VEGF and thrombin induce MKP-1 through distinct signaling pathways: role for MKP-1 in endothelial cell migration

Hirudin delays the progression of diabetic kidney disease by inhibiting glomerular endothelial cell migration and abnormal angiogenesis

BACKGROUND

In the early stages of diabetic kidney disease (DKD), the pathogenesis involves abnormal angiogenesis in the glomerulus. Hirudin, as a natural specific inhibitor of thrombin, has been shown in previous studies to inhibit the migration of various tumor endothelial cells and abnormal angiogenesis. However, its role in DKD remains unclear.

METHODS

The effects of hirudin in DKD were studied using spontaneous type 2 diabetic db/db mice (which develop kidney damage at 8 weeks). Network pharmacology was utilized to identify relevant targets. An in vitro high glucose model was established using mouse glomerular endothelial cells (MGECs) to investigate the effects of hirudin on the migration and angiogenic capacity of MGECs.

RESULTS

Hirudin can ameliorate kidney damage in db/db mice. Network pharmacology suggests its potential association with the VEGFA/VEGFR2 pathway. Western blot and immunohistochemistry demonstrated elevated protein expression levels of VEGFA, VEGFR2, AQP1, and CD31 in db/db mice, while hirudin treatment reduced their expression. In the MGECs high glucose model, hirudin may reverse the enhanced migration and angiogenic capacity of MGECs in a high glucose environment by altering the expression of VEGFA, VEGFR2, AQP1, and CD31. Moreover, the drug effect gradually increases with higher concentrations of hirudin.

CONCLUSIONS

This study suggests that hirudin can improve early-stage diabetic kidney disease kidney damage by inhibiting the migration and angiogenesis of glomerular endothelial cells, thereby further expanding the application scope of hirudin. Additionally, the study found increased expression of AQP1 in DKD, providing a new perspective for further research on the potential pathogenesis of DKD.

Vascular Endothelial Growth Factor A VEGFA Inhibition: An Effective Treatment Strategy for Psoriasis

Psoriasis is an inflammatory skin disease mediated by the immune system and characterized by an inflammatory ring, also known as an epithelial immune microenvironment (EIME). The interaction between the epithelial tissue of the skin and the immune system has a crucial role in the immune cycle of psoriasis. Although the formation of new blood vessels in skin lesions provides energy support for the proliferation of epidermal keratinocytes, the role of angiogenesis in psoriasis has not been extensively studied. Vascular endothelial growth factor A (VEGFA) is a key regulator of angiogenesis that has an important role in the development of psoriasis. VEGFA promotes angiogenesis and directly stimulates epidermal keratinocytes and infiltrating immune cells, thus contributing to the progression of psoriasis. Measuring VEGFA levels to identify angiogenic characteristics in psoriasis patients may be a predictive biomarker for disease severity and response to anti-angiogenic therapy. Clinical data have shown that anti-angiogenic therapy can improve skin lesions in psoriasis patients. Therefore, this study aimed to uncover the underestimated role of blood vessels in psoriasis, explore the relationship between VEGFA and keratinocytes in the EIME, and inspire innovative drug therapies for the treatment of psoriasis.

Growth Factor Deregulation and Emerging Role of Phosphatases in Diabetic Peripheral Artery Disease

Peripheral artery disease is caused by atherosclerosis of lower extremity arteries leading to the loss of blood perfusion and subsequent critical ischemia. The presence of diabetes mellitus is an important risk factor that greatly increases the incidence, the progression and the severity of the disease. In addition to accelerated disease progression, diabetic patients are also more susceptible to develop serious impairment of their walking abilities through an increased risk of lower limb amputation. Hyperglycemia is known to alter the physiological development of collateral arteries in response to ischemia. Deregulation in the production of several critical pro-angiogenic factors has been reported in diabetes along with vascular cell unresponsiveness in initiating angiogenic processes. Among the multiple molecular mechanisms involved in the angiogenic response, protein tyrosine phosphatases are potent regulators by dephosphorylating pro-angiogenic tyrosine kinase receptors. However, evidence has indicated that diabetes-induced deregulation of phosphatases contributes to the progression of several micro and macrovascular complications. This review provides an overview of growth factor alterations in the context of diabetes and peripheral artery disease, as well as a description of the role of phosphatases in the regulation of angiogenic pathways followed by an analysis of the effects of hyperglycemia on the modulation of protein tyrosine phosphatase expression and activity. Knowledge of the role of phosphatases in diabetic peripheral artery disease will help the development of future therapeutics to locally regulate phosphatases and improve angiogenesis.

Hirudin reduces nephropathy microangiopathy in STZ-induced diabetes rats by inhibiting endothelial cell migration and angiogenesis

OBJECTIVE

Kidney is the most common location of microangiopathy in diabetic patients, and we designed this study to investigate the effects of hirudin on renal microangiopathy in STZ-induced diabetes rats and in vitro.

METHODS

We established a diabetes model by intraperitoneal injection of STZ and administered hirudin daily by subcutaneous injection. HE staining was used to assess kidney pathological changes. Western blot and immunochemistry was used to detect the protein expression. Glomerular endothelial cells (GEC) in normal rats were assessed by cell scratch test for migration ability and tubule formation experiment for angiogenesis ability.

RESULTS

Compared with DN rats without any treatment, the serum creatinine, serum Cys C, 24-hour urine protein of DN rats with hirudin treatment were significantly decrease, the kidney/body weight and glomerular area of DN rats with hirudin treatment were all significantly decrease, and also significant improvement in renal pathology revealed by HE staining in DN rats after treating with hirudin. Moreover, we also found that hirudin coun not only significantly increase the prothrombin time and aivated partial thromboplastin time in DN rats, but also significantly decrease the expression of VEGF and TM-1 protein in kidney tissues of DN rats. In vitro, we found that high glucose could promote the migration and angiogensis of GEC, and significantly increased the expression of VEGF and Ang protein, but significantly decreased the expression of THBS1 and Arg1 protein. More importantly was that hirudin could inhibit the migration and angiogensis of GEC, and reversed HG-induced the expression of VEGF, Ang, THBS1 and Arg1 protein in GEC. In addition, we also found that hirudin could not only decrease HG-enhanced the activity of RhoA in GEC, but also decrease HG-enhanced the expression of p-MYPT1/MYPT1, p-p38/p38 protein in GEC.

CONCLUSION

Hirudin reduces nephropathy microangiopathy in STZ-induced diabetes, and might be related to hirudin inhibiting glomerular endothelial cell migration and angiogenesis through Rho-kinase and subsequent p38MAPK/NF-kB signaling pathway.

Exploitation of receptor tyrosine kinases by viral-encoded growth factors

Receptor tyrosine kinases (RTKs) are essential components of cell communication pathways utilized from the embryonic to adult stages of life. These transmembrane receptors bind polypeptide ligands, such as growth factors, inducing signalling cascades that control cellular processes such as proliferation, survival, differentiation, motility and inflammation. Many viruses have acquired homologs of growth factors encoded by the hosts that they infect. Production of growth factors during infection allows viruses to exploit RTKs for entry and replication in cells, as well as for host and environmental dissemination. This review describes the genetic diversity amongst virus-derived growth factors and the mechanisms by which RTK exploitation enhances virus survival, then highlights how viral ligands can be used to further understanding of RTK signalling and function during embryogenesis, homeostasis and disease scenarios.

VEGF Receptor-2 Activation Mediated by VEGF-E Limits Scar Tissue Formation Following Cutaneous Injury

Objective: Vascular endothelial growth factor (VEGF) family members are critical regulators of tissue repair and depending on their distinct pattern of receptor specificity can also promote inflammation and scarring. This study utilized a receptor-selective VEGF to examine the role of VEGF receptor (VEGFR)-2 in scar tissue (ST) formation. Approach: Cutaneous skin wounds were created in mice using a 4 mm biopsy punch and then treated until closure with purified VEGF-E derived from orf virus stain NZ-2. Tissue samples were harvested to measure gene expression using quantitative PCR and to observe ST formation through histological examination and changes in cell populations by immunofluorescence. Results: VEGFR-2-activation with VEGF-E increased expression of anti-inflammatory cytokine interleukin (IL)-10 and reduced macrophage infiltration and myofibroblast differentiation in wounded skin compared with controls. VEGF-E treatment also increased microvascular density and improved pericyte coverage of blood vessels in the healing wounds. The ST that formed following treatment with VEGF-E was reduced in size and showed improved collagen structure. Innovation: The role of VEGFR-2 activation in wound epithelialization and angiogenesis is well established; but its contribution to ST formation is unclear. This study tests the effect of a selective VEGFR-2 activation on ST formation following cutaneous wounding in a murine model. Conclusion: VEGFR-2 stimulation can enhance the quality of skin repair, at least, in part, through the induction of IL-10 expression and dampening of wound inflammation and fibrosis. Therapies that selectively activate VEGFR-2 may therefore be beneficial to treat impaired healing or to prevent excess scarring.

IL-36 and IL-1/IL-17 Drive Immunity to Oral Candidiasis via Parallel Mechanisms

Protection against microbial infection by the induction of inflammation is a key function of the IL-1 superfamily, including both classical IL-1 and the new IL-36 cytokine families. Candida albicans is a frequent human fungal pathogen causing mucosal infections. Although the initiators and effectors important in protective host responses to C. albicans are well described, the key players in driving these responses remain poorly defined. Recent work has identified a central role played by IL-1 in inducing innate Type-17 immune responses to clear C. albicans infections. Despite this, lack of IL-1 signaling does not result in complete loss of immunity, indicating that there are other factors involved in mediating protection to this fungus. In this study, we identify IL-36 cytokines as a new player in these responses. We show that C. albicans infection of the oral mucosa induces the production of IL-36. As with IL-1α/β, induction of epithelial IL-36 depends on the hypha-associated peptide toxin Candidalysin. Epithelial IL-36 gene expression requires p38-MAPK/c-Fos, NF-κB, and PI3K signaling and is regulated by the MAPK phosphatase MKP1. Oral candidiasis in IL-36R-/- mice shows increased fungal burdens and reduced IL-23 gene expression, indicating a key role played by IL-36 and IL-23 in innate protective responses to this fungus. Strikingly, we observed no impact on gene expression of IL-17 or IL-17-dependent genes, indicating that this protection occurs via an alternative pathway to IL-1-driven immunity. Thus, IL-1 and IL-36 represent parallel epithelial cell-driven protective pathways in immunity to oral C. albicans infection.

Widening control of fin inter-rays in zebrafish and inferences about actinopterygian fins

The amputation of a teleost fin rapidly triggers an intricate maze of hierarchically regulated signalling processes which ultimately reconstruct the diverse tissues of the appendage. Whereas the generation of the fin pattern along the proximodistal axis brings with it several well-known developmental regulators, the mechanisms by which the fin widens along its dorsoventral axis remain poorly understood. Utilizing the zebrafish as an experimental model of fin regeneration and studying more than 1000 actinopterygian species, we hypothesized a connection between specific inter-ray regulatory mechanisms and the morphological variability of inter-ray membranes found in nature. To tackle these issues, both cellular and molecular approaches have been adopted and our results suggest the existence of two distinguishable inter-ray areas in the zebrafish caudal fin, a marginal and a central region. The present work associates the activity of the cell membrane potassium channel kcnk5b, the fibroblast growth factor receptor 1 and the sonic hedgehog pathway to the control of several cell functions involved in inter-ray wound healing or dorsoventral regeneration of the zebrafish caudal fin. This ray-dependent regulation controls cell migration, cell-type patterning and gene expression. The possibility that modifications of these mechanisms are responsible for phenotypic variations found in euteleostean species, is discussed.

Mitogen-activated protein kinase phosphatase 1 (MKP-1) in macrophage biology and cardiovascular disease. A redox-regulated master controller of monocyte function and macrophage phenotype

MAPK pathways play a critical role in the activation of monocytes and macrophages by pathogens, signaling molecules and environmental cues and in the regulation of macrophage function and plasticity. MAPK phosphatase 1 (MKP-1) has emerged as the main counter-regulator of MAPK signaling in monocytes and macrophages. Loss of MKP-1 in monocytes and macrophages in response to metabolic stress leads to dysregulation of monocyte adhesion and migration, and gives rise to dysfunctional, proatherogenic monocyte-derived macrophages. Here we review the properties of this redox-regulated dual-specificity MAPK phosphatase and the role of MKP-1 in monocyte and macrophage biology and cardiovascular diseases.

Modulation of VEGF receptor 2 signaling by protein phosphatases

Phosphorylation of serines, threonines, and tyrosines is a central event in signal transduction cascades in eukaryotic cells. The phosphorylation state of any particular protein reflects a balance of activity between kinases and phosphatases. Kinase biology has been exhaustively studied and is reasonably well understood, however, much less is known about phosphatases. A large body of evidence now shows that protein phosphatases do not behave as indiscriminate signal terminators, but can function both as negative or positive regulators of specific signaling pathways. Genetic models have also shown that different protein phosphatases play precise biological roles in health and disease. Finally, genome sequencing has unveiled the existence of many protein phosphatases and associated regulatory subunits comparable in number to kinases. A wide variety of roles for protein phosphatase roles have been recently described in the context of cancer, diabetes, hereditary disorders and other diseases. In particular, there have been several recent advances in our understanding of phosphatases involved in regulation of vascular endothelial growth factor receptor 2 (VEGFR2) signaling. The receptor is the principal signaling molecule mediating a wide spectrum of VEGF signal and, thus, is of paramount significance in a wide variety of diseases ranging from cancer to cardiovascular to ophthalmic. This review focuses on the current knowledge about protein phosphatases' regulation of VEGFR2 signaling and how these enzymes can modulate its biological effects.

Smad4 inhibits cell migration via suppression of JNK activity in human pancreatic carcinoma PANC-1 cells

Smad4 is a common Smad and is a key downstream regulator of the transforming growth factor-β signaling pathway, in which Smad4 often acts as a potent tumor suppressor and functions in a highly context-dependent manner, particularly in pancreatic cancer. However, little is known regarding whether Smad4 regulates other signaling pathways involved in pancreatic cancer. The present study demonstrated that Smad4 downregulates c-Jun N-terminal kinase (JNK) activity using a Smad4 loss-of-function or gain-of-function analysis. Additionally, stable overexpression of Smad4 clearly affected the migration of human pancreatic epithelioid carcinoma PANC-1 cells, but did not affect cell growth. In addition, the present study revealed that upregulation of mitogen-activated protein kinase phosphatase-1 is required for the reduction of JNK activity by Smad4, leading to a decrease in vascular endothelial growth factor expression and inhibiting cell migration. Overall, the present findings indicate that Smad4 may suppress JNK activation and inhibit the tumor characteristics of pancreatic cancer cells.

Functional Analysis of Dual-Specificity Protein Phosphatases in Angiogenesis

Therapeutic perspectives targeting angiogenesis in cancer stimulated an intense investigation of the mechanisms triggering and governing angiogenic processes. Several publications have highlighted the importance of typical dual-specificity phosphatases (DSPs) or MKPs in endothelial cells and their role in controlling different biological functions implicated in angiogenesis such as migration, proliferation, apoptosis, tubulogenesis, and cell adhesion. However, among atypical DSPs, the only one investigated in angiogenesis was DUSP3. We recently identified this DSP as a new key player in endothelial cells and angiogenesis. In this chapter we provide with detailed protocols and models used to investigate the role of DUSP3 in endothelial cells and angiogenesis. We start the chapter with an overview of the role of several DSPs in angiogenesis. We continue with providing a full description of a highly efficient transfection protocol to deplete DUSP3 using small interfering RNA (siRNA) in the primary human umbilical vein endothelial cells (HUVEC). We next describe the major assays used to investigate different processes involved in angiogenesis such as tube formation assay, proliferation assay and spheroids sprouting assay. We finish the chapter by validating our results in DUSP3-knockout mice using in vivo angiogenesis assays such as Matrigel plug and Lewis lung carcinoma cell subcutaneous xenograft model followed by anti-CD31 immunofluorescence and ex vivo aortic ring assay. All methods described can be adapted to other phosphatases and signaling molecules.

Mitogen-activated protein kinase phosphatase-1 promotes neovascularization and angiogenic gene expression

OBJECTIVE

Angiogenesis is the formation of new blood vessels through endothelial cell sprouting. This process requires the mitogen-activated protein kinases, signaling molecules that are negatively regulated by the mitogen-activated protein kinase phosphatase-1 (MKP-1). The purpose of this study was to evaluate the role of MKP-1 in neovascularization in vivo and identify associated mechanisms in endothelial cells.

APPROACH AND RESULTS

We used murine hindlimb ischemia as a model system to evaluate the role of MKP-1 in angiogenic growth, remodeling, and arteriogenesis in vivo. Genomic deletion of MKP-1 blunted angiogenesis in the distal hindlimb and microvascular arteriogenesis in the proximal hindlimb. In vitro, endothelial MKP-1 depletion/deletion abrogated vascular endothelial growth factor-induced migration and tube formation, and reduced proliferation. These observations establish MKP-1 as a positive mediator of angiogenesis and contrast with the canonical function of MKP-1 as a mitogen-activated protein kinase phosphatase, implying an alternative mechanism for MKP-1-mediated angiogenesis. Cloning and sequencing of MKP-1-bound chromatin identified localization of MKP-1 to exonic DNA of the angiogenic chemokine fractalkine, and MKP-1 depletion reduced histone H3 serine 10 dephosphorylation on this DNA locus and blocked fractalkine expression. In vivo, MKP-1 deletion abrogated ischemia-induced fractalkine expression and macrophage and T-lymphocyte infiltration in distal hindlimbs, whereas fractalkine delivery to ischemic hindlimbs rescued the effect of MKP-1 deletion on neovascular hindlimb recovery.

CONCLUSIONS

MKP-1 promoted angiogenic and arteriogenic neovascular growth, potentially through dephosphorylation of histone H3 serine 10 on coding-region DNA to control transcription of angiogenic genes, such as fractalkine. These observations reveal a novel function for MKP-1 and identify MKP-1 as a potential therapeutic target.

Regulation of angiopoietin-1/Tie-2 receptor signaling in endothelial cells by dual-specificity phosphatases 1, 4, and 5

Background

Angiopoietin‐1 (Ang‐1) promotes survival and migration of endothelial cells, in part through the activation of mitogen‐activated protein kinase (MAPK) pathways downstream of Tie‐2 receptors. Dual‐specificity phosphatases (DUSPs) dephosphorylate phosphotyrosine and phosphoserine/phosphothreonine residues on target MAPKs. The mechanisms by which DUSPs modulate MAPK activation in Ang‐1/Tie‐2 receptor signaling are unknown in endothelial cells.

Methods and Results

Expression of various DUSPs in human umbilical vein endothelial cells exposed to Ang‐1 was measured. The functional roles of DUSPs in Ang‐1‐induced regulation of MAPK activation, endothelial cell survival, migration, differentiation, and permeability were measured using selective siRNA oligos. Ang‐1 differentially induces DUSP1, DUSP4, and DUSP5 in human umbilical vein endothelial cells through activation of the PI‐3 kinase, ERK1/2, p38, and SAPK/JNK pathways. Lack‐of‐function siRNA screening revealed that DUSP1 preferentially dephosphorylates p38 protein and is involved in Ang‐1‐induced cell migration and differentiation. DUSP4 preferentially dephosphorylates ERK1/2, p38, and SAPK/JNK proteins and, under conditions of serum deprivation, is involved in Ang‐1‐induced cell migration, several antiapoptotic effects, and differentiation. DUSP5 preferentially dephosphorylates ERK1/2 proteins and is involved in cell survival and inhibition of permeability.

Conclusions

DUSP1, DUSP4, and DUSP5 differentially modulate MAPK signaling pathways downstream of Tie‐2 receptors, thus highlighting the importance of these phosphatases to Ang‐1‐induced angiogenesis.

Thrombomodulin functions as a plasminogen receptor to modulate angiogenesis

Urokinase-type plasminogen activator (uPA) activates plasminogen (Plg) through a major pericellular proteolytic system involved in cell migration and angiogenesis; however, the Plg receptor that participates in uPA-mediated Plg activation has not yet been identified. In this study, we demonstrated that thrombomodulin (TM), a type I transmembrane glycoprotein, is a novel Plg receptor that plays a role in pericellular proteolysis and cell migration. Plg activation at the cell surface and the extent of its cell migration- and invasion-promoting effect are cellular TM expression dependent. Direct binding of Plg and the recombinant TM extracellular domain, with a KD of 0.1-0.3 μM, was determined through surface plasmon resonance analysis. Colocalization of TM, Plg, and the uPA receptor within plasma membrane lipid rafts, at the leading edge of migrating endothelial cells, was demonstrated and was also shown to overlap with areas of major pericellular proteolysis. Moreover, the roles of TM and Plg in neoangiogenesis were demonstrated in vivo through the skin wound-healing model. In conclusion, we propose that TM is a novel Plg receptor that regulates uPA/uPA receptor-mediated Plg activation and pericellular proteolysis within lipid rafts at the leading edge of migrating cells during angiogenesis.

STAT3-mediated coincidence detection regulates noncanonical immediate early gene induction

Signaling pathways interact with one another to form dynamic networks in which the cellular response to one stimulus may depend on the presence, intensity, timing, or localization of other signals. In rare cases, two stimuli may be simultaneously required for cells to elicit a significant biological output. This phenomenon, generally termed "coincidence detection," requires a downstream signaling node that functions as a Boolean AND gate to restrict biological output from a network unless multiple stimuli are received within a specific window of time. Simultaneous activation of the EGF receptor (EGFR) and a thrombin receptor (protease-activated receptor-1, PAR-1) increases the expression of multiple immediate early genes (IEGs) associated with growth and angiogenesis. Using a bioinformatic comparison of IEG promoter regions, we identified STAT3 as a critical transcription factor for the detection of coincident EGFR/PAR-1 activation. EGFR activation induces classical STAT3 Tyr(705) phosphorylation but also initiates an inhibitory signal through the PI3K-AKT signaling axis that prevents STAT3 Ser(727) phosphorylation. Coincident PAR-1 signaling resolves these conflicting EGF-activated pathways by blocking AKT activation and permitting GSK-3α/β-dependent STAT3 Ser(727) phosphorylation and STAT3-dependent gene expression. Functionally, combinatorial EGFR/PAR-1 signaling suppresses EGF-induced proliferation and thrombin-induced leukocyte adhesion and triggers a STAT3-dependent increase in endothelial cell migration. This study reveals a novel signaling role for STAT3 in which the simultaneous presence of extracellular EGF and thrombin is detected at the level of STAT3 post-translational modifications. Collectively, our results describe a novel regulatory mechanism in which combinatorial EGFR/PAR-1 signaling regulates STAT3-dependent IEG induction and endothelial cell migration.

Endometriosis, angiogenesis and tissue factor

Tissue factor (TF), is a cellular receptor that binds the factor VII/VIIa to initiate the blood coagulation cascade. In addition to its role as the initiator of the hemostatic cascade, TF is known to be involved in angiogenesis via intracellular signaling that utilizes the protease activated receptor-2 (PAR-2). We now review the physiologic expression of TF in the endometrium and its altered expression in multiple cell types derived from eutopic and ectopic endometrium from women with endometriosis compared with normal endometrium. Our findings suggest that TF might be an ideal target for therapeutic intervention in endometriosis. We have employed a novel immunoconjugate molecule known as Icon and were able to eradicate endometrial lesions in a mouse model of endometriosis without affecting fertility. These findings have major implications for potential treatment in humans.

Opposing effects of the angiopoietins on the thrombin-induced permeability of human pulmonary microvascular endothelial cells

Background

Angiopoietin-2 (Ang-2) is associated with lung injury in ALI/ARDS. As endothelial activation by thrombin plays a role in the permeability of acute lung injury and Ang-2 may modulate the kinetics of thrombin-induced permeability by impairing the organization of vascular endothelial (VE-)cadherin, and affecting small Rho GTPases in human pulmonary microvascular endothelial cells (HPMVECs), we hypothesized that Ang-2 acts as a sensitizer of thrombin-induced hyperpermeability of HPMVECs, opposed by Ang-1.

Methodology/Principal Findings

Permeability was assessed by measuring macromolecule passage and transendothelial electrical resistance (TEER). Angiopoietins did not affect basal permeability. Nevertheless, they had opposing effects on the thrombin-induced permeability, in particular in the initial phase. Ang-2 enhanced the initial permeability increase (passage, P = 0.010; TEER, P = 0.021) in parallel with impairment of VE-cadherin organization without affecting VE-cadherin Tyr685 phosphorylation or increasing RhoA activity. Ang-2 also increased intercellular gap formation. Ang-1 preincubation increased Rac1 activity, enforced the VE-cadherin organization, reduced the initial thrombin-induced permeability (TEER, P = 0.027), while Rac1 activity simultaneously normalized, and reduced RhoA activity at 15 min thrombin exposure (P = 0.039), but not at earlier time points. The simultaneous presence of Ang-2 largely prevented the effect of Ang-1 on TEER and macromolecule passage.

Conclusions/Significance

Ang-1 attenuated thrombin-induced permeability, which involved initial Rac1 activation-enforced cell-cell junctions, and later RhoA inhibition. In addition to antagonizing Ang-1, Ang-2 had also a direct effect itself. Ang-2 sensitized the initial thrombin-induced permeability accompanied by destabilization of VE-cadherin junctions and increased gap formation, in the absence of increased RhoA activity.

Dexamethasone arterializes venous endothelial cells by inducing mitogen-activated protein kinase phosphatase-1: a novel antiinflammatory treatment for vein grafts?

BACKGROUND

Vein grafting in coronary artery surgery is complicated by a high restenosis rate resulting from the development of vascular inflammation, intimal hyperplasia, and accelerated atherosclerosis. In contrast, arterial grafts are relatively resistant to these processes. Vascular inflammation is regulated by signaling intermediaries, including p38 mitogen-activated protein (MAP) kinase, that trigger endothelial cell (EC) expression of chemokines (eg, interleukin-8, monocyte chemotactic protein-1) and other proinflammatory molecules. Here, we have tested the hypothesis that p38 MAP kinase activation in response to arterial shear stress (flow) may occur more readily in venous ECs, leading to greater proinflammatory activation.

METHODS AND RESULTS

Comparative reverse-transcriptase polymerase chain reaction and Western blotting revealed that arterial shear stress induced p38-dependent expression of monocyte chemotactic protein-1 and interleukin-8 in porcine jugular vein ECs. In contrast, porcine aortic ECs were protected from shear stress-induced expression of p38-dependent chemokines as a result of rapid induction of MAP kinase phosphatase-1. However, we observed with both cultured porcine jugular vein ECs and perfused veins that venous ECs can be protected by brief treatment with dexamethasone, which induced MAP kinase phosphatase-1 to suppress proinflammatory activation.

CONCLUSIONS

Arterial but not venous ECs are protected from proinflammatory activation in response to short-term exposure to high shear stress by the induction of MAP kinase phosphatase-1. Dexamethasone pretreatment arterializes venous ECs by inducing MAP kinase phosphatase-1 and may protect veins from inflammation.

Mitogen-activated protein kinase phosphatase-1 is a key regulator of hypoxia-induced vascular endothelial growth factor expression and vessel density in lung

Although mitogen-activated protein kinase phosphatase-1 (MKP-1) is a key deactivator of MAP kinases, known effectors of lung vessel formation, whether it plays a role in the expression of proangiogenic vascular endothelial growth factor (VEGF) in hypoxic lung is unknown. We therefore hypothesized that MKP-1 is a crucial modulator of hypoxia-stimulated vessel development by regulating lung VEGF levels. Wild-type MKP-1(+/+), heterozygous MKP-1(+/-), and deficient MKP-1(-/-) mice were exposed to sea level (SL), Denver altitude (DA) (1609 m [5280 feet]), and severe high altitude (HYP) (∼5182 m [∼17,000 feet]) for 6 weeks. Hypoxia enhanced phosphorylation of p38 MAP kinase, a substrate of MKP-1, as well as α smooth muscle actin (αSMA) expression in vessels, respiratory epithelium, and interstitium of phosphatase-deficient lung. αSMA-positive vessel (<50 μm outside diameter) densities were markedly reduced, whereas vessel wall thickness was increased in hypoxic MKP-1(-/-) lung. Mouse embryonic fibroblasts (MEFs) of all three genotypes were isolated to pinpoint the mechanism involved in hypoxia-induced vascular abnormalities of MKP-1(-/-) lung. Sustained phosphorylation of p38 MAP kinase was observed in MKP-1-null MEFs in response to hypoxia exposure. Although hypoxia up-regulated VEGF levels in MKP-1(+/+) MEFs eightfold, only a 70% increase in VEGF expression was observed in MKP-1-deficient cells. Therefore, our data strongly suggest that MKP-1 might be the key regulator of vascular densities through the regulation of VEGF levels in hypoxic lung.

A biphasic innate immune MAPK response discriminates between the yeast and hyphal forms of Candida albicans in epithelial cells

Discriminating between commensal and pathogenic states of opportunistic pathogens is critical for host mucosal defense and homeostasis. The opportunistic human fungal pathogen Candida albicans is also a constituent of the normal oral flora and grows either as yeasts or hyphae. We demonstrate that oral epithelial cells orchestrate an innate response to C. albicans via NF-κB and a biphasic MAPK response. Activation of NF-κB and the first MAPK phase, constituting c-Jun activation, is independent of morphology and due to fungal cell wall recognition. Activation of the second MAPK phase, constituting MKP1 and c-Fos activation, is dependent upon hypha formation and fungal burdens and correlates with proinflammatory responses. Such biphasic response may allow epithelial tissues to remain quiescent under low fungal burdens while responding specifically and strongly to damage-inducing hyphae when burdens increase. MAPK/MKP1/c-Fos activation may represent a “danger response” pathway that is critical for identifying and responding to the pathogenic switch of commensal microbes.

Heparin treatment of vascular smooth muscle cells results in the synthesis of the dual-specificity phosphatase MKP-1

The ability of heparin to block proliferation of vascular smooth muscle cells has been well documented. It is clear that heparin treatment can decrease the level of ERK activity in vascular smooth muscle cells that are sensitive to heparin. In this study, the mechanism by which heparin induces decreases in ERK activity was investigated by evaluating the dual specificity phosphatase, MKP-1, in heparin treated cells. Heparin induced MKP-1 synthesis in a time and concentration dependent manner. The time-course of MKP-1 expression correlated with the decrease in ERK activity. Over the same time frame, heparin treatment did not result in decreases in MEK-1 activity which could have, along with constitutive phosphatase activity, accounted for the decrease in ERK activity. Antibodies against a heparin receptor also induced the synthesis of MKP-1 along with decreasing ERK activity. Blocking either phosphatase activity or synthesis also blocked heparin-induced decreases in ERK activity. Consistent with a role for MKP-1, a nuclear phosphatase, heparin treated cells exhibited decreases in nuclear ERK activity more rapidly than cells not treated with heparin. The data support MKP-1 as a heparin-induced phosphatase that dephosphorylates ERK, decreasing ERK activity, in vascular smooth muscle cells.

Synergistic induction of mitogen-activated protein kinase phosphatase-1 by thrombin and epidermal growth factor requires vascular endothelial growth factor receptor-2

OBJECTIVE

To determine the molecular mechanism underlying the synergistic response of mitogen-activated protein kinase phosphatase-1 (MKP-1), which is induced by thrombin and epidermal growth factor (EGF).

METHODS AND RESULTS

MKP-1 induction by thrombin (approximately 6-fold) was synergistically increased (approximately 18-fold) by cotreatment with EGF in cultured endothelial cells. EGF alone did not induce MKP-1 substantially (<2-fold). The synergistic induction of MKP-1 was not mediated by matrix metalloproteinases. The EGF receptor kinase inhibitor AG1478 blocked approximately 70% of MKP-1 induction by thrombin plus EGF (from 18- to 6-fold) but not the response to thrombin alone. An extracellular signal-regulated kinase (ERK)-dependent protease-activated receptor-1 (PAR-1) signal was required for the thrombin alone effect; an ERK-independent PAR-1 signal was necessary for the approximately 12-fold MKP-1 induction by thrombin plus EGF. VEGF induction of MKP-1 was also approximately 12-fold and c-Jun N-terminal kinase (JNK) dependent. Inhibitors of extracellular signal-regulated kinase and JNK activation blocked thrombin plus EGF-induced MKP-1 completely. Furthermore, VEGF receptor 2 depletion blocked the synergistic response without affecting the induction of MKP-1 by thrombin alone.

CONCLUSIONS

We have identified a novel signaling interaction between protease-activated receptor-1 and EGF receptor that is mediated by VEGF receptor 2 and results in synergistic MKP-1 induction.

Ovarian cancer G protein-coupled receptor 1-dependent and -independent vascular actions to acidic pH in human aortic smooth muscle cells

Atherosclerosis is a chronic inflammation disease characterized by acidic micromilieu and the accumulation of numerous bioactive lipid mediators, such as lysophosphatidic acid (LPA) and prostaglandins, in the atherosclerotic lesion. Chronic acidification induced various effects on vascular smooth muscle cells, but the molecular mechanisms underlying these effects remain unknown. In this study, we examine the role of proton-sensing ovarian cancer G protein-coupled receptor 1 (OGR1) in extracellular acidification-induced regulation of cyclooxygenase (COX)-2 induction, PGI(2) production, MAPK phosphatase (MKP)-1 expression, and plasminogen activator inhibitor (PAI)-1 expression and proliferation in human aortic smooth muscle cells (AoSMCs). Experiments with knockdown with small interfering RNA specific to OGR1 and specific inhibitors for G proteins showed that acidification-induced COX-2 expression, PGI(2) production, and MKP-1 expression, but not PAI-1 expression and inhibition of proliferation, were dependent on OGR1 and mainly mediated by G(q/11) protein. LPA remarkably enhanced, through the LPA(1) receptor/G(i) protein, the OGR1-mediated vascular actions to acidic pH. In conclusion, acidic pH-induced vascular actions of AoSMCs can be dissected to OGR1-dependent and -independent pathways: COX-2 expression, PGI(2) production, and MKP-1 expression are mediated by OGR1, but PAI-1 expression and inhibition of proliferation are not. LPA, which is usually thought to be a proatherogenic lipid mediator, may exert antiatherogenic actions under acidic micromilieu through cross-talk between LPA(1)/G(i) protein and OGR1/G(q/11) protein.

Lack of mitogen-activated protein kinase phosphatase-1 protects ApoE-null mice against atherosclerosis

RATIONALE

Multiple protein kinases have been implicated in cardiovascular disease; however, little is known about the role of their counterparts: the protein phosphatases.

OBJECTIVE

To test the hypothesis that mitogen-activated protein kinase phosphatase (MKP)-1 is actively involved in atherogenesis.

METHODS AND RESULTS

Mice with homozygous deficiency in MKP-1 (MKP-1(-/-)) were bred with apolipoprotein (Apo)E-deficient mice (ApoE(-/-)) and the 3 MKP-1 genotypes (MKP-1(+/+)/ApoE(-/-) ; MKP-1(+/-)/ApoE(-/-) and MKP-1(-/-)/ApoE(-/-)) were maintained on a normal chow diet for 16 weeks. The 3 groups of mice exhibited similar body weight and serum lipid profiles; however, both MKP-1(+/-) and MKP-1(-/-) mice had significantly less aortic root atherosclerotic lesion formation than MKP-1(+/+) mice. Less en face lesion was observed in 8-month-old MKP-1(-/-) mice. The reduction in atherosclerosis was accompanied by decreased plasma levels of interleukin-1alpha and tumor necrosis factor alpha, and preceded by increased antiinflammatory cytokine interleukin-10. In addition, MKP-1-null mice had higher levels of plasma stromal cell-derived factor-1a, which negatively correlated with atherosclerotic lesion size. Immunohistochemical analysis revealed that MKP-1 expression was enriched in macrophage-rich areas versus smooth muscle cell regions of the atheroma. Furthermore, macrophages isolated from MKP-1-null mice showed dramatic defects in their spreading/migration and impairment in extracellular signal-regulated kinase, but not c-Jun N-terminal kinase and p38, pathway activation. In line with this, MKP-1-null atheroma exhibited less macrophage content. Finally, transplantation of MKP-1-intact bone marrow into MKP-1-null mice fully rescued the wild-type atherosclerotic phenotype.

CONCLUSION

These findings demonstrate that chronic deficiency of MKP-1 leads to decreased atherosclerosis via mechanisms involving impaired macrophage migration and defective extracellular signal-regulated kinase signaling.

Thrombin induces endothelial arginase through AP-1 activation

Arterial thrombosis is a common disease leading to severe ischemia beyond the obstructing thrombus. Additionally, endothelial dysfunction at the site of thrombosis can be rescued by l-arginine supplementation or arginase blockade in several animal models. Exposure of rat aortic endothelial cells (RAECs) to thrombin upregulates arginase I mRNA and protein levels. In this study, we further investigated the molecular mechanism of thrombin-induced arginase changes in endothelial cells. Thrombin strikingly increased arginase I promoter and enzyme activity in primary cultured RAECs. Using different deletion and point mutations of the promoter, we demonstrated that the activating protein-1 (AP-1) consensus site located at -3,157 bp in the arginase I promoter was a thrombin-responsive element. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay further confirmed that upon thrombin stimulation, c-Jun and activating transcription factor-2 (ATF-2) bound to the AP-1 site, which initiated the transactivation. Moreover, loss-of-function studies using small interfering RNA confirmed that recruitment of these two transcription factors to the AP-1 site was required for thrombin-induced arginase upregulation. In the course of defining the signaling pathway leading to the activation of AP-1 by thrombin, we found thrombin-induced phosphorylation of stress-activated protein kinase/c-Jun-NH(2)-terminal kinase (SAPK/JNK or JNK1/2/3) and p38 mitogen-activated protein kinase, which were followed by the phosphorylation of both c-Jun and ATF-2. These findings reveal the basis for thrombin induction of endothelial arginase I and indicate that arginase inhibition may be an attractive therapeutic alternative in the setting of arterial thrombosis and its associated endothelial dysfunction.

VEGF autoregulates its proliferative and migratory ERK1/2 and p38 cascades by enhancing the expression of DUSP1 and DUSP5 phosphatases in endothelial cells

Vascular endothelial growth factor (VEGF) is a key angiogenic factor that regulates proliferation and migration of endothelial cells via phosphorylation of extracellular signal-regulated kinase-1/2 (ERK1/2) and p38, respectively. Here, we demonstrate that VEGF strongly induces the transcription of two dual-specificity phosphatase (DUSP) genes DUSP1 and DUSP5 in endothelial cells. Using fluorescence microscopy, fluorescence lifetime imaging (FLIM), and fluorescence cross-correlation spectroscopy (FCCS), we found that DUSP1/mitogen-activated protein kinases phosphatase-1 (MKP-1) was localized in both the nucleus and cytoplasm of endothelial cells, where it existed in complex with p38 (effective dissociation constant, K(D)(eff), values of 294 and 197 nM, respectively), whereas DUSP5 was localized in the nucleus of endothelial cells in complex with ERK1/2 (K(D)(eff) 345 nM). VEGF administration affected differentially the K(D)(eff) values of the DUSP1/p38 and DUSP5/ERK1/2 complexes. Gain-of-function and lack-of-function approaches revealed that DUSP1/MKP-1 dephosphorylates primarily VEGF-phosphorylated p38, thereby inhibiting endothelial cell migration, whereas DUSP5 dephosphorylates VEGF-phosphorylated ERK1/2 inhibiting proliferation of endothelial cells. Moreover, DUSP5 exhibited considerable nuclear anchoring activity on ERK1/2 in the nucleus, thereby diminishing ERK1/2 export to the cytoplasm decreasing its further availability for activation.

Mitogen-activated protein (MAP) kinase/MAP kinase phosphatase regulation: roles in cell growth, death, and cancer

Mitogen-activated protein kinase dual-specificity phosphatase-1 (also called MKP-1, DUSP1, ERP, CL100, HVH1, PTPN10, and 3CH134) is a member of the threonine-tyrosine dual-specificity phosphatases, one of more than 100 protein tyrosine phosphatases. It was first identified approximately 20 years ago, and since that time extensive investigations into both mkp-1 mRNA and protein regulation and function in different cells, tissues, and organs have been conducted. However, no general review on the topic of MKP-1 exists. As the subject matter pertaining to MKP-1 encompasses many branches of the biomedical field, we focus on the role of this protein in cancer development and progression, highlighting the potential role of the mitogen-activated protein kinase (MAPK) family. Section II of this article elucidates the MAPK family cross-talk. Section III reviews the structure of the mkp-1 encoding gene, and the known mechanisms regulating the expression and activity of the protein. Section IV is an overview of the MAPK-specific dual-specificity phosphatases and their role in cancer. In sections V and VI, mkp-1 mRNA and protein are examined in relation to cancer biology, therapeutics, and clinical studies, including a discussion of the potential role of the MAPK family. We conclude by proposing an integrated scheme for MKP-1 and MAPK in cancer.

Histone H3 as a novel substrate for MAP kinase phosphatase-1

Mitogen-activated protein (MAP) kinase phosphatase-1 (MKP-1) is a nuclear, dual-specificity phosphatase that has been shown to dephosphorylate MAP kinases. We used a "substrate-trap" technique involving a mutation in MKP-1 of the catalytically critical cysteine to a serine residue ("CS" mutant) to capture novel MKP-1 substrates. We transfected the MKP-1 (CS) mutant and control (wild-type, WT) constructs into phorbol 12-myristate 13-acetate (PMA)-activated COS-1 cells. MKP-1-substrate complexes were immunoprecipitated, which yielded four bands of 17, 15, 14, and 10 kDa with the CS MKP-1 mutant but not the WT MKP-1. The bands were identified by mass spectrometry as histones H3, H2B, H2A, and H4, respectively. Histone H3 was phosphorylated, and purified MKP-1 dephosphorylated histone H3 (phospho-Ser-10) in vitro; whereas, histone H3 (phospho-Thr-3) was unaffected. We have previously shown that thrombin and vascular endothelial growth factor (VEGF) upregulated MKP-1 in human endothelial cells (EC). We now show that both thrombin and VEGF caused dephosphorylation of histone H3 (phospho-Ser-10) and histone H3 (phospho-Thr-3) in EC with kinetics consistent with MKP-1 induction. Furthermore, MKP-1-specific small interfering RNA (siRNA) prevented VEGF- and thrombin-induced H3 (phospho-Ser-10) dephosphorylation but had no effect on H3 (phospho-Thr-3 or Thr-11) dephosphorylation. In summary, histone H3 is a novel substrate of MKP-1, and VEGF- and thrombin-induced H3 (phospho-Ser-10) dephosphorylation requires MKP-1. We propose that MKP-1-mediated H3 (phospho-Ser-10) dephosphorylation is a key regulatory step in EC activation by VEGF and thrombin.

Increased Endothelial Mitogen-Activated Protein Kinase Phosphatase-1 Expression Suppresses Proinflammatory Activation at Sites That Are Resistant to Atherosclerosis

Atherosclerosis is a chronic inflammatory disease of arteries. It is triggered by proinflammatory mediators which induce adhesion molecules (eg, vascular cell adhesion molecule [VCAM]-1) in endothelial cells (ECs) by activating p38 and c-Jun N-terminal kinase (JNK) mitogen-activated protein (MAP) kinases by phosphorylation. Blood flow influences atherosclerosis by exerting shear stress (mechanical drag) on the inner surface of arteries, a force that alters endothelial physiology. Regions of the arterial tree exposed to high shear are protected from endothelial activation, inflammation, and atherosclerosis, whereas regions exposed to low or oscillatory shear are susceptible. We examined whether MAP kinase phosphatase (MKP)-1, a negative regulator of p38 and JNK, mediates the antiinflammatory effects of shear stress. We observed that expression of MKP-1 in cultured ECs was elevated by shear stress, whereas the expression of VCAM-1 was reduced. MKP-1 induction was shown to be necessary for the antiinflammatory effects of shear stress because gene silencing of MKP-1 restored VCAM-1 expression in sheared ECs. Immunostaining revealed that MKP-1 is preferentially expressed by ECs in a high-shear, protected region of the mouse aorta and is necessary for suppression of EC activation at this site, because p38 activation and VCAM-1 expression was enhanced by genetic deletion of MKP-1. We conclude that MKP-1 induction is required for the antiinflammatory effects of shear stress. Thus, our findings reveal a novel molecular mechanism contributing to the spatial distribution of vascular inflammation and atherosclerosis.

MAPK phosphatases as novel targets for rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) represents a challenge for therapeutic interventions due to complex inflammatory signalling pathways underlying its pathogenesis. The MAPK signalling network, a major effector limb of the inflammatory lesion, is an attractive therapeutic target. MAPK phosphatases (MKPs), endogenous negative regulators of MAPK signalling, have received increasing recognition as modulators of inflammatory and immune responses, and hence as a potential therapeutic avenue for RA.

OBJECTIVE

To present the rationale for therapeutically targeting MAPK signalling and explore the case for addressing MKP1 as a novel therapeutic strategy for RA.

METHODS

We summarise literature describing the importance of MAPK signalling in RA and review reports describing the roles of MKPs in modulating innate and adaptive immune responses. Finally we expand on the role of MKP1 in RA pathogenesis and explore data defining MKP1 as a mediator of glucocorticoid action.

CONCLUSION

MKP1 constitutes an exciting, novel potential therapeutic target for RA.

Cytokine-induced arginase activity in pulmonary endothelial cells is dependent on Src family tyrosine kinase activity

We hypothesized that the Src family tyrosine kinases (STKs) are involved in the upregulation of arginase and inducible nitric oxide synthase (iNOS) expression in response to inflammatory stimuli in pulmonary endothelial cells. Treatment of bovine pulmonary arterial endothelial cells (bPAEC) with lipopolysaccharide and tumor necrosis factor-alpha (L/T) resulted in increased urea and nitric oxide (NO) production, and this increase in urea and NO production was inhibited by the STK inhibitor PP1 (10 microM). The STK inhibitors PP2 (10 microM) and herbimycin A (10 microM) also prevented the L/T-induced expression of both arginase II and iNOS mRNA in bPAEC. Together, the data demonstrate a central role of STK in the upregulation of both arginase II and iNOS in bPAEC in response to L/T treatment. To identify the specific kinase(s) required for the induction of urea and NO production, we studied human pulmonary microvascular endothelial cells (hPMVEC) so that short interfering RNA (siRNA) techniques could be employed. We found that hPMVEC express Fyn, Yes, c-Src, Lyn, and Blk and that the protein expression of Fyn, Yes, c-Src, and Lyn could be inhibited with specific siRNA. The siRNA targeting Fyn prevented the cytokine-induced increase in urea and NO production, whereas siRNAs specifically targeting Yes, c-Src, and Lyn had no appreciable effect on cytokine-induced urea and NO production. These findings support our hypothesis that inflammatory stimuli lead to increased urea and NO production through a STK-mediated pathway. Furthermore, these results indicate that the STK Fyn plays a critical role in this process.