Abnormal migration phenotype of mitogen-activated protein kinase-activated protein kinase 2-/- neutrophils in Zigmond chambers containing formyl-methionyl-leucyl-phenylalanine gradients

Mitogen-activated protein kinase-activated protein kinase-2 (MK2) and its role in cell survival, inflammatory signaling, and migration in promoting cancer

Cancer and the immune system share an intimate relationship. Chronic inflammation increases the risk of cancer occurrence and can also drive inflammatory mediators into the tumor microenvironment enhancing tumor growth and survival. The p38 MAPK pathway is activated both acutely and chronically by stress, inflammatory chemokines, chronic inflammatory conditions, and cancer. These properties have led to extensive efforts to find effective drugs targeting p38, which have been unsuccessful. The immediate downstream serine/threonine kinase and substrate of p38 MAPK, mitogen-activated-protein-kinase-activated-protein-kinase-2 (MK2) protects cells against stressors by regulating the DNA damage response, transcription, protein and messenger RNA stability, and motility. The phosphorylation of downstream substrates by MK2 increases inflammatory cytokine production, drives an immune response, and contributes to wound healing. By binding directly to p38 MAPK, MK2 is responsible for the export of p38 MAPK from the nucleus which gives MK2 properties that make it unique among the large number of p38 MAPK substrates. Many of the substrates of both p38 MAPK and MK2 are separated between the cytosol and nucleus and interfering with MK2 and altering this intracellular translocation has implications for the actions of both p38 MAPK and MK2. The inhibition of MK2 has shown promise in combination with both chemotherapy and radiotherapy as a method for controlling cancer growth and metastasis in a variety of cancers. Whereas the current data are encouraging the field requires the development of selective and well tolerated drugs to target MK2 and a better understanding of its effects for effective clinical use.

MAPKAP Kinase-2 Drives Expression of Angiogenic Factors by Tumor-Associated Macrophages in a Model of Inflammation-Induced Colon Cancer

Chronic inflammation increases the risk for colorectal cancer through a variety of mechanisms involving the tumor microenvironment. MAPK-activated protein kinase 2 (MK2), a major effector of the p38 MAPK stress and DNA damage response signaling pathway, and a critical regulator of pro-inflammatory cytokine production, has been identified as a key contributor to colon tumorigenesis under conditions of chronic inflammation. We have previously described how genetic inactivation of MK2 in an inflammatory model of colon cancer results in delayed tumor progression, decreased tumor angiogenesis, and impaired macrophage differentiation into a pro-tumorigenic M2-like state. The molecular mechanism responsible for the impaired angiogenesis and tumor progression, however, has remained contentious and poorly defined. Here, using RNA expression analysis, assays of angiogenesis factors, genetic models, in vivo macrophage depletion and reconstitution of macrophage MK2 function using adoptive cell transfer, we demonstrate that MK2 activity in macrophages is necessary and sufficient for tumor angiogenesis during inflammation-induced cancer progression. We identify a critical and previously unappreciated role for MK2-dependent regulation of the well-known pro-angiogenesis factor CXCL-12/SDF-1 secreted by tumor associated-macrophages, in addition to MK2-dependent regulation of Serpin-E1/PAI-1 by several cell types within the tumor microenvironment.

Propofol inhibits endogenous formyl peptide-induced neutrophil activation and alleviates lung injury

Critically ill patients have a high risk of sepsis. Various studies have demonstrated that propofol has anti-inflammatory effects that may benefit critically ill patients who require anesthesia. However, the mechanism and therapeutic effect remain incompletely understood. Our previous data suggest that propofol can act as a formyl peptide receptor 1 (FPR1) antagonist. Here, we hypothesize that propofol mitigates sepsis-induced acute lung injury (ALI) by inhibiting mitochondria-derived N-formyl peptide-mediated neutrophil activation. Oxidative stress caused by activated neutrophils is involved in the pathogenesis of ALI. In human neutrophils, propofol competitively reduced the release of superoxide and associated reactive oxygen species induced by fMMYALF, a human mitochondria-derived N-formyl peptide, suggesting that propofol effectively suppresses neutrophilic oxidative stress. In addition, propofol significantly inhibited fMMYALF-induced elastase release, chemotaxis, calcium mobilization, and phosphorylation of protein kinase B and mitogen-activated protein kinases. These results indicate that propofol suppresses neutrophil activation by blocking the interaction between endogenous N-formyl peptide and its receptor, FPR1, thus inhibiting downstream signaling. Furthermore, propofol alleviated alveolar wall disruption, edematous changes, and neutrophil infiltration in lipopolysaccharide-induced ALI in mice. Noticeably, propofol improved the survival of sepsis mice. This study indicates that the anti-neutrophil effects of propofol may benefit critically ill septic patients.

Transcriptome sequencing analysis reveals the effect of combinative treatment with low‑intensity pulsed ultrasound and magnesium ions on hFOB1.19 human osteoblast cells

Biodegradable magnesium (Mg) materials are considered ideal as osteosynthesis implants. However, clinical application has proven complex. This is primarily associated with the issue of reducing the extent of implant degradation to a range acceptable for the human body, while simultaneously enhancing osteogenesis or osteoinduction. In the present study, a combination of Mg ions and low-intensity pulsed ultrasound (LIPUS) treatment was applied in hFOB 1.19 human osteoblast cells as a potential strategy to resolve this issue. A total of 7,314 differentially expressed genes (DEGs) and 826 shared DEGs in hFOB1.19 osteoblast cells were identified by microarray analysis following treatment with Mg and/or LIPUS. Gene Ontology analysis demonstrated that among cells treated with a combination of Mg and LIPUS, DEGs were significantly enriched in various functional annotations, including ‘wound healing’, ‘transforming growth factor beta receptor signaling pathway’, ‘transcription, DNA-templated’, ‘receptor complex’, ‘nucleus’, ‘SMAD protein complex’, ‘DNA binding’, ‘metal ion binding’ and ‘GTPase activator activity’. Notably, the transforming growth factor (TGF)-β, mitogen-activated protein kinase (MAPK) and tumor necrosis factor (TNF) signaling pathways were preferentially overrepresented in the Mg and LIPUS combination group, which was subsequently confirmed by reverse transcription-quantitative polymerase chain reaction. Furthermore, genes involved in osteoblast mineralization promotion, including bone morphogenetic protein 6, noggin, bone morphogenetic protein receptor (BMPR)1A, BMPR2 and SMAD 5/8, were significantly upregulated following combination treatment compared with the control group. Genes involved in the promotion of migration, including c-Jun N-terminal kinase, doublecortin, paxillin and Jun proto-oncogene AP-1 transcription factor subunit, were also upregulated in the combination treatment group compared with the control group. The DEG data were supported by morphological observations of the osteoblasts using alizarin red S staining and wound healing assays, which indicated that Mg and LIPUS combinative treatment had a synergistic effect on osteoblast mineralization and migration. Additionally, the combined treatment significantly upregulated metal transporter genes associated with Mg entry, including ATPase Na⁺/K⁺-transporting subunit α1, cyclin and CBS domain divalent metal cation transport mediator 2, K⁺ voltage-gated channel subfamily J member 14, transient receptor potential cation channel (TRP) subfamily M member 7 and TRP subfamily V member 2. In summary, the findings of the present study revealed that combined stimulation with Mg and LIPUS may exhibit a synergistic effect on human osteoblast bone formation through the TGF-β, MAPK and TNF signaling pathways, while also facilitating Mg influx. The present study demonstrated the potential of combinative LIPUS and Mg treatment as a novel therapeutic strategy for enhancing the osteoinduction, biocompatibility and biosafety of biodegradable Mg implants.

MK2 contributes to tumor progression by promoting M2 macrophage polarization and tumor angiogenesis

Chronic inflammation is a major risk factor for colorectal cancer. The p38/MAPKAP Kinase 2 (MK2) kinase axis controls the synthesis of proinflammatory cytokines that mediate both chronic inflammation and tumor progression. Blockade of this pathway has been previously reported to suppress inflammation and to prevent colorectal tumorigenesis in a mouse model of inflammation-driven colorectal cancer, by mechanisms that are still unclear. Here, using whole-animal and tissue-specific MK2 KO mice, we show that MK2 activity in the myeloid compartment promotes tumor progression by supporting tumor neoangiogenesis in vivo. Mechanistically, we demonstrate that MK2 promotes polarization of tumor-associated macrophages into protumorigenic, proangiogenic M2-like macrophages. We further confirmed our results in human cell lines, where MK2 chemical inhibition in macrophages impairs M2 polarization and M2 macrophage-induced angiogenesis. Together, this study provides a molecular and cellular mechanism for the protumorigenic function of MK2.

Pharmacological and genetic inhibition of downstream targets of p38 MAPK in experimental nephrotic syndrome

Nie X, Chanley MA, Pengal R, Thomas DB, Agrawal S, Smoyer WE. Pharmacological and genetic inhibition of downstream targets of p38 MAPK in experimental nephrotic syndrome. Am J Physiol Renal Physiol 314: F602-F613, 2018. First published November 29, 2017; doi: 10.1152/ajprenal.00207.2017 .-The p38 MAPK pathway plays a crucial role in various glomerulopathies, with activation being associated with disease and inhibition being associated with disease amelioration. We hypothesized that the downstream targets of p38 MAPK, MAPK-activated protein kinase 2 and/or 3 (MK2 and/or MK3), play an important role in mediating injury in experimental nephrotic syndrome via their actions on their downstream substrates heat shock protein B1 (HSPB1) and cyclooxygenase-2 (COX-2). To test this hypothesis, the effects of both pharmacological and genetic inhibition of MK2 and MK3 were examined in mouse adriamycin (ADR) and rat puromycin aminonucleoside (PAN) nephropathy models. MK2^-/-, MK3^-/-, and MK2^-/-MK3^-/- mice were generated in the Sv129 background and subjected to ADR-induced nephropathy. MK2 and MK3 protein expression was completely abrogated in the respective knockout genotypes, and massive proteinuria and renal histopathological changes developed after ADR treatment. Furthermore, renal cortical HSPB1 was induced in all four genotypes by day 21, but HSPB1 was activated only in the wild-type and MK3^-/- mice. Expression of the stress proteins HSPB8 and glucose-regulated protein 78 (GRP78) remained unaltered across all genotypes. Finally, while MK2 and/or MK3-knockout downregulated the proinflammatory enzyme COX-2, ADR significantly induced renal cortical COX-2 only in MK2^-/- mice. Additionally, pharmacological MK2 inhibition with PF-318 during PAN-induced nephropathy did not result in significant proteinuria reduction in rats. Together, these data suggest that while the inhibition of MK2 and/or MK3 regulates the renal stress response, our currently available approaches are not yet able to safely and effectively reduce proteinuria in experimental nephrotic syndrome and that other p38MAPK downstream targets should also be considered to improve the future treatment of glomerular disease.

-NOD Mice Having a Lyn Tyrosine Kinase Mutation Exhibit Abnormal Neutrophil Chemotaxis

Neutrophils from NOD (Non-Obese Diabetic) mice exhibited reduced migration speed, decreased frequency of directional changes, and loss of directionality during chemotaxis (compared to wild-type [WT] C57BL/6 mice). Additionally, F-actin of chemotaxing NOD neutrophils failed to orient toward the chemoattractant gradient and NOD neutrophil adhesion was impaired. A point mutation near the autophosphorylation site of Lyn in NOD mice was identified. Point mutations of G to A (G1412 in LynA and G1199 in LynB) cause a change of amino acid E393 (glutamic acid) to K (lysine) in LynA (E₃₉₃ →K) (E₃₇₂ of LynB), affecting fMLP-induced tyrosine phosphorylation. These data indicate that the Lyn mutation in NOD neutrophils is likely responsible for dysregulation of neutrophil adhesion and directed migration, implying the role of Lyn in modulating diabetic patient's susceptibility to bacterial and fungal infections. J. Cell. Physiol. 232: 1689-1695, 2017. © 2016 Wiley Periodicals, Inc.

Pivotal Role of Mitogen-Activated Protein Kinase-Activated Protein Kinase 2 in Inflammatory Pulmonary Diseases

Mitogen-activated protein kinase (MAPK)-activated protein kinase (MK2) is exclusively regulated by p38 MAPK in vivo. Upon activation of p38 MAPK, MK2 binds with p38 MAPK, leading to phosphorylation of TTP, Hsp27, Akt, and Cdc25 that are involved in regulation of various essential cellular functions. In this review, we discuss current knowledge about molecular mechanisms of MK2 in regulation of TNF-α production, NADPH oxidase activation, neutrophil migration, and DNA-damage-induced cell cycle arrest which are involved in the molecular pathogenesis of acute lung injury, pulmonary fibrosis, and non-small-cell lung cancer. Collectively current and emerging new information indicate that developing MK2 inhibitors and blocking MK2-mediated signal pathways are potential therapeutic strategies for treatment of inflammatory and fibrotic lung diseases and lung cancer.

Schwann cells promote endothelial cell migration

Directed cell migration is a crucial orchestrated process in embryonic development, wound healing, and immune response. The underlying substrate can provide physical and/or chemical cues that promote directed cell migration. Here, using electrospinning we developed substrates of aligned poly(lactic-co-glycolic acid) nanofibres to study the influence of glial cells on endothelial cells (ECs) in a 3-dimensional (3D) co-culture model. ECs build blood vessels and regulate their plasticity in coordination with neurons. Likewise, neurons construct nerves and regulate their circuits in coordination with ECs. In our model, the neuro-vascular cross-talk was assessed using a direct co-culture model of human umbilical vein endothelial cells (HUVECs) and rat Schwann cells (rSCs). The effect of rSCs on ECs behavior was demonstrated by earlier and higher velocity values and genetic expression profiles different of those of HUVECs when seeded alone. We observed 2 different gene expression trends in the co-culture models: (i) a later gene expression of angiogenic factors, such as interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF), and (ii) an higher gene expression of genes involved in actin filaments rearrangement, such as focal adhesion kinase (FAK), Mitogen-activated protein kinase-activated protein kinase 13 (MAPKAPK13), Vinculin (VCL), and Profilin (PROF). These results suggested that the higher ECs migration is mainly due to proteins involved in the actin filaments rearrangement and in the directed cell migration rather than the effect of angiogenic factors. This co-culture model provides an approach to enlighten the neurovascular interactions, with particular focus on endothelial cell migration.

Stress-dependent phosphorylation of myocardin-related transcription factor A (MRTF-A) by the p38(MAPK)/MK2 axis

Myocardin-related transcription factor A (MRTF-A) is a known actin-regulated transcriptional coactivator of serum response factor (SRF). Stimulation of actin polymerization activates MRTF-A by releasing it from G-actin and thus allowing it to bind to and activate SRF. Here, we compared protein phosphorylation in MK2/3-deficient cells rescued or not by ectopic expression of MK2 in two independent phosphoproteomic approaches using anisomycin-treated MEF cells and LPS-stimulated mouse macrophages, respectively. Two MRTF-A sites, Ser³⁵¹ (corresponding to Ser³¹² in human) and Ser³⁷¹ (Ser³³³ in human), showed significantly stronger phosphorylation (12-fold and 6-fold increase) in the cells expressing MK2. MRTF-A is phosphorylated at these sites in a stress-, but not in a mitogen-induced manner, and p38^MAPK/MK2 catalytic activities are indispensable for this phosphorylation. MK2-mediated phosphorylation of MRTF-A at Ser³¹² and Ser³³³ was further confirmed in an in vitro kinase assay and using the phospho-protein kinase-D (PKD)-consensus motif antibody (anti-LXRXXpS/pT), the p38^MAPK inhibitor BIRB-796, MK2/3-deficient cells and MRTF-A phospho-site mutants. Unexpectedly, dimerization, subcellular localization and translocation, interaction with actin, SRF or SMAD3 and transactivating potential of MRTF-A seem to be unaffected by manipulating the p38^MAPK/MK2-dependent phosphorylations. Hence, MRTF-A is stress-dependently phosphorylated by MK2 at Ser³¹² and Ser³³³ with so far undetected functional and physiological consequences.

Moving towards a paradigm: common mechanisms of chemotactic signaling in Dictyostelium and mammalian leukocytes

Chemotaxis, or directed migration of cells along a chemical gradient, is a highly coordinated process that involves gradient sensing, motility, and polarity. Most of our understanding of chemotaxis comes from studies of cells undergoing amoeboid-type migration, in particular the social amoeba Dictyostelium discoideum and leukocytes. In these amoeboid cells the molecular events leading to directed migration can be conceptually divided into four interacting networks: receptor/G protein, signal transduction, cytoskeleton, and polarity. The signal transduction network occupies a central position in this scheme as it receives direct input from the receptor/G protein network, as well as feedback from the cytoskeletal and polarity networks. Multiple overlapping modules within the signal transduction network transmit the signals to the actin cytoskeleton network leading to biased pseudopod protrusion in the direction of the gradient. The overall architecture of the networks, as well as the individual signaling modules, is remarkably conserved between Dictyostelium and mammalian leukocytes, and the similarities and differences between the two systems are the subject of this review.

Reprint of Neutrophil cell surface receptors and their intracellular signal transduction pathways

Neutrophils play a critical role in the host defense against bacterial and fungal infections, but their inappropriate activation also contributes to tissue damage during autoimmune and inflammatory diseases. Neutrophils express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine and chemoattractant receptors, Fc-receptors, adhesion receptors such as selectins/selectin ligands and integrins, various cytokine receptors, as well as innate immune receptors such as Toll-like receptors and C-type lectins. The various cell surface receptors trigger very diverse signal transduction pathways including activation of heterotrimeric and monomeric G-proteins, receptor-induced and store-operated Ca(2+) signals, protein and lipid kinases, adapter proteins and cytoskeletal rearrangement. Here we provide an overview of the receptors involved in neutrophil activation and the intracellular signal transduction processes they trigger. This knowledge is crucial for understanding how neutrophils participate in antimicrobial host defense and inflammatory tissue damage and may also point to possible future targets of the pharmacological therapy of neutrophil-mediated autoimmune or inflammatory diseases.

Neutrophil cell surface receptors and their intracellular signal transduction pathways

Neutrophils play a critical role in the host defense against bacterial and fungal infections, but their inappropriate activation also contributes to tissue damage during autoimmune and inflammatory diseases. Neutrophils express a large number of cell surface receptors for the recognition of pathogen invasion and the inflammatory environment. Those include G-protein-coupled chemokine and chemoattractant receptors, Fc-receptors, adhesion receptors such as selectins/selectin ligands and integrins, various cytokine receptors, as well as innate immune receptors such as Toll-like receptors and C-type lectins. The various cell surface receptors trigger very diverse signal transduction pathways including activation of heterotrimeric and monomeric G-proteins, receptor-induced and store-operated Ca^2 + signals, protein and lipid kinases, adapter proteins and cytoskeletal rearrangement. Here we provide an overview of the receptors involved in neutrophil activation and the intracellular signal transduction processes they trigger. This knowledge is crucial for understanding how neutrophils participate in antimicrobial host defense and inflammatory tissue damage and may also point to possible future targets of the pharmacological therapy of neutrophil-mediated autoimmune or inflammatory diseases.

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Neutrophils are crucial players in innate and adaptive immunity.

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Neutrophils also participate in autoimmune and inflammatory diseases.

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Various neutrophil receptors recognize pathogens and the inflammatory environment.

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The various cell surface receptors trigger diverse intracellular signaling.

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Neutrophil receptors and signaling are potential targets in inflammatory diseases.

Exocytosis of neutrophil granule subsets and activation of prolyl isomerase 1 are required for respiratory burst priming

This study tested the hypothesis that priming the neutrophil respiratory burst requires both granule exocytosis and activation of the prolyl isomerase Pin1. Fusion proteins containing the TAT cell permeability sequence and either the SNARE domain of syntaxin-4 or the N-terminal SNARE domain of SNAP-23 were used to examine the role of granule subsets in TNF-mediated respiratory burst priming using human neutrophils. Concentration-inhibition curves for exocytosis of individual granule subsets and for priming of fMLF-stimulated superoxide release and phagocytosis-stimulated H2O2 production were generated. Maximal inhibition of priming ranged from 72 to 88%. Linear regression lines for inhibition of priming versus inhibition of exocytosis did not differ from the line of identity for secretory vesicles and gelatinase granules, while the slopes or the y-intercepts were different from the line of identity for specific and azurophilic granules. Inhibition of Pin1 reduced priming by 56%, while exocytosis of secretory vesicles and specific granules was not affected. These findings indicate that exocytosis of secretory vesicles and gelatinase granules and activation of Pin1 are independent events required for TNF-mediated priming of neutrophil respiratory burst.

P38 and JNK have opposing effects on persistence of in vivo leukocyte migration in zebrafish

The recruitment and migration of macrophages and neutrophils is an important process during the early stages of the innate immune system in response to acute injury. Transgenic pu.1:EGFP zebrafish permit the acquisition of leukocyte migration trajectories during inflammation. Currently, these high-quality live-imaging data are mainly analysed using general statistics, for example, cell velocity. Here, we present a spatio-temporal analysis of the cell dynamics using transition matrices, which provide information of the type of cell migration. We find evidence that leukocytes exhibit types of migratory behaviour, which differ from previously described random walk processes. Dimethyl sulfoxide treatment decreased the level of persistence at early time points after wounding and ablated temporal dependencies observed in untreated embryos. We then use pharmacological inhibition of p38 and c-Jun N-terminal kinase mitogen-activated protein kinases to determine their effects on in vivo leukocyte migration patterns and discuss how they modify the characteristics of the cell migration process. In particular, we find that their respective inhibition leads to decreased and increased levels of persistent motion in leukocytes following wounding. This example shows the high level of information content, which can be gained from live-imaging data if appropriate statistical tools are used.

Coexpressing shRNA with fluorescence tags for quantification of cell migration studies

Understanding migration of cells has many implications in human physiology; some examples include developmental biology, healing, immune responses and tissue remodeling. On the other hand, invasive migration by tumor cells is pathological and is a major cause of mortality amongst cancer sufferers. Cell migration assays have been widely used to quantify potentially metastatic genes. In recent years, the use of RNAi has significantly increased the tools available in cell migration research due to its specific gene targeting for knockdown. The inability to ensure 100% transfection/transduction efficiency reduces the sensitivity of cell migration assays because cells not successfully transfected/transduced with the RNAi are also included in the calculations. This study introduces a different experimental setup mathematically expressed in our named normalized relative infected cell count (N-RICC) that analyses cell migration assays by co-expressing retrovirally transduced shRNA with fluorescence tags from a single vector. Vectors transduced into cells are visible under fluorescence, thus alleviating the problems involved with transduction efficiency by individually identifying cells with targeted genes. Designed shRNAs were targeted against a list of potentially metastatic genes in a highly migratory breast cancer cell line model, MDA-MB-231. We have successfully applied N-RICC analysis to show greater sensitivity of integrin alpha5 (ITGA5) and Ras homologue A (RhoA) in cell metastasis over conventional methods in scratch-wound assays and migration chambers assays.

MAPK usage in periodontal disease progression

In periodontal disease, host recognition of bacterial constituents, including lipopolysaccharide (LPS), induces p38 MAPK activation and subsequent inflammatory cytokine expression, favoring osteoclastogenesis and increased net bone resorption in the local periodontal environment. In this paper, we discuss evidence that the p38/MAPK-activated protein kinase-2 (MK2) signaling axis is needed for periodontal disease progression: an orally administered p38α inhibitor reduced the progression of experimental periodontal bone loss by reducing inflammation and cytokine expression. Subsequently, the significance of p38 signaling was confirmed with RNA interference to attenuate MK2-reduced cytokine expression and LPS-induced alveolar bone loss. MAPK phosphatase-1 (MKP-1), a negative regulator of MAPK activation, was also critical for periodontal disease progression. In MPK-1-deficient mice, p38-sustained activation increased osteoclast formation and bone loss, whereas MKP-1 overexpression dampened p38 signaling and subsequent cytokine expression. Finally, overexpression of the p38/MK2 target RNA-binding tristetraprolin (TTP) decreased mRNA stability of key inflammatory cytokines at the posttranscriptional level, thereby protecting against periodontal inflammation. Collectively, these studies highlight the importance of p38 MAPK signaling in immune cytokine production and periodontal disease progression.

Activation and function of the MAPKs and their substrates, the MAPK-activated protein kinases

The mitogen-activated protein kinases (MAPKs) regulate diverse cellular programs by relaying extracellular signals to intracellular responses. In mammals, there are more than a dozen MAPK enzymes that coordinately regulate cell proliferation, differentiation, motility, and survival. The best known are the conventional MAPKs, which include the extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun amino-terminal kinases 1 to 3 (JNK1 to -3), p38 (α, β, γ, and δ), and ERK5 families. There are additional, atypical MAPK enzymes, including ERK3/4, ERK7/8, and Nemo-like kinase (NLK), which have distinct regulation and functions. Together, the MAPKs regulate a large number of substrates, including members of a family of protein Ser/Thr kinases termed MAPK-activated protein kinases (MAPKAPKs). The MAPKAPKs are related enzymes that respond to extracellular stimulation through direct MAPK-dependent activation loop phosphorylation and kinase activation. There are five MAPKAPK subfamilies: the p90 ribosomal S6 kinase (RSK), the mitogen- and stress-activated kinase (MSK), the MAPK-interacting kinase (MNK), the MAPK-activated protein kinase 2/3 (MK2/3), and MK5 (also known as p38-regulated/activated protein kinase [PRAK]). These enzymes have diverse biological functions, including regulation of nucleosome and gene expression, mRNA stability and translation, and cell proliferation and survival. Here we review the mechanisms of MAPKAPK activation by the different MAPKs and discuss their physiological roles based on established substrates and recent discoveries.

Activation and Function of the MAPKs and Their Substrates, the MAPK-Activated Protein Kinases

The mitogen-activated protein kinases (MAPKs) regulate diverse cellular programs by relaying extracellular signals to intracellular responses. In mammals, there are more than a dozen MAPK enzymes that coordinately regulate cell proliferation, differentiation, motility, and survival. The best known are the conventional MAPKs, which include the extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun amino-terminal kinases 1 to 3 (JNK1 to -3), p38 (α, β, γ, and δ), and ERK5 families. There are additional, atypical MAPK enzymes, including ERK3/4, ERK7/8, and Nemo-like kinase (NLK), which have distinct regulation and functions. Together, the MAPKs regulate a large number of substrates, including members of a family of protein Ser/Thr kinases termed MAPK-activated protein kinases (MAPKAPKs). The MAPKAPKs are related enzymes that respond to extracellular stimulation through direct MAPK-dependent activation loop phosphorylation and kinase activation. There are five MAPKAPK subfamilies: the p90 ribosomal S6 kinase (RSK), the mitogen- and stress-activated kinase (MSK), the MAPK-interacting kinase (MNK), the MAPK-activated protein kinase 2/3 (MK2/3), and MK5 (also known as p38-regulated/activated protein kinase [PRAK]). These enzymes have diverse biological functions, including regulation of nucleosome and gene expression, mRNA stability and translation, and cell proliferation and survival. Here we review the mechanisms of MAPKAPK activation by the different MAPKs and discuss their physiological roles based on established substrates and recent discoveries.

The p38/MK2/Hsp25 pathway is required for BMP-2-induced cell migration

Background

Bone morphogenetic proteins (BMPs) have been shown to participate in the patterning and specification of several tissues and organs during development and to regulate cell growth, differentiation and migration in different cell types. BMP-mediated cell migration requires activation of the small GTPase Cdc42 and LIMK1 activities. In our earlier report we showed that activation of LIMK1 also requires the activation of PAKs through Cdc42 and PI3K. However, the requirement of additional signaling is not clearly known.

Methodology/Principal Findings

Activation of p38 MAPK has been shown to be relevant for a number of BMP-2′s physiological effects. We report here that BMP-2 regulation of cell migration and actin cytoskeleton remodelling are dependent on p38 activity. BMP-2 treatment of mesenchymal cells results in activation of the p38/MK2/Hsp25 signaling pathway downstream from the BMP receptors. Moreover, chemical inhibition of p38 signaling or genetic ablation of either p38α or MK2 blocks the ability to activate the downstream effectors of the pathway and abolishes BMP-2-induction of cell migration. These signaling effects on p38/MK2/Hsp25 do not require the activity of either Cdc42 or PAK, whereas p38/MK2 activities do not significantly modify the BMP-2-dependent activation of LIMK1, measured by either kinase activity or with an antibody raised against phospho-threonine 508 at its activation loop. Finally, phosphorylated Hsp25 colocalizes with the BMP receptor complexes in lamellipodia and overexpression of a phosphorylation mutant form of Hsp25 is able to abolish the migration of cells in response to BMP-2.

Conclusions

These results indicate that Cdc42/PAK/LIMK1 and p38/MK2/Hsp25 pathways, acting in parallel and modulating specific actin regulatory proteins, play a critical role in integrating responses during BMP-induced actin reorganization and cell migration.

Herbal medicinal products target defined biochemical and molecular mediators of inflammatory autoimmune arthritis

Rheumatoid arthritis (RA) is a chronic debilitating disease characterized by synovial inflammation, damage to cartilage and bone, and deformities of the joints. Several drugs possessing anti-inflammatory and immunomodulatory properties are being used in the conventional (allopathic) system of medicine to treat RA. However, the long-term use of these drugs is associated with harmful side effects. Therefore, newer drugs with low or no toxicity for the treatment of RA are actively being sought. Interestingly, several herbs demonstrate anti-inflammatory and anti-arthritic activity. In this review, we describe the role of the major biochemical and molecular mediators in the pathogenesis of RA, and highlight the sites of action of herbal medicinal products that have anti-arthritic activity. With the rapidly increasing use of CAM products by patients with RA and other inflammation-related disorders, our review presents timely information validating the scientific rationale for the use of natural therapeutic products.

Lack of MK2 inhibits myofibroblast formation and exacerbates pulmonary fibrosis

Fibroblasts play a major role in tissue repair and remodeling. Their differentiation into myofibroblasts, marked by increased expression of smooth muscle-specific alpha-actin (alpha-SMA), is believed to be important in wound healing and fibrosis. We have recently described a role for MK2 in this phenotypic differentiation in culture. In this article, we demonstrate that MK2 also regulates myofibroblasts in vivo. Disruption of MK2 in mice prevented myofibroblast formation in a model of pulmonary fibrosis. However, MK2 disruption and consequent lack of myofibroblast formation exacerbated fibrosis rather than ameliorated it as previously postulated. When mice lacking MK2 (MK2-/-) were exposed to bleomycin, more collagen accumulated and more fibroblasts populated fibrotic regions in their lungs than in similarly treated wild-type mice. While there were many vimentin-positive cells in the bleomycin-treated MK2-/- mouse lungs, few alpha-SMA-positive cells were observed in these lungs compared with wild-type mouse lungs. siRNA against MK2 reduced alpha-SMA expression in wild-type mouse embryonic fibroblasts (MEF), consistent with its suppression in MK2-/- MEF. On the other hand expressing constitutively active MK2 in MK2-/- MEF significantly increased alpha-SMA expression. MK2-/-MEF proliferated at a faster rate and produced more collagen; however, they migrated at a slower rate than wild-type MEF. Overexpressing phosphomimicking HSP27, a target of MK2, did not reverse the effect of MK2 disruption on fibroblast migration. MK2 disruption did not affect Smad2 activation by transforming growth factor-beta. Thus, MK2 appears to mediate myofibroblast differentiation, and inhibiting that differentiation might contribute to fibrosis rather than protect against it.

MAPKAPK2-mediated LSP1 phosphorylation and FMLP-induced neutrophil polarization

In neutrophils, the major substrate of MAPKAPK2 (MK2) is an F-actin binding protein LSP1. Studies using mutants of the two potential Serine phosphorylation sites in LSP1 C-terminal F-actin binding region indicated that the major phosphorylation site for MK2 is Ser243 in murine neutrophils (Ser252 in humans). Human phosphoLSP1 antibodies that recognize phosphoSer252 site were prepared and revealed fMLP-induced neutrophil LSP1 phosphorylation. The phosphorylation was inhibited by p38 MAPK (upstream kinase for MK2) inhibitor SB203580. The antibodies also detect LSP1 phosphorylation in murine neutrophils. Immunostaining revealed that in WT murine neutrophils phosphoLSP1 was localized in F-actin enriched lamellipodia and oriented toward the fMLP gradient while non-phosphoLSP1 failed to colocalize with F-actin. In suspension, WT neutrophils exhibited persistent F-actin polarization following fMLP stimulation, while MK2(-/-) neutrophils exhibited transient F-actin polarization. These studies suggest that MK2-regulated LSP1 phosphorylation is involved in stabilization of F-actin polarization during neutrophil chemotaxis.

Heat shock protein 27 regulates neutrophil chemotaxis and exocytosis through two independent mechanisms

The targets of the p38 MAPK pathway responsible for regulation of neutrophil chemotaxis and exocytosis are unknown. One target of this pathway is the actin-binding protein, heat shock protein 27 (Hsp27). Therefore, we tested the hypothesis that Hsp27 mediates p38 MAPK-dependent chemotaxis and exocytosis in human neutrophils through regulation of actin reorganization. Sequestration of Hsp27 by introduction of anti-Hsp27 Ab, but not an isotype Ab, inhibited fMLP-stimulated chemotaxis, increased cortical F-actin in the absence of fMLP stimulation, and inhibited fMLP-stimulated exocytosis. Pretreatment with latrunculin A prevented actin reorganization and the changes in fMLP-stimulated exocytosis induced by Hsp27 sequestration. To determine the role of Hsp27 phosphorylation, wild-type, phosphorylation-resistant, or phosphorylation-mimicking recombinant Hsp27 was introduced into neutrophils by electroporation. The phosphorylation-resistant mutant significantly reduced migration toward fMLP, whereas none of the Hsp27 proteins affected fMLP-stimulated or TNF-alpha-stimulated exocytosis or actin polymerization. Endogenous Hsp27 colocalized with F-actin in unstimulated and fMLP-stimulated neutrophils, whereas phosphorylated Hsp27 showed cytosolic localization in addition to colocalization with F-actin. Our results suggest that Hsp27 regulates neutrophil chemotaxis and exocytosis in an actin-dependent, phosphorylation-independent manner. Phosphorylation of Hsp27 regulates chemotaxis, but not exocytosis, independent of regulation of actin reorganization.

MAPK-activated Protein Kinase-2 (MK2)-mediated Formation and Phosphorylation-regulated Dissociation of the Signal Complex Consisting of p38, MK2, Akt, and Hsp27

The p38 MAPK and heat shock protein 27 (hsp27) form a signaling complex with serine/threonine kinase Akt and MAPK-activated protein kinase-2 (MK2), which plays an important role in controlling stress-induced apoptosis and reorganizing actin cytoskeleton. However, regulation of the complex is poorly understood. In this study, the interaction between p38 and hsp27 was visualized in single living L929 cells using fluorescence resonance energy transfer technology, while their association with Akt was examined by immunoprecipitation analysis. Under normal growth conditions, p38 kinase constitutively interacts with hsp27. When cells were exposed to H(2)O(2) or stimulated by arachidonic acid, this interaction was disrupted. However, inhibition of the activation of p38 and Akt by selective inhibitors or overexpression of the kinase-dead mutant of p38 diminished such effects. Furthermore, mutation of phosphorylation sites of hsp27 renders the interaction resistant to H(2)O(2) and arachidonic acid. It was interesting to find that the interaction disappeared in the cells from MK2-knock-out mice or the cells treated with lemptomycin B that blocks export of MK2 from nucleus to cytosol. However, MK2 is not required for the association of hsp27 with Akt. This study suggests that MK2 mediates the incorporation of p38 into the pre-existing complex of hsp27 with Akt. Phosphorylation of hsp27 finally breaks the signaling complex.

CXCL12 and C5a trigger cell migration via a PAK1/2-p38α MAPK-MAPKAP-K2-HSP27 pathway

Cell migration is critical for many processes, such as angiogenesis, inflammation, development and wound healing, and is also involved in tumour progression and metastasis. Here we show that CXCL12, complement factor 5a (C5a), hepatocyte growth factor (HGF) and platelet-derived growth factor (PDGF)-BB, which stimulate cell migration, also activate p38alpha MAPK. Pharmacological inhibition of this protein kinase with SB 203580 or BIRB 0796, or the genetic ablation of p38alpha MAPK, blocked cell migration induced by the aforementioned chemo-attractants. Macrophages from mice lacking one or more of the other p38 MAPK isoforms showed normal cell migration in response to C5a. We also show that the activation of p38alpha MAPK in response to CXCL12 requires the p21-activated protein kinases (PAK)-1 and PAK-2. MAPKAP-K2 is a protein kinase that is activated by p38alpha MAPK. Reducing its expression using RNA interference blocked CXCL12-induced HeLa cell migration, while macrophages from mice that do not express MAPKAP-K2 failed to migrate in response to C5a. Moreover, RNA interference against the small heat shock protein 27 (HSP27), a physiological substrate of MAPKAP-K2, blocked the CXCL12-induced cell migration. These results demonstrate a general and essential role of the PAK-p38alpha MAPK-MAPKAP-K2-HSP27 signalling pathway in mediating the effects of chemotactic stimuli on cell migration.

Leukocyte-specific protein 1 (LSP1): a regulator of leukocyte emigration in inflammation

LSP1 is an F-actin bundling cytoskeletal protein expressed in hematopoietic lineage and endothelial cells. We investigated the function of this protein by generating and analyzing an LSP1-deficient mouse strain and in this review we describe our findings together with those of other investigators. The results show a complex function of LSP1 in regulating leukocyte recruitment to inflamed sites. Based on current evidence, we propose that the levels of LSP1 on the cytoskeleton and the type of integrin involved are some of the critical elements which affect LSP1 function in modulating the threshold for transmigration.

The mitogen-activated protein kinase (MAPK)-activated protein kinases MK2 and MK3 cooperate in stimulation of tumor necrosis factor biosynthesis and stabilization of p38 MAPK

MK2 and MK3 represent protein kinases downstream of p38 mitogen-activated protein kinase (MAPK). Deletion of the MK2 gene in mice resulted in an impaired inflammatory response although MK3, which displays extensive structural similarities and identical functional properties in vitro, is still present. Here, we analyze tumor necrosis factor (TNF) production and expression of p38 MAPK and tristetraprolin (TTP) in MK3-deficient mice and demonstrate that there are no significant differences with wild-type animals. We show that in vivo MK2 and MK3 are expressed and activated in parallel. However, the level of activity of MK2 is always significantly higher than that of MK3. Accordingly, we hypothesized that MK3 could have significant effects only in an MK2-free background and generated MK2/MK3 double-knockout mice. Unexpectedly, these mice are viable and show no obvious defects due to loss of compensation between MK2 and MK3. However, there is a further reduction of TNF production and expression of p38 and TTP in double-knockout mice compared to MK2-deficient mice. This finding, together with the observation that ectopically expressed MK3 can rescue MK2 deficiency similarly to MK2, indicates that both kinases share the same physiological function in vivo but are expressed to different levels.

Regulation of MAPK-activated protein kinase 5 activity and subcellular localization by the atypical MAPK ERK4/MAPK4

MAPK-activated protein kinase 5 (MK5) was recently identified as a physiological substrate of the atypical MAPK ERK3. Complex formation between ERK3 and MK5 results in phosphorylation and activation of MK5, concomitant stabilization of ERK3, and the nuclear exclusion of both proteins. However, ablation of ERK3 in HeLa cells using small interfering RNA or in fibroblasts derived from ERK3 null mice reduces the activity of endogenous MK5 by only 50%, suggesting additional mechanisms of MK5 regulation. Here we identify the ERK3-related kinase ERK4 as a bona fide interaction partner of MK5. Binding of ERK4 to MK5 is accompanied by phosphorylation and activation of MK5. Furthermore, complex formation also results in the relocalization of MK5 from nucleus to cytoplasm. However unlike ERK3, ERK4 is a stable protein, and its half-life is not modified by the presence or absence of MK5. Finally, although knock-down of ERK4 protein in HeLa cells reduces endogenous MK5 activity by approximately 50%, a combination of small interfering RNAs targeting both ERK4 and ERK3 causes a further reduction in the MK5 activity by more than 80%. We conclude that MK5 activation is dependent on both ERK3 and ERK4 in these cells and that these atypical MAPKs are both physiological regulators of MK5 activity.

Enhanced neutrophil motility by granulocyte colony-stimulating factor: the role of extracellular signal-regulated kinase and phosphatidylinositol 3-kinase

The effect of granulocyte colony-stimulating factor (G-CSF) on human neutrophil motility was studied using videomicroscopy. Stimulation of neutrophils with G-CSF resulted in enhanced motility with morphological change and increased adherence. Enhanced neutrophil motility was detected within 3-5 min after G-CSF stimulation, reached a maximum at 10 min, and was sustained for approximately 35 min. The maximum migration rate was 84.4 +/- 2.9 microm/5 min. A study using the Boyden chamber method revealed that G-CSF-stimulated neutrophils exhibited random migration but not chemotaxis. Enhanced neutrophil motility and morphological change were inhibited by MEK [mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase] inhibitors (PD98059 and U0126), and a phosphatidylinositol 3-kinase (PI3K) inhibitor (wortmannin), but not by a p38 MAPK inhibitor (SB203580). These findings are consistent with the fact that G-CSF selectively activates MEK/ERK and PI3K, but not p38, in neutrophils. MEK/ERK activation was associated with G-CSF-induced redistribution of F-actin and phosphorylated myosin light chain. Enhanced neutrophil motility was observed even in the presence of neutralizing anti-CD18 antibody, which prevented cell adherence. These findings indicate that G-CSF induces human neutrophil migration via activation of MEK/ERK and PI3K.

MAPKAP Kinase 2-Deficient Mice Are Resistant to Collagen-Induced Arthritis

TNF-alpha is a pleiotropic cytokine considered a primary mediator of immune regulation and inflammatory response and has been shown to play a central role in rheumatoid arthritis (RA). MAPKAP kinase 2 (MK2) is a serine/threonine kinase that is regulated through direct phosphorylation by p38 MAPK, and has been shown to be an essential component in the inflammatory response that regulates the biosynthesis of TNF-alpha at a posttranscriptional level. The murine model of collagen-induced arthritis (CIA) is an established disease model to study pathogenic mechanisms relevant to RA. In this study, we report that deletion of the MK2 gene in DBA/1LacJ mice confers protection against CIA. Interestingly, the MK2 heterozygous mutants display an intermediate level of protection when compared with homozygous mutant and wild-type littermates. We show that MK2(-/-) and MK2(+/-) mice exhibit decreased disease incidence and severity in the CIA disease model and reduced TNF-alpha and IL-6 serum levels following LPS/d-Gal treatment compared with wild-type mice. Additionally, we show that levels of IL-6 mRNA in paws of mice with CIA correlate with the disease status. These findings suggest that an MK2 inhibitor could be of great therapeutic value to treat inflammatory diseases like RA.

MAPKAP kinases - MKs - two's company, three's a crowd

Downstream of mitogen-activated protein kinases (MAPKs), three structurally related MAPK-activated protein kinases (MAPKAPKs or MKs) - MK2, MK3 and MK5 - signal to diverse cellular targets. Although there is no known common function for all three MKs, these kinases are involved in important processes: MKs regulate gene expression at the transcriptional and post-transcriptional level, control cytoskeletal architecture and cell-cycle progression, and are implicated in inflammation and cancer.

Defining mitogen-activated protein kinase pathways with mass spectrometry-based approaches

Mitogen-activated protein kinases are a group of ubiquitously expressed kinase pathways that have been conserved from yeast through humans. They control a large number of critical cell functions. Identification of targets of those kinases is necessary to define signal transduction pathways that lead to cell responses. The application of a number of mass spectrometry-based techniques to the identification of phosphoproteins is reviewed. A new proteomic approach is described for the identification of the downstream targets of specific kinases that combines phosphorylation of cell lysates in in vitro kinase reactions by active recombinant kinase with protein separation by two-dimensional (2D) gel electrophoresis or SDS-PAGE and phosphoprotein identification by MALDI-TOF mass spectrometry or by phosphopeptide enrichment and tandem mass spectrometry. The results suggested that a combination of multiple approaches will be required to fully identify phosphoproteomes.

MAP kinases and cell migration

Recent studies have demonstrated that mitogen-activated protein kinases (MAPKs), including Jun N-terminus kinase (JNK), p38 and Erk, play crucial roles in cell migration. JNK, for example, regulates cell migration by phosphorylating paxillin, DCX, Jun and microtubule-associated proteins. Studies of p38 show that this MAPK modulates migration by phosphorylating MAPK-activated protein kinase 2/3 (MAPKAP 2/3), which appears to be important for directionality of migration. Erk governs cell movement by phosphorylating myosin light chain kinase (MLCK), calpain or FAK. Thus, the different kinases in the MAPK family all seem able to regulate cell migration but by distinct mechanisms.

The phosphorylation of CapZ-interacting protein (CapZIP) by stress-activated protein kinases triggers its dissociation from CapZ

A protein expressed in immune cells and muscle was detected in muscle extracts as a substrate for several SAPKs (stress-activated protein kinases). It interacted specifically with the F-actin capping protein CapZ in splenocytes, and was therefore termed 'CapZIP' (CapZ-interacting protein). Human CapZIP was phosphorylated at Ser-179 and Ser-244 by MAPKAP-K2 (mitogen-activated protein kinase-activated protein kinase 2) or MAPKAP-K3 in vitro. Anisomycin induced the phosphorylation of CapZIP at Ser-179 in Jurkat cells, which was prevented by SB 203580, consistent with phosphorylation by MAPKAP-K2 and/or MAPKAP-K3. However, osmotic shock-induced phosphorylation of Ser-179 was unaffected by SB 203580. These and other results suggest that CapZIP is phosphorylated at Ser-179 in cells by MAPKAP-K2/MAPKAP-K3, and at least one other protein kinase. Stress-activated MAP kinase family members phosphorylated human CapZIP at many sites, including Ser-68, Ser-83, Ser-108 and Ser-216. Ser-108 became phosphorylated when Jurkat cells were exposed to osmotic shock, which was unaffected by SB 203580 and/or PD 184352, or in splenocytes from mice that do not express either SAPK3/p38gamma or SAPK4/p38delta. Our results suggest that CapZIP may be phosphorylated by JNK (c-Jun N-terminal kinase), which phosphorylates CapZIP to >5 mol/mol within minutes in vitro. Osmotic shock or anisomycin triggered the dissociation of CapZIP from CapZ in Jurkat cells, suggesting that phosphorylation of CapZIP may regulate the ability of CapZ to remodel actin filament assembly in vivo.

Protein O-GlcNAc modulates motility-associated signaling intermediates in neutrophils

The modification of serine/threonine residues on cytoplasmic and nuclear proteins by N-acetylglucosamine (O-GlcNAc) is suggested to play a role in the regulation of a variety of signal transduction pathways. We have previously shown that glucosamine (GlcNH(2)), a metabolic precursor of O-GlcNAcylation, increases (2)O-GlcNAc and enhances motility in neutrophils. Here, we extend this correlation by showing that a mechanistically distinct means of increasing O-GlcNAc, achieved by inhibition of O-GlcNAc removal with O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc), increases basal cellular motility and directional migration induced by the chemoattractant formyl-methionine-leucine-phenylalanine (fMLP). Furthermore, we demonstrate that O-GlcNAc modulates the activities of signaling intermediates known to regulate neutrophil movement. GlcNH(2) and PUGNAc increase both the basal and fMLP-induced activity of a central mediator of cellular motility, the small GTPase Rac. Phosphoinositide 3-kinase, an important regulator of Rac activity and neutrophil motility, is shown to regulate the signaling pathway on which GlcNH(2) and PUGNAc act. Rac is an important upstream regulatory element in p38 and p44/42 mitogen-activated protein kinase (MAPK) signaling in neutrophils, and these MAPKs are implicated in chemotactic signal transduction. We show that GlcNH(2) and PUGNAc treatment increases p42/44 and p38 MAPK activities and that these increases are associated with activation of upstream MAPK kinases. These data indicate that O-GlcNAcylation is an important signaling element in neutrophils that modulates the activities of several critical signaling intermediates involved in the regulation of cellular movement.

LSP1 is an endothelial gatekeeper of leukocyte transendothelial migration

Leukocyte-specific protein 1 (LSP1), an F-actin binding protein and a major downstream substrate of p38 mitogen-activated protein kinase as well as protein kinase C, has been reported to be important in leukocyte chemotaxis. Although its distribution has been thought to be restricted to leukocytes, herein we report that LSP1 is expressed in endothelium and is essential to permit neutrophil emigration. Using intravital microscopy to directly visualize leukocyte rolling, adhesion, and emigration in postcapillary venules in LSP1-deficient (Lsp1^−/−) mice, we found that LSP1 deficiency inhibits neutrophil extravasation in response to various cytokines (tumor necrosis factor-α and interleukin-1β) and to neutrophil chemokine keratinocyte-derived chemokine in vivo. LSP1 deficiency did not affect leukocyte rolling or adhesion. Generation of Lsp1^−/− chimeric mice using bone marrow transplantation revealed that in mice with Lsp1^−/− endothelial cells and wild-type leukocytes, neutrophil transendothelial migration out of postcapillary venules is markedly restricted. In contrast, Lsp1^−/− neutrophils in wild-type mice were able to extravasate normally. Consistent with altered endothelial function was a reduction in vascular permeability to histamine in Lsp1^−/− animals. Western blot analysis and immunofluorescence microscopy examination confirmed the presence of LSP1 in wild-type but not in Lsp1^−/− mouse microvascular endothelial cells. Cultured human endothelial cells also stained positive for LSP1. Our results suggest that LSP1 expressed in endothelium regulates neutrophil transendothelial migration.

Azithromycin Blocks Neutrophil Recruitment inPseudomonasEndobronchial Infection

Macrolides exert their effects on the host by modulation of immune responses. In this study, we assessed the therapeutic efficacy of azithromycin in a murine model of mucoid Pseudomonas aeruginosa endobronchial infection. The clearance of Pseudomonas from the airway of mice treated with the macrolide azithromycin was not different than untreated mice challenged with Pseudomonas beads. However, the azithromycin-treated mice showed a remarkable reduction in lung cellular infiltrate in response to Pseudomonas beads, as compared with untreated mice. This effect was associated with significant decreases in lung levels of tumor necrosis factor-alpha and keratinocyte-derived chemokine in azithromycin-treated mice compared with untreated mice. Furthermore, there was a significant reduction in the response of both mouse and human neutrophils to chemokine-dependent and -independent chemoattractants when studied in vitro. Inhibition of chemotaxis correlated with azithromycin-mediated inhibition of extracellular signal-regulated kinase-1 and -2 activation. This study indicates that the azithromycin treatment in vivo results in significant reduction in airway-specific inflammation, which occurs in part by inhibition of neutrophil recruitment to the lung through reduction in proinflammatory cytokine expression and inhibition of neutrophil migration via the extracellular signal-regulated kinase-1 and -2 signal transduction pathway.

Discovery and characterization of a substrate selective p38alpha inhibitor

A novel inhibitor of p38 mitogen-activated protein kinase (p38), CMPD1, identified by high-throughput screening, is characterized herein. Unlike the p38 inhibitors described previously, this inhibitor is substrate selective and noncompetitive with ATP. In steady-state kinetics experiments, CMPD1 was observed to prevent the p38alpha-dependent phosphorylation (K(i)(app) = 330 nM) of the splice variant of mitogen-activated protein kinase-activated protein kinase 2 (MK2a) that contains a docking domain for p38alpha and p38beta, but it did not prevent the phosphorylation of ATF-2 (K(i)(app) > 20 microM). In addition to kinetic studies, isothermal titration calorimetry and surface plasmon resonance experiments were performed to elucidate the mechanism of inhibition. While isothermal titration calorimetry analysis indicated that CMPD1 binds to p38alpha, CMPD1 was not observed to compete with ATP for p38alpha, nor was it able to interrupt the binding of p38alpha to MK2a observed by surface plasmon resonance. Therefore, deuterium exchange mass spectrometry (DXMS) was employed to study the p38alpha.CMPD1 inhibitory complex, to provide new insight into the mechanism of substrate selective inhibition. The DXMS data obtained for the p38alpha.CMPD1 complex were compared to the data obtained for the p38alpha.MK2a complex and a p38alpha.active site binding inhibitor complex. Alterations in the DXMS behavior of both p38alpha and MK2a were observed upon complex formation, including but not limited to the interaction between the carboxy-terminal docking domain of MK2a and its binding groove on p38alpha. Alterations in the D(2)O exchange of p38alpha produced by CMPD1 suggest that the substrate selective inhibitor binds in the vicinity of the active site of p38alpha, resulting in perturbations to regions containing nucleotide binding pocket residues, docking groove residues (E160 and D161), and a Mg(2+) ion cofactor binding residue (D168). Although the exact mechanism of substrate selective inhibition by this novel inhibitor has not yet been disclosed, the results suggest that CMPD1 binding in the active site region of p38alpha induces perturbations that may result in the suboptimal positioning of substrates and cofactors in the transition state, resulting in selective inhibition of p38alpha activity.

Catalysis and function of the p38 alpha.MK2a signaling complex

The p38 mitogen-activated protein kinase (p38) pathway is required for the production of proinflammatory cytokines (TNFalpha and IL-1) that mediate the chronic inflammatory phases of several autoimmune diseases. Potent p38 inhibitors, such as the slow tight-binding inhibitor BIRB 796, have recently been reported to block the production of TNFalpha and IL-1beta. Here we analyze downstream signaling complexes and molecular mechanisms, to provide new insight into the function of p38 signaling complexes and the development of novel inhibitors of the p38 pathway. Catalysis, signaling functions, and molecular interactions involving p38alpha and one of its downstream signaling partners, mitogen-activated protein kinase-activated protein kinase 2 (MK2), have been explored by steady-state kinetics, surface plasmon resonance, isothermal calorimetry, and stopped-flow fluorescence. Functional 1/1 signaling complexes (Kd = 1-100 nM) composed of activated and nonactivated forms of p38alpha and a splice variant of MK2 (MK2a) were characterized. Catalysis of MK2a phosphorylation and activation by p38alpha was observed to be efficient under conditions where substrate is saturating (kcat(app) = 0.05-0.3 s(-1)) and nonsaturating (kcat(app)/KM(app) = 1-3 x 10(6) M(-1) s(-1)). Specific interactions between the carboxy-terminal residues of MK2a (370-400) and p38alpha precipitate formation of a high-affinity complex (Kd = 20 nM); the p38alpha-dependent MK2a phosphorylation reaction was inhibited by the 30-amino acid docking domain peptide of MK2a (IC50 = 60 nM). The results indicate that the 30-amino acid docking domain peptide of MK2a is required for the formation of a tight, functional p38alpha.MK2a complex, and that perturbation of the tight-docking interaction between these signaling partners prevents the phosphorylation of MK2a. The thermodynamic and steady-state kinetic characterization of the p38alpha.MK2a signaling complex has led to a clear understanding of complex formation, catalysis, and function on the molecular level.

p38 Mitogen-activated protein kinase regulation of endothelial cell migration depends on urokinase plasminogen activator expression

The migration of endothelial cells in response to various stimulating factors plays an essential role in angiogenesis. The p38 MAPK pathway has been implicated to play an important role in endothelial cell migration because inhibiting p38 MAPK activity down-regulates vascular endothelial growth factor (VEGF)-stimulated migration. Currently, the signaling components in the p38 MAPK activation pathway and especially the mechanisms responsible for p38 MAPK-regulated endothelial cell migration are not well understood. In the present study, we found that p38 MAPK activity is required for endothelial cell migration stimulated by both VEGF and nongrowth factor stimulants, sphingosine 1-phosphate and soluble vascular cell adhesion molecule. By using dominant negative forms of signaling components in the p38 MAPK pathway, we identified that a regulatory pathway consisting of MKK3-p38alpha/gamma-MAPK-activated protein kinase 2 participated in VEGF-stimulated migration. In further studies, we showed that a minimum of a 10-h treatment with SB203580 (specific p38 MAPK inhibitor) was needed to block VEGF-stimulated migration, suggesting an indirect role of p38 MAPK in this cellular event. Most interestingly, the occurrence of SB203580-induced migratory inhibition coincided with a reduction of urokinase plasminogen activator (uPA) expression. Furthermore, agents disrupting uPA and uPA receptor interaction abrogated VEGF-stimulated cell migration. These results suggest a possible association between cell migration and uPA expression. Indeed, VEGF-stimulated migration was not compromised by SB203580 in endothelial cells expressing the uPA transgene; however, VEGF-stimulated migration was inhibited by agents disrupting uPA-uPA receptor interaction. These results thus suggest that the p38 MAPK pathway participates in endothelial cell migration by regulating uPA expression.

Tumor cell locomotion: differential dynamics of spontaneous and induced migration in a 3D collagen matrix

Although great strides have recently been made in elucidating the factors initiating tumor cell migration and the relevant cellular pathways involved, the constituent components of migratory dynamics for individual tumor cell motion have still not been resolved. Utilizing a three-dimensional (3D) collagen assay and computer-assisted, continuous single cell tracking, we investigated the basic parameters for both the spontaneous and norepinephrine-induced migration of highly metastatic MBA-MB-468 breast, PC-3 prostate, and SW 480 colon carcinoma cells. We show that tumor cells do not migrate with uniform migrational structure and speed as previously thought, but rather, the induction of locomotion elicits significant increases in speed, break frequency, and total cell displacement, but decreases in break length and no change in the recruitment of nonlocomotory cells. We furthermore illustrate the corresponding morphological changes of induced tumor cell migration with emphasis on motion in a collagen matrix. These results demonstrate the complexity of tumor cell migration, and the compulsion for incorporating not only knowledge of intracellular pathways, but also fundamental parameters of migratory behavior into any expansive theory of tumor cell migration and metastasis formation. We furthermore establish the analytical methodology of investigating both the stimulation and potential pharmaceutical inhibition of tumor cell migration.

Proteomic identification of Bcl2-associated athanogene 2 as a novel MAPK-activated protein kinase 2 substrate

The p38 MAPK cascade is activated by various stresses or cytokines. Downstream of p38 MAPKs, there are diversification and extensive branching of signaling pathways. Fluorescent two-dimensional difference gel electrophoresis of phosphoprotein-enriched samples from HeLa cells in which p38 MAPK activity was either suppressed or activated enabled us to detect approximately 90 candidate spots for factors involved in p38-dependent pathways. Among these candidates, here we identified four proteins including Bcl-2-associated athanogene 2 (BAG2) by peptide mass fingerprintings. BAG family proteins are highly conserved throughout eukaryotes and regulate Hsc/Hsp70-mediated molecular chaperone activities and apoptosis. The results of two-dimensional immunoblots suggested that the phosphorylation of BAG2 was specifically controlled in a p38 MAPK-dependent manner. Furthermore, BAG2 was directly phosphorylated at serine 20 in vitro by MAPK-activated protein kinase 2 (MAPKAP kinase 2), which is known as a primary substrate of p38 MAPK and mediates several p38 MAPK-dependent processes. We confirmed that MAPKAP kinase 2 is also required for phosphorylation of BAG2 in vivo. Thus, p38 MAPK-MAPKAP kinase 2-BAG2 phosphorylation cascade may be a novel signaling pathway for response to extracellular stresses.