Alterations in subcellular localization of p38 MAPK potentiates endothelin-stimulated COX-2 expression in glomerular mesangial cells

Sphingosine 1-Phosphate Induces Cyclooxygenase-2/Prostaglandin E2 Expression via PKCα-dependent Mitogen-Activated Protein Kinases and NF-κB Cascade in Human Cardiac Fibroblasts

In the regions of tissue injuries and inflammatory diseases, sphingosine 1-phosphate (S1P), a proinflammatory mediator, is increased. S1P may induce the upregulation of cyclooxygenase-2 (COX-2)/prostaglandin E₂ (PGE₂) system in various types of cells to exacerbate heart inflammation. However, the detailed molecular mechanisms by which S1P induces COX-2 expression in human cardiac fibroblasts (HCFs) remain unknown. HCFs were incubated with S1P and analyzed by Western blotting, real time-Polymerase chain reaction (RT-PCR), and immunofluorescent staining. Our results indicated that S1P activated S1PR_1/3-dependent transcriptional activity to induce COX-2 expression and PGE₂ production. S1P recruited and activated PTX-sensitive G_i or -insensitive G_q protein-coupled S1PR and then stimulated PKCα-dependent phosphorylation of p42/p44 MAPK, p38 MAPK, and JNK1/2, leading to activating transcription factor NF-κB. Moreover, S1P-activated NF-κB was translocated into the nucleus and bound to its corresponding binding sites on COX-2 promoters determined by chromatin immunoprecipitation (ChIP) and promoter-reporter assays, thereby turning on COX-2 gene transcription associated with PGE₂ production in HCFs. These results concluded that in HCFs, activation of NF-κB by PKCα-mediated MAPK cascades was essential for S1P-induced up-regulation of the COX-2/PGE₂ system. Understanding the mechanisms of COX-2 expression and PGE₂ production regulated by the S1P/S1PRs system on cardiac fibroblasts may provide rationally therapeutic interventions for heart injury or inflammatory diseases.

Cytoprotective effects of endothelin-1 on mesenchymal stem cells: an in vitro study

Stem cell-based therapies is a promising approach for regenerative therapy in various diseases. Some obstacles remain to be solved before clinical application of the cell therapy is realized, including increasing the survival of transplanted stem cells, reducing loss of transplanted cells, and maintaining adequate vascular supply. Recently, stem cell preconditioning with chemical and pharmacological agents has been shown to increase therapeutic efficacy. The present study investigated the effect of endothelin-1 (ET-1) on survival, angiogenesis, and migration of mesenchymal stem cells (MSCs), in vitro. MSCs were treated with various concentrations of ET-1 and the expression of cyclooxygenase-2 (COX-2), hypoxia-inducible factor-1 (HIF-1), C-X-C chemokine receptor type 4 (CXCR4), C-C chemokine receptor type 2 (CCR2), vascular endothelial growth factor (VEGF), angiopoietin-2 (Ang-2), angiopoietin-4 (Ang-4) and matrix metalloproteinase-2 (MMP-2) were examined. Caspase 3 activity and prostaglandin E2 (PGE2) were determined by ELISA assay. MSCs migration and tube formation potential were assessed using scratch test and three dimensional vessel formation assay. ET-1 enhanced the MSCs viability. In ET-1- treated MSCs, expression of COX-2, HIF-1, CXCR4, CCR2, VEGF, Ang-2, Ang-4 and MMP-2 were increased compared to control groups. Elevation of all these genes were reversed by celecoxib (50 μmol/L), a selective COX-2 inhibitor. PGE2 generation, MSCs migration and tube formation were enhanced by ET-1 conditioning, whereas caspase-3 activity was reduced in these cells, compared to the control group. The results presented here reveal that preconditioning of MSCs with ET-1 has strong cytoprotective effects through activation of survival signalling molecules and trophic factors.

The p38 pathway, a major pleiotropic cascade that transduces stress and metastatic signals in endothelial cells

By gating the traffic of molecules and cells across the vessel wall, endothelial cells play a central role in regulating cardiovascular functions and systemic homeostasis and in modulating pathophysiological processes such as inflammation and immunity. Accordingly, the loss of endothelial cell integrity is associated with pathological disorders that include atherosclerosis and cancer. The p38 mitogen-activated protein kinase (MAPK) cascades are major signaling pathways that regulate several functions of endothelial cells in response to exogenous and endogenous stimuli including growth factors, stress and cytokines. The p38 MAPK family contains four isoforms p38α, p38β, p38γ and p38δ that are encoded by four different genes. They are all widely expressed although to different levels in almost all human tissues. p38α/MAPK14, that is ubiquitously expressed is the prototype member of the family and is referred here as p38. It regulates the production of inflammatory mediators, and controls cell proliferation, differentiation, migration and survival. Its activation in endothelial cells leads to actin remodeling, angiogenesis, DNA damage response and thereby has major impact on cardiovascular homeostasis, and on cancer progression. In this manuscript, we review the biology of p38 in regulating endothelial functions especially in response to oxidative stress and during the metastatic process.

Upregulation of COX-2/PGE2 by ET-1 mediated through Ca2+-dependent signals in mouse brain microvascular endothelial cells

Endothelin-1 (ET-1), a proinflammatory mediator, is elevated in the regions of several brain inflammatory disorders, implying that ET-1 may contribute to inflammatory responses. The deleterious effects of ET-1 on brain endothelial cells may aggravate brain inflammation mediated through the upregulation of cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) system. However, the signaling mechanisms underlying ET-1-induced COX-2 expression in mouse brain microvascular endothelial cells (bEnd.3 cells) remain unclear. Herein, we investigated the effects of Ca2+-dependent protein kinases on ET-1-induced COX-2 expression and PGE2 release in bEnd.3 cells. The data obtained with Western blotting, reverse transcription PCR, and intracellular Ca2+ analyses showed that ET-1-induced COX-2 expression was mediated through phosphatidylinositol-phospholipase C (PI-PLC) and phosphatidylcholine-phospholipase C (PC-PLC)/Ca2+-dependent activation of protein kinase C-alpha (PKC-α) and calmodulin kinase II (CaMKII) cascades. Next, we demonstrated that ET-1 stimulated intracellular Ca2+ increase, phoshorylation of PKC-α, CaMKII, and mitogen-activated protein kinases (MAPKs) (ERK1/2, p38 MAPK, and JNK1/2) and then activated the activating transcription factor 2 (ATF2)/activator protein 1 (AP-1) via Gq/i protein-coupled ETB receptors. Moreover, the data of chromatin immunoprecipitation and promoter reporter assay demonstrated that the activated ATF2/AP-1 and p300 bound to its corresponding binding sites within COX-2 promoter, thereby turning on COX-2 gene transcription. Finally, upregulation of COX-2 by ET-1 promoted PGE2 biosynthesis and release in these cells. Taken together, these results demonstrate that in bEnd.3 cells, Ca2+-dependent PKC-α and CaMKII linking to MAPKs, ATF2/AP-1, and p300 cascade is essential for ET-1-induced COX-2 upregulation. Understanding the mechanisms of COX-2/PGE2 system upregulated by ET-1 on brain microvascular endothelial cells may provide rational therapeutic interventions for brain injury and inflammatory diseases.

Mitogen-activated protein kinase phosphatase (MKP)-1 as a neuroprotective agent: promotion of the morphological development of midbrain dopaminergic neurons

A greater understanding of the mechanisms that promote the survival and growth of dopaminergic neurons is essential for the advancement of cell replacement therapies for Parkinson's disease (PD). Evidence supports a role for the mitogen-activated protein kinase p38 in the demise of dopaminergic neurons, while mitogen-activated protein kinase phosphatase-1 (MKP-1), which negatively regulates p38 activity, has not yet been investigated in this context. Here, we show that MKP-1 is expressed in dopaminergic neurons cultured from E14 rat ventral mesencephalon (VM). When dopaminergic neurons were transfected to overexpress MKP-1, they displayed a more complex morphology than their control counterparts in vitro. Specifically, MKP-1-transfection induced significant increases in neurite length and branching with a maximum increase observed in primary branches. We demonstrate that inhibition of dopaminergic neurite growth induced by treatment of rat VM neurons with the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) in vitro is mediated by p38 and is concomitant with a significant and selective decrease in MKP-1 expression in these neurons. We further show that overexpression of MKP-1 in dopaminergic neurons contributes to neuroprotection against the effects of 6-OHDA. Collectively, we report that MKP-1 can promote the growth and elaboration of dopaminergic neuronal processes and can help protect them from the neurotoxic effects of 6-OHDA. Thus, we propose that strategies aimed at augmenting MKP-1 expression or activity may be beneficial in protecting dopaminergic neurons and may provide potential therapeutic approaches for PD.

Up-regulation of COX-2/PGE2 by endothelin-1 via MAPK-dependent NF-κB pathway in mouse brain microvascular endothelial cells

Background

Endothelin-1 (ET-1) is a proinflammatory mediator and elevated in the regions of several brain injury and inflammatory diseases. The deleterious effects of ET-1 on endothelial cells may aggravate brain inflammation mediated through the regulation of cyclooxygenase-2 (COX-2)/prostaglandin E₂ (PGE₂) system in various cell types. However, the signaling mechanisms underlying ET-1-induced COX-2 expression in brain microvascular endothelial cells remain unclear. Herein we investigated the effects of ET-1 in COX-2 regulation in mouse brain microvascular endothelial (bEnd.3) cells.

Results

The data obtained with Western blotting, RT-PCR, and immunofluorescent staining analyses showed that ET-1-induced COX-2 expression was mediated through an ET_B-dependent transcriptional activation. Engagement of G_i- and G_q-protein-coupled ET_B receptors by ET-1 led to phosphorylation of ERK1/2, p38 MAPK, and JNK1/2 and then activated transcription factor NF-κB. Moreover, the data of chromatin immunoprecipitation (ChIP) and promoter reporter assay demonstrated that the activated NF-κB was translocated into nucleus and bound to its corresponding binding sites in COX-2 promoter, thereby turning on COX-2 gene transcription. Finally, up-regulation of COX-2 by ET-1 promoted PGE₂ release in these cells.

Conclusions

These results suggested that in mouse bEnd.3 cells, activation of NF-κB by ET_B-dependent MAPK cascades is essential for ET-1-induced up-regulation of COX-2/PGE₂ system. Understanding the mechanisms of COX-2 expression and PGE₂ release regulated by ET-1/ET_B system on brain microvascular endothelial cells may provide rationally therapeutic interventions for brain injury or inflammatory diseases.

Anti-inflammatory effects of mapracorat, a novel selective glucocorticoid receptor agonist, is partially mediated by MAP kinase phosphatase-1 (MKP-1)

Mapracorat is a novel selective glucocorticoid receptor agonist (SEGRA), structurally distinct from corticosteroids. In preclinical studies, mapracorat potently inhibits the production of a variety of inflammatory mediators including cytokines and prostaglandin E2 (PGE(2)), with limited side effects associated with traditional corticosteroids. The objective of this study was to delineate the mechanisms underlying the anti-inflammatory properties of mapracorat. We found that mapracorat potently inhibited the production of GM-CSF and TNF-α in LPS-stimulated Raw 264.7 macrophages. Mapracorat also substantially attenuated the expression of COX-2 and the production of PGE(2). The inhibition of mapracorat on the inflammatory response was dose-dependent, and substantially inhibitory effects were observed at concentrations in the 10-100 nm range. Examination of the activation kinetics of p38 and its downstream target MAPK-activated protein kinase-2 (MK-2) revealed a shortened activation course after LPS stimulation in cells pretreated with mapracorat. Supporting the notion that mapracorat augments a feedback control mechanism restraining the p38 pathway, we found that mapracorat enhanced the expression of MAPK phosphatase-1 (MKP-1), a critical negative regulator of MAPKs that drive the production of cytokines and other inflammatory mediators. While mapracorat alone did not stimulate MKP-1 expression, it markedly enhanced the expression of MKP-1 in cells stimulated by LPS, in a similar manner and potency to the augmenting effect of dexamethasone. Blocking MKP-1 expression by triptolide also abolished the accelerating effects of mapracorat on p38 and MK-2 deactivation, further supporting a role of MKP-1 in the anti-inflammatory mechanism of mapracorat. Taken together, these results indicate that mapracorat exerts its anti-inflammatory effects, at least in part, by augmenting MKP-1 expression.

c-Src-dependent EGF receptor transactivation contributes to ET-1-induced COX-2 expression in brain microvascular endothelial cells

Background

Endothelin-1 (ET-1) is elevated and participates in the regulation of several brain inflammatory disorders. The deleterious effects of ET-1 on endothelial cells may aggravate brain inflammation mediated through the upregulation of cyclooxygenase-2 (COX-2) gene expression. However, the signaling mechanisms underlying ET-1-induced COX-2 expression in brain microvascular endothelial cells remain unclear.

Objective

The goal of this study was to examine whether ET-1-induced COX-2 expression and prostaglandin E₂ (PGE₂) release were mediated through a c-Src-dependent transactivation of epidermal growth factor receptor (EGFR) pathway in brain microvascular endothelial cells (bEnd.3 cells).

Methods

The expression of COX-2 induced by ET-1 was evaluated by Western blotting and RT-PCR analysis. The COX-2 regulatory signaling pathways were investigated by pretreatment with pharmacological inhibitors, short hairpin RNA (shRNA) or small interfering RNA (siRNA) transfection, chromatin immunoprecipitation (ChIP), and promoter activity reporter assays. Finally, we determined the PGE₂ level as a marker of functional activity of COX-2 expression.

Results

First, the data showed that ET-1-induced COX-2 expression was mediated through a c-Src-dependent transactivation of EGFR/PI3K/Akt cascade. Next, we demonstrated that ET-1 stimulated activation (phosphorylation) of c-Src/EGFR/Akt/MAPKs (ERK1/2, p38 MAPK, and JNK1/2) and then activated the c-Jun/activator protein 1 (AP-1) via G_q/i protein-coupled ET_B receptors. The activated c-Jun/AP-1 bound to its corresponding binding sites within COX-2 promoter, thereby turning on COX-2 gene transcription. Ultimately, upregulation of COX-2 by ET-1 promoted PGE₂ biosynthesis and release in bEnd.3 cells.

Conclusions

These results demonstrate that in bEnd.3 cells, c-Src-dependent transactivation of EGFR/PI3K/Akt and MAPKs linking to c-Jun/AP-1 cascade is essential for ET-1-induced COX-2 upregulation. Understanding the mechanisms of COX-2 expression and PGE₂ release regulated by ET-1/ET_B system on brain microvascular endothelial cells may provide rational therapeutic interventions for brain injury and inflammatory diseases.

Simvastatin prevents ERK activation in myocardial hypertrophy of spontaneously hypertensive rats

BACKGROUND

Statins exert regression of left ventricular hypertrophy independent of their plasma cholesterol-lowering actions. However, the underlying mechanism is not clear.

METHODS

We tested the hypothesis that the extracellular signal-regulated kinases (ERKs) signaling pathway could be a target of simvastatin (SIM) and involved in SIM-induced LVH regression in spontaneously hypertensive rats (SHR). Fourteen 14-week old-SHR males were randomly divided into a SHR SIM group (n = 7) or a SHR control group (n = 7). The SHR SIM group was given SIM 40 mg/kg · d via injection ig, while the SHR control group was routinely given only vehicle (0.5% carboxymethyl cellulose ig). Seven Wistar Kyoto rats served as normal controls.

RESULTS

Ten weeks of treatment with SIM in SHR had no influence on blood pressure. The ratio of left ventricle weight to body weight in the SHR SIM group was decreased significantly compared to that in the SHR control group (p < 0.05). Among the three groups there was no significant difference in total ERK expression (p > 0.05). SIM treatment caused a significant reduction in the expression of phosphorylated-ERK, the kinase activity of ERK, the levels of mitogen-activated protein kinase phosphatase-1 protein and its mRNA (p <0.01 for all).

CONCLUSIONS

The Hydroxymethylglutaryl coenzyme A reductase inhibitor SIM prevents the activation of ERK in SHR to mediate regression of myocardial hypertrophy in SHR.

Mechanisms regulating the nuclear translocation of p38 MAP kinase

p38 mitogen-activated protein kinase (MAPK) is of fundamental importance in a cell's response to environmental stresses, cytokines and DNA damage. p38 resides in the cytoplasm of resting cells, and translocates into the nucleus upon activation, yet the exact mechanisms remain largely unclear. We show here that the phosphorylation-dependent nuclear translocation of p38 is a common phenomenon when cells are stimulated with various stresses. On the other hand, the nuclear export of p38 requires its dephosphorylation, and it is exported both in a MK2-dependent and a nuclear export signal (NES)-independent manner. Although different p38-regulated/activated protein kinase (PRAK) mutants all dictate the intracellular localization of p38, results from a PRAK-deficient cell line indicate that it plays no role in this process. Microtubule depolymerizing reagent nocodazole and dynein inhibitor EHNA both block the nuclear translocation of p38, demonstrating roles for microtubules and dynein in p38 transport. Taken together, stress-induced nuclear accumulation of p38 is a phosphorylation-dependent, microtubule- and dynein-associated process.

Dysregulation of p38 and MKP-1 in response to NOD1/TLR4 stimulation in sarcoid bronchoalveolar cells

RATIONALE

Sarcoidosis is a systemic inflammatory disorder characterized by distinct up-regulation of Th1 cytokines, such as tumor necrosis factor (TNF)-α and IL-12. The mechanism underlying this up-regulation remains unclear. Recognition of microbial moieties through Toll-like or Nod-like receptors evokes sequential activation of mitogen-activated protein kinases (MAPKs), which plays a role in Th1-immune response.

OBJECTIVES

To test the hypothesis that dysregulation in MAPK signaling in response to microbial stimulation is important in mediating Th1 response in sarcoidosis.

METHODS

Ex vivo cultured bronchoalveolar lavage (BAL) cells isolated from patients with sarcoidosis and control subjects were stimulated with low-dose Toll-like receptor 4 (TLR4) and nucleotide-binding oligomerization domain 1 (NOD1) ligands as a model of microbial stimulation, and MAPK signaling and inflammatory response were analyzed.

MEASUREMENTS AND MAIN RESULTS

BAL cells from patients with sarcoidosis exhibited higher basal p38 activity, greater p38 phosphorylation, and more robust production of TNF-α and IL-12/IL-23p40 on stimulation with NOD1 and TLR4 agonists than cells isolated from control subjects. In contrast, control BAL cells had greater basal extracellular signal-regulated kinase (ERK) activity and NOD1 and TLR4 agonists preferentially activated the ERK pathway. Inhibition of p38, but not ERK, attenuated production of both IL12/IL23p40 and TNF-α. Interestingly, stimulation of cells from patients with sarcoidosis with either NOD1 or TLR4 ligand failed to induce MAPK phosphatase 1 (MKP-1). Adenovirus-mediated overexpression of MKP-1 attenuated p38 activation and decreased the production of IL12/IL23p40 and TNF-α in sarcoid BAL cells.

CONCLUSIONS

Our results suggest that enhanced p38 signaling in response to microbial products is caused by abnormal regulation of MKP-1 and contributes to heightened inflammation in sarcoidosis.

p38gamma mitogen-activated protein kinase suppresses chondrocyte production of MMP-13 in response to catabolic stimulation

OBJECTIVE

The signaling protein p38 mitogen-activated protein kinase is required for inflammatory signaling in chondrocytes that regulates matrix metalloproteinase (MMP) production. We sought to determine the role of specific p38 isoforms in chondrocyte catabolic signaling in response to IL-1beta and fibronectin fragments (Fn-f).

METHODS

Human articular chondrocytes isolated from normal ankle cartilage from tissue donors or from osteoarthritic knee cartilage obtained during knee replacement were stimulated with IL-1beta or Fn-f, with or without pretreatment with p38 inhibitors (SB203580 or BIRB796) or growth factors (IGF-1 and OP-1). p38 isoform phosphorylation was measured by antibody array and immunoblotting. MMP-13 expression was measured by real-time polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), and immunoblotting. Chondrocytes were transfected with plasmids expressing constitutively active (CA) p38gamma or with adenovirus expressing dominant negative (DN) p38gamma.

RESULTS

Stimulation of chondrocytes with either IL-1beta or Fn-f led to enhanced phosphorylation of p38alpha and p38gamma, with little phosphorylation of p38beta or p38delta isoforms. p38alpha localized to the nucleus and p38gamma to the cytosol. Inhibition of both p38alpha and p38gamma with BIRB796 resulted in less inhibition of MMP-13 production in response to IL-1beta or FN-f than did inhibition of only p38alpha with SB203580. Transfection with CA p38gamma resulted in decreased MMP-13 production while transduction with DN p38gamma resulted in increased MMP-13 production. IGF-1 and OP-1 pretreatment inhibited p38alpha phosphorylation but not p38gamma phosphorylation.

CONCLUSIONS

p38gamma is activated by catabolic stimulation of human articular chondrocytes, but interestingly suppresses MMP-13 production. Treatments that increase p38gamma activation may be of therapeutic benefit in reducing chondrocyte production of MMP-13.

Upregulation of fibronectin expression by COX-2 is mediated by interaction with ELMO1

Engulfment and cell motility 1 (ELMO1), a bipartite guanine nucleotide exchange factor (GEF) for the small GTPase Rac 1, was identified as a susceptibility gene for glomerular disease. Here, we reported that ELMO1 interacted with COX-2 in human mesangial cells. Furthermore, we identified ELMO1 as a posttranslational regulator of COX-2 activity. We demonstrated that COX-2 cyclooxygenase activity increased fibronectin promoter activity. The protein-protein interaction between ELMO1 and COX-2 increased the cyclooxygenase activity of COX-2 and, correspondingly, fibronectin expression. We also found that ET625, the dominant negative form of ELMO1 lacking Rac1 activity, interacted with COX-2, increased cyclooxygenase activity of COX-2 and enhanced COX-2-mediated fibronectin upregulation. To further rule out Rac1 as an ELMO1-mediated regulator of COX-2 activity, we employed the constitutive active Rac1, Rac1(Q63E), and demonstrated that Rac1 signaling has no effect on COX-2-mediated fibronectin promoter activity. These results suggest that ELMO1 contributes to the development of glomerular injury through serving as a regulator of COX-2 activity. The interaction of ELMO1 with COX-2 could play an important role in the development and progression of renal glomerular injury.

Effect of endothelin-1 on cyclooxygenase-2 expression in human hormone refractory prostate cancer cells

The present study aimed to explore the effects and possible mechanisms of recombinant human endothelin (ET)-1 on cyclooxygenase (COX)-2 expression in human hormone refractory prostate cancer PC3 cells. PC3 cells were treated with 100 nmol/l ET-1 for the indicated times (3, 6, 9, 12 and 24 h) and concentrations (0.1, 1, 10 and 100 nmol/l) for 24 h. Moreover, 100 nmol/l ET-1 was used to treat PC3 cells alone or in combination with endothelin A receptor (ET(A)R) antagonist BQ123 (1 μmol/l), endothelin B receptor (ET(B)R) antagonist BQ788 (1 μmol/l), MAPK/extracellular signal-regulated kinase kinase (MEK)-selective inhibitor, PD98059 (10 μmol/l), p38 mitogen-activated protein kinase (MAPK) antagonist SB203580 (5 μmol/l) or epidermal growth factor receptor (EGFR) antagonist AG1478 (0.1 μmol/l) for 24 h. COX-2 mRNA and protein expression was detected in the PC3 cells by reverse transcription-polymerase chain reaction and Western blot analysis. ET-1 induced a time- and dose-dependent increase in the mRNA and protein expression of COX-2 in the PC3 cells. BQ123, LY294002, SC203580 and AG1478 prevented the expression of COX-2 in the PC3 cells (P<0.05), while BQ788 did not. ET-1 induced the up-regulation of COX-2 in the PC3 cells. ET(A)R may be involved in the process. Several signaling pathways, including p42/44 MAPK, p38 MAPK and EGFR, are therefore implicated in the regulation of COX-2 expression.

Matrix metalloproteinase (MMP)-1 and MMP-3 induce macrophage MMP-9: evidence for the role of TNF-alpha and cyclooxygenase-2

Matrix metalloproteinase (MMP)-9 (gelatinase B) participates in a variety of diverse physiologic and pathologic processes. We recently characterized a cyclooxygenase-2 (COX-2)-->PGE(2)-->EP4 receptor axis that regulates macrophage MMP-9 expression. In the present studies, we determined whether MMPs, commonly found in inflamed and neoplastic tissues, regulate this prostanoid-EP receptor axis leading to enhanced MMP-9 expression. Results demonstrate that exposure of murine peritoneal macrophages and RAW264.7 macrophages to MMP-1 (collagenase-1) or MMP-3 (stromelysin-1) lead to a marked increase in COX-2 expression, PGE(2) secretion, and subsequent induction of MMP-9 expression. Proteinase-induced MMP-9 expression was blocked in macrophages preincubated with the selective COX-2 inhibitor celecoxib or transfected with COX-2 small interfering RNA (siRNA). Likewise, proteinase-induced MMP-9 was blocked in macrophages preincubated with the EP4 antagonist ONO-AE3-208 or transfected with EP4 siRNA. Exposure of macrophages to MMP-1 and MMP-3 triggered the rapid release of TNF-alpha, which was blocked by MMP inhibitors. Furthermore, both COX-2 and MMP-9 expression were inhibited in macrophages preincubated with anti-TNF-alpha IgG or transfected with TNF-alpha siRNA. Thus, proteinase-induced MMP-9 expression by macrophages is dependent on the release of TNF-alpha, induction of COX-2 expression, and PGE(2) engagement of EP4. The ability of MMP-1 and MMP-3 to regulate macrophage secretion of PGE(2) and expression of MMP-9 defines a nexus between MMPs and prostanoids that is likely to play a role in the pathogenesis of chronic inflammatory diseases and cancer. These data also suggest that this nexus is targetable utilizing anti-TNF-alpha therapies and/or selective EP4 antagonists.

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.

Pyk2 mediates endothelin-1 signaling via p130Cas/BCAR3 cascade and regulates human glomerular mesangial cell adhesion and spreading

Calcium-regulated non-receptor proline-rich tyrosine kinase 2 (Pyk2) is a critical mediator of endothelin-1 (ET-1) signaling in human glomerular mesangial cells (GMC). We aimed to identify which small G-protein is acting downstream of Pyk2. Dominant interfering Pyk2 construct, termed calcium regulated non kinase (CRNK) or green fluorescent protein (control) were expressed in GMC using adenovirus-mediated gene transfer. ET-1 stimulation resulted in a significant increase of Pyk2 phosphorylation accompanied by GTP-loading of Rap1 and RhoA. CRNK expression inhibited ET-1-induced autophosphorylation of endogenous Pyk2 and diminished Rap1, but not RhoA, activation. The mechanism linking Pyk2 and Rap1 included (1) increased autophosphorylation of Pyk2 associated with p130Cas, (2) augmented p130Cas Y165 and Y249 phosphorylation, and (3) enhanced p130Cas-BCAR3 complex formation. CRNK expression prevented p130Cas phosphorylation and attenuated p130Cas association with BCAR3. Downregulation of endogenous BCAR3 protein expression using an siRNA technique led to a significant decrease in Rap1 activation in response to ET-1. We observed that endogenous Pyk2 was important for GMC adhesion and spreading. Our data suggest that ET-1 stimulated the GTPase Rap1 (but neither RhoA nor Ras) by a mechanism involving Pyk2 activation and recruitment of the p130Cas/BCAR3 complex in GMC.

Antioxidant activity of growth hormone-releasing hormone antagonists in LNCaP human prostate cancer line

Hypothalamic growth hormone-releasing hormone (GHRH) controls the release of growth hormone and acts as a growth factor in various tumors. Potent antagonistic analogues of GHRH have been synthesized that strongly suppress the growth of diverse cancers through several mechanisms. However, the influence of GHRH antagonists on the redox (reduction/oxidation) status of cancers has not been investigated. Cellular generation of reactive oxygen species (ROS) is central to redox signaling and is implicated in the initiation, development, and progression of cancer. In this study, we evaluated by Western blot the effects in vitro of GHRH and its antagonist JMR-132 on proliferating cell nuclear antigen, tumor suppressor protein p53, transcription factor NF-kappaB p50 and its phosphorylated form, caspase 3, and cleaved caspase 3 in the LNCaP human prostate cancer cell line. GHRH stimulated and GHRH antagonist inhibited the expression of the major antioxidant enzymes, as well as the expression of COX 2 and cytochrome c oxidase IV, which are enzymes involved in the generation of ROS. GHRH augmented and GHRH antagonist suppressed lipid and protein oxidative stress markers, as well as the intracellular generation of ROS. In all these tests, GHRH antagonists exerted strong antioxidant activity. Because the metabolism of ROS and oxidative stress have been associated with initiation and progression of not only prostate tumors but also other malignancies, our findings reinforce previous experimental evidence that GHRH antagonists could be useful for cancer therapy.

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.

Role of JNK in network formation of human lung microvascular endothelial cells

The signaling mechanisms in vasculogenesis and/or angiogenesis remain poorly understood, limiting the ability to regulate growth of new blood vessels in vitro and in vivo. Cultured human lung microvascular endothelial cells align into tubular networks in the three-dimensional matrix, Matrigel. Overexpression of MAPK phosphatase-1 (MKP-1), an enzyme that inactivates the ERK, JNK, and p38 pathways, inhibited network formation of these cells. Adenoviral-mediated overexpression of recombinant MKP-3 (a dual specificity phosphatase that specifically inactivates the ERK pathway) and dominant negative or constitutively active MEK did not attenuate network formation in Matrigel compared with negative controls. This result suggested that the ERK pathway may not be essential for tube assembly, a conclusion which was supported by the action of specific MEK inhibitor PD 184352, which also did not alter network formation. Inhibition of the JNK pathway using SP-600125 or l-stereoisomer (l-JNKI-1) blocked network formation, whereas the p38 MAPK blocker SB-203580 slightly enhanced it. Inhibition of JNK also attenuated the number of small vessel branches in the developing chick chorioallantoic membrane. Our results demonstrate a specific role for the JNK pathway in network formation of human lung endothelial cells in vitro while confirming that it is essential for the formation of new vessels in vivo.

Reactive oxygen species mediate ET-1-induced activation of ERK1/2 signaling in cultured feline esophageal smooth muscle cells

Reactive oxygen species (ROS) have been shown to play a critical role in propagating the signals of several growth factors, peptide hormones, and cytokines, such as epidermal growth factor, insulin, and interleukin-1. We investigated a possible role for ROS generation in mediating the action of ET-1 on activation of ERK1/2 in cultured feline esophageal smooth muscle cells (ESMC). Confluent layers of ESMC were stimulated by 10nM ET-1; activation of ERK was examined by western blot analysis with phospho-specific antibodies of ERKs. ET-1 induced ERK1/2 phosphorylation in a dose- and time- dependent manner. ERK1/2 activation by ET-1 reached the maximal levels at 5min showing slight activation up to 20min, and then slowly declined. It was confirmed that the activation of ERK1/2 was reduced by MEK inhibitor PD98059. We observed the dose-dependent inhibitory effect of diphenyleneiodonium (DPI), an inhibitor of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase on the ET-1-enhanced ERK1/2 phosphorylation in ESMC. Pretreatment of ESMC with N-acetylcysteine, a ROS scavenger, also attenuated the ET-1-induced ERK1/2 activation. In addition, DPI significantly inhibited the ET-1- induced ROS production when ROS was measured as a function of DCF fluorescence. The results suggest that ROS might be critical mediators of the ET-1-induced ERK1/2 signaling events in ESMC.

Transforming Growth Factor-β1 Impairs Endothelin-1-Mediated Contraction of Brain Vessels by Inducing Mitogen-Activated Protein (MAP) Kinase Phosphatase-1 and Inhibiting p38 MAP Kinase

Brain levels of transforming growth factor-beta1 (TGF-beta1) are increased in Alzheimer's disease and have been implicated in the associated cerebrovascular pathology. We recently reported that transgenic mice that overexpress TGF-beta1 (TGF+ mice) display, with aging, selectively reduced endothelin-1 (ET-1)-mediated contractions. Because ET-1 is a key regulator of cerebrovascular tone and homeostasis, we investigated how increased levels of TGF-beta1 could selectively alter this contractile response. We found that ETA receptors, via activation of p38 mitogen-activated protein (MAP) kinase, mediate the ET-1-induced contraction in mouse cerebral arteries, a response significantly decreased in aged TGF+ mice (-39%; p < 0.01) despite unaltered ETA receptor levels or affinity. In cerebrovascular smooth muscle cell cultures, long-term treatment with TGF-beta1 significantly decreased (>50%; p < 0.05) the ET-1-induced activation of the p38 MAPK/27-kDa heat shock protein (HSP27) signaling pathway. This occurred with no effect upstream to p38 MAP kinase but with the concomitant induction of mitogen-activated protein kinase phosphatase-1 (MKP-1) expression. Inhibition of MKP-1 expression with Ro-31-8220 or suppression of MKP-1 expression by short interfering RNA restored the ET-1-mediated p38 MAP kinase response. These results disclose a new role for long-term increases of TGF-beta1 in modulating cerebrovascular tone by dampening ET-1-mediated activation of the p38 MAPK/HSP27 signaling pathway. Such changes in ET-1-mediated signaling may help maintain vascular wall homeostasis by compensating for the diminished dilatory function induced by TGF-beta1 and amyloid-beta; brain levels of these two molecules are increased in patients with Alzheimer's disease.

The p38 mitogen-activated protein kinase (MAPK) pathway in rheumatoid arthritis

Chronic inflammatory processes are based on a sustained and tightly regulated communication network among different cells types. This network comprises extracellular mediators such as cytokines, chemokines and matrix-degrading proteases, which orchestrate the participation of cells in the chronic inflammatory process. The mirrors of this outside communication world are intracellular transcription factor pathways, which shuttle information about inflammatory stimuli to the cell nucleus. This review examines the function of one key signal transduction pathway of inflammation--the p38 mitogen-activated protein kinases (p38MAPK). The signalling pathway is considered as crucial for the induction and maintenance of chronic inflammation, and its components thus emerge as interesting molecular targets of small molecule inhibitors for controlling inflammation. This review not only summarises the current knowledge of activation, regulation and function of the p38MAPK pathway but also examines the role of this pathway in clinical disease. It gives an overview of current evidence of p38MAPK activation in inflammatory arthritis and elaborates the key molecular determinants which contribute to p38MAPK activation in joint disease.

Helicobacter pylori VacA enhances prostaglandin E2 production through induction of cyclooxygenase 2 expression via a p38 mitogen-activated protein kinase/activating transcription factor 2 cascade in AZ-521 cells

Treatment of AZ-521 cells with Helicobacter pylori VacA increased cyclooxygenase 2 (COX-2) mRNA in a time- and dose-dependent manner. A p38 mitogen-activated protein kinase (MAPK) inhibitor, SB203580, blocked elevation of COX-2 mRNA levels, whereas PD98059, which blocks the Erk1/2 cascade, partially suppressed the increase. Consistent with involvement of p38 MAPK, VacA-induced accumulation of COX-2 mRNA was reduced in AZ-521 cells overexpressing a dominant-negative p38 MAPK (DN-p38). Phosphatidylinositol-specific phospholipase C, which inhibits VacA-induced p38 MAPK activation, blocked VacA-induced COX-2 expression. In parallel with COX-2 expression, VacA increased prostaglandin E(2) (PGE(2)) production, which was inhibited by SB203580 and NS-398, a COX-2 inhibitor. VacA-induced PGE(2) production was markedly attenuated in AZ-521 cells stably expressing DN-p38. VacA increased transcription of a COX-2 promoter reporter gene and activated a COX-2 promoter containing mutated NF-kappaB or NF-interleukin-6 sites but not a mutated cis-acting replication element (CRE) site, suggesting direct involvement of the activating transcription factor 2 (ATF-2)/CREB-binding region in VacA-induced COX-2 promoter activation. The reduction of ATF-2 expression in AZ-521 cells transformed with ATF-2-small interfering RNA duplexes resulted in suppression of COX-2 expression. Thus, VacA enhances PGE(2) production by AZ-521 cells through induction of COX-2 expression via the p38 MAPK/ATF-2 cascade, leading to activation of the CRE site in the COX-2 promoter.

Spike protein of SARS-CoV stimulates cyclooxygenase-2 expression via both calcium-dependent and calcium-independent protein kinase C pathways

We have previously shown that the nucleocapsid protein of SARS-associated coronavirus (SARS-CoV) activated cyclooxygenase-2 (COX-2) expression. In this study, we identified another viral protein, the spike of SARS-CoV, which played an important role in virus-stimulated COX-2 expression after screening all genes from the SARS-CoV genome. We found that an upstream calcium-dependent PKC isozyme PKC alpha that modulates the downstream ERK/NF-kappaB pathway through an influx of extracellular Ca2+ is induced by the spike protein of SARS-CoV. The ERK/NF-kappaB was identified to be involved in the activation of COX-2 promoter and production of COX-2 protein in HEK293T cells. We also demonstrated that another unusual pathway, the calcium-independent PI3K/PKC epsilon/JNK/CREB pathway, functioned in cooperation with the calcium-dependent pathway to induce COX-2 expression upon stimulation by spike protein. This pathway can be blocked by PKC epsilon-specific, small interfering RNA, PI3K/JNK kinase-specific inhibitors as well as dominant negative JNK. PKC epsilon-specific siRNA also attenuated the phosphorylation of JNK. Our results provide evidence that helps us understand the function of SRAS-CoV spike protein in SARS pathogenesis.

Relationship between 12/15-lipoxygenase and COX-2 in mesangial cells: potential role in diabetic nephropathy

The 12/15-lipoxygenase (12/15-LO) and cyclooxygenase-2 (COX-2) pathways of arachidonate metabolism have been implicated in the pathogenesis of diabetic nephropathy (DN). In this study, we evaluated whether there is an interplay between 12/15-LO and COX-2 pathways in mesangial cells (MC). We utilized MC, microdissected glomeruli and renal cortical tissues. Transfections with cDNAs or short hairpin RNAs (shRNAs) were performed to overexpress or knockdown 12/15-LO and COX-2, respectively. Reverse transcription-polymerase chain reactions and Western blotting were used for evaluating mRNA and protein expression, respectively. We observed that the expression of both 12/15-LO and COX-2 were increased in high glucose stimulated rat MC relative to normal glucose, and also in cortical tissues from diabetic db/db and streptozotocin-injected mice relative to corresponding control mice. Treatment of rat MC with the 12/15-LO product, 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), significantly increased COX-2 expression as well as levels of the COX-2 product, prostaglandin E(2) (PGE(2)). Interestingly, treatment of rat MC with PGE(2) led to a reciprocal increase in 12/15-LO expression as well as levels of 12(S)-HETE. The 12/15-LO shRNA could significantly attenuate COX-2 protein expression and vice versa. Furthermore, COX-2 expression levels were lower in MC and glomeruli from 12/15-LO knockout mice relative to control. Conversely, mouse MC stably overexpressing 12/15-LO had greater levels of COX-2 expression relative to mock-transfected cells. These new results indicate for the first time that 12/15-LO and COX-2 pathways can cross-talk and activate each other in MC. These novel interactions may amplify their effects on the progression of DN.

Activation of p38 Has Opposing Effects on the Proliferation and Migration of Endothelial Cells

Pathological conditions such as hypertension and hyperglycemia as well as abrasions following balloon angioplasty all lead to endothelial dysfunction that impacts disease morbidity. These conditions are associated with the elaboration of a variety of cytokines and increases in p38 activity in endothelial cells. However, the relationship between enhanced p38 activity and endothelial cell function remains poorly understood. To investigate the effect of enhanced p38 MAPK activity on endothelial cell function, we expressed an activated mutant of MEK6 (MEK6E), an upstream regulator of p38. Expression of MEK6E activated p38 and resulted in phosphorylation of its downstream substrate, heat shock protein 27 (Hsp27). Activation of p38 was not sufficient to induce apoptosis; however, it did induce p38-dependent cell cycle arrest. MEK6E expression was sufficient to inhibit ERK phosphorylation triggered by growth factors and integrin engagement. MAPK phosphatase-1 (MKP-1) expression was increased upon p38 activation, and expression of a "substrate-trapping" MKP-1 was sufficient to restore ERK activity. Activation of p38 was sufficient to induce cell migration, which was accompanied by alterations in actin architecture characterized by enhanced lamellipodia. Co-expression of a mutant form of Hsp27, lacking all three phosphorylation sites, reversed MEK6E-induced cell migration and altered the cytoskeletal changes induced by p38 activation. Collectively, these results suggest that cellular decisions regarding migration and proliferation are influenced by p38 activity and that prolonged activation of p38 may result in an anti-angiogenic phenotype that contributes to endothelial dysfunction.

Spinal p38beta isoform mediates tissue injury-induced hyperalgesia and spinal sensitization

Antagonist studies show that spinal p38 mitogen-activated protein kinase plays a crucial role in spinal sensitization. However, there are two p38 isoforms found in spinal cord and the relative contribution of these two to hyperalgesia is not known. Here we demonstrate that the isoforms are distinctly expressed in spinal dorsal horn: p38alpha in neurons and p38beta in microglia. In lieu of isoform selective inhibitors, we examined the functional role of these two individual isoforms in nociception by using intrathecal isoform-specific antisense oligonucleotides to selectively block the expression of the respective isoform. In these rats, down-regulation of spinal p38beta, but not p38alpha, prevented nocifensive flinching evoked by intraplantar injection of formalin and hyperalgesia induced by activation of spinal neurokinin-1 receptors through intrathecal injection of substance P. Both intraplantar formalin and intrathecal substance P produced an increase in spinal p38 phosphorylation and this phosphorylation (activation) was prevented when spinal p38beta, but not p38alpha, was down-regulated. Thus, spinal p38beta, probably in microglia, plays a significant role in spinal nociceptive processing and represents a potential target for pain therapy.

The Role of Mitogen-activated Protein Kinase Phosphatase-1 in the Response of Alveolar Macrophages to Lipopolysaccharide

Mitogen-activated protein (MAP) kinases are critical mediators of innate immune responses. In response to lipopolysaccharide (LPS), MAP kinases are rapidly activated and play an important role in the production of proinflammatory cytokines. Although a number of MAP kinase phosphatases (MKPs) have been identified, their roles in the control of cytokine production have not been well defined. In the present report, we investigated the role of MKP-1 in alveolar macrophages stimulated with LPS. We found that LPS triggered transient activation of three MAP kinase subfamilies, ERK, JNK, and p38, in both immortalized and primary murine alveolar macrophages. MKP-1 was rapidly induced by LPS, and its induction correlated with the dephosphorylation of these MAP kinases. Blocking MKP-1 with triptolide prolonged the activities of both JNK and p38 in immortalized alveolar macrophages. Stimulation of primary alveolar macrophages isolated from MKP-1-deficient mice with LPS resulted in a prolonged p38 phosphorylation compared with wild type alveolar macrophages. Accordingly, these MKP-1-deficient alveolar macrophages also mounted a more robust and rapid tumor necrosis factor alpha production than their wild type counterparts. Adenovirus-mediated MKP-1 overexpression significantly attenuated tumor necrosis factor alpha production in immortalized alveolar macrophages. Finally, MKP-1 was induced by a group of corticosteroids frequently prescribed for the treatment of inflammatory lung diseases, and the anti-inflammatory potencies of these drugs closely correlated with their abilities to induce MKP-1. Our studies indicated that MKP-1 plays an important role in dampening the inflammatory responses of alveolar macrophages. We speculate that MKP-1 may represent a novel target for therapeutic intervention of inflammatory lung diseases.

Inhibition of cyclooxygenase-1 and -2 expression by targeting the endothelin a receptor in human ovarian carcinoma cells

PURPOSE AND EXPERIMENTAL DESIGN

New therapies against cancer are based on targeting cyclooxygenase (COX)-2. Activation of the endothelin A receptor (ET(A)R) by endothelin (ET)-1 is biologically relevant in several malignancies, including ovarian carcinoma. In this tumor, the ET-1/ET(A)R autocrine pathway promotes mitogenesis, apoptosis protection, invasion, and neoangiogenesis. Because COX-1 and COX-2 are involved in ovarian carcinoma progression, we investigated whether ET-1 induced COX-1 and COX-2 expression through the ET(A)R at the mRNA and protein level in HEY and OVCA 433 ovarian carcinoma cell lines by Northern blot, reverse transcription-PCR, Western blot, and immunohistochemistry; we also investigated the activity of the COX-2 promoter by luciferase assay and the release of prostaglandin (PG) E(2) by ELISA.

RESULTS

ET-1 significantly increases the expression of COX-1 and COX-2, COX-2 promoter activity, and PGE(2) production. These effects depend on ET(A)R activation and involve multiple mitogen-activated protein kinase (MAPK) signaling pathways, including p42/44 MAPK, p38 MAPK, and transactivation of the epidermal growth factor receptor. COX-2 inhibitors and, in part, COX-1 inhibitor blocked ET-1-induced PGE(2) and vascular endothelial growth factor release, indicating that both enzymes participate in PGE(2) production to a different extent. Moreover, inhibition of human ovarian tumor growth in nude mice after treatment with the potent ET(A)R-selective antagonist ABT-627 is associated with reduced COX-2 and vascular endothelial growth factor expression.

CONCLUSIONS

These results indicate that impairing COX-1 and COX-2 and their downstream effect by targeting ET(A)R can be therapeutically advantageous in ovarian carcinoma treatment. Pharmacological blockade of the ET(A)R is an attractive strategy to control COX-2 induction, which has been associated with ovarian carcinoma progression and chemoresistance.

Signals that Initiate, Augment, and Provide Directionality for Human Keratinocyte Motility

Human keratinocytes (HK) migration plays a critical role in the re-epithelialization of acute skin wounds. Although extracellular matrices (ECM) and growth factors (GF) are the two major pro-motility signals, their functional relationship remains unclear. We investigated how ECM and GF regulate HK motility under defined conditions: (1) in the absence of GF and ECM and (2) with or without GF with cells apposed to a known pro-motility ECM. Our results show that HK migrate on selected ECM even in the total absence of GF. This suggests that certain ECM alone are able to "initiate" HK migration. Unlike ECM, however, GF alone cannot initiate HK migration. HK cannot properly migrate when plated in the presence of GF, regardless of the concentration, without an ECM substratum. The role of GF, instead, is to augment ECM-initiated motility and provide directionality. To gain insights into the mechanism of action by ECM and GF, we compared, side-by-side, the roles of three major mitogen-activated protein kinase cascades, extracellular-signal-regulated kinase (ERK)1/2, p38, and c-Jun N-terminal kinase (JNK). Our data show that ERK1/2 is involved in mediating collagen's initiation signal and GF's augmentation signal. p38 is specific for GF's augmentation signal. JNK is uninvolved in HK motility. Constitutively activated p38 and ERK1/2 alone could not initiate HK migration. Co-expression of both constitutively activated p38 and ERK1/2, however, could partially mimic the pro-motility effects of collagen and GF. This study reveals for the first time the specific functions of ECM and GF in cell motility.

Extracellular Matrix-induced Cyclooxygenase-2 Regulates Macrophage Proteinase Expression

Chronic inflammatory diseases are characterized by the persistent presence of macrophages and other mononuclear cells, tissue destruction, cell proliferation, and the deposition of extracellular matrix (ECM). The tissue degradation is mediated, in part, by enhanced proteinase expression by macrophages. It has been demonstrated recently that macrophage proteinase expression can be stimulated or inhibited by purified ECM components. However, in an intact ECM the biologically active domains of matrix components may be masked either by tertiary conformation or by complex association with other matrix molecules. In an effort to determine whether a complex ECM produced by vascular smooth muscle cells (SMC) regulates macrophage degradative phenotype, we prepared insoluble SMC matrices and examined their ability to regulate proteinase expression by RAW264.7 and thioglycollate-elicited peritoneal macrophages. Here we demonstrate that macrophage engagement of SMC-ECM triggers PKC-dependent activation of MAPK(erk1/2) leading to increased expression of cyclooxygenase (COX)-2 and prostaglandin (PG) E(2) synthesis. The addition of PGE(2) to macrophage cultures stimulates their expression of both urokinase-type plasminogen activator and MMP-9, and the selective COX-2 inhibitor NS-398 blocks ECM-induced proteinase expression. Moreover, ECM-induced PGE(2) and MMP-9 expression by elicited COX-2(-/-) macrophages is markedly reduced when compared with the response of either COX-2(+/-) or COX-2(+/+) macrophages. These data clearly demonstrate that SMC-ECM exerts a regulatory role on the degradative phenotype of macrophages via enhanced urokinase-type plasminogen activator and MMP-9 expression, and identify COX-2 as a targetable component of the signaling pathway leading to increased proteinase expression.