P38 MAPK: critical molecule in thrombin-induced NF-kappa B-dependent leukocyte recruitment

Phosphoproteomic analysis of thrombin- and p38 MAPK-regulated signaling networks in endothelial cells

Endothelial dysfunction is a hallmark of inflammation and is mediated by inflammatory factors that signal through G protein–coupled receptors including protease-activated receptor-1 (PAR1). PAR1, a receptor for thrombin, signals via the small GTPase RhoA and myosin light chain intermediates to facilitate endothelial barrier permeability. PAR1 also induces endothelial barrier disruption through a p38 mitogen-activated protein kinase–dependent pathway, which does not integrate into the RhoA/MLC pathway; however, the PAR1-p38 signaling pathways that promote endothelial dysfunction remain poorly defined. To identify effectors of this pathway, we performed a global phosphoproteome analysis of thrombin signaling regulated by p38 in human cultured endothelial cells using multiplexed quantitative mass spectrometry. We identified 5491 unique phosphopeptides and 2317 phosphoproteins, four distinct dynamic phosphoproteome profiles of thrombin-p38 signaling, and an enrichment of biological functions associated with endothelial dysfunction, including modulators of endothelial barrier disruption and a subset of kinases predicted to regulate p38-dependent thrombin signaling. Using available antibodies to detect identified phosphosites of key p38-regulated proteins, we discovered that inhibition of p38 activity and siRNA-targeted depletion of the p38α isoform increased basal phosphorylation of extracellular signal–regulated protein kinase 1/2, resulting in amplified thrombin-stimulated extracellular signal–regulated protein kinase 1/2 phosphorylation that was dependent on PAR1. We also discovered a role for p38 in the phosphorylation of α-catenin, a component of adherens junctions, suggesting that this phosphorylation may function as an important regulatory process. Taken together, these studies define a rich array of thrombin- and p38-regulated candidate proteins that may serve important roles in endothelial dysfunction.

Arginine vasopressin receptor 2 activation promotes microvascular permeability in sepsis

Methicillin-resistant Staphylococcus aureus (MRSA) sepsis is a severe condition associated with vascular leakage and poor prognosis. The hemodynamic management of sepsis targets hypotension, but there is no specific treatment available for vascular leakage. Arginine vasopressin (AVP) has been used in sepsis to promote vasoconstriction by activating AVP receptor 1 (V₁R). However, recent evidence suggests that increased fluid retention may be associated with the AVP receptor 2 (V₂R) activation worsening the outcome of sepsis. Hence, we hypothesized that the inhibition of V₂R activation ameliorates the severity of microvascular hyperpermeability during sepsis. The hypothesis was tested using a well-characterized and clinically relevant ovine model of MRSA pneumonia/sepsis and in vitro assays of human lung microvascular endothelial cells (HMVECs). in vivo experiments demonstrated that the treatment of septic sheep with tolvaptan (TLVP), an FDA-approved V₂R antagonist, significantly attenuated the sepsis-induced fluid retention and markedly reduced the lung water content. These pathological changes were not affected by the treatment with V₂R agonist, desmopressin (DDAVP). Additionally, the incubation of cultured HMVECs with DDAVP, and DDAVP along with MRSA significantly increased the paracellular permeability. Finally, both the DDAVP and MRSA-induced hyperpermeability was significantly attenuated by TLVP. Subsequent protein and gene expression assays determined that the V₂R-induced increase in permeability is mediated by phospholipase C beta (PLCβ) and the potent permeability factor angiopoietin-2. In conclusion, our results indicate that the activation of the AVP-V₂R axis is critical in the pathophysiology of severe microvascular hyperpermeability during Gram-positive sepsis. The use of the antagonist TLVP should be considered as adjuvant treatment for septic patients. The results from this clinically relevant animal study are highly translational to clinical practice.

Effect of Rho-kinase Inhibitor, Y27632, on Porcine Corneal Endothelial Cell Culture, Inflammation and Immune Regulation

PURPOSE

To investigate the effect of the Rho-kinase inhibitor, Y27632, on pig corneal endothelial cell (pCEC) culture, and on inflammation and immune regulation of the responses of human cells to pCECs.

METHODS

pCECs were cultured with/without Y27632 to assess cell proliferation and in vitro wound healing assay. The level of MCP-1 and VEGF in pCECs stimulated with human TNF-α were measured. Proliferation of human PBMCs stimulated with pCECs, and cytokine production in human T cells, and monocyte migration after stimulation were investigated.

RESULTS

Y27632 promoted pCEC proliferation, prevented pCEC death, and enhanced in vitro wound healing. After stimulation, there were significantly lower levels of MCP-1 and VEGF measured in pCECs cultured with Y27632, and significantly reduced human PBMC proliferation, cytokine production, and monocyte migration.

CONCLUSIONS

The application of the Rho-kinase inhibitor will be beneficial when culturing pCECs, and may provide a novel therapy to reduce inflammation after corneal xenotransplantation.

Melanoma upregulates ICAM-1 expression on endothelial cells through engagement of tumor CD44 with endothelial E-selectin and activation of a PKCα-p38-SP-1 pathway

Cancer metastasis involves multistep adhesive interactions between tumor cells (TCs) and endothelial cells (ECs), but the molecular mechanisms of intercellular communication in the tumor microenvironment remain elusive. Using static and flow coculture systems in conjunction with flow cytometry, we discovered that certain receptors on the ECs are upregulated on melanoma cell adhesion. Direct contact but not separate coculture between human umbilical endothelial cells (HUVECs) and a human melanoma cell line (Lu1205) increased intercellular adhesion molecule 1 (ICAM-1) and E-selectin expression on HUVECs by 3- and 1.5-fold, respectively, compared with HUVECs alone. The nonmetastatic cell line WM35 failed to promote ICAM-1 expression changes in HUVECs on contact. Enzyme-linked immunosorbent assay (ELISA) revealed that EC-TC contact has a synergistic effect on the expression of the cytokines interleukin (IL)-8, IL-6, and growth-related oncogene α (Gro-α). By using E-selectin cross-linking and beads coated with CD44 immunopurified from Lu1205 cells, we showed that CD44/selectin ligation was responsible for the ICAM-1 up-regulation on HUVECs. Protein kinase Cα (PKC-α) activation was found to be the downstream target of the CD44/selectin-initiated signaling, as ICAM-1 elevation was inhibited by siRNA targeting PKCα or a dominant negative form of PKCα (PKCα DN). Western blot analysis and electrophoretic mobility shift assays (EMSAs) showed that TC-EC contact mediated p38 phosphorylation and binding of the transcription factor SP-1 to its regulation site. In conclusion, CD44/selectin binding signals ICAM-1 up-regulation on the EC surface through a PKCα-p38-SP-1 pathway, which further enhances melanoma cell adhesion to ECs during metastasis.

Pharmacological inhibition of p38 mitogen-activated protein kinases affects KC/CXCL1-induced intraluminal crawling, transendothelial migration, and chemotaxis of neutrophils in vivo

p38 mitogen-activated protein kinase (MAPK) signalling is critical in the pathophysiology of a variety of inflammatory processes. Leukocyte recruitment to the site of inflammation is a multistep process governed by specific signalling cascades. After adhesion in the lumen, many leukocytes crawl to optimal sites at endothelial junctions and transmigrate to extravascular tissue in a Mac-1-dependent manner. The signalling mechanisms that regulate postadhesion steps of intraluminal crawling, transmigration, and chemotaxis in tissue remain incompletely understood. The present study explored the effect of p38 MAPK inhibitor SB203580 on various parameters of neutrophil recruitment triggered by chemokine KC (CXCL1) gradient. Neutrophil-endothelial interactions in microvasculature of murine cremaster muscle were determined using intravital microscopy and time-lapsed video analysis. SB203580 (100 nM) did not change leukocyte rolling but significantly attenuated neutrophil adhesion, emigration, and transmigration and impaired the initiation of neutrophil crawling and transmigration. In response to KC chemotactic gradient, SB203580 significantly reduced the velocity of migration and chemotaxis index of neutrophils in tissue. The upregulation of Mac-1 expression in neutrophils stimulated by KC was significantly blunted by SB203580 in vitro. Collectively, our findings demonstrate that pharmacological suppression of p38 MAPK significantly impairs multiple steps of neutrophil recruitment in vivo.

The beneficial effects of a direct thrombin inhibitor, dabigatran etexilate, on the development and stability of atherosclerotic lesions in apolipoprotein E-deficient mice : dabigatran etexilate and atherosclerosis

PURPOSE

Dabigatran etexilate (DE) constitutes a novel, direct thrombin inhibitor. Regarding the association of thrombin with atherogenesis, we assessed the effects of DE on the development and stability of atherosclerotic lesions in apolipoprotein-E deficient (ApoE-/-) mice.

MATERIALS-METHODS

Fifty male ApoE-/- mice were randomized to receive western-type diet either supplemented with DE 7.5 mg DE/g chow) (DE-group, n = 25) or matching placebo as control (CO-group, n = 25) for 12 weeks. After this period, all mice underwent carotid artery injury with ferric chloride and the time to thrombotic total occlusion (TTO) was measured. Then, mice were euthanatized and each aortic arch was analyzed for the mean plaque area, the content of macrophages, elastin, collagen, nuclear factor kappaB (NFκB), vascular cell adhesion molecule-1 (VCAM-1), matrix metalloproteinase-9 (MMP-9) and its inhibitor (TIMP-1).

RESULTS

DE-group showed significantly longer TTO compared to CO-group (8.9 ± 2.3 min vs 3.5 ± 1.1 min, p < 0.001) and the mean plaque area was smaller in DE-group than CO-group (441.00 ± 160.01 × 10(3) μm(2) vs 132.12 ± 32.17 × 10(3) μm(2), p < 0.001). Atherosclerotic lesions derived from DE-treated mice showed increased collagen (p = 0.043) and elastin (p = 0.031) content, thicker fibrous caps (p < 0.001) and reduced number of internal elastic lamina ruptures per mm of arterial girth (p < 0.001) when compared to CO-group. Notably, DE treatment seemed to promote plaque stability possibly by reducing concentrations of NFκB, VCAM-1, macrophages and MMP-9 and increasing TIMP-1 within atherosclerotic lesions (p < 0.05).

CONCLUSIONS

DE attenuates arterial thrombosis, reduces lesion size and may promote plaque stability in ApoE-/- mice. The plaque-stabilizing effects of chronic thrombin inhibition might be the result of the favorable modification of inflammatory mechanisms.

Dao-Tan decoction inhibits tumor necrosis factor-α-induced intercellular adhesion molecule-1 expression by blocking JNK and p38 signaling pathways in human umbilical vein endothelial cells

CONTEXT

Dao-Tan decoction (DTD) is a Chinese herb prescription used to treat atherosclerosis or dizziness for centuries. Previous study shows that DTD could inhibit intercellular adhesion molecule-1 (ICAM-1) expression induced by tumor necrosis factor-α (TNF-α). However, its mechanism has never been clearly described.

OBJECTIVE

To examine the hypothesis that DTD might inhibit TNF-α-induced ICAM-1 expression through regulating the mitogen-activated protein kinase (MAPK) pathways, involving Jun N-terminal kinase (JNK) and p38.

MATERIALS AND METHODS

The rats were orally administrated with DTD for 3 days (2.3 g/kg per day), then the serum was collected. Human umbilical vein endothelial cells (HUVECs) were cultured and stimulated by TNF-α with or without DTD serum. The expression of ICAM-1 mRNA was examined by reverse transcription-polymerase chain reaction and the expression of p38 and JNK was examined by Western blot analysis.

RESULTS

DTD serum significantly inhibits TNF-α-induced ICAM-1 expression by 17-41% on HUVECs. TNF-α-induced JNK and p38 activations, which were involved in ICAM-1 expression, were significantly inhibited with DTD serum treatment by 10-50% on HUVEC.

DISCUSSION AND CONCLUSION

Based on the theory of traditional Chinese medicine (TCM), pathogenesis of atherosclerosis is caused by "blood" and "phlegm" attached on blood vessels. DTD has a function of "dissolving phlegm", thus it is chosen for the treatment of atherosclerosis. This study demonstrated that DTD could inhibit the expression of ICAM-1, by significantly preventing the activation of JNK and p38, which are important factors of atherosclerosis. Therefore, the present study indicates the pharmacological basis for treatment of atherosclerosis with DTD.

Regulation of inflammatory response in human chondrocytes by lentiviral mediated RNA interference against S100A10

OBJECTIVE

The aim of the present study was to evaluate the effects of S100A10 silencing on the inflammatory response in human chondrocytes (HCs).The inflammation induced by lipopolysaccharide (LPS) was investigated in HCs in which the S100A10 was blocked with a lentiviral shRNA vector.

METHODS

A lentiviral shRNA vector targeting S100A10 was constructed and packaged to effectively block S100A10 expression in HCs. HCs were infected with the lentivirus. S100A10 expression levels in HCs were detected by western blot analysis. Enzyme-linked immunosorbent assay (ELISA) was employed to evaluate the change of cytokine secretion levels. The effects of S100A10 silencing on the activation of mitogen-activated protein kinases (MAPKs) and NF-κB signaling pathway were also determined by western blot analysis. In addition, fluo-3-AM was used to demonstrate the change in calcium mobilization.

RESULTS

Lentivirus effectively infected the HCs and inhibited the expression of S100A10. HCs with downregulated S100A10 showed significantly decreased production of inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-10. S100A10 silencing markedly suppressed the activation of MAPKs induced by LPS. Furthermore, the calcium concentration increase in HCs stimulated by LPS was also inhibited by S100A10 knockdown.

CONCLUSION

Our investigation demonstrated that S100A10 might be considered as a potential target for anti-inflammatory treatment.

Regulatory mechanisms of interleukin-8 production induced by tumour necrosis factor-α in human hepatocellular carcinoma cells

Interleukin (IL)-8 plays the critical role in the initiation of micro-environmental inflammation responsible for tumour growth and patient prognosis. This study aimed at investigating the molecular mechanisms of IL-8 production from human hepatocellular carcinoma (HCC) cells. The levels of IL-8 and phosphorylation of p38 mitogen-activated protein kinase (MAPK), ERK1/2 and Akt in MHCC-97H cells were measured by ELISA, Western blot and immunofluorescence. NF-κB p65 protein nuclear translocation was determined by non-radioactive NF-κB p50/p65 transcription factor activity kit and cell bio-behaviours were detected by the real-time cell-monitoring system. Tumour necrosis factor-α (TNF-α) significantly induced phosphorylation of p38 MAPK, ERK, Akt and production of IL-8 from HCC cells, which were prevented by SB203580 (p38 MAPK inhibitor), PD98059 (ERK inhibitor), LY294002 and Wortmannin (PI3K inhibitor) and SB328437 (CCR3 inhibitor). TNF-α could significantly increase the translocation of NF-κB p65 protein into the nucleus in a dose-dependent manner, while SB203580 partially inhibited. In inflammatory micro-environment, HCC auto-produced IL-8 through p38 MAPK, ERK and PI3K/Akt signalling pathways, where the p38 MAPK is a central factor to activate the NF-κB pathway and regulate the expression of IL-8 production. There was a potential cross-talking between receptors.

Thrombin induces MCP-1 expression through Rho-kinase and subsequent p38MAPK/NF-κB signaling pathway activation in vascular endothelial cells

Thrombin has been shown to increase expression of chemokines such as monocyte chemoattractant protein 1 (MCP-1) in endothelial cells, leading to the development of atherosclerosis. However, the precise mechanism of this induction remains unknown. In the present study, we investigated whether the small G protein RhoA, and its effector, Rho-kinase are involved in MCP-1 induction by thrombin in endothelial cells. Y-27632, a specific Rho-kinase inhibitor, potently inhibited MCP-1 induction by thrombin. Y-27632 significantly decreased the chemotactic activity of thrombin-stimulated supernatants of endothelial cells on monocytes. Importantly, fasudil, a specific Rho-kinase inhibitor, attenuated MCP-1 gene expression in the aorta of db/db mice. Y-27632 attenuated thrombin-mediated phosphorylation of p38MAPK and p65, indicating that Rho-kinase mediates thrombin-induced MCP-1 expression through p38MAPK and NF-κB activation. Our findings demonstrate that the Rho/Rho-kinase signaling pathway plays a critical role in thrombin-mediated MCP-1 expression and function, and suggest that Rho/Rho-kinase may be an important target in the development of new therapeutic strategies for atherosclerosis.

ATX-LPA receptor axis in inflammation and cancer

Lysophosphatidic acid (LPA, 1- or 2-acyl-sn-glycerol 3-phosphate) mediates a plethora of physiological and pathological activities via interactions with a series of high affinity G protein-coupled receptors (GPCR). Both LPA receptor family members and autotaxin (ATX/LysoPLD), the primary LPA-producing enzyme, are aberrantly expressed in many human breast cancers and several other cancer lineages. Using transgenic mice expressing either an LPA receptor or ATX, we recently demonstrated that the ATX-LPA receptor axis plays a causal role in breast tumorigenesis and cancer-related inflammation, further validating the ATX-LPA receptor axis as a rich therapeutic target in cancer.

Signal transduction pathways involved in brain death-induced renal injury

Kidneys derived from brain death organ donors show an inferior survival when compared to kidneys derived from living donors. Brain death is known to induce organ injury by evoking an inflammatory response in the donor. Neuronal injury triggers an inflammatory response in the brain, leading to endothelial dysfunction and the release of cytokines in the circulation. Serum levels of interleukin-6, -8, -10, and monocyte chemoattractant protein-1 (MCP-1) are increased after brain death. Binding with cytokine-receptors in kidneys stimulates activation of nuclear factor-kappa B (NF-kappaB), selectins, adhesion molecules and production of chemokines leading to cellular influx. Mitogen-activated protein kinases (MAP-kinases) mediate inflammatory responses and together with NF-kappaB they seem to play an important role in brain death induced renal injury. Altering the activation state of MAP-kinases could be a promising drug target for early intervention to reduce cerebral injury related donor kidney damage and improve outcome after transplantation.

Is thrombin a key player in the 'coagulation-atherogenesis' maze?

In addition to its established roles in the haemostatic system, thrombin is an intriguing coagulation protease demonstrating an array of effects on endothelial cells, vascular smooth muscle cells (VSMC), monocytes, and platelets, all of which are involved in the pathophysiology of atherosclerosis. There is mounting evidence that thrombin acts as a powerful modulator of many processes like regulation of vascular tone, permeability, migration and proliferation of VSMC, recruitment of monocytes into the atherosclerotic lesions, induction of diverse pro-inflammatory markers, and all of these are related to the progression of cardiovascular disease. Recent studies in transgenic mice models indicate that the deletion of the natural thrombin inhibitor heparin cofactor II promotes an accelerated atherogenic state. Moreover, the reduction of thrombin activity levels in apolipoprotein E-deficient mice, because of the administration of the direct thrombin inhibitor melagatran, attenuates plaque progression and promotes stability in advanced atherosclerotic lesions. The combined evidence points to thrombin as a pivotal contributor to vascular pathophysiology. Considering the clinical development of selective anticoagulants including direct thrombin inhibitors, it is a relevant moment to review the different thrombin-induced mechanisms that contribute to the initiation, formation, progression, and destabilization of atherosclerotic plaques.

Receptor tyrosine kinase EphA2 mediates thrombin-induced upregulation of ICAM-1 in endothelial cells in vitro

Thrombin potently induces endothelial inflammation. One of the responses is upregulation of adhesion molecules such as ICAM-1, resulting in enhanced leukocyte attachment to the endothelium. In this report, we examine the contribution of EphA2 in thrombin-induced expression of ICAM-1 in human umbilical vein endothelial cells (HUVECs). We showed that thrombin transiently induced tyrosine- phosphorylation of EphA2 in a Src-kinase dependent manner. This transactivation was mediated through PAR-1, because a PAR-1 specific agonistic peptide also transactivated EphA2. Expression knockdown of endogenous EphA2 by siRNAs blocked ICAM-1 upregulation and leukocyte/endothelium attachment induced by thrombin. Overexpression of exogenous mouse EphA2 rescued both ICAM-1 expression and leukocyte attachment induced by thrombin in endogenous EphA2-knockdown HUVECs. Mechanistically, we showed EphA2 knockdown suppressed thrombin-induced serine 536 phosphorylation of NFkappaB, an event critical of ICAM-1 transcriptional upregulation. Collectively, our results strongly suggest EphA2 is a necessary component for thrombin-induced ICAM-1 upregulation.

A novel mechanism of erythrocyte capture from circulation in humans

OBJECTIVE

The capture of blood cells from the circulation is mediated by highly specialized adhesion molecules. These molecules contribute to the specificity of recruitment for various subsets. Here, we used a simple substrate of hyaluronic acid to investigate the specificity of CD44-mediated recruitment from human whole blood under shear conditions.

MATERIALS AND METHODS

Human whole blood was perfused through a parallel-plate flow chamber, which mimics intravascular conditions. Microscopy was used to directly observe blood-cell interactions with adhesion molecule substrates.

RESULTS

Erythrocytes, but not leukocytes, efficiently tethered to and rolled on the hyaluronic acid substrate. These interactions were demonstrated to be mediated by CD44 and regulated by the sialic acid content of the cells. Inflammatory stimuli did not result in enhanced erythrocyte rolling. Rather, interactions were restricted to aged erythrocytes approaching senescence. This mechanism of erythrocyte capture from the blood flow was found to be restricted to primates and not conserved across mammalian species.

CONCLUSION

This is the first report of erythrocyte tethering and rolling under shear conditions, a behavior, until now, thought to be exclusive to leukocytes. It may represent an important mechanism to identify, capture, and clear old erythrocytes during normal homeostasis or clot formation.

ROS generation in endothelial hypoxia and reoxygenation stimulates MAP kinase signaling and kinase-dependent neutrophil recruitment

Reactive oxygen species (ROS)-induced injury has been shown to occur during the reperfusion phase of ischemia-reperfusion and ROS are known to induce signaling events. We hypothesized that oxygen sensing in endothelial cells is also dependent on internal redox changes during hypoxia and that endothelial cells respond to changing oxygen environments via signaling, switching to an inflammatory phenotype. Endothelial cells exposed to relative hypoxia or the mitochondrial inhibitors rotenone, antimycin A, or FCCP show loss of mitochondrial membrane potential. During hypoxia, an increase in cytoplasmic ROS and glutathione S-transferase activity occurred, suggesting changes in intracellular redox state, mimicked with rotenone or FCCP but inhibited by antimycin A. Phosphorylation of stress-responsive mitogen-activated protein kinases occurred in hypoxia and was rapid and prolonged. Phosphorylation was inhibited by vitamin C, N-acetyl cysteine, or antimycin A. Chelation of intracellular calcium inhibits phosphorylation but the mitochondrial transition pore inhibitor cyclosporin A had no effect. Reoxygenation caused a further round of signaling, which was rapid but transient. Functionally, adhesion of neutrophils after hypoxia-reoxygenation under flow is ROS, P-selectin, and MAPK dependent. Therefore, changes in cellular signaling and phenotype are abrogated by ROS scavengers and suggest their use as therapeutic agents in ischemia-reperfusion.

PAR1-mediated NFkappaB activation promotes survival of prostate cancer cells through a Bcl-xL-dependent mechanism

We have previously reported that protease-activated receptor 1 (PAR1 or thrombin receptor) is over-expressed in metastatic prostate cancer cell lines compared to prostate epithelial cells. In this study, we examined 1,074 prostate biopsies by tissue microarray analysis and demonstrated that PAR1 expression is significantly increased in prostate cancer compared to normal prostate epithelial cells and benign prostatic hyperplasia. We hypothesized that PAR1 activation contributed to prostate cancer cell progression. We demonstrated that stimulation of PAR1 by thrombin or thrombin receptor activating peptide (TRAP6), in androgen-independent DU145 and PC-3 cells resulted in increased DNA binding activity of the NFkappaB p65 subunit. IL-6 and IL-8 levels were also elevated in conditioned media by at least two-fold within 4-6 h of PAR1 activation. This induction of cytokine production was abrogated by pretreatment of cells with the NFkappaB inhibitor caffeic acid phorbol ester. The p38 and ERK1/2 MAPK signaling cascades were also activated by PAR1 stimulation, whereas the SAPK/JNK pathway was unaffected. Inhibition of p38 and ERK1/2 by SB-203589 and PD-098059, respectively, did not abrogate NFkappaB activity, suggesting an independent induction of NFkappaB by PAR1 stimulation. Furthermore, TUNEL assay showed that activation of PAR1 attenuated docetaxel induced apoptosis through the upregulation of the Bcl-2 family protein Bcl-xL. Akt activation was not observed, suggesting that drug resistance induced by PAR1 was independent of PI3K signaling pathway. Because thrombin and PAR1 are over-expressed in prostate cancer patients, targeting the inhibition of their interaction may attenuate NFkappaB signaling transduction resulting in decreased drug resistance and subsequent survival of prostate cancer cells.

Minocycline confers early but transient protection in the immature brain following focal cerebral ischemia-reperfusion

The incidence of neonatal stroke is high and currently there are no strategies to protect the neonatal brain from stroke or reduce the sequelae. Agents capable of modifying inflammatory processes hold promise. We set out to determine whether delayed administration of one such agent, minocycline, protects the immature brain in a model of transient middle cerebral artery (MCA) occlusion in 7-day-old rat pups. Injury volume in minocycline (45 mg/kg/dose, beginning at 2 h after MCA occlusion) and vehicle-treated pups was determined 24 h and 7 days after onset of reperfusion. Accumulation of activated microglia/macrophages, phosphorylation of mitogen-activated protein kinase (MAPK) p38 in the brain, and concentrations of inflammatory mediators in plasma and brain were determined at 24 h. Minocycline significantly reduced the volume of injury at 24 h but not 7 days after transient MCA occlusion. The beneficial effect of minocycline acutely after reperfusion was not associated with changed ED1 phenotype, nor was the pattern of MAPK p38 phosphorylation altered. Minocycline reduced accumulation of IL-1beta and CINC-1 in the systemic circulation but failed to affect the increased levels of IL-1beta, IL-18, MCP-1 or CINC-1 in the injured brain tissue. Therefore, minocycline provides early but transient protection, which is largely independent of microglial activation or activation of the MAPK p38 pathway.

Tissue factor mediates inflammation

The role of tissue factor (TF) in inflammation is mediated by blood coagulation. TF initiates the extrinsic blood coagulation that proceeds as an extracellular signaling cascade by a series of active serine proteases: FVIIa, FXa, and thrombin (FIIa) for fibrin clot production in the presence of phospholipids and Ca2+. TF upregulation resulting from its enhanced exposure to clotting factor FVII/FVIIa often manifests not only hypercoagulable but also inflammatory state. Coagulant mediators (FVIIa, FXa, and FIIa) are proinflammatory, which are largely transmitted by protease-activated receptors (PAR) to elicit inflammation including the expression of tissue necrosis factor, interleukins, adhesion molecules (MCP-1, ICAM-1, VCAM-1, selectins, etc.), and growth factors (VEGF, PDGF, bFGF, etc.). In addition, fibrin, and its fragments are also able to promote inflammation. In the event of TF hypercoagulability accompanied by the elevations in clotting signals including fibrin overproduction, the inflammatory consequence could be enormous. Antagonism to coagulation-dependent inflammation includes (1) TF downregulation, (2) anti-coagulation, and (3) PAR blockade. TF downregulation and anti-coagulation prevent and limit the proceeding of coagulation cascade in the generation of proinflammatory coagulant signals, while PAR antagonists block the transmission of such signals. These approaches are of significance in interrupting the coagulation-inflammation cycle in contribution to not only anti-inflammation but also anti-thrombosis for cardioprotection.

Inhibition of mammalian target of rapamycin potentiates thrombin-induced intercellular adhesion molecule-1 expression by accelerating and stabilizing NF-kappa B activation in endothelial cells

We addressed the regulatory function of mammalian target of rapamycin (mTOR) in the mechanism of thrombin-induced ICAM-1 gene expression in endothelial cells. Pretreatment of HUVECs with rapamycin, an inhibitor of mTOR, augmented thrombin-induced ICAM-1 expression. Inhibition of mTOR by this approach promoted whereas over-expression of mTOR inhibited thrombin-induced transcriptional activity of NF-kappaB, an essential regulator of ICAM-1 transcription. Analysis of the NF-kappaB signaling pathway revealed that inhibition of mTOR potentiated IkappaB kinase activation resulting in a rapid and persistent phosphorylation of IkappaBalpha on Ser32 and Ser36, a requirement for IkappaBalpha degradation. Consistent with these data, we observed a more efficient and stable nuclear localization of RelA/p65 and, subsequently, the DNA binding activity of NF-kappaB by thrombin following mTOR inhibition. These data define a novel role of mTOR in down-regulating thrombin-induced ICAM-1 expression in endothelial cells by controlling a delayed and transient activation of NF-kappaB.

HIV-1 Tat protein-induced VCAM-1 expression in human pulmonary artery endothelial cells and its signaling

Expression of cell adhesion molecule in endothelial cells upon activation by human immunodeficiency virus (HIV) infection is associated with the development of atherosclerotic vasculopathy. We postulated that induction of vascular cell adhesion molecule-1 (VCAM-1) by HIV-1 Tat protein in endothelial cells might represent an early event that could culminate in inflammatory cell recruitment and vascular injury. We determined the role of HIV-1 Tat protein in VCAM-1 expression in human pulmonary artery endothelial cells (HPAEC). HIV-1 Tat protein treatment significantly increased cell-surface expression of VCAM-1 in HPAEC. Consistently, mRNA expression of VCAM-1 was also increased by HIV-1 Tat protein as measured by RT-PCR. HIV-1 Tat protein-induced VCAM-1 expression was abolished by the NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC) and the p38 MAPK inhibitor SB-203580. Furthermore, HIV-1 Tat protein enhanced DNA binding activity of NF-kappaB, facilitated nuclear translocation of NF-kappaB subunit p65, and increased production of reactive oxygen species (ROS). Similarly to VCAM-1 expression, HIV-1 Tat protein-induced NF-kappaB activation and ROS generation were abrogated by PDTC and SB-203580. These data indicate that HIV-1 Tat protein is able to induce VCAM-1 expression in HPAEC, which may represent a pivotal early molecular event in HIV-induced vascular/pulmonary injury. These data also suggest that the molecular mechanism underlying the HIV-1 Tat protein-induced VCAM-1 expression may involve ROS generation, p38 MAPK activation, and NF-kappaB translocation, which are the characteristics of pulmonary endothelial cell activation.

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.

Concentration-dependent differential effects of quercetin on rat aortic smooth muscle cells

Quercetin is one of the most ubiquitous bioflavonoids in foods of plant origin. Although quercetin is generally considered to provide protection against oxidative injury and inflammation, recent studies have demonstrated that its cytoprotective effects occur within a narrow concentration range. We attempted to examine the concentration-dependent effect on proliferation and inflammation in the primary culture of rat aortic smooth muscle cells. We demonstrate that quercetin inhibited [3H]thymidine incorporation into rat aortic smooth muscle cells only at concentrations < or =50 microM in a concentration-dependent manner. Nevertheless, quercetin, at concentrations > or =100 microM, reduced cell viability; this was further characterized as being due to apoptosis, which occurred through the proteolytic activation of pro-caspase-3. Additionally, the phosphorylation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38MAPK) substantially increased in rat aortic smooth muscle cells exposed to 100 microM quercetin, results which differ from observations by others and ourselves of cells exposed to < or =50 microM quercetin. Unlike P-JNK and P-p38, the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/ERK2) was not significantly affected by the concentration-dependent effects of quercetin. Surprisingly, the adverse effects of higher concentrations of quercetin could be ameliorated by adding the antioxidants, catalase, and N-acetylcysteine (NAC). Furthermore, the electrophoretic mobility shift assay (EMSA) showed that rat aortic smooth muscle cells exposed to quercetin at concentrations of < or =50 microM caused concentration-dependent inhibition of nuclear factor kappa B (NF-kappaB) activity, whereas concentrations of > or =100 microM resulted in increased NF-kappaB binding activity. We demonstrate for the first time that quercetin at low concentrations has antiproliferative and antiinflammatory effects, but at concentrations of > or =100 microM, is likely to induce the opposite effects on rat aortic smooth muscle cells.

Role of CL-100, a dual specificity phosphatase, in thrombin-induced endothelial cell activation

Using a cDNA microarray screening approach, we have identified seven novel thrombin-responsive genes in human umbilical vein endothelial cells that were verifiable by Northern blot analysis. Among them CL-100, a dual-specificity phosphatase also known as MAP kinase phosphatase-1 (MKP-1), showed greatest induction by thrombin. Steady-state levels of CL-100 mRNA induction by thrombin peaked at 1 h and declined rapidly (t1/2 approximately 45 min). Induction by thrombin was protease-activated receptor-1-mediated, protein synthesis-independent, and transcriptionally regulated. Metabolic labeling followed by immunoprecipitation verified that the thrombin-induced CL-100 mRNA was translated into protein. We found that both Src-kinase and p42/p44 ERK activity are critical for thrombin-induced CL-100 expression, whereas phosphatidylinositol 3-kinase and protein kinase C activity were not required. Antisense-mediated inhibition of CL-100 was shown to prolong thrombin-induced ERK activity in endothelial cells, concomitant with an inhibition in thrombin-induced PDGF-A (platelet-derived growth factor A) and PDGF-B gene expression and an up-regulation in thrombin-induced VCAM-1 and E-selectin gene expression. Inhibition of ERK activation by PD98059 in endothelial cells was shown to potentiate thrombin-induced expression of PDGF-B (approximately 3-fold) while inhibiting thrombin-induced VCAM-1 and E-selectin gene expression by 60 and 70%, respectively. These results suggested that induced expression of the CL-100 phosphatase and its subsequent regulation of ERK activity play a key regulatory role in the thrombin signaling pathway and in the transcriptional regulation of pathologically important "endothelial cell activation genes."

Endothelium as an organ system

The endothelium is a highly dynamic cell layer that is involved in a multitude of physiologic functions, including the control of vasomotor tone, the trafficking of cells and nutrients, the maintenance of blood fluidity, and the growth of new blood vessels. Over the past several decades, advances in basic research of the endothelium have far outstripped those in the clinic. One explanation for this growing bench-to-bedside chasm relates to the inflexible and largely outdated nature of the present-day medical infrastructure. The constraints of medical subspecialization have created a conceptual blind spot, namely, the inability to appreciate the endothelium for what it is: a cell layer that is teeming with life, every bit as active as any other organ in the body. The overall goal of this review is to bring the endothelium "to life" and to argue that future breakthroughs in biomedicine are contingent on acceptance of the endothelium as a bona fide organ system.

Thrombin and phenotypic modulation of the endothelium

Thrombin signaling in the endothelium is linked to multiple phenotypic changes, including alterations in permeability, vasomotor tone, and leukocyte trafficking. The thrombin signal is transduced, at least in part, at the level of gene transcription. In this review, we focus on the role of thrombin signaling and transcriptional networks in mediating downstream gene expression and endothelial phenotype. In addition, we report the results of DNA microarrays in control and thrombin-treated endothelial cells. We conclude that (1) thrombin induces the upregulation and downregulation of multiple genes in the endothelium, (2) thrombin-mediated gene expression involves a multitude of transcription factors, and (3) future breakthroughs in the field will depend on a better understanding of the spatial and temporal dynamics of these transcriptional networks.

Signal-dependent distribution of cell surface P-selectin in clathrin-coated pits affects leukocyte rolling under flow

Flowing leukocytes roll on P-selectin that is mobilized from secretory granules to the surfaces of endothelial cells after stimulation with histamine or thrombin. Before it is internalized, P-selectin clusters in clathrin-coated pits, which enhances its ability to support leukocyte rolling. We found that thrombin and histamine induced comparable exocytosis of P-selectin on endothelial cells. However, compared with histamine, thrombin decreased the recruitment of P-selectin into clathrin-coated pits, slowed the internalization of P-selectin, and reduced the number and stability of neutrophils rolling on P-selectin. Significantly more RhoA was activated in thrombin- than in histamine-stimulated endothelial cells. Inhibitors of RhoA or its effector, Rho kinase, reversed thrombin's ability to inhibit the internalization and adhesive function of P-selectin in endothelial cells. Experiments with transfected cells confirmed that the inhibitory actions of thrombin and Rho kinase on P-selectin required its cytoplasmic domain. Thus, a signaling event affects both the function and clearance of a protein that enters the constitutive clathrin-mediated endocytic pathway.