Fidelity and spatio-temporal control in MAP kinase (ERKs) signalling

The Brain at High Altitude: From Molecular Signaling to Cognitive Performance

The brain requires over one-fifth of the total body oxygen demand for normal functioning. At high altitude (HA), the lower atmospheric oxygen pressure inevitably challenges the brain, affecting voluntary spatial attention, cognitive processing, and attention speed after short-term, long-term, or lifespan exposure. Molecular responses to HA are controlled mainly by hypoxia-inducible factors. This review aims to summarize the cellular, metabolic, and functional alterations in the brain at HA with a focus on the role of hypoxia-inducible factors in controlling the hypoxic ventilatory response, neuronal survival, metabolism, neurogenesis, synaptogenesis, and plasticity.

A Long-Lasting PARP1-Activation Mediates Signal-Induced Gene Expression

This overview presents recent evidence for a long-lasting PARP1 activation by a variety of signal transduction mechanisms, mediating signal-induced gene expression and chromatin remodeling. This mode of PARP1 activation has been reported in a variety of cell types, under physiological conditions. In this mechanism, PARP1 is not transiently activated by binding to DNA breaks. Moreover, damaged DNA interfered with this long-lasting PARP1 activation.

DUSP7 inhibits cervical cancer progression by inactivating the RAS pathway

To determine the differentially expressed proteins (DEPs) between paired samples of cervical cancer (CC) and paracancerous tissue by quantitative proteomics and to examine the effects of DUSP7 expression on the tumorigenesis and progression of CC. Proteomic profiles of three paired samples of CC and paracancerous tissue were quantitatively analysed to identify DEPs. The relationship between DEP expression and patient clinicopathological characteristics and prognosis was evaluated. The effects of the selected DEPs on CC progression were examined in SIHA cells. A total of 129 DEPs were found. Western blot and immunohistochemistry (IHC) staining analyses confirmed the results from quantitative proteomic analysis showing that the selected DEP, HRAS, P-ERK1/2, and PLD1 levels were increased, whereas the DUSP7 level was decreased in CC tissue compared with the paired normal paracancerous tissues. The IHC results from the CC TMA analysis showed that the decreased expression of DUSP7 (p = 0.045 and 0.044) was significantly associated with a tumour size >2 cm and parametrial infiltration. In addition, the decreased expression of DUSP7 and increased expression of p-ERK1/2 were adversely related to patient relapse (p = 0.003 and 0.001) and survival (p = 0.034 and 0.006). The expression of HRAS and p-ERK1/2 was decreased in DUSP7-SIHA cells compared with NC-SIHA cells (p = 0.0003 and 0.0026). Biological functions in vitro, including invasion, migration and proliferation and tumour formation in vivo were decreased in DUSP7-SIHA cells (all p < 0.05) but increased in shDUSP7-SIHA cells (all p < 0.05). DUSP7 inhibits cervical cancer progression by inactivating the RAS pathway.

Comparison of Expression of Chemokine Receptor 4 in Maternal Decidua and Chorionic Villi in Women with Spontaneous Miscarriages and Women Opting for Termination of Viable Pregnancies

Background:

Early pregnancy losses can be a distressing experience both for the parents and the treating clinician. We aim to explore the role of chemokine receptor 4 (CXCR4) in early pregnancy losses by comparing its expression among patients with spontaneous miscarriages and patients undergoing termination of viable pregnancies for unwanted pregnancies.

Aim:

The aim of the study was to investigate the expression of CXCR4 in early pregnancy losses and correlate the various clinical parameters with differential expression of the above receptor in the chorionic villi and maternal decidua.

Study and Setting:

The present study is a case-“control study done in a tertiary care center.

Methodology:

Fifty patients attending outdoor and antenatal clinic of the hospital aged 18-40 years with spontaneous miscarriage under 20 weeks of gestational age were included as cases and compared with fifty females of comparable age group (18-40 years) seeking medical termination of pregnancy as controls. Chorionic villi and decidua obtained from the cases and controls were analyzed for CXCR4 expression.

Statistical Analysis:

The results were analyzed using mean ± standard deviation, percentiles values, Chi-square test, and P value to determine the association of CXCR4 expression in decidua and chorionic villi of cases versus controls.

Results:

CXCR4 expression was significantly downregulated in cases as compared to the controls with P < 0.001. The mean normalized ratio of CXCR4 expression to housekeeping gene (β Actin) expression in the case group was 1.607 ± 1.108 and in the control group, it was 2.506 ± 1.457. There was a strong correlation between the expression of CXCR4 and maternal age. With increasing age, the expression of CXCR4 was more downregulated in both the cases and control groups (P < 0.001). The expression of CXCR4 was elevated in controls as compared to cases in <30 years age group (P = 0.009). CXCR4 expression was higher in primigravida than in multigravida (P = 0.001), and as the number of previous miscarriages increased, the expression of CXCR4 was found to be decreased (P = 0.021).

Conclusion:

CXCR4 expression is significantly reduced in women with spontaneous miscarriages in comparison with viable pregnancies. and possibly, therapies targeted at increasing the expression of CXCR4 can be used as a treatment modality for management of spontaneous miscarriages.

Over-expressed, N-terminally truncated BRAF is detected in the nucleus of cells with nuclear phosphorylated MEK and ERK

BRAF is a cytoplasmic protein kinase, which activates the MEK-ERK signalling pathway. Deregulation of the pathway is associated with the presence of BRAF mutations in human cancer, the most common being V600E BRAF, although structural rearrangements, which remove N-terminal regulatory sequences, have also been reported. RAF-MEK-ERK signalling is normally thought to occur in the cytoplasm of the cell. However, in an investigation of BRAF localisation using fluorescence microscopy combined with subcellular fractionation of Green Fluorescent Protein (GFP)-tagged proteins expressed in NIH3T3 cells, surprisingly, we detected N-terminally truncated BRAF (ΔBRAF) in both nuclear and cytoplasmic compartments. In contrast, ΔCRAF and full-length, wild-type BRAF (WTBRAF) were detected at lower levels in the nucleus while full-length V600EBRAF was virtually excluded from this compartment. Similar results were obtained using ΔBRAF tagged with the hormone-binding domain of the oestrogen receptor (hbER) and with the KIAA1549-ΔBRAF translocation mutant found in human pilocytic astrocytomas. Here we show that GFP-ΔBRAF nuclear translocation does not involve a canonical Nuclear Localisation Signal (NLS), but is suppressed by N-terminal sequences. Nuclear GFP-ΔBRAF retains MEK/ERK activating potential and is associated with the accumulation of phosphorylated MEK and ERK in the nucleus. In contrast, full-length GFP-WTBRAF and GFP-V600EBRAF are associated with the accumulation of phosphorylated ERK but not phosphorylated MEK in the nucleus. These data have implications for cancers bearing single nucleotide variants or N-terminal deleted structural variants of BRAF.

Transforming growth factor-β downregulates sGC subunit expression in pulmonary artery smooth muscle cells via MEK and ERK signaling

TGFβ activation during newborn lung injury decreases the expression of pulmonary artery smooth muscle cell (PASMC)-soluble guanylate cyclase (sGC), a critical mediator of nitric oxide signaling. Using a rat PASMC line (CS54 cells), we determined how TGFβ downregulates sGC expression. We found that TGFβ decreases sGC expression through stimulating its type I receptor; TGFβ type I receptor (TGFβR1) inhibitors prevented TGFβ-1-mediated decrease in sGCα1 subunit mRNA levels in the cells. However, TGFβR1-Smad mechanisms do not regulate sGC; effective knockdown of Smad2 and Smad3 expression and function did not protect sGCα1 mRNA levels during TGFβ-1 exposure. A targeted small-molecule kinase inhibitor screen suggested that MEK signaling regulates sGC expression in TGFβ-stimulated PASMC. TGFβ activates PASMC MEK/ERK signaling; CS54 cell treatment with TGFβ-1 increased MEK and ERK phosphorylation in a biphasic, time- and dose-dependent manner. Moreover, MEK/ERK activity appears to be required for TGFβ-mediated sGC expression inhibition in PASMC; MEK and ERK inhibitors protected sGCα1 mRNA expression in TGFβ-1-treated CS54 cells. Nuclear ERK activity is sufficient for sGC regulation; heterologous expression of a nucleus-retained, constitutively active ERK2-MEK1 fusion protein decreased CS54 cell sGCα1 mRNA levels. The in vivo relevance of this TGFβ-MEK/ERK-sGC downregulation pathway is suggested by the detection of ERK activation and sGCα1 protein expression downregulation in TGFβ-associated mouse pup hyperoxic lung injury, and the determination that ERK decreases sGCα1 protein expression in TGFβ-1-treated primary PASMC obtained from mouse pups. These studies identify MEK/ERK signaling as an important pathway by which TGFβ regulates sGC expression in PASMC.

Extracellular signal-regulated kinase 2 has duality in function between neuronal and astrocyte expression following neonatal hypoxic-ischaemic cerebral injury

Key points

This study identifies phosphorylated extracellular signal‐regulated kinase (ERK) to be immediately diminished followed by a rapid if transient increase for up to 4 h following hypoxic–ischaemic insult (HI) in the neonatal mouse.

Phosphorylated ERK up‐regulation was prevented with systemic injection of the mitogen‐activated protein kinase kinase (MEK) inhibitor SL327. Treatment with SL327 both pre‐ and post‐HI gave a strong reduction in the number of dying cells and microgliosis.

By utilising transgenic mouse mutations, we observe that neuronal ERK2 significantly contributes to tissue damage, while ERK1 and astrocytic ERK2 are neuroprotective.

Compared to global inactivation, selective cell‐specific interference with ERK activity could result in stronger neuroprotection.

Abstract

Hypoxia–ischaemia (HI) is a major cause of neonatal brain injury resulting in cerebral palsy, epilepsy, cognitive impairment and other neurological disabilities. The role of extracellular signal‐regulated kinase (ERK) isoforms and their mitogen‐activated protein kinase kinase (MEK)‐dependent phosphorylation in HI has previously been explored but remains unresolved at cellular level. This is pertinent given the growing awareness of the role of non‐neuronal cells in neuroprotection. Using a modified Rice–Vannucci model of HI in the neonatal mouse we observed time‐ and cell‐dependent ERK phosphorylation (pERK), with strongly up‐regulated pERK immunoreactivity first in periventricular white matter axons within 15–45 min of HI, followed by forebrain astrocytes and neurons (1–4 h post‐HI), and return to baseline by 16 h. We explored the effects of pharmacological ERK blockade through the MEK inhibitor SL327 on neonatal HI‐brain damage following HI alone (30 or 60 min) or lipopolysaccharide (LPS)‐sensitised HI insult (30 min). Global inhibition of ERK phosphorylation with systemically applied SL327 abolished forebrain pERK immunoreactivity, and significantly reduced cell death and associated microglial activation at 48 h post‐HI. We then explored the effects of cell‐specific ERK2 deletion alone or in combination with global ERK1 knockout under the same conditions of HI insult. Neuronal ERK2 deletion strongly decreased infarct size, neuronal cell death and microglial activation in grey matter following both HI alone or LPS‐sensitised HI. ERK1 deletion attenuated the protective effect of neuronal ERK2 deletion. Removal of astroglial ERK2 produced a reverse response, with a 3‐ to 4‐fold increase in microglial activation and cell death. Our data suggest a cell‐specific and time‐dependent role of ERK in neonatal HI, with a predominant, neurotoxic effect of neuronal ERK2, which is counteracted by neuroprotection by ERK1 and astrocytic ERK2. Overall, global pharmacological inhibition of ERK phosphorylation is strongly neuroprotective.

This study identifies phosphorylated extracellular signal‐regulated kinase (ERK) to be immediately diminished followed by a rapid if transient increase for up to 4 h following hypoxic–ischaemic insult (HI) in the neonatal mouse.

Phosphorylated ERK up‐regulation was prevented with systemic injection of the mitogen‐activated protein kinase kinase (MEK) inhibitor SL327. Treatment with SL327 both pre‐ and post‐HI gave a strong reduction in the number of dying cells and microgliosis.

By utilising transgenic mouse mutations, we observe that neuronal ERK2 significantly contributes to tissue damage, while ERK1 and astrocytic ERK2 are neuroprotective.

Compared to global inactivation, selective cell‐specific interference with ERK activity could result in stronger neuroprotection.

Analysis of Ras/ERK Compartmentalization by Subcellular Fractionation

A vast number of stimuli use the Ras/Raf/MEK/ERK signaling cascade to transmit signals from their cognate receptors, in order to regulate multiple cellular functions, including key processes such as proliferation, cell cycle progression, differentiation, and survival. The duration, intensity and specificity of the responses are, in part, controlled by the compartmentalization/subcellular localization of the signaling intermediaries. Ras proteins are found in different plasma membrane microdomains and endomembranes. At these localizations, Ras is subject to site-specific regulatory mechanisms, distinctively engaging effector pathways and switching-on diverse genetic programs to generate a multitude of biological responses. The Ras effector pathway leading to ERKs activation is also subject to space-related regulatory processes. About half of ERK1/2 substrates are found in the nucleus and function mainly as transcription factors. The other half resides in the cytosol and other cellular organelles. Such subcellular distribution enhances the complexity of the Ras/ERK cascade and constitutes an essential mechanism to endow variability to its signals, which enables their participation in the regulation of a broad variety of functions. Thus, analyzing the subcellular compartmentalization of the members of the Ras/ERK cascade constitutes an important factor to be taken into account when studying specific biological responses evoked by Ras/ERK signals. Herein, we describe methods for such purpose.

MKP-1 negative regulates Staphylococcus aureus induced inflammatory responses in Raw264.7 cells: roles of PKA-MKP-1 pathway and enhanced by rolipram

MAP phosphatases (MKP)-1 acts as an important regulator of innate immune response through a mechanism of control and attention both MAPK and NF-κB molecules during bacterial infection. However, the regulatory role of MKP-1 in the interplay between MAPK and NFκB pathway molecules is still not fully understood. In present study, we showed a direct interactions of p38, ERK or IκBα with MKP-1, and demonstrated that MKP-1 was a pivotal feedback control for both MAP kinases and NF-κB pathway in response to S. aureus. In addition, we found that rolipram had anti-inflammatory activity and repressed IκBα activation induced by S. aureus via PKA-MKP-1 pathway. Our report also demonstrated that PKA-cα can directly bind to IκBα upon S. aureus stimulation, which influenced the downstream signaling of PKA pathway, including altered the expression of MKP-1. These results presented a novel mechanism of PKA and IκB pathway, which may be targeted for treating S. aureus infection.

Mitogen-Activated Protein Kinases and Mitogen Kinase Phosphatase 1: A Critical Interplay in Macrophage Biology

Macrophages are necessary in multiple processes during the immune response or inflammation. This review emphasizes the critical role of the mitogen-activated protein kinases (MAPKs) and mitogen kinase phosphatase-1 (MKP-1) in the functional activities of macrophages. While the phosphorylation of MAPKs is required for macrophage activation or proliferation, MKP-1 dephosphorylates these kinases, thus playing a balancing role in the control of macrophage behavior. MKP-1 is a nuclear-localized dual-specificity phosphatase whose expression is regulated at multiple levels, including at the transcriptional and post-transcriptional level. The regulatory role of MKP-1 in the interplay between MAPK phosphorylation/dephosphorylation makes this molecule a critical regulator of macrophage biology and inflammation.

Age-specific functional epigenetic changes in p21 and p16 in injury-activated satellite cells

The regenerative capacity of muscle dramatically decreases with age because old muscle stem cells fail to proliferate in response to tissue damage. Here, we uncover key age-specific differences underlying this proliferative decline: namely, the genetic loci of cyclin/cyclin-dependent kinase (CDK) inhibitors (CDKIs) p21 and p16 are more epigenetically silenced in young muscle stem cells, as compared to old, both in quiescent cells and those responding to tissue injury. Interestingly, phosphorylated ERK (pERK) induced in these cells by ectopic FGF2 is found in association with p21 and p16 promoters, and moreover, only in the old cells. Importantly, in the old satellite cells, FGF2/pERK silences p21 epigenetically and transcriptionally, which leads to reduced p21 protein levels and enhanced cell proliferation. In agreement with the epigenetic silencing of the loci, young muscle stem cells do not depend as much as old on ectopic FGF/pERK for their myogenic proliferation. In addition, other CDKIs, such asp15(INK4B) and p27(KIP1) , become elevated in satellite cells with age, confirming and explaining the profound regenerative defect of old muscle. This work enhances our understanding of tissue aging, promoting strategies for combating age-imposed tissue degeneration.

Identification of binding sites for C-terminal pro-gastrin-releasing peptide (GRP)-derived peptides in renal cell carcinoma: a potential target for future therapy

OBJECTIVE

To determine the expression and biology of the neuroendocrine growth factor gastrin-releasing peptide (GRP) and other proGRP-derived peptides in renal cancer.

MATERIALS AND METHODS

Receptor binding studies, enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay, were used to quantitate the presence of proGRP-derived peptide receptors and their ligands in renal cancer cell lines and human renal cancers. Biological activity of proGRP peptides was confirmed with proliferation, migration, and extracellular-signal-regulated kinases 1 and 2 (ERK1/2) activation assays in vitro. In vivo, ACHN renal cancer xenografts were treated with proGRP-derived peptides to assess tumour size and necrosis. hypoxia-inducible factor 1α (HIF1α) and vascular endothelial growth factor (VEGF) expression were investigated with Western blotting and ELISA respectively, to determine the possible contribution of the proGRP peptides to tumour viability.

RESULTS

In ACHN cells that expressed both proGRP- and GRP-receptors, the expression of proGRP binding sites was 80-fold greater than the GRP-receptor (GRPR). C-terminal proGRP-derived peptides stimulated the activation of ERK1/2, but with a different time course to GRP, consistent with the suggestion that these peptides may have unique cellular functions. Both GRP and proGRP47-68 stimulated proliferation and migration of ACHN cells in vitro, but only GRP reduced the extent of tumour necrosis in ACHN xenografts. GRP, but not proGRP47-68, was able to induce HIF1α and VEGF expression in ACHN cells. This may account in part for the reduction in necrosis after GRP treatment. C-terminal proGRP-derived peptides were present in all three renal cancer cell lines and a panel of human renal cancers, but mature amidated GRP was absent.

CONCLUSION

C-terminal proGRP peptides are more abundant in renal cancers and their cell lines than the more extensively studied amidated peptide, GRP. These results suggest that C-terminal proGRP-derived peptides may be a better target for novel renal cancer treatments.

Feedforward regulation of mRNA stability by prolonged extracellular signal-regulated kinase activity

Extracellular signal-regulated kinase (ERK) plays a central role in signal transduction networks and cell fate decisions. Sustained ERK activation induces cell differentiation, whereas transient ERK results in the proliferation of several types of cells. Sustained ERK activity stabilizes the proteins of early-response gene products. However, the effect of ERK activity duration on mRNA stability is unknown. We analyzed the quantitative relationship between the duration of four ERK activity kinetics and the mRNA expression profile in growth factor-treated cells. Time-course transcriptome analysis revealed that the cells with prolonged ERK activity generally showed sustained mRNA expression of late response genes but not early or mid genes. Selected late response genes decayed more rapidly in the presence of a specific ERK inhibitor than a general transcription inhibitor and the decay rate was not related to the number of AU-rich elements. Our results suggest that sustained ERK activity plays an important role in the lifespan of the mRNA encoded by late response genes, in addition to the previously demonstrated role in protein stabilization of early-response genes, including transcription factors regulating the transcription of mid and late genes. This double-positive regulation of ligand-induced genes, also termed feedforward regulation, is critical in cell fate decisions.

p53 protein-mediated up-regulation of MAP kinase phosphatase 3 (MKP-3) contributes to the establishment of the cellular senescent phenotype through dephosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2)

Growth arrest is one of the essential features of cellular senescence. At present, the precise mechanisms responsible for the establishment of the senescence-associated arrested phenotype are still incompletely understood. Given that ERK1/2 is one of the major kinases controlling cell growth and proliferation, we examined the possible implication of ERK1/2. Exposure of normal rat epithelial cells to etoposide caused cellular senescence, as manifested by enlarged cell size, a flattened cell body, reduced cell proliferation, enhanced β-galactosidase activity, and elevated p53 and p21. Senescent cells displayed a blunted response to growth factor-induced cell proliferation, which was preceded by impaired ERK1/2 activation. Further analysis revealed that senescent cells expressed a significantly higher level of mitogen-activated protein phosphatase 3 (MKP-3, a cytosolic ERK1/2-targeted phosphatase), which was suppressed by blocking the transcriptional activity of the tumor suppressor p53 with pifithrin-α. Inhibition of MKP-3 activity with a specific inhibitor or siRNA enhanced basal ERK1/2 phosphorylation and promoted cell proliferation. Apart from its role in growth arrest, impairment of ERK1/2 also contributed to the resistance of senescent cells to oxidant-elicited cell injury. These results therefore indicate that p53-mediated up-regulation of MKP-3 contributes to the establishment of the senescent cellular phenotype through dephosphorylating ERK1/2. Impairment of ERK1/2 activation could be an important mechanism by which p53 controls cellular senescence.

Mitochondrial MKP1 is a target for therapy-resistant HER2-positive breast cancer cells

The MAPK phosphatase MKP1 (DUSP1) is overexpressed in many human cancers, including chemoresistant and radioresistant breast cancer cells, but its functional contributions in these settings are unclear. Here, we report that after cell irradiation, MKP1 translocates into mitochondria, where it prevents apoptotic induction by limiting accumulation of phosphorylated active forms of the stress kinase JNK. Increased levels of mitochondrial MKP1 after irradiation occurred in the mitochondrial inner membrane space. Notably, cell survival regulated by mitochondrial MKP1 was responsible for conferring radioresistance in HER2-overexpressing breast cancer cells, due to the fact that MKP1 serves as a major downstream effector in the HER2-activated RAF-MEK-ERK pathway. Clinically, we documented MKP1 expression exclusively in HER2-positive breast tumors, relative to normal adjacent tissue from the same patients. MKP1 overexpression was also detected in irradiated HER2-positive breast cancer stem-like cells (HER2(+)/CD44(+)/CD24(-/low)) isolated from a radioresistant breast cancer cell population after long-term radiation treatment. MKP1 silencing reduced clonogenic survival and enhanced radiosensitivity in these stem-like cells. Combined inhibition of MKP1 and HER2 enhanced cell killing in breast cancer. Together, our findings identify a new mechanism of resistance in breast tumors and reveal MKP1 as a novel therapeutic target for radiosensitization.

Targeting cysteine rich C1 domain of Scaffold protein Kinase Suppressor of Ras (KSR) with anthocyanidins and flavonoids - a binding affinity characterization study

Kinase Suppressor of Ras (KSR) is a molecular scaffold that interacts with the core kinase components of the ERK cascade, Raf, MEK, ERK to provide spatial and temporal regulation of Ras-dependent ERK cascade signaling. Interruption of this mechanism can have a high influence in inhibiting the downstream signaling of the mutated tyrosine kinase receptor kinase upon ligand binding. Still none of the studies targeted to prevent the binding of Raf, MEK binding on kinase suppressor of RAS. In that perspective the cysteine rich C1 domain of scaffold proteins kinase suppressor of Ras-1 was targeted rather than its ATP binding site with small ligand molecules like flavones and anthocyanidins and analyzed through insilico docking studies. The binding energy evaluation shows the importance of hydroxyl groups at various positions on the flavone and anthocyanidin nucleus. Over all binding interaction shows these ligands occupied the potential sites of cysteine rich C1 domain of scaffold protein KSR.

Cellular responses to hypoxia in the pulmonary circulation

Hypoxia can be defined as a reduction in available oxygen, whether in a whole organism or in a tissue or cell. It is a real life cause of pulmonary hypertension in humans both in terms of patients with chronic hypoxic lung disease and people living at high altitude. The effect of hypoxia on the pulmonary vasculature can be described in two ways; Hypoxic pulmonary vasoconstriction (HPV) (resulting from smooth muscle cell contraction) and pulmonary vascular remodelling (PVR) (resulting from pulmonary vascular cell proliferation). The pulmonary artery is made up of three resident cell types, the endothelial (intima), smooth muscle (media) and fibroblast (adventitia) cells. This review will examine the effects of hypoxia on the cells of the pulmonary vasculature and give an insight into the possible underlying mechanisms.

Methanol and ethanol modulate responses to danger- and microbe-associated molecular patterns

Methanol is a byproduct of cell wall modification, released through the action of pectin methylesterases (PMEs), which demethylesterify cell wall pectins. Plant PMEs play not only a role in developmental processes but also in responses to herbivory and infection by fungal or bacterial pathogens. Molecular mechanisms that explain how methanol affects plant defenses are poorly understood. Here we show that exogenously supplied methanol alone has weak effects on defense signaling in three dicot species, however, it profoundly alters signaling responses to danger- and microbe-associated molecular patterns (DAMPs, MAMPs) such as the alarm hormone systemin, the bacterial flagellum-derived flg22 peptide, and the fungal cell wall-derived oligosaccharide chitosan. In the presence of methanol the kinetics and amplitudes of DAMP/MAMP-induced MAP kinase (MAPK) activity and oxidative burst are altered in tobacco and tomato suspension-cultured cells, in Arabidopsis seedlings and tomato leaf tissue. As a possible consequence of altered DAMP/MAMP signaling, methanol suppressed the expression of the defense genes PR-1 and PI-1 in tomato. In cell cultures of the grass tall fescue (Festuca arundinacea, Poaceae, Monocots), methanol alone activates MAPKs and increases chitosan-induced MAPK activity, and in the darnel grass Lolium temulentum (Poaceae), it alters wound-induced MAPK signaling. We propose that methanol can be recognized by plants as a sign of the damaged self. In dicots, methanol functions as a DAMP-like alarm signal with little elicitor activity on its own, whereas it appears to function as an elicitor-active DAMP in monocot grasses. Ethanol had been implicated in plant stress responses, although the source of ethanol in plants is not well established. We found that it has a similar effect as methanol on responses to MAMPs and DAMPs.

PKD1 mediates negative feedback of PI3K/Akt activation in response to G protein-coupled receptors

We examined whether protein kinase D1 (PKD1) mediates negative feeback of PI3K/Akt signaling in intestinal epithelial cells stimulated with G protein-coupled receptor (GPCR) agonists. Exposure of intestinal epithelial IEC-18 cells to increasing concentrations of the PKD family inhibitor kb NB 142­70, at concentrations that inhibited PKD1 activation, strikingly potentiated Akt phosphorylation at Thr³⁰⁸ and Ser⁴⁷³ in response to the mitogenic GPCR agonist angiotensin II (ANG II). Enhancement of Akt activation by kb NB 142-70 was also evident in cells with other GPCR agonists, including vasopressin and lysophosphatidic acid. Cell treatment rovincial Hospital Affiliated to Shandong University, Jinan, China with the structurally unrelated PKD family inhibitor CRT0066101 increased Akt phosphorylation as potently as kb NB 142–70. Knockdown of PKD1 with two different siRNAs strikingly enhanced Akt phosphorylation in response to ANG II stimulation in IEC-18 cells. To determine whether treatment with kb NB 142–70 enhances accumulation of phosphatidylinositol (3,4,5)-trisphosphate (PIP₃) in the plasma membrane, we monitored the redistribution of Akt-pleckstrin homology domain-green fluorescent protein (Akt-PH-GFP) in single IEC-18 cells. Exposure to kb NB 142–70 strikingly increased membrane accumulation of Akt-PH-GFP in response to ANG II. The translocation of the PIP₃ sensor to the plasma membrane and the phosphorylation of Akt was completed prevented by prior exposure to the class I p110α specific inhibitor A66. ANG II markedly increased the phosphorylation of p85α detected by a PKD motif-specific antibody and enhanced the association of p85α with PTEN. Transgenic mice overexpressing PKD1 showed a reduced phosphorylation of Akt at Ser⁴⁷³ in intestinal epithelial cells compared to wild type littermates. Collectively these results indicate that PKD1 activation mediates feedback inhibition of PI3K/Akt signaling in intestinal epithelial cells in vitro and in vivo.

REV, A BRET-Based Sensor of ERK Activity

Networks of signaling molecules are activated in response to environmental changes. How are these signaling networks dynamically integrated in space and time to process particular information? To tackle this issue, biosensors of single signaling pathways have been engineered. Bioluminescence resonance energy transfer (BRET)-based biosensors have proven to be particularly efficient in that matter due to the high sensitivity of this technology to monitor protein-protein interactions or conformational changes in living cells. Extracellular signal-regulated kinases (ERK) are ubiquitously expressed and involved in many diverse cellular functions that might be encoded by the strength and spatio-temporal pattern of ERK activation. We developed a BRET-based sensor of ERK activity, called Rluc8-ERKsubstrate-Venus (REV). As expected, BRET changes of REV were correlated with ERK phosphorylation, which is required for its kinase activity. In neurons, the nature of the stimuli determines the strength, the location, or the moment of ERK activation, thus highlighting how acute modulation of ERK may encode the nature of initial stimulus to specify the consequences of this activation. This study provides evidence for suitability of REV as a new biosensor to address biological questions.

Ras and Rap1 govern spatiotemporal dynamic of activated ERK in pituitary living cells

The Ras/Raf/MEK/ERK is a conserved signalling pathway involved in the control of fundamental cellular processes. Despite extensive research, how this pathway can process a myriad of diverse extracellular inputs into substrate specificity to determine biological outcomes is not fully understood. It has been established that the ERK1/2 pathway is an integrative point in the control of the pituitary function exerted by various extracellular signals. In addition we previously established that the GTPases Ras and Rap1 play a key role in the regulation of ERK1/2-dependent prolactin transcription by EGF or the cAMP-dependent neuropeptide VIP. In this report, using the FRET-based biosensor of ERK activity (EKAR) in the pituitary GH4C1 cell line, we show that both EGF and VIP tightly control the spatiotemporal dynamic of activated ERK with different magnitude and duration. Importantly, we provide the first evidence of a differential control of cytoplasmic and nuclear pools of activated ERK by the GTPases Ras and Rap1. Ras is required for nuclear magnitude and duration of EGF-dependent ERK activation, whereas it is required for both VIP-activated cytoplasmic and nuclear ERK pools. Rap1 is exclusively involved in VIP-activated ERK nuclear pool. Moreover, consistent with the control of the nuclear pool of activated ERK by the GTPases, we observe the same differential role of Ras and Rap1 on ERK nuclear translocation triggered by EGF or VIP. Together these findings identify Ras and Rap1 as determinant partners in shaping nuclear and cytoplasmic ERK kinetics in response to EGF and VIP, which in turn should control pituitary secretion.

Hypoxia changes the expression of the epidermal growth factor (EGF) system in human hearts and cultured cardiomyocytes

Background

The epidermal growth factor (EGF) receptors HER2 and HER4 and the ligands HB-EGF and NRG1 are crucial for heart development. The purpose of our study was to investigate the role of the complete EGF system in relation to hypoxia of the heart.

Methodology/Principal Findings

We examined the mRNA expression by real time PCR of the 4 receptors and 12 ligands from the EGF-system in paired normoxic and hypoxic biopsies isolated from human hearts during coronary artery bypass operation. Compared to normoxic biopsies, hypoxic samples showed down-regulation of HER2 (P = 0.0005) and NRG1 (both α (P = 0.02) and β (P = 0.03) isoforms). In contrast, HB-EGF (P = 0.0008), NRG2β (P = 0.01) and EGFR (P = 0.02) were up-regulated. As HER2 is essential for heart development and we find its expression reduced under hypoxia we investigated the effect of HER2 inhibition in hypoxic HL-1 cardiomyocytes by treatment with trastuzumab (20 nM). This resulted in inhibition of cardiomyocyte proliferation, but interestingly only in hypoxic cells. Co-treatment of HL-1 cells with HB-EGF (10 nM) but not with NRG-1 (5 ng/ml) rescued the cardiomyocytes from HER2 inhibition. HL-1 cardiomyocytes exposed to hypoxia revealed nuclear translocation of activated MAPK and the activity of this downstream signaling molecule was decreased by HER2 inhibition (20 nM trastuzumab), and re-established by HB-EGF (10 nM).

Conclusions/Significance

Hypoxia in the human heart alters the expression of the EGF system. Mimicking the HER2 down-regulation seen in the human heart in cultured cardiomyocytes inhibited their proliferation under hypoxic conditions. Interestingly, HB-EGF is induced in the hypoxic human hearts, and rescues hypoxic cardiomyocytes from the effect of HER2 inhibition in the in vitro model. The results have implications for future treatment strategies of patients with ischemic heart disease.

A kinetic model of ERK cyclic pathway on substrate control

Extracellular signal-regulated kinase (ERK) is a key factor in the widely used signaling cascade of phosphorylation-dephosphorylation cycles and plays pivotal roles in many aspects of biological processes. Experimental studies in yeast and in Drosophila embryo have suggested that the phosphorylation and spatial localization of ERK are influenced by the level of its downstream substrates. However, the mechanism, through which these substrates control properties of ERK signaling, has been unclear. I propose a mass-action kinetic model of ERK cycle with its substrate, and demonstrate that the substrate can modulate the ERK activity by directly interacting with ERK. The model shows that the addition of substrate controls the level of ERK phosphorylation positively or negatively, depending on the balance between dissociation constants of ERK-substrate interaction and properties of ERK cyclic signaling in the absence of the substrate. In addition, by considering cellular compartments, cytosol and nucleus, the substrate can lead to nuclear accumulation of ERK, suggesting that the substrate can act as a nuclear anchor of ERK. The model gives a possible mechanism that can account for substrate-mediated modulation of ERK signaling.

Mathematical modeling reveals the functional implications of the different nuclear shuttling rates of Erk1 and Erk2

The mitogen-activated protein kinase (MAPK) family of proteins is involved in regulating cellular fates such as proliferation, differentiation and apoptosis. In particular, the dynamics of the Erk/Mek system, which has become the canonical example for MAPK signaling systems, have attracted considerable attention. Erk is encoded by two genes, Erk1 and Erk2, that until recently had been considered equivalent as they differ only subtly at the sequence level. However, these proteins exhibit radically different trafficking between cytoplasm and nucleus and this fact may have functional implications. Here we use spatially resolved data on Erk1/2 to develop and analyze spatio-temporal models of these cascades, and we discuss how sensitivity analysis can be used to discriminate between mechanisms. Our models elucidate some of the factors governing the interplay between signaling processes and the Erk1/2 localization in different cellular compartments, including competition between Erk1 and Erk2. Our approach is applicable to a wide range of signaling systems, such as activation cascades, where translocation of molecules occurs. Our study provides a first model of Erk1 and Erk2 activation and their nuclear shuttling dynamics, revealing a role in the regulation of the efficiency of nuclear signaling.

Differential expression and functional analysis of the tristetraprolin family during early differentiation of 3T3-L1 preadipocytes

The tristetraprolin (TTP) family comprises zinc finger-containing AU-rich element (ARE)-binding proteins consisting of three major members: TTP, ZFP36L1, and ZFP36L2. The present study generated specific antibodies against each TTP member to evaluate its expression during differentiation of 3T3-L1 preadipocytes. In contrast to the inducible expression of TTP, results indicated constitutive expression of ZFP36L1 and ZFP36L2 in 3T3-L1 preadipocytes and their phosphorylation in response to differentiation signals. Physical RNA pull-down and functional luciferase assays revealed that ZFP36L1 and ZFP36L2 bound to the 3' untranslated region (UTR) of MAPK phosphatase-1 (MKP-1) mRNA and downregulated Mkp-1 3'UTR-mediated luciferase activity. Mkp-1 is an immediate early gene for which the mRNA is transiently expressed in response to differentiation signals. The half-life of Mkp-1 mRNA was longer at 30 min of induction than at 1 h and 2 h of induction. Knockdown of TTP or ZFP36L2 increased the Mkp-1 mRNA half-life at 1 h of induction. Knockdown of ZFP36L1, but not ZFP36L2, increased Mkp-1 mRNA basal levels via mRNA stabilization and downregulated ERK activation. Differentiation induced phosphorylation of ZFP36L1 through ERK and AKT signals. Phosphorylated ZFP36L1 then interacted with 14-3-3, which might decrease its mRNA destabilizing activity. Inhibition of adipogenesis also occurred in ZFP36L1 and TTP knockdown cells. The findings indicate that the differential expression of TTP family members regulates immediate early gene expression and modulates adipogenesis.

Regulation of MEK/ERK pathway output by subcellular localization of B-Raf

The strength and duration of intracellular signalling pathway activation is a key determinant of the biological outcome of cells in response to extracellular cues. This has been particularly elucidated for the Ras/Raf/MEK [mitogen-activated growth factor/ERK (extracellular-signal-regulated kinase) kinase]/ERK signalling pathway with a number of studies in fibroblasts showing that sustained ERK signalling is a requirement for S-phase entry, whereas transient ERK signalling does not have this capability. A major unanswered question, however, is how a cell can sustain ERK activation, particularly when ERK-specific phosphatases are transcriptionally up-regulated by the pathway itself. A major point of ERK regulation is at the level of Raf, and, to sustain ERK activation in the presence of ERK phosphatases, sustained Raf activation is a requirement. Three Raf proteins exist in mammals, and the activity of all three is induced following growth factor stimulation of cells, but only B-Raf activity is maintained at later time points. This observation points to B-Raf as a regulator of sustained ERK activation. In the present review, we consider evidence for a link between B-Raf and sustained ERK activation, focusing on a potential role for the subcellular localization of B-Raf in this key physiological event.

Diallyl disulfide induces MUC5B expression via ERK2 in human airway epithelial cells

Garlic has been shown to have antimicrobial, hypolipidemic, antithrombotic, antitumor and immunostimulatory properties. The medicinal effects of garlic are derived from the flavonoid and organosulfur components. Diallyl disulfide (DADS), an organosulfur, is the main component responsible for the diverse biological effects of garlic. However, the effects of DADS on mucin gene expression in airway epithelial cells have not been reported to date. Therefore, this study was performed to investigate the effects and brief signaling pathway of DADS associated with MUC5B expression in NCI-H292 epithelial cells using RT-PCR, ELISA, western blot, immunocytochemistry and cell transfection with siRNA. DADS induced MUC5B expression and activated the phosphorylation of ERK1/2 MAPK. In addition, U0126 inhibited DADS-induced MUC5B expression and DADS-activated phosphorylation of ERK1/2 MAPK. Moreover, the immunopositive cells for MUC5B protein did not appear after treatment of DADS with U0126, and the knockdown of ERK2 MAPK by ERK2 MAPK siRNA significantly blocked DADS-induced MUC5B mRNA expression. However, DADS did not activate the phosphorylation of p38 MAPK, and SB203580 did not inhibit DADS-induced MUC5B expression. This is the first study to show that DADS-induced MUC5B expression appears to be regulated by activation of the ERK2 MAPK signaling pathway in human NCI-H292 airway epithelial cells.

Deficiency in the extracellular signal-regulated kinase 1 (ERK1) protects leptin-deficient mice from insulin resistance without affecting obesity

AIMS/HYPOTHESIS

Extracellular signal-regulated kinase (ERK) activity is increased in adipose tissue in obesity and type 2 diabetes mellitus and strong evidences suggests that it is implicated in the downregulation of insulin signalling and action in the insulin-resistant state. To determine the role of ERK1 in obesity-associated insulin resistance in vivo, we inactivated Erk1 (also known as Mapk3) in obese leptin-deficient mice (ob/ob).

METHODS

Mice of genotype ob/ob-Erk1⁻(/)⁻ were obtained by crossing Erk1⁻(/)⁻ mice with ob/ob mice. Glucose tolerance and insulin sensitivity were studied in 12-week-old mice. Tissue-specific insulin sensitivity, insulin signalling, liver steatosis and adipose tissue inflammation were determined.

RESULTS

While ob/ob-Erk1⁻(/)⁻ and ob/ob mice exhibited comparable body weight and adiposity, ob/ob-Erk1⁻(/)⁻ mice did not develop hyperglycaemia and their glucose tolerance was improved. Hyperinsulinaemic-euglycaemic clamp studies demonstrated an increase in whole-body insulin sensitivity in the ob/ob-Erk1⁻(/)⁻ mice associated with an increase in both insulin-stimulated glucose disposal in skeletal muscles and adipose tissue insulin sensitivity. This occurred in parallel with improved insulin signalling in both tissues. The ob/ob-Erk1⁻(/)⁻ mice were also partially protected against hepatic steatosis with a strong reduction in acetyl-CoA carboxylase level. These metabolic improvements were associated with reduced expression of mRNA encoding inflammatory cytokine and T lymphocyte markers in the adipose tissue.

CONCLUSIONS/INTERPRETATION

Our results demonstrate that the targeting of ERK1 could partially protect obese mice against insulin resistance and liver steatosis by decreasing adipose tissue inflammation and by increasing muscle glucose uptake. Our results indicate that deregulation of the ERK1 pathway could be an important component in obesity-associated metabolic disorders.

Four-dimensional dynamics of MAPK information processing systems

Mitogen activated protein kinase (MAPK) cascades process a myriad of stimuli received by cell-surface receptors and generate precise spatio-temporal guidance for multiple target proteins, dictating receptor-specific cellular outcomes. Computational modelling reveals that the intrinsic topology of MAPK cascades enables them to amplify signal sensitivity and amplitude, reduce noise and display intricate dynamic properties, which include toggle switches, excitation pulses and oscillations. Specificity of signaling responses can be brought about by signal-induced feedback and feedforward wiring imposed on the MAPK cascade backbone. Intracellular gradients of protein activities arise from the spatial separation of opposing reactions in kinase-phosphatase cycles. The membrane confinement of the initiating kinase in MAPK cascades and cytosolic localization of phosphatases can result in precipitous gradients of phosphorylated signal-transducers if they spread solely by diffusion. Endocytotic trafficking of active kinases driven by molecular motors and traveling waves of protein phosphorylation can propagate phosphorylation signals from the plasma membrane to the nucleus, especially in large cells, such as Xenopus eggs.

Role of protein kinase D signaling in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers with dismal survival rates. Its intransigence to conventional therapy renders PDAC an aggressive disease with early metastatic potential. Thus, novel targets for PDAC therapy are urgently needed. Multiple signal transduction pathways are implicated in progression of PDAC. These pathways stimulate production of intracellular messengers in their target cells to modify their behavior, including the lipid-derived diacylglycerol (DAG). One of the prominent intracellular targets of DAG is the protein kinase C (PKC) family. However, the mechanisms by which PKC-mediated signals are decoded by the cell remain incompletely understood. Protein kinase D1 (PKD or PKD1, initially called atypical PKCμ), is the founding member of a novel protein kinase family that includes two additional protein kinases that share extensive overall homology with PKD, termed PKD2, and PKD3. The PKD family occupies a unique position in the signal transduction pathways initiated by DAG and PKC. PKD lies downstream of PKCs in a novel signal transduction pathway implicated in the regulation of multiple fundamental biological processes. We and others have shown that PKD-mediated signaling pathways promote mitogenesis and angiogenesis in PDAC. Our recent observations demonstrate that PKD also potentiates chemoresistance and invasive potential of PDAC cells. This review will briefly highlight diverse biological roles of PKD family in multiple neoplasias including PDAC. Further, this review will underscore our latest advancement with the development of a potent PKD family inhibitor and its effect both in vitro and in vivo in PDAC.

TMKP1 is a novel wheat stress responsive MAP Kinase phosphatase localized in the nucleus

The regulation of plant signalling responses by Mitogen-Activated Protein Kinases (MAPKs)-mediated protein phosphorylation is well recognized. MAP kinase phosphatases (MKPs) are negative regulators of MAPKs in eukaryotes. We report here the identification and the characterization of TMKP1, the first wheat MKP (Triticum turgidum L. subsp. Durum). Expression profile analyses performed in two durum wheat cultivars showing a marked difference in salt and drought stress tolerance, revealed a differential regulation of TMKP1. Under salt and osmotic stress, TMKP1 is induced in the sensitive wheat variety and repressed in the tolerant one. A recombinant TMKP1 was shown to be an active phosphatase and capable to interact specifically with two wheat MAPKs (TMPK3 and TMPK6). In BY2 tobacco cells transiently expressing GFP::TMKP1, the fusion protein was localized into the nucleus. Interestingly, the deletion of the N-terminal non catalytic domain results in a strong accumulation of the truncated fusion protein in the cytoplasm. In addition, when expressed in BY2 cells, TMPK3 and TMPK6 fused to red fluorescent protein (RFP) were shown to be present predominantly in the nucleus. Surprisingly, when co-expressed with the N-terminal truncated TMKP1 fusion protein; both kinases are excluded from the nuclear compartment and accumulate in the cytoplasm. This strongly suggests that TMKP1 interacts in vivo with TMPK3 and TMPK6 and controls their subcellular localization. Taken together, our results show that the newly isolated wheat MKP might play an active role in modulating the plant cell responses to salt and osmotic stress responses.

Ligand-specific c-Fos expression emerges from the spatiotemporal control of ErbB network dynamics

Activation of ErbB receptors by epidermal growth factor (EGF) or heregulin (HRG) determines distinct cell-fate decisions, although signals propagate through shared pathways. Using mathematical modeling and experimental approaches, we unravel how HRG and EGF generate distinct, all-or-none responses of the phosphorylated transcription factor c-Fos. In the cytosol, EGF induces transient and HRG induces sustained ERK activation. In the nucleus, however, ERK activity and c-fos mRNA expression are transient for both ligands. Knockdown of dual-specificity phosphatases extends HRG-stimulated nuclear ERK activation, but not c-fos mRNA expression, implying the existence of a HRG-induced repressor of c-fos transcription. Further experiments confirmed that this repressor is mainly induced by HRG, but not EGF, and requires new protein synthesis. We show how a spatially distributed, signaling-transcription cascade robustly discriminates between transient and sustained ERK activities at the c-Fos system level. The proposed control mechanisms are general and operate in different cell types, stimulated by various ligands.

Induced overexpression of protein kinase D1 stimulates mitogenic signaling in human pancreatic carcinoma PANC-1 cells

Neurotensin (NT) stimulates protein kinase D1 (PKD1), extracellular signal regulated kinase (ERK), c-Jun N-terminal Kinase (JNK), and DNA synthesis in the human pancreatic adenocarcinoma cell line PANC-1. To determine the effect of PKD1 overexpression on these biological responses, we generated inducible stable PANC-1 clones that express wild-type (WT) or kinase-dead (K618N) forms of PKD1 in response to the ecdysone analog ponasterone-A (PonA). NT potently stimulated c-Jun Ser(63) phosphorylation in both wild type and clonal derivatives of PANC-1 cells. PonA-induced expression of WT, but not K618N PKD1, rapidly blocked NT-mediated c-Jun Ser(63) phosphorylation either at the level of or upstream of MKK4, a dual-specificity kinase that leads to JNK activation. This is the first demonstration that PKD1 suppresses NT-induced JNK/cJun activation in PANC-1 cells. In contrast, PKD1 overexpression markedly increased the duration of NT-induced ERK activation in these cells. The reciprocal influence of PKD1 signaling on pro-mitogenicERK and pro-apopotic JNK/c-Jun pathways prompted us to examine whether PKD1 overexpression promotes DNA synthesis and proliferation of PANC-1 cells. Our results show that PKD1 overexpression increased DNA synthesis and cell numbers of PANC-1 cells cultured in regular dishes or in polyhydroxyethylmethacrylate [Poly-(HEMA)]-coated dishes to eliminate cell adhesion (anchorage-independent growth). Furthermore, PKD1 overexpression markedly enhanced DNA synthesis induced by NT (1-10 nM). These results indicate that PKD1 mediates mitogenic signaling in PANC-1 and suggests that this enzyme could be a novel target for the development of therapeutic drugs that restrict the proliferation of these cells.

Novel nuclear nesprin-2 variants tether active extracellular signal-regulated MAPK1 and MAPK2 at promyelocytic leukemia protein nuclear bodies and act to regulate smooth muscle cell proliferation

Nuclear and cytoplasmic scaffold proteins have been shown to be essential for temporal and spatial organization, as well as the fidelity, of MAPK signaling pathways. In this study we show that nesprin-2 is a novel extracellular signal-regulated MAPK1 and 2 (ERK1/2) scaffold protein that serves to regulate nuclear signaling by tethering these kinases at promyelocytic leukemia protein nuclear bodies (PML NBs). Using immunofluorescence microscopy, GST pull-down and immunoprecipitation, we show that nesprin-2, ERK1/2, and PML colocalize and bind to form a nuclear complex. Interference of nesprin-2 function, by either siRNA-mediated knockdown or overexpression of a dominant negative nesprin-2 fragment, augmented ERK1/2 nuclear signaling shown by increased SP1 activity and ELK1 phosphorylation. The functional outcome of nesprin-2 disruption and the resultant sustained ERK1/2 signal was increased proliferation. Importantly, these activities were not induced by previously identified nuclear envelope (NE)-targeted nesprin-2 isoforms but rather were mediated by novel nuclear isoforms that lacked the KASH domain. Taken together, this study suggests that nesprin-2 is a novel intranuclear scaffold, essential for nuclear ERK1/2 signaling fidelity and cell cycle progression.

CREB and AP-1 activation regulates MKP-1 induction by LPS or M-CSF and their kinetics correlate with macrophage activation versus proliferation

MAPK phosphatase-1 (MKP-1) is a protein phosphatase that plays a crucial role in innate immunity. This phosphatase inactivates ERK1/2, which are involved in two opposite functional activities of the macrophage, namely proliferation and activation. Here we found that although macrophage proliferation and activation induce MKP-1 with different kinetics, gene expression is mediated by the proximal promoter sequences localized between -380 and -180 bp. Mutagenesis experiments of the proximal element determined that CRE/AP-1 is required for LPS- or M-CSF-induced activation of the MKP-1 gene. Moreover, the results from gel shift analysis and chromatin immunoprecipitation indicated that c-Jun and CREB bind to the CRE/AP-1 box. The distinct kinetics shown by M-CSF and LPS correlates with the induction of JNK and c-jun, as well as the requirement for Raf-1. The signal transduction pathways that activate the induction of MKP-1 correlate kinetically with induction by M-CSF and LPS.

Extracellular signal-regulated kinase 1/2 activation counteracts morphine tolerance in the periaqueductal gray of the rat

Repeated administration of opioids produces long-lasting changes in micro-opioid receptor (MOR) signaling that underlie behavioral changes such as tolerance. Mitogen-activated protein kinase (MAPK) pathways, including MAPK extracellular signal-regulated kinases (ERK1/2), are modulated by opioids and are known to produce long-lasting changes in cell signaling. Thus, we tested the hypothesis that ERK1/2 activation contributes to the development and/or expression of morphine tolerance mediated by the periaqueductal gray (PAG). Changes in phosphorylated ERK1/2 expression were assessed with confocal microscopy and compared to behavioral measures of tolerance to the antinociceptive effects of chronic morphine administration. Repeated microinjection of morphine into the PAG produced tolerance and caused a significant increase in ERK1/2 phosphorylation, an effect not evident with acute morphine microinjection. Microinjection of the MAPK/ERK kinase inhibitor, 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto)butadiene ethanolate (U0126), into the PAG had no effect on antinociception produced by acute morphine administration. However, repeated coadministration of U0126 and morphine into the PAG blocked ERK1/2 phosphorylation and enhanced the development of morphine tolerance. Coadministration of U0126 with morphine only on the test day also enhanced the expression of morphine tolerance. Administration of the irreversible opioid receptor antagonist beta-chlornaltrexamine blocked the activation of ERK1/2 caused by repeated morphine microinjections, demonstrating that ERK1/2 activation was a MOR-mediated event. In summary, these studies show that chronic morphine administration alters ERK1/2 signaling and that disruption of ERK1/2 signaling enhances both the development and expression of morphine tolerance. Contrary to expectations, these data indicate that ERK1/2 activation opposes the development of morphine tolerance.

Erk1/2 MAP kinases are required for epidermal G2/M progression

Erk1/2 mitogen-activated protein kinases (MAPKs) are often hyperactivated in human cancers, where they affect multiple processes, including proliferation. However, the effects of Erk1/2 loss in normal epithelial tissue, the setting of most extracellular signal-regulated kinase (Erk)-associated neoplasms, are unknown. In epidermis, loss of Erk1 or Erk2 individually has no effect, whereas simultaneous Erk1/2 depletion inhibits cell division, demonstrating that these MAPKs are necessary for normal tissue self-renewal. Growth inhibition caused by Erk1/2 loss is rescued by reintroducing Erk2, but not by activating Erk effectors that promote G1 cell cycle progression. Unlike fibroblasts, in which Erk1/2 loss decreases cyclin D1 expression and induces G1/S arrest, Erk1/2 loss in epithelial cells reduces cyclin B1 and c-Fos expression and induces G2/M arrest while disrupting a gene regulatory network centered on cyclin B1-Cdc2. Thus, the cell cycle stages at which Erk1/2 activity is required vary by cell type, with Erk1/2 functioning in epithelial cells to enable progression through G2/M.

Smooth muscle archvillin is an ERK scaffolding protein

ERK influences a number of pathways in all cells, but how ERK activities are segregated between different pathways has not been entirely clear. Using immunoprecipitation and pulldown experiments with domain-specific recombinant fragments, we show that smooth muscle archvillin (SmAV) binds ERK and members of the ERK signaling cascade in a domain-specific, stimulus-dependent, and pathway-specific manner. MEK binds specifically to the first 445 residues of SmAV. B-Raf, an upstream regulator of MEK, constitutively interacts with residues 1-445 and 446-1250. Both ERK and 14-3-3 bind to both fragments, but in a stimulus-specific manner. Phosphorylated ERK is associated only with residues 1-445. An ERK phosphorylation site was determined by mass spectrometry to reside at Ser132. A phospho-antibody raised to this site shows that the site is phosphorylated during alpha-agonist-mediated ERK activation in smooth muscle tissue. Phosphorylation of SmAV by ERK decreases the association of phospho-ERK with SmAV. These results, combined with previous observations, indicate that SmAV serves as a new ERK scaffolding protein and provide a mechanism for regulation of ERK binding, activation, and release from the signaling complex.

Cocaine- and amphetamine-regulated transcript accelerates termination of follicle-stimulating hormone-induced extracellularly regulated kinase 1/2 and Akt activation by regulating the expression and degradation of specific mitogen-activated protein kinase phosphatases in bovine granulosa cells

Pleiotropic actions of cocaine- and amphetamine-regulated transcript (CART) are well described in the central nervous system and periphery, but the intracellular mechanisms mediating biological actions of CART are poorly understood. Although CART is not expressed in mouse ovaries, we have previously established CART as a novel intracellular regulator of estradiol production in bovine granulosa cells. We demonstrated that inhibitory actions of CART on estradiol production are mediated through inhibition of FSH-induced cAMP accumulation, Ca(2+) influx, and aromatase mRNA expression via a G(o/i)-dependent pathway. We also reported that FSH-induced estradiol production is dependent on Erk1/2 and Akt signaling, and CART may regulate other signaling proteins downstream of cAMP essential for estradiol production. Here, we demonstrate that CART is a potent inhibitor of FSH-stimulated Erk1/2 and Akt signaling and the mechanisms involved. Transient CART stimulation of bovine granulosa cells shortens the duration of FSH-induced Erk1/2 and Akt signaling whereas a prolonged (24 h) CART treatment blocks Erk1/2 and Akt activation in response to FSH. This CART-induced accelerated termination of Erk1/2 and Akt signaling is mediated both by induced expression and impaired ubiquitin-mediated proteasome degradation of dual specific phosphatase 5 (DUSP5) and protein phosphatase 2A. Results also support existence of a negative feedback loop in which CART via a G(o/i)-MAPK kinase dependent pathway activates Erk1/2, and the latter induces DUSP5 expression. Moreover, small interfering RNA mediated ablation of DUSP5 and/or protein phosphatase 2A prevents the CART-induced early termination of Erk1/2 and Akt signaling. Results provide novel insight into the intracellular mechanism of action of CART in regulation of FSH-induced MAPK signaling.

Transient activation of the MAP kinase signaling pathway by the forward signaling of EphA4 in PC12 cells

In the present study, we demonstrate that ephrin-A5 is able to induce a transient increase of MAP kinase activity in PC12 cells. However, the effects of ephrin-A5 on the MAP kinase signaling pathway are about three-fold less than that of EGF. In addition, we demonstrate that EphA4 is the only Eph member expressed in PC12 cells, and that tyrosine phosphorylation induced by ephrin-A5 treatment is consistent with the magnitude and longevity of MAP kinase activation. Experiments using the Ras dominant negative mutant N17Ras reveal that Ras plays a pivotal role in ephrin-A5-induced MAP kinase activation in PC12 cells. Importantly, we found that the EphA4 receptor is rapidly internalized by endocytosis upon engagement of ephrin-A5, leading to a subsequent reduction in the MAP kinase activation. Together, these data suggest a novel regulatory mechanism of differential Ras-MAP kinase signaling kinetics exhibited by the forward signaling of EphA4 in PC12 cells.

Mitogen-induced recruitment of ERK and MSK to SRE promoter complexes by ternary complex factor Elk-1

Many eukaryotic genes are acutely regulated by extra-cellular signals. The c-fos serum response element (SRE) mediates transcriptional activation in response to mitogens through serum response factor (SRF)-dependent recruitment of Elk-1, a mitogen-activated protein kinase (MAPK)-responsive transcription factor. How subsequent events at SRE promoters stimulate initiation of transcription has yet to be fully resolved. Here we show that extra-cellular signal-regulated kinase (ERK) and mitogen and stress-activated kinase (MSK) are recruited to SRE promoter complexes in vitro and in vivo. Their recruitment in vitro correlates with Elk-1 binding and for ERK the D domain/KIM of Elk-1 is specifically involved. In vivo, recruitment of ERK and MSK is stimulated by mitogens, correlates with histone H3 phosphorylation and is impaired by Elk-1 knockdown. Immunocytochemistry and confocal microscopy reveal that ERK appears to associate to some extent with initiating rather than elongating RNA polymerase II. Taken together, our data add to the body of evidence implying that ERK and related MAPKs may fulfil a generic role at the promoters of acutely regulated genes.

Extracellular ATP activates the PLC/PKC/ERK signaling pathway through the P2Y2 purinergic receptor leading to the induction of early growth response 1 expression and the inhibition of viability in human endometrial stromal cells

ATP is an extracellular signaling molecule that activates specific G protein-coupled P2Y receptors in most cell types to mediate diverse biological effects. ATP has been shown to activate the phospholipase C (PLC)/diacylglycerol/protein kinase C (PKC) pathway in various systems. However, little is known about the signaling events in human endometrial stromal cells (hESCs). The objective of this study was to examine the presence of the P2Y2 receptor and the effects of exogenous ATP on the intracellular mitogen-activated protein kinases (MAPKs) signaling pathway, immediate early genes expression, and cell viability in hESCs. Western blot analysis, gene array analysis, and MTT assay for cell viability were performed. The current study demonstrated the existence of the P2Y2 purinergic receptor in hESCs. UTP and ATP activated MAPK in a dose- and time-dependent manner. Suramin (a P2-purinoceptor antagonist), neomycin (a PLC inhibitor), staurosporin (a PKC inhibitor), and PD98059 (a MEK inhibitor) significantly attenuated the ATP-induced activation of MAPK. ATP activated ERK1/2 and induced translocation of activated ERK1/2 to the nucleus. The gene array for 23 genes associated with members of the mitogenic pathway cascade and immediate early genes revealed that the expression of early growth response 1 was increased. In addition, MTT assay revealed an inhibition effect of ATP on cell viability. ATP activated MAPKs through the P2Y2 purinoceptor/PLC/PKC/ERK signaling pathway and induced translocation of ERK1/2 into the nucleus. Further, ATP induced the expression of early growth response 1 and inhibited cell viability in hESCs.