Nuclear Extracellular Signal-regulated Kinase Research Articles

Nucleic acid sensing promotes inflammatory monocyte migration through biased coagulation factor VIIa signaling

AbstractProtease activated receptors (PARs) are cleaved by coagulation proteases and thereby connect hemostasis with innate immune responses. Signaling of the tissue factor (TF) complex with factor VIIa (FVIIa) via PAR2 stimulates extracellular signal-regulated kinase (ERK) activation and cancer cell migration, but functions of cell autonomous TF-FVIIa signaling in immune cells are unknown. Here, we show that myeloid cell expression of FVII but not of FX is crucial for inflammatory cell recruitment to the alveolar space after challenge with the double-stranded viral RNA mimic polyinosinic:polycytidylic acid [Poly(I:C)]. In line with these data, genetically modified mice completely resistant to PAR2 cleavage but not FXa-resistant PAR2–mutant mice are protected from lung inflammation. Poly(I:C)-stimulated migration of monocytes/macrophages is dependent on ERK activation and mitochondrial antiviral signaling (MAVS) but independent of toll-like receptor 3 (TLR3). Monocyte/macrophage-synthesized FVIIa cleaving PAR2 is required for integrin αMβ2-dependent migration on fibrinogen but not for integrin β1-dependent migration on fibronectin. To further dissect the downstream signaling pathway, we generated PAR2S365/T368A-mutant mice deficient in β-arrestin recruitment and ERK scaffolding. This mutation reduces cytosolic, but not nuclear ERK phosphorylation by Poly(I:C) stimulation, and prevents macrophage migration on fibrinogen but not fibronectin after stimulation with Poly(I:C) or CpG-B, a single-stranded DNA TLR9 agonist. In addition, PAR2S365/T368A-mutant mice display markedly reduced immune cell recruitment to the alveolar space after Poly(I:C) challenge. These results identify TF-FVIIa-PAR2-β-arrestin–biased signaling as a driver for lung infiltration in response to viral nucleic acids and suggest potential therapeutic interventions specifically targeting TF-VIIa signaling in thrombo-inflammation.

On the inference of ERK signaling dynamics from protein biosensor measurements.

The extracellular signal-regulated kinase (ERK) signaling pathway plays prominent roles in cell growth, proliferation, and differentiation. ERK signaling is dynamic, involving phosphorylation/dephosphorylation, nucleocytoplasmic shuttling, and interactions with scores of protein substrates in the cytosol and in the nucleus. Live-cell fluorescence microscopy using genetically encoded ERK biosensors offers the potential to infer those dynamics in individual cells. In this study, we have monitored ERK signaling using four commonly used translocation- and Förster resonance energy transfer-based biosensors in a common cell stimulation context. Consistent with previous reports, we found that each biosensor responds with unique kinetics; it is clear that there is not a single dynamic signature characterizing the complexity of ERK phosphorylation, translocation, and kinase activity. In particular, the widely adopted ERK Kinase Translocation Reporter (ERKKTR) gives a readout that reflects ERK activity in both compartments. Mathematical modeling offers an interpretation of the measured ERKKTR kinetics, in relation to cytosolic and nuclear ERK activity, and suggests that biosensor-specific dynamics substantially influence the measured output.

ERK phosphorylation disrupts the intramolecular interaction of capicua to promote cytoplasmic translocation of capicua and tumor growth.

Activation of receptor tyrosine kinase signaling inactivates capicua (CIC), a transcriptional repressor that functions as a tumor suppressor, via degradation and/or cytoplasmic translocation. Although CIC is known to be inactivated by phosphorylation, the mechanisms underlying the cytoplasmic translocation of CIC remain poorly understood. Therefore, we aimed to evaluate the roles of extracellular signal-regulated kinase (ERK), p90RSK, and c-SRC in the epidermal growth factor receptor (EGFR) activation-induced cytoplasmic translocation of CIC and further investigated the molecular basis for this process. We found that nuclear ERK induced the cytoplasmic translocation of CIC-S. We identified 12 serine and threonine (S/T) residues within CIC, including S173 and S301 residues that are phosphorylated by p90RSK, which contribute to the cytoplasmic translocation of CIC-S when phosphorylated. The amino-terminal (CIC-S-N) and carboxyl-terminal (CIC-S-C) regions of CIC-S were found to interact with each other to promote their nuclear localization. EGF treatment disrupted the interaction between CIC-S-N and CIC-S-C and induced their cytoplasmic translocation. Alanine substitution for the 12S/T residues blocked the cytoplasmic translocation of CIC-S and consequently enhanced the tumor suppressor activity of CIC-S. Our study demonstrates that ERK-mediated disruption of intramolecular interaction of CIC is critical for the cytoplasmic translocation of CIC, and suggests that the nuclear retention of CIC may represent a strategy for cancer therapy.

Non-canonical β-adrenergic activation of ERK at endosomes.

G-protein-coupled receptors (GPCRs), the largest family of signalling receptors, as well as important drug targets, are known to activate extracellular-signal-regulated kinase (ERK)-a master regulator of cell proliferation and survival1. However, the precise mechanisms that underlie GPCR-mediated ERK activation are not clearly understood2-4. Here we investigated how spatially organized β2-adrenergic receptor (β2AR) signalling controls ERK. Using subcellularly targeted ERK activity biosensors5, we show that β2AR signalling induces ERK activity at endosomes, but not at the plasma membrane. This pool of ERK activity depends on active, endosome-localized Gαs and requires ligand-stimulated β2AR endocytosis. We further identify an endosomally localized non-canonical signalling axis comprising Gαs, RAF and mitogen-activated protein kinase kinase, resulting in endosomal ERK activity that propagates into the nucleus. Selective inhibition of endosomal β2AR and Gαs signalling blunted nuclear ERK activity, MYC gene expression and cell proliferation. These results reveal a non-canonical mechanism for the spatial regulation of ERK through GPCR signalling and identify a functionally important endosomal signalling axis.

Molecular Mechanism of GPCR‐mediated ERK Pathway in Cancer

G protein-coupled receptors (GPCRs) are known to activate extracellular-signal-regulated kinase (ERK), a master regulator of cell proliferation and survival and a key oncogenic component. The co-occurrence of KRAS and GNAS (which encodes Gsa) mutations has been reported in several cancers including pancreatic ductal adenocarcinoma (PDAC), hinting at synergistic roles of these two pathways in activating pro-tumorigenic ERK. However, the precise mechanisms and the role underlying GPCR-mediated ERK regulation are not clearly understood. Here we investigated how the spatially organized β2-adrenergic receptor (b2AR) signaling controls ERK using FRET-based ERK activity biosensors targeted to various subcellular regions, which enable us to interrogate spatial and temporal regulation of ERK activity in living cells. In b2AR expressing HEK293 cells, epinephrine induces ERK activity at the endosome and in the nucleus, but not at the plasma membrane. This pool of ERK activity depends on endosome-localized active Gsa and requires ligand-stimulated b2AR endocytosis. The inhibition of endosomal b2AR and Gsa signaling using endosome-targeted nanobody and peptide inhibitor decreased basal nuclear ERK activity and proliferation in AsPC-1 cells, a PDAC cell line. The discovery of endosomal Gsa-mediated ERK activation could add the missing spatiotemporal information of GPCR regulation of ERK and also fill in the gap in our knowledge of GPCR signaling in cancer development, providing the basis for new therapeutic strategies for PDAC.

Activation of extracellular signal-regulated kinase is associated with hepatocellular carcinoma with aggressive phenotypes.

Sorafenib inhibits multiple kinase signaling pathways, including the rat sarcoma virus (Ras)/rapidly accelerated fibrosarcoma (Raf)/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway, and is a promising therapy for hepatocellular carcinoma (HCC). However, the role of ERK activation in HCC remains unclear. This study was designed to investigate the potential link between ERK activation and aggressive HCC phenotypes. We evaluated nuclear ERK expression by immunohistochemistry in 154 resected HCC nodules from 136 patients. We then investigated the associations of ERK expression with the clinicopathological characteristics of HCC, c-MET expression, and the molecular subclass biomarkers Ki-67, keratin19 (KRT19, CK19, or K19), and sal-like protein4. Multivariate Cox regression analysis was carried out to determine independent prognostic factors for overall survival and recurrence-free survival. The effects of ERK activation by hepatocyte growth factor (HGF) on eight HCC cell lines were further examined. High-level nuclear expression of ERK was observed in 20 (13%) of 154 nodules and was significantly associated with higher serum alpha-fetoprotein levels (P = 0.034), poorer differentiation (P = 0.003), a higher Ki-67 index (P < 0.001), high-level expression of c-MET (P = 0.008), KRT19 (P = 0.002), or sal-like protein4 (P < 0.001), and shorter overall survival (multivariate hazard ratio 3.448; P = 0.028) and recurrence-free survival (multivariate hazard ratio 2.755; P = 0.004). HCC cells treated with hepatocyte growth factor showed enhanced cell proliferation together with ERK activation and upregulated KRT19 expression, both of which were inhibited by sorafenib. High-level ERK activation is associated with a KRT19-positive highly proliferative subtype of HCC with a dismal prognosis. These findings support the key role of the hepatocyte growth factor/c-MET/ERK axis in HCC progression.

Ligand-dependent spatiotemporal signaling profiles of the μ-opioid receptor are controlled by distinct protein-interaction networks

Ligand-dependent differences in the regulation and internalization of the μ-opioid receptor (MOR) have been linked to the severity of adverse effects that limit opiate use in pain management. MOR activation by morphine or [d-Ala2,N-MePhe4, Gly-ol]enkephalin (DAMGO) causes differences in spatiotemporal signaling dependent on MOR distribution at the plasma membrane. Morphine stimulation of MOR activates a Gαi/o–Gβγ–protein kinase C (PKC) α phosphorylation pathway that limits MOR distribution and is associated with a sustained increase in cytosolic extracellular signal-regulated kinase (ERK) activity. In contrast, DAMGO causes a redistribution of the MOR at the plasma membrane (before receptor internalization) that facilitates transient activation of cytosolic and nuclear ERK. Here, we used proximity biotinylation proteomics to dissect the different protein-interaction networks that underlie the spatiotemporal signaling of morphine and DAMGO. We found that DAMGO, but not morphine, activates Ras-related C3 botulinum toxin substrate 1 (Rac1). Both Rac1 and nuclear ERK activity depended on the scaffolding proteins IQ motif-containing GTPase-activating protein-1 (IQGAP1) and Crk-like (CRKL) protein. In contrast, morphine increased the proximity of the MOR to desmosomal proteins, which form specialized and highly-ordered membrane domains. Knockdown of two desmosomal proteins, junction plakoglobin or desmocolin-1, switched the morphine spatiotemporal signaling profile to mimic that of DAMGO, resulting in a transient increase in nuclear ERK activity. The identification of the MOR-interaction networks that control differential spatiotemporal signaling reported here is an important step toward understanding how signal compartmentalization contributes to opioid-induced responses, including anti-nociception and the development of tolerance and dependence.

Nuclear ERK Translocation is Mediated by Protein Kinase CK2 and Accelerated by Autophosphorylation.

The extracellular signal-regulated kinases (ERK) 1 and 2 (ERK1/2) are members of the mitogen-activated protein kinase (MAPK) family. Upon stimulation, these kinases translocate from the cytoplasm to the nucleus, where they induce physiological processes such as proliferation and differentiation. The mechanism of translocation of this kinase involves phosphorylation of two Ser residues within a nuclear translocation signal (NTS), which allows binding to importin7 and a subsequent penetration via nuclear pores. However, the regulation of this process and the protein kinases involved are not yet clear. To answer this point we developed specific anti phospho-SPS antibody, used this and other antibodies in Western blots and crystalized the phospho-mimetic mutated ERK. Here we show that the phosphorylation of both Ser residues is mediated mainly by casein kinase 2 (CK2) and that active ERK may assist in the phosphorylation of the N-terminal Ser. We also demonstrate that the phosphorylation is dependent on the release of ERK from cytoplasmic anchoring proteins. Crystal structure of the phosphomimetic ERK revealed that the NTS phosphorylation creates an acidic patch in ERK. Our model is that in resting cells ERK is bound to cytoplasmic anchors, which prevent its NTS phosphorylation. Upon stimulation, phosphorylation of the ERK TEY domain releases ERK and allows phosphorylation of its NTS by CK2 and active ERK to generate a negatively charged patch in ERK, binding to importin 7 and nuclear translocation. These results provide an important role of CK2 in regulating nuclear ERK activities.

Automated FRET quantification shows distinct subcellular ERK activation kinetics in response to graded EGFR signaling in Drosophila.

Threshold responses to an activity gradient allow a single signaling pathway to yield multiple outcomes. Extracellular signal-regulated kinase (ERK) is one such signal, which couples receptor tyrosine kinase signaling with multiple cellular responses in various developmental processes. Recent advances in the development of fluorescent biosensors for live imaging have enabled the signaling activities accompanying embryonic development to be monitored in real time. Here, we used an automated computational program to quantify the signals of a fluorescence resonance energy transfer (FRET) reporter for activated ERK, and we used this system to monitor the spatio-temporal dynamics of ERK during neuroectoderm patterning in Drosophila embryos. We found that the cytoplasmic and nuclear ERK activity gradients show distinct kinetics in response to epidermal growth factor receptor activation. The ERK activation patterns implied that the cytoplasmic ERK activity is modulated into a threshold response in the nucleus.

Effects of carbachol on apoptosis in human chronic myelogenous leukemic K562 cell line

Objectives: Muscarinic receptors mediate diverse actions ofacetylcholine in the central nervous system and in non-nervoustissues innervated by the parasympathetic nervous system.Our study aims to evaluate the potential association of theM3 muscarinic receptor with K562 cell proliferation and death.Materials and Methods: Cell proliferation was evaluatedby bromodeoxyuridine (BrDU) incorporation. To show early,late apoptosis and cell death, cells were labelled with AnnexinV, propidium iodide (PI) and analyzed by flow cytometry. Nuclearextracellular signal-regulated kinase (ERK/pERK) expressionwas measured by western blot analysis.Results: Treatment with carbachol (CCh) for 48h decreased cellnumber. Exposing K562 cells to CCh for 24h decreased the number ofearly apoptotic cells but did not change the number of late apoptotic andnecrotic cells. CCh treatment for 48h increased the number of necroticcells, but decreased the number of early and late apoptotic cells. Inresponse to CCh, nuclear ERK expression was increased and this effectwas reversed by 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide(4DAMP). Nuclear pERK expression was decreased in CCh treatedcells, 4DAMP did not reverse the effect.Conclusion: Our data suggest that cholinergic agonist CChaffects cell proliferation in K562 cells not only through muscarinicreceptors but also through other cholinergic receptors.

Retraction for Plotnikov et al., "Nuclear Extracellular Signal-Regulated Kinase 1 and 2 Translocation Is Mediated by Casein Kinase 2 and Accelerated by Autophosphorylation".

Retraction for Plotnikov et al., "Nuclear Extracellular Signal-Regulated Kinase 1 and 2 Translocation Is Mediated by Casein Kinase 2 and Accelerated by Autophosphorylation".

Photoactivation of Extracellular‐Signal‐Regulated Kinase Signaling in Target Cells by Femtosecond Laser

AbstractOptogenetics employs light to manipulate cellular events such as activation of molecular channels, signaling molecules, and gene transcription, by transfection with engineered light‐sensitive proteins. In the last decade, great progresses in life science have been made by optogenetics, but the gene transfection limits its further medical applications. In this study, it is reported that a short flash of femtosecond‐laser stimulation can directly activate extracellular signal‐regulated kinase (ERK), an essential signaling pathway, in target cells, without any optogenetic technology. This all‐optical approach can be easily accomplished by a two‐photon or confocal microscope coupled with a femtosecond laser. The photostimulation can initiate immediate ERK translocation into nucleus and exit back to cytosol. The nuclear ERK level can be regulated by combination of multiple photostimulations. Subsequent up‐regulation of phosphorylated endogenous eIF4E indicates successful activation of the ERK signaling pathway. Occasionally, ERK activation in the surrounding cells of the stimulation is observed. Some key signaling cascades in the ERK2 pathway activated by photostimulation is further clarified. Altogether, this all‐optical method can activate ERK without any exogenous chemicals or proteins and thus be with promissing potential for related research.

Endosomal signaling of the receptor for calcitonin gene-related peptide mediates pain transmission

G protein-coupled receptors (GPCRs) are considered to function primarily at the plasma membrane, where they interact with extracellular ligands and couple to G proteins that transmit intracellular signals. Consequently, therapeutic drugs are designed to target GPCRs at the plasma membrane. Activated GPCRs undergo clathrin-dependent endocytosis. Whether GPCRs in endosomes control pathophysiological processes in vivo and are therapeutic targets remains uncertain. We investigated the contribution of endosomal signaling of the calcitonin receptor-like receptor (CLR) to pain transmission. Calcitonin gene-related peptide (CGRP) stimulated CLR endocytosis and activated protein kinase C (PKC) in the cytosol and extracellular signal regulated kinase (ERK) in the cytosol and nucleus. Inhibitors of clathrin and dynamin prevented CLR endocytosis and activation of cytosolic PKC and nuclear ERK, which derive from endosomal CLR. A cholestanol-conjugated antagonist, CGRP8-37, accumulated in CLR-containing endosomes and selectively inhibited CLR signaling in endosomes. CGRP caused sustained excitation of neurons in slices of rat spinal cord. Inhibitors of dynamin, ERK, and PKC suppressed persistent neuronal excitation. CGRP8-37-cholestanol, but not unconjugated CGRP8-37, prevented sustained neuronal excitation. When injected intrathecally to mice, CGRP8-37-cholestanol inhibited nociceptive responses to intraplantar injection of capsaicin, formalin, or complete Freund's adjuvant more effectively than unconjugated CGRP8-37 Our results show that CLR signals from endosomes to control pain transmission and identify CLR in endosomes as a therapeutic target for pain. Thus, GPCRs function not only at the plasma membrane but also in endosomes to control complex processes in vivo. Endosomal GPCRs are a drug target that deserve further attention.

The Role of ERK Signaling in Experimental Autoimmune Encephalomyelitis.

Extracellular signal-regulated kinase (ERK) signaling plays a crucial role in regulating immune cell function and has been implicated in autoimmune disorders. To date, all commercially available inhibitors of ERK target upstream components, such as mitogen-activated protein (MAP) kinase/ERK kinase (MEKs), but not ERK itself. Here, we directly inhibit nuclear ERK translocation by a novel pharmacological approach (Glu-Pro-Glu (EPE) peptide), leading to an increase in cytosolic ERK phosphorylation during T helper (Th)17 cell differentiation. This was accompanied by diminished secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine influencing the encephalitogenicity of Th17 cells. Neither the production of the cytokine interleukin (IL)-17 nor the proliferation rate of T cells was affected by the EPE peptide. The in vivo effects of ERK inhibition were challenged in two independent variants of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Overall, ERK inhibition had only a very minor impact on the clinical disease course of EAE. This indicates that while ERK translocation might promote encephalitogenicity in T cells in vitro by facilitating GM-CSF production, this effect is overcome in more complex in vivo animal models of central nervous system (CNS) autoimmunity.

Modeling Cellular Noise Underlying Heterogeneous Cell Responses in the Epidermal Growth Factor Signaling Pathway.

Cellular heterogeneity, which plays an essential role in biological phenomena, such as drug resistance and migration, is considered to arise from intrinsic (i.e., reaction kinetics) and extrinsic (i.e., protein variability) noise in the cell. However, the mechanistic effects of these types of noise to determine the heterogeneity of signal responses have not been elucidated. Here, we report that the output of epidermal growth factor (EGF) signaling activity is modulated by cellular noise, particularly by extrinsic noise of particular signaling components in the pathway. We developed a mathematical model of the EGF signaling pathway incorporating regulation between extracellular signal-regulated kinase (ERK) and nuclear pore complex (NPC), which is necessary for switch-like activation of the nuclear ERK response. As the threshold of switch-like behavior is more sensitive to perturbations than the graded response, the effect of biological noise is potentially critical for cell fate decision. Our simulation analysis indicated that extrinsic noise, but not intrinsic noise, contributes to cell-to-cell heterogeneity of nuclear ERK. In addition, we accurately estimated variations in abundance of the signal proteins between individual cells by direct comparison of experimental data with simulation results using Apparent Measurement Error (AME). AME was constant regardless of whether the protein levels varied in a correlated manner, while covariation among proteins influenced cell-to-cell heterogeneity of nuclear ERK, suppressing the variation. Simulations using the estimated protein abundances showed that each protein species has different effects on cell-to-cell variation in the nuclear ERK response. In particular, variability of EGF receptor, Ras, Raf, and MEK strongly influenced cellular heterogeneity, while others did not. Overall, our results indicated that cellular heterogeneity in response to EGF is strongly driven by extrinsic noise, and that such heterogeneity results from variability of particular protein species that function as sensitive nodes, which may contribute to the pathogenesis of human diseases.

Conversion of graded phosphorylation into switch-like nuclear translocation via autoregulatory mechanisms in ERK signalling.

The phosphorylation cascade in the extracellular signal-regulated kinase (ERK) pathway is a versatile reaction network motif that can potentially act as a switch, oscillator or memory. Nevertheless, there is accumulating evidence that the phosphorylation response is mostly linear to extracellular signals in mammalian cells. Here we find that subsequent nuclear translocation gives rise to a switch-like increase in nuclear ERK concentration in response to signal input. The switch-like response disappears in the presence of ERK inhibitor, suggesting the existence of autoregulatory mechanisms for ERK nuclear translocation involved in conversion from a graded to a switch-like response. In vitro reconstruction of ERK nuclear translocation indicates that ERK-mediated phosphorylation of nucleoporins regulates ERK translocation. A mathematical model and knockdown experiments suggest a contribution of nucleoporins to regulation of the ERK nuclear translocation response. Taken together, this study provides evidence that nuclear translocation with autoregulatory mechanisms acts as a switch in ERK signalling.

Effects of nuclear factor-κB and ERK signaling transduction pathway inhibitors on human melanoma cell proliferation in vitro

The present study aimed to investigate the effects of blocking nuclear factor (NF)-κB and/or extracellular signal-regulated kinase (ERK) signaling pathways on proliferation and apoptosis of melanoma cells in vitro. A375 Human melanoma cells were treated with U0126 (ERK signaling pathway inhibitor) and BMS-345541 (NF-κB inhibitor), alone or in combination. At 12, 24 and 48 h after treatment, cell viability was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, cell cycle progression and apoptosis were evaluated by flow cytometry, and Bcl-2 protein content was determined by western blot analysis. BMS-345541 and U0126 significantly inhibited A375 cell proliferation in a dose- and time-dependent manner (P<0.01). The rate of proliferation inhibition at 24 h was 35.41±1.38% for BMS-345541 alone, 30.64±2.86% for U0126 alone, and 77.27±2.70% for BMS-345541 and U0126 in combination. The difference between combination and single treatment was significantly different (P<0.01). The proportion of cells in S phase was 14.20, 18.40 and 22.64% following treatment with BMS-345541, U0126, and BMS-345541 and U0126 in combination, respectively; these values were all significantly reduced compared with the untreated control group (P<0.01). The apoptosis rate was 24.98±1.03% in the BMS-345541 group, 13.96±0.96% in the U0126 group and 38.91±1.46% in the combination group; all significantly increased compared with the control group (P<0.01). Bcl-2 protein content in A375 cells was significantly increased following treatment with BMS-345541 and U0126, alone or in combination, when compared with the untreated control group (P<0.01). Therefore, NF-κB and ERK signaling pathway inhibitors may serve as potential therapeutic targets for melanoma.

Synthesis and biological evaluation of a novel class of curcumin analogs as anti-inflammatory agents for prevention and treatment of sepsis in mouse model.

A novel class of asymmetric mono-carbonyl analogs of curcumin (AMACs) were synthesized and screened for anti-inflammatory activity. These analogs are chemically stable as characterized by UV absorption spectra. In vitro, compounds 3f, 3m, 4b, and 4d markedly inhibited lipopolysaccharide (LPS)-induced expression of pro-inflammatory cytokines tumor necrosis factor-α and interleukin-6 in a dose-dependent manner, with IC50 values in low micromolar range. In vivo, compound 3f demonstrated potent preventive and therapeutic effects on LPS-induced sepsis in mouse model. Compound 3f downregulated the phosphorylation of extracellular signal-regulated kinase (ERK)1/2 MAPK and suppressed IκBα degradation, which suggests that the possible anti-inflammatory mechanism of compound 3f may be through downregulating nuclear factor kappa binding (NF-κB) and ERK pathways. Also, we solved the crystal structure of compound 3e to confirm the asymmetrical structure. The quantitative structure–activity relationship analysis reveals that the electron-withdrawing substituents on aromatic ring of lead structures could improve activity. These active AMACs represent a new class of anti-inflammatory agents with improved stability, bioavailability, and potency compared to curcumin. Our results suggest that 3f may be further developed as a potential agent for prevention and treatment of sepsis or other inflammation-related diseases.

Mitogen-activated protein kinase phosphatase-1 inhibition and sustained extracellular signal-regulated kinase 1/2 activation in camptothecin-induced human colon cancer cell death

Camptothecins are commonly used chemotherapeutics; in some models, they enhance signaling via the mitogen-activated protein kinase (MAPK) pathway through effects on upstream kinases. To evaluate the impact of camptothecin (CPT) on MAPKs in human colon cancer, we studied HCT116 and CaCo2 colon cancer cells. We found that HCT116 cells highly express mitogen-activated protein kinase phosphatase-1 (MKP1), which selectively inactivates extracellular signal-regulated kinase (ERK), whereas MKP1 levels were undetectable in CaCo2 cells. CPT did not affect ERK activity in CaCo2 cells, but did induce a striking increase in ERK activity in HCT116 cells in association with a corresponding decrease in MKP1. The reduction in MKP1 expression occurred at a posttranscriptional level and was blocked by the proteasome inhibitor MG132, whereas that CPT-induced downregulation of MKP1 was not due to proteasome-mediated degradation. Treatment of HCT116 cells with CPT induced a sustained activation of nuclear ERK, which was required for CPT-induced apoptosis. P38 and JNK activity were unaffected by CPT, suggesting that the effects of CPT are mediated specifically by ERK. These results suggest that targeting dual-specificity MAPK phosphatases in colon cancer cells may be a viable strategy for optimizing camptothecin-based therapeutic protocols.

Dynamic Regulation of Extracellular Signal-Regulated Kinase (ERK) by Protein Phosphatase 2A Regulatory Subunit B56γ1 in Nuclei Induces Cell Migration

Extracellular signal-regulated kinase (ERK) signalling plays a central role in various biological processes, including cell migration, but it remains unknown what factors directly regulate the strength and duration of ERK activation. We found that, among the B56 family of protein phosphatase 2A (PP2A) regulatory subunits, B56γ1 suppressed EGF-induced cell migration on collagen, bound to phosphorylated-ERK, and dephosphorylated ERK, whereas B56α1 and B56β1 did not. B56γ1 was immunolocalized in nuclei. The IER3 protein was immediately highly expressed in response to costimulation of cells with EGF and collagen. Knockdown of IER3 inhibited cell migration and enhanced dephosphorylation of ERK. Analysis of the time course of PP2A-B56γ1 activity following the costimulation showed an immediate loss of phosphatase activity, followed by a rapid increase in activity, and this activity then remained at a stable level that was lower than the original level. Our results indicate that the strength and duration of the nuclear ERK activation signal that is initially induced by ERK kinase (MEK) are determined at least in part by modulation of the phosphatase activity of PP2A-B56γ1 through two independent pathways.