to impaired chromatin remodelers, PI3K/mTOR, and PAK1-regulated MAPK

Neurodevelopmental disorders (NDDs) and cancer share proteins, pathways, and mutations. Their clinical symptoms are different. However, individuals with NDDs have higher probabilities of eventually developing cancer. Here, we review the literature and ask how the shared features can lead to different medical conditions and why having an NDD first can increase the chances of malignancy. To explore these vital questions, we focus on dysregulated PI3K/mTOR, a major brain cell growth pathway in differentiation, and MAPK, a critical pathway in proliferation, a hallmark of cancer. Differentiation is governed by chromatin organization, making aberrant chromatin remodelers highly likely agents in NDDs. Dysregulated chromatin organization and accessibility influence the lineage of specific cell brain types at specific embryonic development stages. PAK1, with pivotal roles in brain development and in cancer, also regulates MAPK. We review, clarify, and connect dysregulated pathways with dysregulated proliferation and differentiation in cancer and NDDs and highlight PAK1 role in brain development and MAPK regulation. Exactly how PAK1 activation controls brain development, and why specific chromatin remodeler components, e.g., BAF170 encoded by SMARCC2 in autism, await clarification.

A mixture containing the herbicides Mesotrione and Atrazine imposes toxicological risks on workers of Partamona helleri

A mixture of Mesotrione and Atrazine (Calaris®) has been reported as an improvement of the atrazine herbicides, which are agrochemicals used for weed control. However, its possible harmful effects on non-target organisms, including pollinators, needs to be better understood. In this work, the effects of the mix of herbicides on food consumption, behaviour (walking distance, and meandering), and the morphology of the midgut of the stingless bee Partamona helleri were studied. Foragers were orally exposed to different concentrations of the mix. The concentrations leading to 10% and 50% mortality (LC₁₀ and LC₅₀, respectively) were estimated and used in the analysis of behaviour and morphology. The ingestion of contaminated diets (50% aqueous sucrose solution + mix) led to a reduction in food consumption by the bees when compared to the control, bees fed a non-contaminated diet (sucrose solution). Ingestion of the LC₅₀ diet reduced locomotor activity, increased meandering, induced the degradation of the epithelium and peritrophic matrix, and also changed the number of cells positive for signalling-pathway proteins in the midgut. These results show the potential toxicological effects and environmental impacts of the mix of herbicides in beneficial insects, including a native bee.

Apigenin Decreases Acinar Cell Damage in Pancreatitis

OBJECTIVE

Chronic pancreatitis is the consequence of multiple episodes of recurrent acute pancreatitis (RAP). We hypothesized that apigenin can minimize the sequelae of RAP by limiting acinar cells' proinflammatory signaling pathways.

METHODS

AR42J acinar cells were treated in vitro with transforming growth factor β (TGF-β), apigenin, and other inhibitors. Dual luciferase reporter assay measured parathyroid hormone-related protein (PTHrP) promoter activity. MAPK/ERK pathway activity was assessed by immunoblotting and in vivo by immunohistochemistry with a cerulein-induced RAP mouse model. Nuclear factor κ B nuclear localization was analyzed in vitro in cells stimulated with tumor necrosis factor α. Primary acini were isolated and treated with cerulein; interleukin 6 messenger RNA was measured comparing PTHrP wild-type and knockout mice.

RESULTS

Apigenin and PD98059 each downregulated TGF-β stimulation of PTHrP P3 promoter activity. In a RAP mouse model, apigenin reduced pERK nuclear localization in acinar cells and preserved acinar cell architecture. Apigenin suppressed tumor necrosis factor α-mediated signaling by decreasing nuclear factor κ B nuclear localization and decreased interleukin 6 messenger RNA levels via a PTHrP-dependent mechanism.

CONCLUSIONS

Apigenin reduced inflammatory responses in experimental models of RAP. The mechanisms mediating the actions of apigenin, in part, are owing to attenuation of PTHrP and TGF-β proinflammatory signaling.

A parental requirement for dual-specificity phosphatase 6 in zebrafish

Background

Signaling cascades, such as the extracellular signal-regulated kinase (ERK) pathway, play vital roles in early vertebrate development. Signals through these pathways are initiated by a growth factor or hormone, are transduced through a kinase cascade, and result in the expression of specific downstream genes that promote cellular proliferation, growth, or differentiation. Tight regulation of these signals is provided by positive or negative modulators at varying levels in the pathway, and is required for proper development and function. Two members of the dual-specificity phosphatase (Dusp) family, dusp6 and dusp2, are believed to be negative regulators of the ERK pathway and are expressed in both embryonic and adult zebrafish, but their specific roles in embryogenesis remain to be fully understood.

Results

Using CRISPR/Cas9 genome editing technology, we generated zebrafish lines harboring germ line deletions in dusp6 and dusp2. We do not detect any overt defects in dusp2 mutants, but we find that approximately 50% of offspring from homozygous dusp6 mutants do not proceed through embryonic development. These embryos are fertilized, but are unable to proceed past the first zygotic mitosis and stall at the 1-cell stage for several hours before dying by 10 h post fertilization. We demonstrate that dusp6 is expressed in gonads of both male and female zebrafish, suggesting that loss of dusp6 causes defects in germ cell production. Notably, the 50% of homozygous dusp6 mutants that complete the first cell division appear to progress through embryogenesis normally and give rise to fertile adults.

Conclusions

The fact that offspring of homozygous dusp6 mutants stall prior to activation of the zygotic genome, suggests that loss of dusp6 affects gametogenesis and/or parentally-directed early development. Further, since only approximately 50% of homozygous dusp6 mutants are affected, we postulate that ERK signaling is tightly regulated and that dusp6 is required to keep ERK signaling within a range that is permissive for proper embryogenesis. Lastly, since dusp6 is expressed throughout zebrafish embryogenesis, but dusp6 mutants do not exhibit defects after the first cell division, it is possible that other regulators of the ERK pathway compensate for loss of dusp6 at later stages.

Electronic supplementary material

The online version of this article (10.1186/s12861-018-0164-6) contains supplementary material, which is available to authorized users.

Increases in the expression of Na+ /H+ exchanger 1 and 3 are associated with insulin signalling in the ruminal epithelium

Na⁺ /H⁺ exchanger (NHE), which catalyses the exchange of extracellular Na⁺ for intracellular H⁺ , is of importance in the maintenance of Na⁺ and pH homoeostasis for rumen epithelial cells. Studies in ruminants showed that high concentrate diets could increase the expression of NHE in ruminal epithelium. Results of recent studies further indicated that insulin, as an important hormone closely related to dietary concentrate, could enhance the expression of NHE. In this study, we have investigated the mechanisms of insulin regulating the expression of NHE in rumen epithelial cells and its potential role in dietary modulation of NHE expression in ruminal epithelium of cows. In primary culture, insulin increased phosphorylation of ERK 1/2 and AKT in rumen epithelial cells. However, this promotion was diminished by insulin receptor inhibitor. Insulin also stimulated NHE1 and NHE3 expression. But this increase was suppressed by insulin receptor inhibitor, ERK inhibitor and AKT inhibitor. In the present animal experiment, NHE1 and NHE3 expression increased in rumen epithelium of cows ingesting a high concentrate diet (HC, 60% concentrate), accompanied by increased insulin concentration in plasma, compared to those feeding a low concentrate diet (LC, 20% concentrate). Furthermore, the phosphorylation of ERK1/2 and AKT was higher in the rumen epithelium of the HC group than those in the LC group. Collectively, these results indicate that diet-dependent change of NHE1 and NHE3 abundance was mediated, at least in part, by plasma insulin through the ERK and AKT pathway.

Oxidant effects and toxicity of Croton campestris in Drosophila melanogaster

CONTEXT

Croton campestris A.St.-Hil. (Euphorbiaceae) is a species native to Northeast Brazil used by traditional communities for the treatment of a variety of health problems. However, potential toxicological effects of this plant are unknown.

OBJECTIVE

The potential toxicity of the hydroalcoholic extract of C. campestris leaves on Drosophila melanogaster insect model, additionally with phytochemical constitution and cellular mechanisms mediating the action of extract were analysed in this study.

MATERIALS AND METHODS

Constituents of the extract were evaluated by HPLC. In vitro antioxidant potential of extract was analysed by DPPH, ABTS and FRAP. Flies injected culture medium mixed with extract (0.1-50 mg/mL) for 72 h. After, ROS production was evaluated by DCF-DA oxidation. Phosphorylation of MAPK signalling pathway was investigated by Western blotting method. Activity of antioxidant enzymes was analysed in homogenates.

RESULTS

Major components of the extract include quercetin (38.11 ± 0.06 mg/g), caffeic acid (20.06 ± 0.17 mg/g) and kaempferol (15.45 ± 0.05 mg/g). Consumption of the extract impaired locomotor performance and induced fly death of flies (LC₅₀ of 26.51 mg/mL). Augmented ROS formation and SOD, CAT and GST activity were observed from 0.1 mg/mL. JNK and p38 kinases phosphorylation was modulated and Paraquat-induced toxicity was augmented by extract.

DISCUSSION AND CONCLUSION

Our data show important toxicological effects of C. campestris leading to increased mortality and impaired locomotor performance accompanied by induction of cell stress markers in flies. The study draws attention to the indiscriminate use of plant extracts.

Spatial Control of Biochemical Modification Cascades and Pathways

Information transmission in cells occurs through complex networks of proteins and genes and is relayed through cascades of biochemical modifications, which are typically studied through ordinary differential equations. However, it is becoming increasingly clear that spatial factors can strongly influence chemical information transmission in cells. In this article, we systematically disentangle the effects of space in signaling cascades. This is done by examining the effects of localization/compartmentalization and diffusion of enzymes and substrates in multiple variants of chemical modification cascades. This includes situations where the modified form of species at one stage 1) acts as an enzyme for the next stage; 2) acts as a substrate for the next stage; and 3) is involved in phosphotransfer. Our analysis reveals the multiple effects of space in signal transduction cascades. Although in some cases space plays a modulatory effect (itself of interest), in other cases, spatial regulation and control can profoundly affect the nature of information processing as a result of the subtle interplay between the patterns of localization of species, diffusion, and the nature of the modification cascades. Our results provide a platform for disentangling the role of space and spatial control in multiple cellular contexts and a basis for engineering spatial control in signaling cascades through localization/compartmentalization.

On the Quest of Cellular Functions of PEA-15 and the Therapeutic Opportunities

Phosphoprotein enriched in astrocytes, 15 KDa (PEA-15), a ubiquitously expressed small protein in all mammals, is known for decades for its potent interactions with various protein partners along distinct biological pathways. Most notable interacting partners of PEA-15 include extracellular signal-regulated kinase 1 and 2 (ERK1/2) in the mitogen activated protein kinase (MAPK) pathway, the Fas-associated death domain (FADD) protein involving in the formation of the death-inducing signaling complex (DISC), and the phospholipase D1 (PLD1) affecting the insulin sensitivity. However, the actual cellular functions of PEA-15 are still mysterious, and the question why this protein is expressed in almost all cell and tissue types remains unanswered. Here we synthesize the most recent structural, biological, and clinical studies on PEA-15 with emphases on its anti-apoptotic, anti-proliferative, and anti-inflammative properties, and propose a converged protective role of PEA-15 that maintains the balance of death and survival in different cell types. Under conditions that this delicate balance is unsustainable, PEA-15 may become pathological and lead to various diseases, including cancers and diabetes. Targeting PEA-15 interactions, or the use of PEA-15 protein as therapeutics, may provide a wider window of opportunities to treat these diseases.

A single mechanism can explain network-wide insulin resistance in adipocytes from obese patients with type 2 diabetes

The response to insulin is impaired in type 2 diabetes. Much information is available about insulin signaling, but understanding of the cellular mechanisms causing impaired signaling and insulin resistance is hampered by fragmented data, mainly obtained from different cell lines and animals. We have collected quantitative and systems-wide dynamic data on insulin signaling in primary adipocytes and compared cells isolated from healthy and diabetic individuals. Mathematical modeling and experimental verification identified mechanisms of insulin control of the MAPKs ERK1/2. We found that in human adipocytes, insulin stimulates phosphorylation of the ribosomal protein S6 and hence protein synthesis about equally via ERK1/2 and mTORC1. Using mathematical modeling, we examined the signaling network as a whole and show that a single mechanism can explain the insulin resistance of type 2 diabetes throughout the network, involving signaling both through IRS1, PKB, and mTOR and via ERK1/2 to the nuclear transcription factor Elk1. The most important part of the insulin resistance mechanism is an attenuated feedback from the protein kinase mTORC1 to IRS1, which spreads signal attenuation to all parts of the insulin signaling network. Experimental inhibition of mTORC1 using rapamycin in adipocytes from non-diabetic individuals induced and thus confirmed the predicted network-wide insulin resistance.

β-Adrenergic receptor-mediated transactivation of epidermal growth factor receptor decreases cardiomyocyte apoptosis through differential subcellular activation of ERK1/2 and Akt

β-Adrenergic receptor (βAR)-mediated transactivation of epidermal growth factor receptor (EGFR) has been shown to relay pro-survival effects via unknown mechanisms. We hypothesized that acute βAR-mediated EGFR transactivation in the heart promotes differential subcellular activation of ERK1/2 and Akt, promoting cell survival through modulation of apoptosis. C57BL/6 mice underwent acute i.p. injection with isoproterenol (ISO)±AG 1478 (EGFR antagonist) to assess the impact of βAR-mediated EGFR transactivation on the phosphorylation of ERK1/2 (P-ERK1/2) and Akt (P-Akt) in distinct cardiac subcellular fractions. Increased P-ERK1/2 and P-Akt were observed in cytosolic, plasma membrane and nuclear fractions following ISO stimulation. Whereas the P-ERK1/2 response was EGFR-sensitive in all fractions, the P-Akt response was EGFR-sensitive only in the plasma membrane and nucleus, results confirmed in primary rat neonatal cardiomyocytes (RNCM). βAR-mediated EGFR-transactivation also decreased apoptosis in serum-depleted RNCM, as measured via TUNEL as well as caspase 3 activity/cleavage, which were sensitive to the inhibition of either ERK1/2 (PD184352) or Akt (LY-294002) signaling. Caspase 3 activity/cleavage was also sensitive to the inhibition of transcription, which, with an increase in nuclear P-ERK1/2 and P-Akt in response to ISO, suggested that βAR-mediated EGFR transactivation may regulate apoptotic gene transcription. An Apoptosis PCR Array identified tnfsf10 (TRAIL) to be altered by ISO in an EGFR-sensitive manner, results confirmed via RT-PCR and ELISA measurement of both membrane-bound and soluble cardiomyocyte TRAIL levels. βAR-mediated EGFR transactivation induces differential subcellular activation of ERK1/2 and Akt leading to increased cell survival through the modulation of caspase 3 activity and apoptotic gene expression in cardiomyocytes.

Fluoxetine signature on hippocampal MAPK signalling in sex-dependent manner

A growing body of evidence indicates that mitogen-activated protein kinase (MAPK) participates in various stress-induced responses and is considered to be one of the pathophysiological mechanisms in depression. Surprisingly, the effect of antidepressants on MAPKs is almost unexplored, particularly from the perspective of sexes. The present study investigates the cytoplasm-nuclear distribution of MAPK family, c-Jun N-terminal kinases (JNKs) 1, 2 and 3; extracellular signal-regulated kinases (ERKs) 1 and 2; and p38 kinases, as well as their phosphoisoforms in the hippocampus of chronically stressed female and male rats and upon chronic fluoxetine treatment. Additionally, we analysed crosstalk between MAPK signalling and depressive-like behaviour which correlated with brain-derived neurotrophic factor (BDNF) expression. Our results emphasize a gender-specific and compartment-dependent response of MAPKs to stress and fluoxetine. In females, stress decreased pp38 and pJNK and induced cytosolic retention of pERKs which reduced all nuclear pMAPKs. These changes correlated with altered BDNF expression and behaviour. Similarly, in males, stress decreased pp38 but promoted nuclear translocation of pJNKs and pERKs. These stress alterations of pMAPKs in males were not associated with BDNF expression and depressive-like behaviour. Fluoxetine treatment in stressed females upregulated whole pMAPK signalling particularly those in nucleus which was followed with BDNF expression and normalization of behaviour. In stressed males, fluoxetine affected only cytosolic pJNKs, while nuclear pMAPK signalling and BDNF expression were unaffected even though fluoxetine normalized behaviour. Overall, our results suggest existence of gender-specific mechanism of fluoxetine on nuclear pMAPK/BDNF signalling and depressive-like behaviour and reinforce the antidepressant dogma that females and males respond differently to certain antidepressants.

Effects of valproate sodium on extracellular signal-regulated kinase 1/2 phosphorylation following hippocampal neuronal epileptiform discharge in rats

The aim of the present study was to investigate the effects of valproate sodium (VPAS) on the phosphorylation extracellular signal-regulated kinase 1/2 (ERK1/2) following hippocampal neuronal epileptiform discharge in rat neurons. The study used neurons from female and male neonate Sprague-Dawley (SD) rats (at least 24 h old), which were rapidly decapitated. Following the successful development of the epileptiform discharge cell model, the neurons were divided into two groups, the VPAS group and the control group. In the concentration-response experiment, the neurons were incubated with three different concentrations of VPAS (50, 75 and 100 mg/l) 30 min prior to the epileptiform discharge. The expression of phosphorylated ERK1/2 (p-ERK1/2) was examined using an immunofluorescence technique. In the time-response experiment, the neurons were incubated with VPAS (50 mg/l) and monitored at different time-points (30 min prior to the epileptiform discharge and 0 min, 30 min, 2 h and 6 h subsequent to epileptiform discharge), and western blotting was employed to measure the changes in p-ERK1/2 protein expression. No significant differences in the expression of p-ERK1/2 among the neurons treated with different concentrations of VPAS were identified in the concentration-response experiment. However, in the time-response experiment, the expression of p-ERK1/2 30 min prior to the epileptiform discharge was significantly lower compared with that at the other time-points. Furthermore, 50 mg/l VPAS was capable of decreasing the action potential frequency of the neuronal epileptiform discharge. ERK1/2 was excessively and persistently activated following the epileptiform discharge of the neurons. In addition, a low concentration of VPAS was effective at inhibiting the phosphorylation of ERK1/2 at an earlier period of neuronal epileptiform discharge.

Organization of the ER-Golgi interface for membrane traffic control

Coat protein complex I (COPI) and COPII are required for bidirectional membrane trafficking between the endoplasmic reticulum (ER) and the Golgi. While these core coat machineries and other transport factors are highly conserved across species, high-resolution imaging studies indicate that the organization of the ER-Golgi interface is varied in eukaryotic cells. Regulation of COPII assembly, in some cases to manage distinct cellular cargo, is emerging as one important component in determining this structure. Comparison of the ER-Golgi interface across different systems, particularly mammalian and plant cells, reveals fundamental elements and distinct organization of this interface. A better understanding of how these interfaces are regulated to meet varying cellular secretory demands should provide key insights into the mechanisms that control efficient trafficking of proteins and lipids through the secretory pathway.

CCL2/CCR2 chemokine signaling coordinates survival and motility of breast cancer cells through Smad3 protein- and p42/44 mitogen-activated protein kinase (MAPK)-dependent mechanisms

Increased cell motility and survival are important hallmarks of metastatic tumor cells. However, the mechanisms that regulate the interplay between these cellular processes remain poorly understood. In these studies, we demonstrate that CCL2, a chemokine well known for regulating immune cell migration, plays an important role in signaling to breast cancer cells. We report that in a panel of mouse and human breast cancer cell lines CCL2 enhanced cell migration and survival associated with increased phosphorylation of Smad3 and p42/44MAPK proteins. The G protein-coupled receptor CCR2 was found to be elevated in breast cancers, correlating with CCL2 expression. RNA interference of CCR2 expression in breast cancer cells significantly inhibited CCL2-induced migration, survival, and phosphorylation of Smad3 and p42/44MAPK proteins. Disruption of Smad3 expression in mammary carcinoma cells blocked CCL2-induced cell survival and migration and partially reduced p42/44MAPK phosphorylation. Ablation of MAPK phosphorylation in Smad3-deficient cells with the MEK inhibitor U0126 further reduced cell survival but not migration. These data indicate that Smad3 signaling through MEK-p42/44MAPK regulates CCL2-induced cell motility and survival, whereas CCL2 induction of MEK-p42/44MAPK signaling independent of Smad3 functions as an alternative mechanism for cell survival. Furthermore, we show that CCL2-induced Smad3 signaling through MEK-p42/44MAPK regulates expression and activity of Rho GTPase to mediate CCL2-induced breast cancer cell motility and survival. With these studies, we characterize an important role for CCL2/CCR2 chemokine signaling in regulating the intrinsic relationships between breast cancer cell motility and survival with implications on the metastatic process.

Melanocortin 5 receptor signaling and internalization: role of MAPK/ERK pathway and β-arrestins 1/2

The Melanocortin 5 receptor (MC5R) is a G-protein coupled receptor (GPCR) that exhibits high affinity for α-MSH. Here we present evidence for MC5R-GFP internalization and subsequent recycling to cell surface, in α-MSH-stimulated HeLa cells. This melanocortin induces a biphasic activation of ERK1/2 with an early peak at 15min, a G(i)-protein driven, β-arrestins 1/2 independent process, and a late sustained activation that is regulated by β-arrestins 1/2. ERK1/2 lead to downstream phosphorylation of 90-kDa ribosomal S6 kinases (p90RSK) and mitogen- and stress-activated protein kinase 1 (MSK1). Only a small fraction (10%) of phosphorylated p90RSK and ERK1/2 translocates to the nucleus inducing c-Fos expression. α-MSH also activates CREB through cAMP/PKA pathway. In 3T3-L1 adipocytes, where MC5R is endogenously expressed, α-MSH also induces phosphorylation and cytosolic retention of the same signaling molecules. These findings provide new evidence on the signaling mechanisms underlying MC5R biological response to α-MSH.

Significance of decoy receptor 3 (Dcr3) and external-signal regulated kinase 1/2 (Erk1/2) in gastric cancer

Background

Decoy receptor 3 (DcR3), a member of the tumor necrosis factor receptor (TNFR) superfamily, is associated with anti-tumor immunity suppression. It is highly expressed in many tumors, and its expression can be regulated by the MAPK/MEK/ERK signaling pathway. The MAPK/MEK/ERK pathway has been reported to be a regulator in tumor occurrence, development and clonal expansion. External-signal regulated kinase (ERK) is a vital member of this pathway.

Results

The expression of DcR3 and ERK1/2 in tumor tissues of gastric cancer patients was significantly higher than the non-cancerous group (P < 0.05). There was no statistical difference among tumor tissues from patients with different ages or gender, and even of different differentiation (P > 0.05). However, in patients with stage I gastric cancer, the DcR3 and ERK1/2 levels were significantly lower than patients with more advanced stages.

Conclusions

DcR3 and ERK1/2 play a vital role in the development of gastric cancer, and they may be new markers for indicating the efficiency of gastric cancer treatment in the future.

Cotton GhMKK5 affects disease resistance, induces HR-like cell death, and reduces the tolerance to salt and drought stress in transgenic Nicotiana benthamiana

Mitogen-activated protein kinase (MAPK) cascades are involved in various processes from plant growth and development to biotic and abiotic stress responses. MAPK kinases (MAPKKs), which link MAPKs and MAPKK kinases (MAPKKKs), play crucial roles in MAPK cascades to mediate a variety of stress responses in plants. However, few MAPKKs have been functionally characterized in cotton (Gossypium hirsutum). In this study, a novel gene, GhMKK5, from cotton belonging to the group C MAPKKs was isolated and characterized. The expression of GhMKK5 can be induced by pathogen infection, abiotic stresses, and multiple defence-related signal molecules. The overexpression of GhMKK5 in Nicotiana benthamiana enhanced the plants' resistance to the bacterial pathogen Ralstonia solanacearum by elevating the expression of pathogen resistance (PR) genes, including PR1a, PR2, PR4, PR5, and NPR1, but increased the plants' sensitivity to the oomycete pathogen Phytophthora parasitica var. nicotianae Tucker. Importantly, GhMKK5-overexpressing plants displayed markedly elevated expression of reactive oxygen species-related and cell death marker genes, such as NtRbohA and NtCDM, and resulted in hypersensitive response (HR)-like cell death characterized by the accumulation of H(2)O(2). Furthermore, it was demonstrated that GhMKK5 overexpression in plants reduced their tolerance to salt and drought stresses, as determined by statistical analysis of seed germination, root length, leaf water loss, and survival rate. Drought obviously accelerated the cell death phenomenon in GhMKK5-overexpressing plants. These results suggest that GhMKK5 may play an important role in pathogen infection and the regulation of the salt and drought stress responses in plants.

ERK is involved in the reorganization of somatosensory cortical maps in adult rats submitted to hindlimb unloading

Sensorimotor restriction by a 14-day period of hindlimb unloading (HU) in the adult rat induces a reorganization of topographic maps and receptive fields. However, the underlying mechanisms are still unclear. Interest was turned towards a possible implication of intracellular MAPK signaling pathway since Extracellular-signal-Regulated Kinase 1/2 (ERK1/2) is known to play a significant role in the control of synaptic plasticity. In order to better understand the mechanisms underlying cortical plasticity in adult rats submitted to a sensorimotor restriction, we analyzed the time-course of ERK1/2 activation by immunoblot and of cortical reorganization by electrophysiological recordings, on rats submitted to hindlimb unloading over four weeks. Immunohistochemistry analysis provided evidence that ERK1/2 phosphorylation was increased in layer III neurons of the somatosensory cortex. This increase was transient, and parallel to the changes in hindpaw cortical map area (layer IV). By contrast, receptive fields were progressively enlarged from 7 to 28 days of hindlimb unloading. To determine whether ERK1/2 was involved in cortical remapping, we administered a specific ERK1/2 inhibitor (PD-98059) through osmotic mini-pump in rats hindlimb unloaded for 14 days. Results demonstrate that focal inhibition of ERK1/2 pathway prevents cortical reorganization, but had no effect on receptive fields. These results suggest that ERK1/2 plays a role in the induction of cortical plasticity during hindlimb unloading.

The MAP kinase signaling cascades: a system of hundreds of components regulates a diverse array of physiological functions

Sequential activation of kinases within the mitogen-activated protein (MAP) kinase (MAPK) cascades is a common, and evolutionary-conserved mechanism of signal transduction. Four MAPK cascades have been identified in the last 20 years and those are usually named according to the MAPK components that are the central building blocks of each of the cascades. These are the extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-Terminal kinase (JNK), p38, and ERK5 cascades. Each of these cascades consists of a core module of three tiers of protein kinases termed MAPK, MAPKK, and MAP3K, and often two additional tiers, the upstream MAP4K and the downstream MAPKAPK, which can complete five tiers of each cascade in certain cell lines or stimulations. The transmission of the signal via each cascade is mediated by sequential phosphorylation and activation of the components in the sequential tiers. These cascades cooperate in transmitting various extracellular signals and thus control a large number of distinct and even opposing cellular processes such as proliferation, differentiation, survival, development, stress response, and apoptosis. One way by which the specificity of each cascade is regulated is through the existence of several distinct components in each tier of the different cascades. About 70 genes, which are each translated to several alternatively spliced isoforms, encode the entire MAPK system, and allow the wide array of cascade's functions. These components, their regulation, as well as their involvement together with other mechanisms in the determination of signaling specificity by the MAPK cascade is described in this review. Mis-regulation of the MAPKs signals usually leads to diseases such as cancer and diabetes; therefore, studying the mechanisms of specificity-determination may lead to better understanding of these signaling-related diseases.

ERK-1 MAP kinase prevents TNF-induced apoptosis through bad phosphorylation and inhibition of Bax translocation in HeLa Cells

Extracellular signal-regulated kinase (ERK) 1/2 signaling is involved in tumor cell survival through the regulation of Bcl-2 family members. To explore this further and to demonstrate the central role of the mitochondria in the ERK1/2 pathway we used the HeLa cellular model where apoptosis was induced by tumor necrosis factor (TNF) and cycloheximide (CHX). We show that HeLa cells overexpressing ERK-1 displayed resistance to TNF and CHX. HeLa cells overexpressing a kinase-deficient form of ERK-1 (K71R) were more sensitive to TNF and CHX. In the ERK-1 cells, Bad was phosphorylated during TNF + CHX treatment. In the HeLa wt cells and in the K71R clones TNF and CHX decreased Bad phosphorylation. ERK-1 cells treated with TNF and CHX did not release cytochrome c from the mitochondria. By contrast, HeLa wt and K71R clones released cytochrome c. Bax did not translocate to the mitochondria in ERK-1 cells treated with TNF + CHX. Conversely, HeLa wt and K71R clones accumulated Bax in the mitochondria. In the HeLa wt cells and in both ERK-1 transfectants Bid was cleaved and accumulated in the mitochondria. The caspase-8 inhibitor IETD-FMK and the mitochondrial membrane permeabilization inhibitor bongkrekic acid (BK), partially prevented cell death by TNF + CHX. Anisomycin, a c-Jun N-terminal kinases activator, increased TNF-killing. The ERK-1 cells were resistant to TNF and anisomycin, whereas K71R clones resulted more sensitive. Our study demonstrates that in HeLa cells the ERK-1 kinase prevents TNF + CHX apoptosis by regulating the intrinsic mitochondrial pathway through different mechanisms. Inhibition of the intrinsic pathway is sufficient to almost completely prevent cell death.

A combination of multisite phosphorylation and substrate sequestration produces switchlike responses

The phosphorylation of a protein on multiple sites has been proposed to promote the switchlike regulation of protein activity. Recent theoretical work, however, indicates that multisite phosphorylation, by itself, is less effective at creating switchlike responses than had been previously thought. The phosphorylation of a protein often alters its spatial localization, or its association with other proteins, and this sequestration can alter the accessibility of the substrate to the relevant kinases and phosphatases. Sequestration thus has the potential to interact with multisite phosphorylation to modulate ultrasensitivity and threshold. Here, using simple ordinary differential equations to represent phosphorylation, dephosphorylation, and binding/sequestration, we demonstrate that the combination of multisite phosphorylation and regulated substrate sequestration can produce a response that is both a good threshold and a good switch. Several strategies are explored, including both stronger and weaker sequestration with successive phosphorylations, as well as combinations that are more elaborate. In some strategies, such as when phosphorylation and dephosphorylation are segregated, a near-optimal switch is possible, where the effective Hill number equals the number of phosphorylation sites.

Independent phenotype of binuclear hepatocytes and cellular localization of UbD

Mice fed DDC (0.1%) for 10 weeks, and then withdrawn from the drug for 1 month, retain the ability to form Mallory-Denk bodies (MDBs) when the drug is refed for 7 days. The number of liver cells that form MDBs increased and partially replaced normal liver cells, at the end of 7 days of refeeding DDC. The MDBs that formed were associated with increased expression of UbD (also called FAT10) in the Mallory-Denk body forming cells. UbD is over expressed in 70% of human HCCs, but its cellular localization is not well established. UbD belongs to the UbL family (ubiquitin-like), and can be linked to others proteins with their 2 C-terminal glycine to lysine. By Western Blot, UbD was found to be covalently linked with proteins. We performed immunohistochemistry on tissue from mouse liver and found that UbD was located in the cytoplasm and in one or two nuclei of the same hepatocyte. However, in primary cell culture, UbD formed speckles within the cytoplasm of the liver cell. A similar pattern of cytoplasmic localization was observed in the Hepa 1-6 cell lines, which over expressed UbD fused with GFP at the C-Terminal. The localization and the control of UbD localization remain unclear. The identification of proteins that interact with UbD and the post translational modification of UbD would help to determine the regulation of this localization and function.

The subcellular localization of MEK and ERK--a novel nuclear translocation signal (NTS) paves a way to the nucleus

The ERK cascade is a central signaling pathway that regulates a large number of intracellular processes including proliferation, differentiation, development and also survival or apoptosis. The induction of so many distinct and even opposing cellular processes raises the question as to how the signaling specificity of the cascade is regulated. In the past few years, subcellular localization of components of the ERK cascade was shown to play an important role in specificity determination. Here we describe the dynamic subcellular localization of Raf kinases, MEKs, and particularly ERKs, which translocate into the nucleus during many cellular processes to induce transcription. We also describe in details the recent identification of a novel nuclear translocation mechanism for ERKs, which is based on a nuclear translocation sequence (NTS) within their kinase insert domain (KID). Phosphorylation of this domain, mainly upon stimulation, allows ERKs to interact with the nuclear importing protein - importin7, which mediates the penetration of the interacting ERKs into the nucleus via nuclear pores. Interestingly, the NTS is not specific to ERKs, and seems to be a general signal for regulating nuclear accumulation of various proteins, including MEKs, upon their stimulation. Better understanding of this mechanism may clarify the role of the massive nuclear translocation of many regulatory proteins shortly after their stimulation.

Differentiation-dependent association of phosphorylated extracellular signal-regulated kinase with the chromatin of osteoblast-related genes

The ERK/MAP kinase pathway is an important regulator of gene expression and differentiation in postmitotic cells. To understand how this pathway controls gene expression in bone, we examined the subnuclear localization of P-ERK in differentiating osteoblasts. Induction of differentiation was accompanied by increased ERK phosphorylation and expression of osteoblast-related genes, including osteocalcin (Bglap2) and bone sialoprotein (Ibsp). Confocal immunofluorescence microscopy revealed that P-ERK colocalized with the RUNX2 transcription factor in the nuclei of differentiating cells. Interestingly, a portion of this nuclear P-ERK was directly bound to the proximal promoter regions of Bglap2 and Ibsp. Furthermore, the level of P-ERK binding to chromatin increased with differentiation, whereas RUNX2 binding remained relatively constant. The P-ERK-chromatin interaction was seen only in RUNX2-positive cells, required intact RUNX2-selective enhancer sequences, and was blocked with MAPK inhibition. These studies show for the first time that RUNX2 specifically targets P-ERK to the chromatin of osteoblast-related genes, where it may phosphorylate multiple substrates, including RUNX2, resulting in altered chromatin structure and gene expression.

Nuclear protein kinases: still enigmatic components in plant cell signalling

Plants constantly face changing conditions in their environment. Unravelling the transduction mechanisms from signal perception at the plasma membrane level down to gene expression in the nucleus is a fascinating challenge. Protein phosphorylation, catalysed by protein kinases, is one of the major posttranslational modifications involved in the specificity, kinetic(s) and intensity of a signal transduction pathway. Although commonly assumed, the involvement of nuclear protein kinases in signal transduction is often poorly characterized. In particular, both their regulation and mode of action remain to be elucidated and may lead to the unveiling of new original mechanisms. For example, unlike animal cells, plant cells contain only a few strictly nucleus-localized protein kinases, which calls into question the role of this cellular distribution between the cytosol and the nucleus in their activation and functions. The control of their nucleocytoplasmic trafficking appears to play a major role in their regulation, probably through promoting interactions with their substrates under specific cellular conditions. However, recent findings showing that the nucleus can generate complex networks of second messengers (e.g. Ca(2+)or diacyglycerol) suggest that nuclear protein kinases could play an active role in the decoding of such signals.

Thioredoxin regulates cell cycle via the ERK1/2-cyclin D1 pathway

Thioredoxin (TRX) is a key component of redox regulation and has been indicated to play an essential role in cell survival and growth. Here, we investigated the molecular mechanism of TRX in the regulation of cell survival and growth by using RNA interference (RNAi) in A549 lung cancer and MCF7 breast cancer cells. TRX knockdown did not significantly increase the basal level of cell death without exposure to stress, but CDDP-induced cell death was enhanced. Meanwhile, TRX knockdown resulted in significant cell-cycle arrest at the G(1) phase. Cyclin D1 expression was reduced by TRX knockdown at the protein and mRNA levels. TRX knockdown caused suppression of activation of the cyclin D1 promoter through elements including AP-1. TRX knockdown also reduced the levels of phosphorylated ERK1/2 and the nuclear translocation of ERK 1/2 induced by EGF. These results suggest that TRX is an important regulator of the cell cycle in the G(1) phase via cyclin D1 transcription and the ERK/AP-1 signaling pathways.

Antioxidant effect of estrogen on bovine aortic endothelial cells

OBJECTIVE

This study discussed the role of estrogen as an antioxidant in the damage of vascular endothelial cells.

DESIGN

We treated bovine aortic endothelial cells (bAEC) either with 1mM of H(2)O(2) alone or with 1 microM of 17beta-estradiol (E(2)) for 24h followed by 1mM of H(2)O(2) for 3h. The cell survival was evaluated by MTT assay, cellular apoptosis by fluorescence activated cell sorter (FACS) and Hoechst 33342 staining, oxidative stress by intracellular reactive oxygen species (ROS) and apoptosis after oxidative stress by western blotting for phospho-p38, p38, and Bcl-2.

RESULTS

MTT assay showed that bAEC viability was reduced to 55.7+/-3.0% and 39.1+/-3.7% after 30 and 60 min of H(2)O(2) treatment, respectively. E(2) and H(2)O(2) treated cells did not show significant decrease in the cell survival. Similarly the FACS analysis and Hoechst 33342 stain showed that the latter decreased cellular apoptosis induced by H(2)O(2). Intracellular ROS increased by 181.6+/-68.9% in the former and by 37.0+/-3.9% in the latter (P<0.05). The expression of phospho-p38 mitogen-activated protein kinase (MAPK) was higher in the latter.

CONCLUSIONS

E(2) mediates antioxidant effects on the oxidative stress induced by H(2)O(2). This antioxidant effect on bAEC may elucidate the scientific basis of hormone therapy for maintaining cardiovascular integrity in postmenopausal women.

Phosphorylation of Williams syndrome transcription factor by MAPK induces a switching between two distinct chromatin remodeling complexes

Changes in the environment of a cell precipitate extracellular signals and sequential cascades of protein modification and elicit nuclear transcriptional responses. However, the functional links between intracellular signaling-dependent gene regulation and epigenetic regulation by chromatin-modifying proteins within the nucleus are largely unknown. Here, we describe novel epigenetic regulation by MAPK cascades that modulate formation of an ATP-dependent chromatin remodeling complex, WINAC (WSTF Including Nucleosome Assembly Complex), an SWI/SNF-type complex containing Williams syndrome transcription factor (WSTF). WSTF, a specific component of two chromatin remodeling complexes (SWI/SNF-type WINAC and ISWI-type WICH), was phosphorylated by the stimulation of MAPK cascades in vitro and in vivo. Ser-158 residue in the WAC (WSTF/Acf1/cbpq46) domain, located close to the N terminus of WSTF, was identified as a major phosphorylation target. Using biochemical analysis of a WSTF mutant (WSTF-S158A) stably expressing cell line, the phosphorylation of this residue (Ser-158) was found to be essential for maintaining the association between WSTF and core BAF complex components, thereby maintaining the ATPase activity of WINAC. WINAC-dependent transcriptional regulation of vitamin D receptor was consequently impaired by this WSTF mutation, but the recovery from DNA damage mediated by WICH was not impaired. Our results suggest that WSTF serves as a nuclear sensor of the extracellular signals to fine-tune the chromatin remodeling activity of WINAC. WINAC mediates a previously unknown MAPK-dependent step in epigenetic regulation, and this MAPK-dependent switching mechanism between the two functionally distinct WSTF-containing complexes might underlie the diverse functions of WSTF in various nuclear events.

Extracellular signal-regulated kinase 1 (ERK1) and ERK2 play essential roles in osteoblast differentiation and in supporting osteoclastogenesis

Osteoblasts and chondrocytes arise from common osteo-chondroprogenitor cells. We show here that inactivation of ERK1 and ERK2 in osteo-chondroprogenitor cells causes a block in osteoblast differentiation and leads to ectopic chondrogenic differentiation in the bone-forming region in the perichondrium. Furthermore, increased mitogen-activated protein kinase signaling in mesenchymal cells enhances osteoblast differentiation and inhibits chondrocyte differentiation. These observations indicate that extracellular signal-regulated kinase 1 (ERK1) and ERK2 play essential roles in the lineage specification of mesenchymal cells. The inactivation of ERK1 and ERK2 resulted in reduced beta-catenin expression, suggesting a role for canonical Wnt signaling in ERK1 and ERK2 regulation of skeletal lineage specification. Furthermore, inactivation of ERK1 and ERK2 significantly reduced RANKL expression, accounting for a delay in osteoclast formation. Thus, our results indicate that ERK1 and ERK2 not only play essential roles in the lineage specification of osteo-chondroprogenitor cells but also support osteoclast formation in vivo.

PPAR-γ agonists and their effects on IGF-I receptor signaling: Implications for cancer

It is now well established that the development and progression of a variety of human malignancies are associated with dysregulated activity of the insulin-like growth factor (IGF) system. In this regard, promising drugs have been developed to target the IGF-I receptor or its ligands. These therapies are limited by the development of insulin resistance and compensatory hyperinsulinemia, which in turn, may stimulate cancer growth. Novel therapeutic approaches are, therefore, required. Synthetic PPAR-γ agonists, such as thiazolidinediones (TZDs), are drugs universally used as antidiabetic agents in patients with type 2 diabetes. In addition of acting as insulin sensitizers, PPAR-γ agonists mediate in vitro and in vivo pleiotropic anticancer effects. At least some of these effects appear to be linked with the downregulation of the IGF system, which is induced by the cross-talk of PPAR-γ agonists with multiple components of the IGF system signaling. As hyperinsulinemia is an emerging cancer risk factor, the insulin lowering action of PPAR-γ agonists may be expected to be also beneficial to reduce cancer development and/or progression. In light of these evidences, TZDs or other PPAR-γ agonists may be exploited in those tumors "addicted" to the IGF signaling and/or in tumors occurring in hyperinsulinemic patients.

Proteomic analysis reveals upregulation of RKIP in S-180 implanted BALB/C mouse after treatment with ascorbic acid

Tumor cells have an invasive and metastatic phenotype that is the main cause of death for cancer patients. Tumor establishment and penetration consists of a series of complex processes involving multiple changes in gene expression. In this study, intraperitoneal administration of a high concentration of ascorbic acid inhibited tumor establishment and increased survival of BALB/C mice implanted with S-180 sarcoma cancer cells. To identify proteins involved in the ascorbic acid-mediated inhibition of tumor progression, changes in the liver proteome associated with ascorbic acid treatment of BALB/C mice implanted with S-180 were investigated using two-dimensional gel electrophoresis and mass spectrometry. Eleven protein spots were identified whose expression was different between control and ascorbic acid treatment groups. In particular, Raf kinase inhibitory protein (RKIP) and annexin A5 expression were quantitatively up-regulated. The increase in RKIP protein level was detected in the tumor tissue and accompanied by an increase in mRNA level. Our results suggest a possibility that these proteins are related to the ascorbic acid-mediated suppression of tumor formation.

PAP1 signaling involves MAPK signal transduction

Pancreatitis-associated protein 1 (PAP1) belongs to the Reg family of secretory proteins. Several important biological roles have been attributed to PAP1 but the signaling pathways activated by this protein remain only partially understood. Here, we describe the intracellular pathways triggered by PAP1 in a pancreatic acinar cell line. Taking advantage of the fact that PAP1 induces its own transcription, we performed ChIP assays to analyze the recruitment of transcriptional factors on its promoter. Our results show that PAP1 increased the transactivation activity of pap1 and the binding on its promoter of the nuclear factors C/EBPbeta, P-CREB, P-ELK1, EGR1, STAT3, and ETS2, which are downstream targets of MAPK signaling. p44/42, p38, and JNK MAPKs activity increased after PAP1 treatment. In addition, pharmacological inhibition of these kinases markedly inhibited the induction of pap1 mRNA. Taken together, these results indicated that the mechanism of PAP1 action involves the activation of the MAPK superfamily.

How ERK1/2 activation controls cell proliferation and cell death: Is subcellular localization the answer?

Extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) are members of the mitogen-activated protein kinase super family that can mediate cell proliferation and apoptosis. The Ras-Raf-MEK-ERK signaling cascade controlling cell proliferation has been well studied but the mechanisms involved in ERK1/2-mediated cell death are largely unknown. This review focuses on recent papers that define ERK1/2 translocation to the nucleus and the proteins involved in the cytosolic retention of activated ERK1/2. Cytosolic retention of ERK1/2 denies access to the transcription factor substrates that are responsible for the mitogenic response. In addition, cytosolic ERK1/2, besides inhibiting survival and proliferative signals in the nucleus, potentiates the catalytic activity of some proapoptotic proteins such as DAP kinase in the cytoplasm. Studies that further define the function of cytosolic ERK1/2 and its cytosolic substrates that enhance cell death will be essential to harness this pathway for developing effective treatments for cancer and chronic inflammatory diseases.

Involvement of mitogen-activated protein kinases and nuclear factor kappa B pathways in signaling COX-2 expression in chronic rhinosinusitis

OBJECTIVE

To investigate the signal pathways involved in cyclooxygenase-2 (COX-2) expression in chronic rhinosinusitis (CRS).

METHODS

The expressions of COX-2, p38 mitogen-activated protein kinase (p38MAPK), extracellular signal-regulated kinase (ERK), and nuclear factor kappa B (NF-kappaB) in nasal mucosa were detected by immunohistological stain and polymerase chain reaction (PCR). Their expressions and prostaglandin E2 (PGE(2)) release were determined by PCR, Western blot and enzyme immunoassay (EIA) in human nasal epithelia (HNE) cells after lipopolysaccharide (LPS) induction, and/or small interfering RNA (siRNA) transfection.

RESULTS

Positive protein expressions of COX-2, p38MAPK, ERK, NF-kappaB subunits were detected in epithelial and inflammatory cells. Their mRNA levels were significantly higher in CRS than controls (P < 0.05). The expressions varied in time and concentration-dependent manner in LPS-induced HNE cells. COX-2 expression was suppressed by siRNAs of P38MAPK, ERK, and NF-kappaB; however, COX-2-specific siRNA had no blocking effect on them. SiRNAs of P38MAPK or ERK could block NF-kappaB, but NF-kappaB-specific siRNA had no blocking effect on the former. SiRNA of p38MAPK, or ERK did not inhibit each other.

CONCLUSION

Upregulation of COX-2 expression suggested its role as a mediator in CRS. ERK and p38MAPK pathways were involved in signaling COX-2 through NF-kappaB pathway.

Activation of a nuclear-localized SIPK in tobacco cells challenged by cryptogein, an elicitor of plant defence reactions

When a plant cell is challenged by a well-defined stimulus, complex signal transduction pathways are activated to promote the modulation of specific sets of genes and eventually to develop adaptive responses. In this context, protein phosphorylation plays a fundamental role through the activation of multiple protein kinase families. Although the involvement of protein kinases at the plasma membrane and cytosolic levels are now well-documented, their nuclear counterparts are still poorly investigated. In the field of plant defence reactions, no known study has yet reported the activation of a nuclear protein kinase and/or its nuclear activity in plant cells, although some protein kinases, e.g. MAPK (mitogen-activated protein kinase), are known to be translocated into the nucleus. In the present study, we investigated the ability of cryptogein, a proteinaceous elicitor of tobacco defence reactions, to induce different nuclear protein kinase activities. We found that at least four nuclear protein kinases are activated in response to cryptogein treatment in a time-dependent manner, some of them exhibiting Ca(2+)-dependent activity. The present study focused on one 47 kDa protein kinase with a Ca(2+)-independent activity, closely related to the MAPK family. After purification and microsequencing, this protein kinase was formally identified as SIPK (salicyclic acid-induced protein kinase), a biotic and abiotic stress-activated MAPK of tobacco. We also showed that cytosolic activation of SIPK is not sufficient to promote a nuclear SIPK activity, the latter being correlated with cell death. In that way, the present study provides evidence of a functional nuclear MAPK activity involved in response to an elicitor treatment.

The ubiquitin ligase RPM-1 and the p38 MAPK PMK-3 regulate AMPA receptor trafficking

Ubiquitination occurs at synapses, yet its role remains unclear. Previous studies demonstrated that the RPM-1 ubiquitin ligase organizes presynaptic boutons at neuromuscular junctions in C. elegans motorneurons. Here we find that RPM-1 has a novel postsynaptic role in interneurons, where it regulates the trafficking of the AMPA-type glutamate receptor GLR-1 from synapses into endosomes. Mutations in rpm-1 cause the aberrant accumulation of GLR-1 in neurites. Moreover, rpm-1 mutations enhance the endosomal accumulation of GLR-1 observed in mutants for lin-10, a Mint2 ortholog that promotes GLR-1 recycling from Syntaxin-13 containing endosomes. As in motorneurons, RPM-1 negatively regulates the pmk-3/p38 MAPK pathway in interneurons by repressing the protein levels of the MAPKKK DLK-1. This regulation of PMK-3 signaling is critical for RPM-1 function with respect to GLR-1 trafficking, as pmk-3 mutations suppress both lin-10 and rpm-1 mutations. Positive or negative changes in endocytosis mimic the effects of rpm-1 or pmk-3 mutations, respectively, on GLR-1 trafficking. Specifically, RAB-5(GDP), an inactive mutant of RAB-5 that reduces endocytosis, mimics the effect of pmk-3 mutations when introduced into wild-type animals, and occludes the effect of pmk-3 mutations when introduced into pmk-3 mutants. By contrast, RAB-5(GTP), which increases endocytosis, suppresses the effect of pmk-3 mutations, mimics the effect of rpm-1 mutations, and occludes the effect of rpm-1 mutations. Our findings indicate a novel specialized role for RPM-1 and PMK-3/p38 MAPK in regulating the endosomal trafficking of AMPARs at central synapses.

Dynamic regulation of bHLH-PAS-type transcription factor NXF gene expression and neurotrophin dependent induction of the transcriptional control activity

While neurotrophin is known to be involved in a variety of neuronal functions inducing several immediate early genes and activating several signaling molecules, the correspondence with downstream cascades remains to be defined in detail. Here we show that a bHLH-PAS transcription factor, NXF, is a new member genes under the control of neurotrophin. The PI3K-Akt system, an important cell-protection-signaling cascade under the control of the neurotrophin receptor, was also revealed to contribute to the mechanism of NXF mRNA induction. Activation of MAPK under the control of the neurotrophin receptor resulted in NXF protein phosphorylation as well as enhancement of NXF transcriptional activity. This newly identified NXF gene system may provide a new insight into neurotrophin biology, which reflects the target gene functions.

The N-terminal domain of ERK1 accounts for the functional differences with ERK2

The Extracellular Regulated Kinase 1 and 2 transduce a variety of extracellular stimuli regulating processes as diverse as proliferation, differentiation and synaptic plasticity. Once activated in the cytoplasm, ERK1 and ERK2 translocate into the nucleus and interact with nuclear substrates to induce specific programs of gene expression. ERK1/2 share 85% of aminoacid identity and all known functional domains and thence they have been considered functionally equivalent until recent studies found that the ablation of either ERK1 or ERK2 causes dramatically different phenotypes. To search a molecular justification of this dichotomy we investigated whether the different functions of ERK1 and 2 might depend on the properties of their cytoplasmic-nuclear trafficking. Since in the nucleus ERK1/2 is predominantly inactivated, the maintenance of a constant level of nuclear activity requires continuous shuttling of activated protein from the cytoplasm. For this reason, different nuclear-cytoplasmic trafficking of ERK1 and 2 would cause a differential signalling capability. We have characterised the trafficking of fluorescently tagged ERK1 and ERK2 by means of time-lapse imaging in living cells. Surprisingly, we found that ERK1 shuttles between the nucleus and cytoplasm at a much slower rate than ERK2. This difference is caused by a domain of ERK1 located at its N-terminus since the progressive deletion of these residues converted the shuttling features of ERK1 into those of ERK2. Conversely, the fusion of this ERK1 sequence at the N-terminus of ERK2 slowed down its shuttling to a similar value found for ERK1. Finally, computational, biochemical and cellular studies indicated that the reduced nuclear shuttling of ERK1 causes a strong reduction of its nuclear phosphorylation compared to ERK2, leading to a reduced capability of ERK1 to carry proliferative signals to the nucleus. This mechanism significantly contributes to the differential ability of ERK1 and 2 to generate an overall signalling output.

IGF and insulin receptor signaling in breast cancer

Major molecular abnormalities in breast cancer include the deregulation of several components of the IGF system. It is well recognized that the epithelial breast cancer cells commonly overexpress the IGF-I receptor while IGF-II is expressed by the tumor stroma. In view to the fact that the IGF-IR has mitogenic, pro-invasive and anti-apoptotic effects and mediates resistance to a variety of anti-cancer therapies, breast cancer is expected to be a candidate to therapeutic approaches aimed to inhibit the IGF-IR. However, there is increasing awareness that IGF system in cancer undergoes signal diversification by various mechanisms. One of these mechanisms is the aberrant expression of insulin receptor (IR) isoform A (IR-A), which is a high affinity receptor for both insulin and IGF-II, in breast cancer cells. Moreover, overexpression of both IGF-IR and IR-A in breast cancer cells, leads to overexpression of hybrid IR/IGF-IR receptors (HRs) as well. Upon binding to IGF-II, both IR-A and HRs may activate unique signaling patterns, which predominantly mediate proliferative effects. A better understanding of IGF system signal diversification in breast cancer has important implications for cancer prevention measures, which should include control of insulin resistance and associated hyperinsulinemia. Moreover, in addition to the IGF-IR, both IR-A and HRs should be also considered as molecular targets for anti-cancer therapies.

Constitutive activity of JNK2 alpha2 is dependent on a unique mechanism of MAPK activation

c-Jun N-terminal kinases (JNKs) are part of the mitogen-activated protein kinase (MAPK) family and are important regulators of cell growth, proliferation, and apoptosis. Typically, a sequential series of events are necessary for MAPK activation: phosphorylation, dimerization, and then subsequent translocation to the nucleus. Interestingly, a constitutively active JNK isoform, JNK2alpha2, possesses the ability to autophosphorylate and has been implicated in several human tumors, including glioblastoma multiforme. Because overexpression of JNK2alpha2 enhances several tumorigenic phenotypes, including cell growth and tumor formation in mice, we studied the mechanisms of JNK2alpha2 autophosphorylation and autoactivation. We find that JNK2alpha2 dimerization in vitro and in vivo occurs independently of its autophosphorylation but is dependent on nine amino acids, known as the alpha-region. Alanine scanning mutagenesis of the alpha-region reveals that five specific mutants (L218A, K220A, G221A, I224A, and F225A) prevent JNK2alpha2 dimerization rendering JNK2alpha2 inactive and incapable of stimulating tumor formation. Previous studies coupled with additional mutagenesis of neighboring isoleucines and leucines (I208A, I214A, I231A, and I238A) suggest that a leucine zipper may play an important role in JNK2alpha2 homodimerization. We also show that a kinase-inactive JNK2alpha2 mutant can interact with and inhibit wild type JNK2alpha2 autophosphorylation, suggesting that JNK2alpha2 undergoes trans-autophosphorylation. Together, our results demonstrate that JNK2alpha2 differs from other MAPK proteins in two major ways; its autoactivation/autophosphorylation is dependent on dimerization, and dimerization most likely precedes autophosphorylation. In addition, we show that dimerization is essential for JNK2alpha2 activity and that prevention of dimerization may decrease JNK2alpha2 induced tumorigenic phenotypes.

Desipramine-induced Ca-independent apoptosis in Mg63 human osteosarcoma cells: dependence on P38 mitogen-activated protein kinase-regulated activation of caspase 3

1. It has been shown that the antidepressant desipramine is able to induce increases in [Ca(2+)](i) and cell death in MG63 human osteosacroma cells, but whether apoptosis is involved is unclear. In the present study, the effect of desipramine on apoptosis and the underlying mechanisms were explored. It was demonstrated that desipramine induced cell death in a concentration- and time-dependent manner. 2. Cells treated with 100-800 mmol/L desipramine showed typical apoptotic features, including an increase in sub-diploid nuclei and activation of caspase 3, indicating that these cells underwent apoptosis. Immunoblotting revealed that 100 mmol/L desipramine activated extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK). Although pretreatment of cells with 20 mmol/L PD98059 (an ERK inhibitor) or 20 mmol/L SP600125 (an inhibitor of JNK) did not inhibit cell death, the addition of 20 mmol/L SB203580 (a p38 MAPK inhibitor) partially rescued cells from apoptosis. Desipramine-induced caspase 3 activation required p38 MAPK activation. 3. Pretreatment of cells with BAPTA/AM (20 mmol/L) to prevent desipramine-induced increases in [Ca(2+)](i) did not protect cells from death. 4. The results of the present study suggest that, in MG63 human osteosarcoma cells, desipramine causes Ca(2+)-independent apoptosis by inducing p38 MAPK-associated activation of caspase 3.

Phospho-ERK staining is a poor indicator of the mutational status of BRAF and NRAS in human melanoma

Mutated BRAF and NRAS are suspected to contribute to melanomagenesis by activation of extracellular signal-regulated kinase (ERK). To test this notion, we analyzed the presence of phosphorylated ERK1/2 in 170 melanomas with established NRAS/BRAF mutational status and well-documented clinical follow-up by immunohistochemistry. Several notable observations were obtained: (i) phospho-ERK staining was very heterogeneous within the tumor; (ii) in most cases, ERK was phosphorylated in only a minority of tumor cells; (iii) the percentage of phospho-ERK-positive cells was not correlated with the mutational status of NRAS and/or BRAF; (iv) the Raf kinase inhibitor protein (RKIP) was expressed homogeneously in virtually all melanoma samples not reflecting the inhomogeneity of phospho-ERK; and, finally, (v) neither the portion of phospho-ERK-positive tumor cells nor the RKIP staining intensity showed any correlation to the clinical course of the patients. Furthermore, the ability of BRAF mutant melanoma cells to downregulate mitogen-activated protein kinase activation was shown in melanoma cell lines cultured at high densities or under nonadherent conditions. Our findings suggest that mitogen-activated protein kinase (MAPK) activity is subject to regulation even in BRAF/NRAS mutant melanoma cells and that high MAPK pathway signaling may be important only in distinct subsets of tumor cells.

Signaling crossroads: the function of Raf kinase inhibitory protein in cancer, the central nervous system and reproduction

The Raf kinase inhibitory protein 1 (RKIP-1) and its orthologs are conserved throughout evolution and widely expressed in eukaryotic organisms. In its non-phosphorylated form RKIP-1 negatively regulates the Raf/MEK/ERK pathway by interfering with the activity of Raf-1. In its phosphorylated state, RKIP-1 dissociates from Raf-1 and inhibits GRK-2, a negative regulator of G-protein coupled receptors (GPCRs). Available data indicate that the phosphorylation of RKIP-1 by PKC can stimulate both the Raf/MEK/ERK and GPCR pathways. RKIP-1 has also been implicated as a negative regulator of the NF-kappaB pathway. Recent studies have shown that phosphorylated RKIP-1 binds to the centrosomal and kinetochore regions of metaphase chromosomes, where it may be involved in regulating the partitioning of chromosomes and the progression through mitosis. The collective evidence indicates that RKIP-1 regulates the activity and mediates the crosstalk between several important cellular signaling pathways. A variety of ablative interventions suggest that reduced RKIP-1 function may influence metastasis, angiogenesis, resistance to apoptosis, and genome integrity. Attenuation of RKIP-1 may also affect cardiac and neurological functions, spermatogenesis, sperm decapacitation, and reproductive behavior. In this review, the role of RKIP-1 in cellular signaling, and especially its functions revealed using a mouse knockout model, are discussed.

Radiofrequency radiation (900 MHz) induces Egr-1 gene expression and affects cell-cycle control in human neuroblastoma cells

Many environmental signals, including ionizing radiation and UV rays, induce activation of Egr-1 gene, thus affecting cell growth and apoptosis. The paucity and the controversial knowledge about the effect of electromagnetic fields (EMF) exposure of nerve cells prompted us to investigate the bioeffects of radiofrequency (RF) radiation on SH-SY5Y neuroblastoma cells. The effect of a modulated RF field of 900 MHz, generated by a wire patch cell (WPC) antenna exposure system on Egr-1 gene expression, was studied as a function of time. Short-term exposures induced a transient increase in Egr-1 mRNA level paralleled with activation of the MAPK subtypes ERK1/2 and SAPK/JNK. The effects of RF radiations on cell growth rate and apoptosis were also studied. Exposure to RF radiation had an anti-proliferative activity in SH-SY5Y cells with a significant effect observed at 24 h. RF radiation impaired cell cycle progression, reaching a significant G2-M arrest. In addition, the appearance of the sub-G1 peak, a hallmark of apoptosis, was highlighted after a 24-h exposure, together with a significant decrease in mRNA levels of Bcl-2 and survivin genes, both interfering with signaling between G2-M arrest and apoptosis. Our results provide evidence that exposure to a 900 MHz-modulated RF radiation affect both Egr-1 gene expression and cell regulatory functions, involving apoptosis inhibitors like Bcl-2 and survivin, thus providing important insights into a potentially broad mechanism for controlling in vitro cell viability.

Differentiation of gastric surface mucous cells (GSM06) induced by air-liquid interface is regulated partly through mitogen-activated protein kinase pathway

BACKGROUND AND AIM

The aim of the present study was to examine the role of mitogen-activated protein (MAP) kinase pathway on gastric surface epithelium using an established cell culture model in which differentiation is promoted in GSM06 cells by air-liquid interface.

METHODS

A double-dish culture system of mouse gastric surface mucous cell line GSM06 in Ham's F12 medium supplemented with 10% fetal calf serum and 50 microg/mL gentamicin at 37 degrees C in a humidified atmosphere of 5% CO(2) in air was used for an air-liquid interface. Culture cells were examined on histology, cell proliferation was evaluated by bromodeoxy-uridine (BrdU) uptake, and western blot analysis of extracellular signal-regulated kinase (ERK)1/2 and phosphate ERK1/2. On day 3, U0126, an inhibitor of MAP kinase kinase (MEK), was added to medium of incubated cells.

RESULTS

GSM06 cells were differentiated with an air-liquid interface for 3 weeks. Compared to immersion control culture, phosphorylated ERK 1/2 expression increased significantly. This increase was completely suppressed with U0126, and tall columnar cells developed by air-liquid interface in GSM06 were not observed in U0126-treated cells. Increase in BrdU uptake with air-liquid interface was suppressed by U0126.

CONCLUSION

These results suggested that MAP kinase signaling, activated by air-liquid interface, was, at least in part, related to cell differentiation in GSM06 cells induced by air-liquid interface.