The seven-transmembrane-spanning receptors for endothelin and thrombin cause proliferation of airway smooth muscle cells and activation of the extracellular regulated kinase and c-Jun NH2-terminal kinase groups of mitogen-activated protein kinases

Protease-activated receptors in health and disease

Proteases are signaling molecules that specifically control cellular functions by cleaving protease-activated receptors (PARs). The four known PARs are members of the large family of G protein-coupled receptors. These transmembrane receptors control most physiological and pathological processes and are the target of a large proportion of therapeutic drugs. Signaling proteases include enzymes from the circulation; from immune, inflammatory epithelial, and cancer cells; as well as from commensal and pathogenic bacteria. Advances in our understanding of the structure and function of PARs provide insights into how diverse proteases activate these receptors to regulate physiological and pathological processes in most tissues and organ systems. The realization that proteases and PARs are key mediators of disease, coupled with advances in understanding the atomic level structure of PARs and their mechanisms of signaling in subcellular microdomains, has spurred the development of antagonists, some of which have advanced to the clinic. Herein we review the discovery, structure, and function of this receptor system, highlight the contribution of PARs to homeostatic control, and discuss the potential of PAR antagonists for the treatment of major diseases.

Galectin-3 Mediates Thrombin-Induced Vascular Smooth Muscle Cell Migration

Vascular smooth muscle cell (VSMC) migration is an important step in the progression and development of vulnerable plaques. Thrombin is involved in both physiological and pathological processes of atherosclerosis. Therefore, the elucidation of the mechanisms underlying thrombin-induced VSMC migration is essential for devising effective treatments aimed at the prevention of plaque instability. In this study, we found that thrombin activated MAPK signaling pathways and increased the expression of galectin-3, which was also a well-known factor in atherosclerosis. Knockdown of galectin-3 by specific small interfering RNA (siRNA) blocked thrombin-induced activation of ERK1/2 and p38 MAPK, but not JNK MAPK. Src/FAK phosphorylation was also shown to be activated by thrombin. FAK autophosphorylation at Y397 was most significantly inhibited by galectin-3 siRNA. Galectin-3 siRNA or specific inhibitor (P38 MAPK inhibitor and ERK1/2 inhibitor) effectively prevented thrombin-induced VSMC migration via reducing paxillin expression. These findings demonstrate, for the first time, that thrombin stimulation of VSMC migration and paxillin expression are regulated by galectin-3, and ERK1/2, p38 MAPK, and Src/FAK signaling pathways are involved in this process. These results are beneficial to clarify the role of galectin-3 in thrombin-induced advanced lesions in atherosclerosis and shed new insights into the regulatory mechanism of VSMC migration in combating plaque rupture.

Silencing of tissue factor by antisense deoxyoligonucleotide prevents monocrotaline/LPS renal injury in mice

Tissue factor (TF) is involved in monocrotaline (MCT)/lipopolysaccharide (LPS) hepatotoxicity. It is not known whether MCT/LPS can cause renal toxicity and whether TF is involved in this toxicity. Thus, the present study was undertaken to investigate the potential renal toxicity after MCT/LPS co-treatment and the involvement of TF in this toxicity. MCT was delivered to ND4 male mice (200 mg/kg) per os followed 4 h later by treatment with LPS ip (6 mg/kg) to investigate its effect on kidney. We injected TF antisense oligonucleotide (TF-AS) intravenously (i.v) in mice prior to LPS treatment, to block TF, and measured their blood urea nitrogen (BUN), creatinine (CRE), alkaline phosphatase (ALP), and potassium. In MCT/LPS co-treated group, fibrin was detected on the glomerular capillary lumina, distal tubules of renal cortex, and the necrotic tubules of renal medulla. An elevation of BUN, creatinine, and the BUN/creatinine ratio was seen in mice with MCT/LPS co-treatment, compared to animals receiving LPS or MCT alone. Simultaneously, an aggressive tubular necrosis was seen in the medullary tubules in the same group which may account for the oliguria observed in these animals. Fourfold inductions in the plasma TF level was detected at 10 h after MCT/LPS co-treatment which increased to 18-fold at 24 h. Increased blood level of leptin, interleukin-6 (IL-6) and downregulation of tubular chemokine (C-X-C motif) ligand 16 (CXCL16) are characteristic features in MCT/LPS co-treated animal. On the other hand, mice injected with TF-AS in the presence of MCT/LPS co-treatment showed no elevation of the blood BUN, creatinine, potassium, and normal levels of the proinflammatory molecules. TF-AS injection significantly prevented glomerular and tubular fibrin deposition, tubular necrosis, and improvement of the animal survivability. Renal toxicity involving TF can be prevented successfully by the use of TF-AS.

Thrombin induces EGF receptor expression and cell proliferation via a PKC(delta)/c-Src-dependent pathway in vascular smooth muscle cells

OBJECTIVE

Thrombin upregulates expression of several proteins in vascular smooth muscle cells (VSMCs) which may contribute to atherosclerosis. Here, we investigated the mechanisms underlying thrombin-induced EGF receptor (EGFR) expression and its effect on VSMCs.

METHODS AND RESULTS

Normal rat VSMCs were used. First, Western blotting and RT-PCR analyses showed that thrombin induces the expression of EGFR at transcription and translation levels in VSMCs. Second, pharmacological inhibitors, dominant negative mutants, and short hairpin RNA interference (shRNA) technology enabled us to demonstrate that thrombin-induced EGFR expression is mediated through PKC(delta)/c-Src-dependent transactivation of EGFR linking to PI3K/Akt and ERK1/2. We further investigated whether the transcription factors AP-1 and NF-kappaB are involved in this response by a promoter assay. Finally, data obtained by using EGFR shRNA technology and XTT assay demonstrated that thrombin-enhanced VSMC proliferation was mediated through upregulation of EGFR.

CONCLUSIONS

Our results demonstrate that thrombin-enhanced VSMC proliferation was mediated through upregulation of EGFR via a PKC(delta)/c-Src-dependent transactivation of EGFR, PI3K-Akt, and ERK, and AP-1/NF-kappaB pathway.

Thrombin induces Egr-1 expression in fibroblasts involving elevation of the intracellular Ca2+ concentration, phosphorylation of ERK and activation of ternary complex factor

Background

The serine protease thrombin catalyzes fibrin clot formation by converting fibrinogen into fibrin. Additionally, thrombin stimulation leads to an activation of stimulus-responsive transcription factors in different cell types, indicating that the gene expression pattern is changed in thrombin-stimulated cells. The objective of this study was to analyze the signaling cascade leading to the expression of the zinc finger transcription factor Egr-1 in thrombin-stimulated lung fibroblasts.

Results

Stimulation of 39M1-81 fibroblasts with thrombin induced a robust and transient biosynthesis of Egr-1. Reporter gene analysis revealed that the newly synthesized Egr-1 was biologically active. The signaling cascade connecting thrombin stimulation with Egr-1 gene expression required elevated levels of cytosolic Ca²⁺, the activation of diacylgycerol-dependent protein kinase C isoenzymes, and the activation of extracellular signal-regulated protein kinase (ERK). Stimulation of the cells with thrombin triggered the phosphorylation of the transcription factor Elk-1. Expression of a dominant-negative mutant of Elk-1 completely prevented Egr-1 expression in stimulated 39M1-81 cells, indicating that Elk-1 or related ternary complex factors connect the intracellular signaling cascade elicited by activation of protease-activated receptors with transcription of the Egr-1 gene. Lentiviral-mediated expression of MAP kinase phosphatase-1, a dual-specific phosphatase that dephosphorylates and inactivates ERK in the nucleus, prevented Elk-1 phosphorylation and Egr-1 biosynthesis in thrombin stimulated 39M1-81 cells, confirming the importance of nuclear ERK and Elk-1 for the upregulation of Egr-1 expression in thrombin-stimulated lung fibroblasts. 39M1-81 cells additionally express M₁ muscarinic acetylcholine receptors. A comparison between the signaling cascades induced by thrombin or carbachol showed no differences, except that signal transduction via M₁ muscarinic acetylcholine receptors required the transactivation of the EGF receptor, while thrombin signaling did not.

Conclusion

This study shows that stimulus-transcription coupling in thrombin-treated lung fibroblasts relies on the elevation of the intracellular Ca²⁺-concentration and the activation of PKC and ERK. In the nucleus, ternary complex factors function as key proteins linking the intracellular signaling cascade with enhanced transcription of the Egr-1 gene. This study further shows that the dominant-negative Elk-1 mutant is a valuable tool to study Elk-1-mediated gene transcription.

Transcriptional regulation of monocyte chemotactic protein-1 release by endothelin-1 in human airway smooth muscle cells involves NF-kappaB and AP-1

BACKGROUND AND PURPOSE

Endothelin-1 (ET-1) is implicated in airway inflammation in asthma, but the mechanisms of its effects are poorly understood. We studied the effect of ET-1 on expression of the chemokine, monocyte chemotactic protein-1 (MCP-1), in primary cultures of human airway smooth muscle cells.

EXPERIMENTAL APPROACH

MCP-1 release was measured by elisa. Pharmacological antagonists/inhibitors, reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting were used to study ET receptors and kinase cascades. Transcriptional regulation was studied by real-time RT-PCR, transient transfection studies and chromatin immunoprecipitation assay. Major findings were confirmed in cells from three donors and mechanistic studies in cells from one donor.

KEY RESULTS

ET-1 increased MCP-1 release through an ET(A) and ET(B) receptor-dependent mechanism. ET-1 increased MCP-1 mRNA levels but not mRNA stability suggesting it was acting transcriptionally. ET-1 increased the activity of an MCP-1 promoter-reporter construct. Serial deletions of the MCP-1 promoter mapped ET-1 effects to a region between -213 and -128 base pairs upstream of the translation start codon, containing consensus sequences for activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB). ET-1 promoted binding of AP-1 c-Jun subunit and NF-kappaB p65 subunit to the MCP-1 promoter. Blocking the inhibitor of kappaB kinase-2 with 2-[(aminocarbonyl)amino]-5-[4-fluorophenyl]-3-thiophenecarboxamide (TPCA-1) decreased ET-1-stimulated MCP-1 production. p38 and p44/p42 mitogen-activated protein kinases were involved in upstream signalling.

CONCLUSIONS AND IMPLICATIONS

ET-1 regulated MCP-1 transcriptionally, via NF-kappaB and AP-1. The upstream signalling involved ET(A), ET(B) receptors, p38 and p44/p42 mitogen-activated protein kinases. These may be targets for novel asthma therapies.

Airway smooth muscle in asthma

Airway smooth muscle plays a multifaceted role in the pathogenesis of asthma. We review the current understanding of the contribution of airway myocytes to airway inflammation, airway wall remodeling, and airflow obstruction in this prevalent disease syndrome. Together, these roles make airway smooth muscle an attractive target for asthma therapy.

Airway smooth muscle growth in asthma: proliferation, hypertrophy, and migration

Increased airway smooth muscle mass is present in fatal and non-fatal asthma. However, little information is available regarding the cellular mechanism (i.e., hyperplasia vs. hypertrophy). Even less information exists regarding the functional consequences of airway smooth muscle remodeling. It would appear that increased airway smooth muscle mass would tend to increase airway narrowing and airflow obstruction. However, the precise effects of increased airway smooth muscle mass on airway narrowing are not known. This review will consider the evidence for airway smooth muscle cell proliferation and hypertrophy in asthma, potential functional effects, and biochemical mechanisms.

PDGF-induced human airway smooth muscle cell proliferation requires STAT3 and the small GTPase Rac1

The signal transducers and activators of transcription (STAT) family of transcription factors regulates a variety of biological functions including cellular proliferation, transformation, apoptosis, and differentiation. We have previously determined that PDGF activates the STAT pathway in human airway smooth muscle cells (HASMC) and that the Jak and Src kinases are required for both PDGF-induced STAT activation and HASMC proliferation. As increased airway smooth muscle (ASM) volume is associated with airflow obstruction and disease severity in patients with asthma, it is important to elucidate the cellular and molecular pathways that regulate ASM accumulation. In this paper, we investigated the requirement of STAT3 for PDGF-induced HASMC proliferation. We demonstrate that knockdown of STAT3 expression in HASMC resulted in a significant decrease in mitogen-induced cellular proliferation. Additionally, PDGF-induced activation of STAT3 required the small GTP-binding protein Rac1, and Rac1 was also required for PDGF-induced HASMC proliferation. Furthermore, PDGF treatment induced STAT3 and Rac1 to physically associate and translocate to the nucleus, identifying one mechanism by which STAT3 is regulated in response to PDGF in HASMC. Finally, we determined that STAT3 expression is required for PDGF-mediated regulation of cell cycle targets cyclin D3 and p27. These data define a novel mitogenic signaling pathway in airway smooth muscle cells leading from PDGF to Rac1 and STAT3 and subsequent cell cycle gene regulation. Thus, targeting STAT3 may prove to be a novel therapeutic approach for patients with severe asthma and significant airway wall remodeling, as manifested by ASM accumulation.

G protein regulation of MAPK networks

G proteins provide signal-coupling mechanisms to heptahelical cell surface receptors and are critically involved in the regulation of different mitogen-activated protein kinase (MAPK) networks. The four classes of G proteins, defined by the G(s), G(i), G(q) and G(12) families, regulate ERK1/2, JNK, p38MAPK, ERK5 and ERK6 modules by different mechanisms. The alpha- as well as betagamma-subunits are involved in the regulation of these MAPK modules in a context-specific manner. While the alpha- and betagamma-subunits primarily regulate the MAPK pathways via their respective effector-mediated signaling pathways, recent studies have unraveled several novel signaling intermediates including receptor tyrosine kinases and small GTPases through which these G-protein subunits positively as well as negatively regulate specific MAPK modules. Multiple mechanisms together with specific scaffold proteins that can link G-protein-coupled receptors or G proteins to distinct MAPK modules contribute to the context-specific and spatio-temporal regulation of mitogen-activated protein signaling networks by G proteins.

Isoproterenol suppresses cytokine-induced RANTES secretion in human lung epithelial cells through the inhibition of c-jun N-terminal kinase pathway

It has been reported that beta2-agonists may potentially exert some anti-inflammatory action in addition to bronchodilation that may contribute to their beneficial effects on asthma control. Bronchial epithelial cells are well known to respond to a range of stimuli by producing various biologically active mediators that can influence airway inflammation. RANTES (regulated on activation, normal T cells expressed and secreted) plays an important role in the pathophysiology of airway inflammation of asthmatics through its chemotactic activity for eosinophils. In this study, the authors investigated whether cytokine-induced RANTES release from BEAS-2B human bronchial epithelial cells could be modulated by beta-agonist isoproterenol (ISO). The possible involvement of c-jun N-terminal kinase (JNK) pathway was also studied. Combination of tumor necrosis factor-alpha and interleukin-1beta (cytokine mix) increased RANTES release from BEAS-2B cells and stimulated JNK activity. Similar to JNK inhibitor SP600125, ISO inhibited not only the production of RANTES but also the activation of JNK pathway in cytokine mix-stimulated BEAS-2B cells. The effect of ISO was mediated by the beta2-adrenoceptor, since it was blocked by ICI 118,551, a selective beta2-receptor antagonist, but not by atenolol, a selective beta1-receptor antagonist. Adenylyl cyclase activator forskolin reproduced the effects of ISO. Isoproterenol was found to inhibit the release of RANTES from the human bronchial epithelial cells, at least in part, through the inhibition of JNK signaling pathway.

Vascular endothelial growth factor promotes cardiomyocyte differentiation of embryonic stem cells

Embryonic stem cells (ESCs) overexpressing the vascular endothelial growth factor (VEGF) improve cardiac function in mouse models of myocardial ischemia and infarction by mechanisms that are poorly understood. Here we studied the effects of VEGF on cardiomyocyte differentiation of mouse ESCs in vitro. We used flow cytometry to determine the expression of alpha-myosin heavy chain (alpha-MHC), cardiac troponin I (cTn-I), and Nkx2.5 in differentiated ESCs. VEGF (20 ng/ml) significantly enhanced alpha-MHC, cTn-I, and Nkx2.5 expression in differentiated ESCs. Western blot analysis confirmed these findings. We found that VEGF receptor FMS-like tyrosine kinase-1 (Flt-1) and fetal liver kinase-1 (Flk-1) expression increased during ESC differentiation. Antibodies against Flk-1 totally blocked and against Flt-1 partially blocked VEGF-induced NKx2.5-positive-stained cells. The ERK inhibitor PD-098059 abolished VEGF-induced cardiomyocyte differentiation of ESCs. Our results suggest that VEGF promotes cardiomyocyte differentiation predominantly by ERK-mediated Flk-1 activation and, to a lesser extent, by Flt-1 activation. These findings may be of significance for stem cell and growth factor therapies to regenerate failing cardiomyocytes.

Endothelin-1 regulates proliferative responses, both alone and synergistically with PDGF, in rat tracheal smooth muscle cells

The peptide, endothelin-1 (ET-1) regulates proliferative responses in numerous cell types. Recently, a dual ET receptor antagonist was shown to prevent the increase in airway smooth muscle cell (SMC) proliferation that accompanies airway smooth muscle remodeling in a rat model of experimental asthma. Thus, we used [(3)H]-thymidine incorporation assays and western immunoblotting to identify signaling pathways that regulate proliferative responses in cultured rat tracheal SMC. Our data indicate that ET-1 activation of the ET A receptor subtype induced [(3)H]-thymidine incorporation and activation of ERK 1/2 in primary rat tracheal SMC. ET-1-induced [(3)H]-thymidine incorporation and activation of ERK 1/2 were inhibited by pretreatment of SMC with pertussis toxin or down regulation of phorbol ester responsive isoforms of PKC. While ET- 1-induced ERK 1/2 activation was unaffected following inhibition of Rho kinase, ET-1-induced [(3)H]-thymidine incorporation was abrogated. ET-1 also potentiated [(3)H]-thymidine incorporation as well as cell proliferation of SMC stimulated with PDGF-BB and this response did not appear to be regulated by ERK1/ 2. These data demonstrate that ET-1 induces activation of multiple G proteins that regulate rat tracheal SMC proliferative responses, likely through signaling pathways downstream of ERK1/2 and Rho kinase.

Reactive oxidant and p42/44 MAP kinase signaling is necessary for mechanical strain-induced proliferation in pulmonary epithelial cells

Mechanical strain is necessary for normal lung growth and development. Individuals with respiratory failure are supported with mechanical ventilation, leading to altered lung growth and injury. Understanding signaling pathways initiated by mechanical strain in lung epithelial cells will help guide development of strategies aimed at optimizing strain-induced lung growth while mitigating ventilator-induced lung injury. To study strain-induced proliferative signaling, focusing on the role of reactive oxidant species (ROS) and p42/44 mitogen-activated protein (MAP) kinase, human pulmonary epithelial H441 and MLE15 cells were exposed to equibiaxial cyclic mechanical strain. ROS were increased within 15 min of strain. N-acetylcysteine inactivated strain-induced ROS and inhibited p42/44 MAP kinase phosphorylation and strain-induced proliferation. PD98059 and UO126, p42/44 MAP kinase inhibitors, blocked strain-induced proliferation. To verify the specificity of p42/44 MAP kinase inhibition, cells were transfected with dominant-negative mitogen-activated protein kinase kinase-1 plasmid DNA. Transfected cells did not proliferate in response to mechanical strain. To determine whether strain-induced tyrosine kinase activity is necessary for strain-induced ROS-p42/44 MAP kinase signaling, genistein, a tyrosine kinase inhibitor, was used. Genistein did not block strain-induced ROS production or p42/44 MAP kinase phosphorylation. Gadolinium, a mechanosensitive calcium channel blocker, blocked strain-induced ROS production and p42/44 MAP kinase phosphorylation but not strain-induced tyrosine phosphorylation. These data support ROS production and p42/44 MAP kinase phosphorylation being involved in a common strain-induced signaling pathway, necessary for strain-induced proliferation in pulmonary epithelial cells, with a parallel strain-induced tyrosine kinase pathway.

Extracellular pressure stimulates colon cancer cell proliferation via a mechanism requiring PKC and tyrosine kinase signals

Pressure in colonic tumours may increase during constipation, obstruction or peri-operatively. Pressure enhances colonocyte adhesion by a c-Src- and actin-cytoskeleton-dependent PKC-independent pathway. We hypothesized that pressure activates mitogenic signals.

METHODS

Malignant colonocytes on a collagen I matrix were subjected to 15 mmHg pressure. ERK, p38, c-Src and Akt phosphorylation and PKCalpha redistribution were assessed by western blot after 30 min and PKC activation by ELISA. Cells were counted after 24 h and after inhibition of each signal, tyrosine phosphorylation or actin depolymerization.

RESULTS

Pressure time-dependently increased SW620 and HCT-116 cell counts on collagen or fibronectin (P < 0.01). Pressure increased the SW620 S-phase fraction from 28 +/- 1 to 47 +/- 1% (P = 0.0002). Pressure activated p38, ERK, and c-Src (P < 0.05 each) but not Akt/PKB. Pressure decreased cytosolic PKC activity, and translocated PKCalpha to a membrane fraction. Blockade of p38, ERK, c-Src or PI-3-K or actin depolymerization did not inhibit pressure-stimulated proliferation. However, global tyrosine kinase blockade (genistein) and PKC blockade (calphostin C) negated pressure-induced proliferation.

CONCLUSIONS

Extracellular pressure stimulates cell proliferation and activates several signals. However, the mitogenic effect of pressure requires only tyrosine kinase and PKCalpha activation. Pressure may modulate colon cancer growth and implantation by two distinct pathways, one stimulating proliferation and the other promoting adhesion.

Mechanosensation and endothelin in astrocytes--hypothetical roles in CNS pathophysiology

Endothelin (ET) is a potent autocrine mitogen produced by reactive and neoplastic astrocytes. ET has been implicated in the induction of astrocyte proliferation and other transformations engendered by brain pathology, and in promoting the malignant behavior of astrocytomas. Reactive astrocytes containing ET are found in the periphery/penumbra of a wide array of CNS pathologies. Virtually all brain pathology deforms the surrounding parenchyma, either by direct mass effect or edema. Mechanical stress is a well established stimulus for ET production and release by other cell types, but has not been well studied in the brain. However, numerous studies have illustrated that astrocytes can sense mechanical stress and translate it into chemical messages. Furthermore, the ubiquitous reticular meshwork formed by interconnected astrocytes provides an ideal morphology for sensing and responding to mechanical disturbances. We have recently demonstrated stretch-induced ET production by astrocytes in vitro. Inspired by this finding, the purpose of this article is to review the literature on (1) astrocyte mechanosensation, and (2) the endothelin system in astrocytes, and to consider the hypothesis that mechanical induction of the ET system may influence astrocyte functioning in CNS pathophysiology. We conclude by discussing evidence supporting future investigations to determine whether specific inhibition of stretch-activated ion channels may represent a novel strategy for treating or preventing CNS disturbances, as well as the relevance to astrocyte-derived tumors.

Mitogen-activated protein kinase signalling pathways in IL-1 beta-dependent rat airway smooth muscle proliferation

Asthma is associated with abnormal airway smooth muscle (ASM) growth that may contribute to airway narrowing and hyperresponsiveness. We investigated the role of mitogen-activated protein kinase (MAPK) pathway in IL-1beta induced ASM proliferation in the rat. Rat tracheal ASM cells were dissociated and maintained in culture. We examined the effect of selective MAPK inhibitors, SB239063 (a p38 MAPK inhibitor), U0126 (a mitogen-activated and extracellular regulated kinase kinase, MEK-1, inhibitor which inhibits downstream extracellular regulated kinase, ERK, activity), and SP600125 (a c-jun N-terminal kinase, JNK, inhibitor) on IL-1beta-induced proliferation. Proliferation of ASM cells was significantly increased following exposure to IL-1beta in a dose-dependent manner. p38, JNK and ERK MAPKs were activated by IL-1beta in a time-dependent manner, with peak activation time at 30, 60 min and at 6 h, respectively. This activation was inhibited by their respective inhibitors. SP600125 (20 microM) had no effect on IL-1beta-induced ERK and p38 phosphorylation. SB239063, U0126 and SP600125 dose-dependently inhibited IL-1beta-dependent proliferation at doses that inhibit the activities of p38, ERK and JNK MAPKs, respectively. No additive or synergistic effects were observed on proliferative responses with any combination of these compounds. In conclusion, the three major MAPK pathways, ERK as well as the p38 MAPK and JNK pathways, are independent regulators of IL-1beta-dependent proliferation of rat ASM.

Yersinia YopJ inhibits pro-inflammatory molecule expression in human bronchial epithelial cells

Human bronchial epithelial cell pro-inflammatory molecule expression plays a role in the pathogenesis of airway diseases. We hypothesize that Yersinia outer protein-J (YopJ), a Yersinia virulence effector which inhibits mitogen activated protein (MAP) kinase kinases (MKKs), attenuates epithelial cell pro-inflammatory molecule expression. 16HBE14o-cells were co-transfected with cDNAs encoding Yersinia pseudotuberculosis YopJ or empty vector. Expression of YopJ reduced activation of extracellular signal regulated kinase (ERK)-2, Jun amino terminal kinase (JNK)-1 and IkappaB kinase (IKK)-beta. YopJ also blocked transactivation of NF-kappaB and AP-1 promoter sequences which has been shown to regulate chemokine expression. Finally, expression of YopJ reduced transcription from the IL-8, RANTES (regulated upon activation, normal T cell expressed and secreted) and intercellular adhesion molecule (ICAM)-1 promoters. We conclude that YopJ expression blocks the innate immune response in lung epithelial cells, the site of Yersinia pestis infection. Inhibition of bronchial epithelial cell responses by YopJ is consistent with the notion that MAP kinases regulates bronchial epithelial cell pro-inflammatory molecule expression.

Mitogenic signaling pathways in airway smooth muscle

Increased airway smooth muscle mass has been demonstrated in patients with asthma, bronchopulmonary dysplasia and most recently, cystic fibrosis. These observations emphasize the need for further knowledge of the events involved in airway smooth muscle mitogenesis and hypertrophy. Workers in the field have developed cell culture systems involving tracheal and bronchial myocytes from different species. An emergent body of literature indicates that mutual signal transduction pathways control airway smooth muscle cell cycle entry across species lines. This article reviews what is known about mitogen-activated signal transduction in airway myocytes. The extracellular signal regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI 3-kinase) pathways appear to be key positive regulators of airway smooth muscle mitogenesis; recent studies have also demonstrated specific roles for reactive oxygen and the JAK/STAT pathway. It is also possible that growth factor stimulation of airway smooth muscle concurrently elicits signaling through negative regulatory intermediates such as p38 mitogen-activated protein (MAP) kinase and protein kinase C (PKC) delta, conceivably as a defense against extreme growth.

Ras and mitogen-activated protein kinase kinase kinase-1 coregulate activator protein-1- and nuclear factor-kappaB-mediated gene expression in airway epithelial cells

In 16HBE14o- human bronchial epithelial cells, maximal tumor necrosis factor (TNF)-alpha-induced interleukin (IL)-8 expression depends on the activation of two distinct signaling pathways, one constituted in part by activator protein (AP)-1 and the other by nuclear factor (NF)-kappaB. We examined the upstream signaling intermediates responsible for IL-8 and granulocyte-macrophage colony-stimulating factor (GM-CSF) expression in this system, hypothesizing that p21 Ras and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase (MEKK)-1 function as common upstream activators of both the AP-1 and NF-kappaB pathways. TNF-alpha treatment induced both Ras and MEKK1 activation. Dominant-negative forms of Ras (N17Ras) and MEKK1 (MEKK1-KM) each inhibited TNF-alpha-induced transcription from IL-8 and GM-CSF promoters. Ras was required for maximal activation of extracellular signal-regulated kinase (ERK) and Jun amino terminal kinase (JNK) as well as AP-1 and NF-kappaB transcriptional activities, but not for activation of IkappaB kinase (IKK)-beta, an upstream activator of NF-kappaB. MEKK1 was required for maximal activation of ERK, JNK, and IKK, as well as for maximal AP-1 and NF-kappaB transcriptional activities. We conclude that Ras regulates TNF-alpha-induced chemokine expression by activating the AP-1 pathway and enhancing transcriptional function of NF-kappaB, whereas MEKK1 activates both the AP-1 and NF-kappaB pathways.

Blockade of tissue factor: treatment for organ injury in established sepsis

Blockade of tissue factor before lethal sepsis prevents acute lung injury and renal failure in baboons, indicating that activation of coagulation by tissue factor is an early event in the pathogenesis of acute lung injury and organ dysfunction. We hypothesized that blockade of tissue factor would also attenuate these injuries in established sepsis by prevention of further fibrin deposition and inflammation. Twelve male baboons received heat-killed Escherichia coli intravenously followed 12 hours later by live E. coli infusion. Six animals were treated 2 hours after the live bacteria with site-inactivated Factor VIIa, a competitive tissue factor inhibitor, and six animals were vehicle-treated sepsis control subjects. Animals were ventilated and monitored for 48 hours. Physiologic and hematologic parameters were measured every 6 hours, and pathologic evaluation was performed after 48 hours. Animals treated with site inactivated Factor VIIa had less severe lung injury, with preserved gas exchange, better lung compliance and histology scores, and decreased lung wet/dry weight. In treated animals, urine output was higher, metabolic acidosis was attenuated, and renal tubular architecture was protected. Coagulopathy was attenuated, and plasma interleukin-6, interleukin-8, and soluble tumor necrosis factor receptor-1 levels were significantly lower in the treated animals. These results show that blockade of coagulation attenuates acute lung and renal injury in established Gram-negative sepsis accompanied by antiinflammatory effects of therapy.

c-Jun N-terminal kinase (JNK) mediates feedback inhibition of the insulin signaling cascade

Activation of the c-Jun N-terminal kinase (JNK) by proinflammatory cytokines inhibits insulin signaling, at least in part, by stimulating phosphorylation of rat/mouse insulin receptor substrate 1 (Irs1) at Ser(307) (Ser(312) in human IRS1). Here we show that JNK mediated feedback inhibition of the insulin signal in mouse embryo fibroblasts, 3T3-L1 adipocytes, and 32D(IR) cells. Insulin stimulation of JNK activity required phosphatidylinositol 3-kinase and Grb2 signaling. Moreover, activation of JNK by insulin was inhibited by a cell-permeable peptide that disrupted the interaction of JNK with cellular proteins. However, the direct binding of JNK to Irs1 was not required for its activation by insulin, whereas direct binding was required for Ser(307) phosphorylation of Irs1. Insulin-stimulated Ser(307) phosphorylation was reduced 80% in cells lacking JNK1 and JNK2 or in cells expressing a mutant Irs1 protein lacking the JNK binding site. Reduced Ser(307) phosphorylation was directly related to increased insulin-stimulated tyrosine phosphorylation, Akt phosphorylation, and glucose uptake. These results support the hypothesis that JNK is a negative feedback regulator of insulin action by phosphorylating Ser(307) in Irs1.

Regulation of human airway epithelial cell IL-8 expression by MAP kinases

Recent studies indicate that maximal IL-8 protein expression requires activation of NF-kappaB as well as activation of the MAP kinases ERK, JNK, and p38. However, the precise relationship between NF-kappaB transactivation and MAP kinase activation remains unclear. We examined the requirements of NF-kappaB, ERK, JNK, and p38 for TNF-alpha-induced transcription from the IL-8 promoter in a human bronchial epithelial cell line. Treatment with TNF-alpha induced activation of all three MAP kinases. Using a combination of chemical and dominant-negative inhibitors, we found that inhibition of NF-kappaB, ERK, and JNK, but not p38, each decreased TNF-alpha-induced transcription from the IL-8 promoter. Inhibition of JNK signaling also substantially reduced TNF-alpha-induced NF-kappaB transactivation, whereas inhibition of ERK and p38 had no effect. On the other hand, ERK was required and sufficient for TNF-alpha-induced activation of activator protein (AP)-1 promoter sequences, which together function as a basal level enhancer. JNK activation was also required for AP-1 transactivation. Finally, inhibition of p38 attenuated IL-8 protein abundance, suggesting that p38 regulates IL-8 expression in a posttranscriptional manner. We conclude that, in human airway epithelial cells, MAP kinases may regulate IL-8 promoter activity by NF-kappaB-dependent (in the case of JNK) and -independent (ERK) processes, as well as by posttranscriptional mechanisms (p38).

Epidermal growth factor and thrombin induced proliferation of immortalized human keratinocytes is coupled to the synthesis of Egr-1, a zinc finger transcriptional regulator

The epidermal growth factor (EGF) receptor is highly expressed in HaCaT keratinocytes as shown by Western blotting. Stimulation of HaCaT cells with EGF, and also with the serine protease thrombin, induced DNA synthesis, measured by incorporation of 5-bromo-2'-deoxyuridine into the DNA of proliferating cells. Using antibodies directed against the active form of the EGF receptor, we show that in HaCaT cells EGF and thrombin triggered a rapid activation of the EGF receptor, followed by the phosphorylation and activation of the extracellular signal-regulated protein kinase (ERK). Moreover, EGF and thrombin induced a transient synthesis of the zinc finger transcriptional regulator Egr-1. Proliferation, activation of ERK, and biosynthesis of Egr-1 was completely inhibited in EGF or thrombin-treated HaCaT cells by the MAP kinase kinase inhibitor PD98059 and by AG1487, an EGF receptor-specific tyrosine kinase inhibitor. These data indicate that phosphorylation and activation of both the EGF receptor and ERK are essential for mitogenic signaling via EGF and thrombin. The synthesis of Egr-1 in HaCaT cells as a result of EGF or thrombin stimulation suggests that Egr-1 may be an important "late" part of the EGF and thrombin-initiated signaling cascades. We postulate that Egr-1 may function as a "third messenger" in keratinocytes connecting mitogenic stimulation with changes in gene transcription.

Mast cell chymase modifies cell-matrix interactions and inhibits mitogen-induced proliferation of human airway smooth muscle cells

The hallmarks of chronic, severe asthma include prominent airway inflammation and airway smooth muscle (ASM) hypertrophy and hyperplasia. One of the factors that contribute to the injury and repair process within the airway is activation of proteases and turnover of extracellular matrix components. Mast cells, which are present in increased numbers in the asthmatic airway, are a rich source of the neutral protease chymase, which can degrade several basement membrane components. Recent data suggest that proteases also play a critical role in regulating the expression of CD44, the primary receptor for the matrix glycosaminoglycan hyaluronan. In this study we investigated the effects of chymase treatment on human ASM cell function. We found that chymase degraded the smooth muscle cell pericellular matrix. This was accompanied by an increased release of fibronectin and soluble CD44, but not soluble ICAM-1 or soluble hyaluronan, into the conditioned medium. In addition, chymase inhibited T cell adhesion to ASM and dramatically reduced epidermal growth factor-induced smooth muscle cell proliferation. These data suggest that the local release of mast cell chymase may have profound effects on ASM cell function and airway remodeling.

Ketoconazole suppresses prostaglandin E(2)-induced cyclooxygenase-2 expression in human epidermoid carcinoma A-431 cells

Cyclooxygenase-2 is a key enzyme in the conversion of arachidonic acid to prostaglandins. The overexpression of cyclooxygenase-2 has been reported in skin cancer cells, and may be involved in carcinogenesis. Prostaglandin E2, the end product of cyclooxygenase-2-induced catalysis, autoamplifies the cyclooxygenase-2 expression. It is suggested that an anti-mycotic drug, ketoconazole may inhibit carcinogenesis. We herein investigated if ketoconazole may inhibit prostaglandin E2-induced cyclooxygenase-2 expression in human epidermoid carcinoma A-431 cells. Ketoconazole suppressed prostaglandin E2-induced cyclooxygenase-2 protein and mRNA expression and promoter activation in A-431; the suppressive effects of ketoconazole were counteracted by cyclic adenosine monophosphate analog. Analyses using deleted or mutated cyclooxygenase-2 promoters revealed that cyclic adenosine monophosphate response element (- 59 to - 53 bp) on the promoter was involved in prostaglandin E2-induced stimulation and ketoconazole-induced inhibition of the promoter activity. Electrophoretic mobility shift assays indicated that cyclic adenosine monophosphate response element binding protein and activating transcription factor-1 may constitutively bind to cyclic adenosine monophosphate response element on cyclooxygenase-2 promoter. Prostaglandin E2 increased the proportion of phosphorylated forms among total bound cyclic adenosine monophosphate response element binding protein/activating transcription factor-1, and the effect was suppressed by ketoconazole. Prostaglandin E2 induced the phosphorylation of cyclic adenosine monophosphate response element binding protein and activating transcription factor-1, and the phosphorylation was suppressed by cyclic adenosine monophosphate-dependent protein kinase (protein kinase A) inhibitor, indicating protein kinase A-mediated phosphorylation. Ketoconazole suppressed the prostaglandin E2-induced phosphorylation of cyclic adenosine monophosphate response element binding protein/activating transcription factor-1. Prostaglandin E2 increased intracellular cyclic adenosine monophosphate level by activating adenylate cyclase in A-431, and the increase was suppressed by ketoconazole. These results suggest that ketoconazole may suppress prostaglandin E2-induced cyclooxygenase-2 expression by inhibiting the cyclic adenosine monophosphate signal in A-431, and stress its anti-cancer effect.

Heterotrimeric G protein signaling: role in asthma and allergic inflammation

Asthma and rhinitis are pathophysiologic conditions associated with a prototypical allergic response to inhaled allergens consisting of both neuromechanical and inflammatory components. Heptahelical receptors that bind guanosine triphosphate-binding proteins (G proteins), referred to as G protein-coupled receptors (GPCRs), have been intimately linked with asthma and allergic inflammation for many years. G protein signaling mediates responses throughout the immune, nervous, and muscular systems that might contribute to the pathogenesis of allergic processes and asthma. For example, GPCR agonists or antagonists are used as therapies for asthma either by promoting airway smooth muscle relaxation (beta2 adrenergic receptor agonists) or by inhibiting inflammation in the nasal mucosa and airways (cysteinyl leukotriene receptor antagonists). The focus of this review is to explore how downstream signaling cascades elicited by GPCR activation contribute to the allergic phenotype and the mechanism by which pharmaceuticals alter signaling to generate a therapeutic effect. We also discuss physiologic modulators of G protein signaling, such as regulator of G protein signaling proteins and G protein receptor kinases, inasmuch as they represent potential new therapeutic targets in the treatment of atopy and other inflammatory conditions.

Thrombin-stimulated cell proliferation mediated through activation of Ras/Raf/MEK/MAPK pathway in canine cultured tracheal smooth muscle cells

The elevated level of thrombin has been detected in the airway fluids of asthmatic patients and shown to stimulate cell proliferation in tracheal smooth muscle cells (TSMCs). However, the implication of thrombin in the cell proliferation was not completely understood. In this study, thrombin stimulated [3H]thymidine incorporation and p42/p44 mitogen-activated protein kinase (MAPK) phosphorylation in a time- and concentration-dependent manner in TSMCs. Pretreatment of TSMCs with pertussis toxin (PTX) significantly inhibited [3H]thymidine incorporation and phosphorylation of MAPK induced by thrombin. These responses were attenuated by tyrosine kinase inhibitors genistein and herbimycin A, phosphatidyl inositide (PI)-phospholipase C (PLC) inhibitor U73122, protein kinase C inhibitor GF109203X, removal of Ca2+ by addition of BAPTA/AM plus EGTA, PI 3-kinase inhibitors wortmannin and LY294002, and inhibitor of MEK1/2 PD98059. Furthermore, overexpression of dominant negative mutants, H-Ras-15A and Raf-N4, significantly suppressed p42/p44 MAPK activation induced by thrombin and PDGF-BB, indicating that Ras and Raf may be required for activation of these kinases. These results conclude that the mitogenic effect of thrombin was mediated through the activation of Ras/Raf/MEK/MAPK pathway. Thrombin-mediated MAPK activation was modulated by PI-PLC, Ca2+, PKC, tyrosine kinase, and PI 3-kinase associated with cell proliferation in canine cultured TSMCs.

The p38 mitogen-activated protein kinase pathway plays a critical role in thrombin-induced endothelial chemokine production and leukocyte recruitment

Thrombin, the terminal serine protease in the coagulation cascade, is a proinflammatory molecule in vivo and induces endothelial activation in vitro. The cellular signaling mechanisms involved in this function are unknown. The role of the p38 mitogen-activated protein kinase (MAPK) signaling pathway in thrombin-induced chemokine production was studied. Phosphorylation of both p38 MAPK and its substrate, ATF-2, was observed in human umbilical vein endothelial cells (HUVECs) stimulated with thrombin, with a maximum after 5 minutes of stimulation. Using the selective p38 MAPK inhibitor SB203580, there was a significant decrease in thrombin-induced interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1) protein production and messenger RNA steady-state levels. In addition, SB203580 decreased IL-8 and MCP-1 production induced by the thrombin receptor-1 agonist peptide (TRAP), suggesting functional links between the thrombin G protein-coupled receptor and the p38 MAPK pathway. Furthermore, endothelial activation in the presence of SB203580 decreased the chemotactic activity of thrombin-stimulated HUVEC supernatant on neutrophils and monocytic cells. In contrast, the p42/p44 MAPK pathway did not appear to be involved in thrombin- or TRAP-induced endothelial chemokine production, because there was no reduction in the presence of the p42/p44-specific inhibitor PD98059. These results demonstrate that the p38 rather than p42/44 MAPK signaling pathway plays an important role in thrombin-induced endothelial proinflammatory activation and suggest that inhibition of p38 MAPK may be an interesting target for anti-inflammatory strategies in vascular diseases combining thrombosis and inflammation. (Blood. 2001;98:667-673)

Beta2-adrenergic receptor/cyclic adenosine monophosphate (cAMP) leads to JNK activation through Rho family small GTPases

Gi- and Gq-coupled G protein-coupled receptors (GPCRs) have been shown to activate c-Jun N-terminal kinase (JNK), a subfamily of mitogen-activated protein kinases (MAPKs), through Rho family small GTPases in mammalian cells. We investigated the signaling pathway linking the Gs-coupled beta2-adrenergic receptor with JNK, using smooth muscle DDT1 MF-2 cells, which natively express the beta2-adrenergic receptor. Stimulation of the beta2-adrenergic receptor activated JNK in a time-dependent manner, and a cell-permeable cyclic adenosine monophosphate analogue (8-Br-cAMP) activated JNK. The beta2-adrenergic receptor- or 8-Br-cAMP-induced activation of JNK required Rho family small GTPases. Also, the beta2-adrenergic receptor or 8-Br-cAMP induced activation of Rho family small GTPases. These results demonstrate that the beta2-adrenergic receptor/cAMP leads to JNK activation through Rho family small GTPases in DDT1 MF-2 cells. Activation of Rho family small GTPases may provide a common step in GPCR-mediated JNK activation.

Cdc42, but not RhoA, regulates cyclin D1 expression in bovine tracheal myocytes

We previously demonstrated that Rac1 increased cyclin D1 promoter activity in an extracellular signal-regulated kinase (ERK)-independent, antioxidant-sensitive manner. Here, we examined the regulation of cyclin D1 expression by Cdc42 and RhoA. Overexpression of active Cdc42, but not of RhoA, induced transcription from the cyclin D1 promoter. Furthermore, dominant negative Cdc42, but not RhoA, attenuated platelet-derived growth factor-mediated activation of the cyclin D1 promoter. Overexpression of active Cdc42 increased cyclin D1 protein abundance in COS cells. Cdc42-induced cyclin D1 promoter activation was independent of ERK as evidenced by insensitivity to PD-98059, an inhibitor of mitogen-activated protein kinase/ERK kinase (MEK). Furthermore, Cdc42 was neither sufficient nor required for activation of ERK. Similar to Rac1-induced cyclin D1 expression, pretreatment with the antioxidants catalase and ebselen inhibited Cdc42-mediated transcription from the cyclin D1 promoter. Finally, like Rac1, active Cdc42 induced transactivation of the cyclin D1 promoter cAMP response element binding protein/activating transcription factor-2 binding site. Together, these data suggest that in airway smooth muscle cells, Cdc42 and Rac1 share a common signaling pathway to cyclin D1 promoter activation.

p38 MAP kinase negatively regulates cyclin D1 expression in airway smooth muscle cells

We have demonstrated that platelet-derived growth factor (PDGF) stimulates p38 mitogen-activated protein (MAP) kinase activation in bovine tracheal myocytes, suggesting that p38 is involved in growth regulation. We therefore examined whether p38 regulates expression of cyclin D1, a G(1) cyclin required for cell cycle traversal. The chemical p38 inhibitors SB-202190 and SB-203580 each increased basal and PDGF-induced cyclin D1 promoter activity and protein abundance. Overexpression of a dominant negative allele of MAP kinase kinase-3 (MKK3), an upstream activator of p38alpha, had similar effects. Conversely, active MKK3 and MKK6, both of which increase p38alpha activity, each decreased transcription from the cyclin D1 promoter. Together, these data demonstrate that p38 negatively regulates cyclin D1 expression. We tested whether p38 regulates cyclin D1 expression via inhibition of extracellular signal-regulated kinase (ERK) activation. Chemical inhibitors of p38 induced modest ERK phosphorylation and activation. However, dominant negative MKK3 was insufficient to activate ERK, and active MKK3 and MKK6 did not attenuate platelet-derived growth factor-mediated ERK activation. These data are consistent with the notion that p38alpha negatively regulates cyclin D1 expression via an ERK-independent pathway.

ERK activation and mitogenesis in human airway smooth muscle cells

Asthmatic airways are characterized by an increase in smooth muscle mass, due mainly to hyperplasia. Many studies suggest that extracellular signal-regulated kinases 1 and 2 (ERK1 and ERK2, respectively), one group of the mitogen-activated protein (MAP) kinase superfamily, play a key role in the signal transduction pathway leading to cell proliferation. PGE(2) and forskolin inhibited mitogen-induced ERK activation. Inhibition of MAP kinase kinases 1 and 2 (MEK1 and MEK2, respectively), which are upstream from ERK, with the specific MEK inhibitor U-0126 blocked both cell proliferation and ERK activation. In addition, U-0126 inhibited mitogen-induced activation of p90 ribosomal S6 kinase and expression of c-Fos and cyclin D1, all of which are downstream from ERK in the signaling cascade that leads to cell proliferation. Antisense oligodeoxynucleotides directed to ERK1 and -2 mRNAs reduced ERK protein and cell proliferation. These results indicate that ERK is required for human airway smooth muscle cell proliferation. Thus targeting the control of ERK activation may provide a new therapeutic approach for hyperplasia seen in asthma.

Effects of endothelin-1 and nitric oxide on proliferation of cultured guinea pig bronchial smooth muscle cells

The proliferative effects of endothelin-1 (ET-1), both alone and in combination with epidermal growth factor (EGF), and the effect of nitric oxide (NO) on the cell proliferation were investigated in cultured guinea pig bronchial smooth muscle cells. ET-1 (10-100 nM) alone augmented cell proliferation, and was additive to the effect of EGF (0.48 nM) in a concentration-dependent manner. An ET(A) antagonist, BQ-123 (10 microM), reduced the cell-proliferative effect of ET-1, whereas an ET(B) antagonist, BQ-788 (10 microM), did not influence the effect. A NO donor, SIN-1 (10 nM-1 microM), reduced the cell-proliferative effect of ET-1 in a concentration-dependent manner. The effect of SIN-1 (1 microM) was partly, but significantly, reversed by a soluble guanylyl cyclase inhibitor, ODQ (1 microM). These results suggest that ET-1 acts not only as a co-mitogen with EGF but also as a mitogen alone, and that its action is mediated through activation of ET(A) receptors. Therefore, ET-1 may contribute to airway remodeling, a pathophysiological hallmark of asthma. In addition, NO, which is produced mainly in the airway epithelium and is partly mediated through cGMP-dependent pathway, may reduce the phenomenon.

The endothelin system in human saphenous vein graft disease

Saphenous vein graft stenosis is a significant clinical complication for coronary artery bypass patients. Endothelin-1, a peptide synthesised by vascular endothelial cells, is the most potent known vasoconstrictor and has mitogenic properties. Recent advances in our knowledge of endothelin-1 synthesis and endothelin receptor expression and function in normal and atherosclerotic human saphenous vein imply a role for the peptide in the progression of vein graft failure. Manipulation of the endothelin system, by selective receptor antagonism or inhibition of the specific endothelin-converting enzymes may, therefore, represent a novel therapeutic target for treating vein graft disease.

Mechanisms of thrombin-induced MAPK activation associated with cell proliferation in human cultured tracheal smooth muscle cells

The elevated level of thrombin has been detected in the airway fluids of asthmatic patients. However, the implication of thrombin in the pathogenesis of bronchial hyperreactivity was not completely understood. Therefore, in this study we investigated the effect of thrombin on cell proliferation and p42/p44 mitogen-activated protein kinase (MAPK) activation in human tracheal smooth muscle cells (TSMCs). Thrombin stimulated [3H]thymidine incorporation and p42/p44 MAPK phosphorylation in a time- and concentration-dependent manner in TSMCs. Pretreatment of TSMCs with pertussis toxin (PTX) significantly inhibited [3H]thymidine incorporation and phosphorylation of MAPK induced by thrombin. These responses were attenuated by tyrosine kinase inhibitors genistein and herbimycin A, phosphatidyl inositide (PI)-phospholipase C (PLC) inhibitor U73122, protein kinase C (PKC) inhibitor GF109203X, removal of Ca(2+) by addition of BAPTA/AM plus EGTA, and PI 3-kinase inhibitors wortmannin and LY294002. In addition, thrombin-induced [3H]-thymidine incorporation and p42/p44 MAPK phosphorylation was completely inhibited by PD98059 (an inhibitor of MEK1/2), indicating that activation of MEK1/2 was required for these responses. Furthermore, overexpression of dominant negative mutants, RasN17 and Raf-301, significantly suppressed p42/p44 MAPK activation induced by thrombin and PDGF-BB, indicating that Ras and Raf may be required for activation of these kinases. These results conclude that the mitogenic effect of thrombin was mediated through the activation of Ras/Raf/MEK/MAPK pathway. Thrombin-mediated MAPK activation was modulated by PI-PLC, Ca(2+), PKC, tyrosine kinase, and PI 3-kinase associated with cell proliferation in cultured human TSMCs.

Mammalian mitogen-activated protein kinase signal transduction pathways activated by stress and inflammation

The molecular details of mammalian stress-activated signal transduction pathways have only begun to be dissected. This, despite the fact that the impact of these pathways on the pathology of chronic inflammation, heart disease, stroke, the debilitating effects of diabetes mellitus, and the side effects of cancer therapy, not to mention embryonic development, innate and acquired immunity, is profound. Cardiovascular disease and diabetes alone represent the most significant health care problems in the developed world. Thus it is not surprising that understanding these pathways has attracted wide interest, and in the past 10 years, dramatic progress has been made. Accordingly, it is now becoming possible to envisage the transition of these findings to the development of novel treatment strategies. This review focuses on the biochemical components and regulation of mammalian stress-regulated mitogen-activated protein kinase (MAPK) pathways. The nuclear factor-kappa B pathway, a second stress signaling paradigm, has been the subject of several excellent recent reviews (258, 260).

The importance of ERK activity in the regulation of cyclin D1 levels and DNA synthesis in human cultured airway smooth muscle

The relationship between persistent ERK (extracellular signal-regulated kinase) activity, cyclin D1 protein and mRNA levels and cell cycle progression in human cultured airway smooth muscle was examined in response to stimulation by ET-1 (endothelin-1), thrombin and bFGF (basic fibroblast growth factor). Thrombin (0.3 and 3 u ml(-1)) and bFGF (0.3 and 3 nM) increased ERK activity for more than 2 h and increased cell number, whereas ET-1 (100 nM) transiently stimulated ERK activity and was non-mitogenic. The MEK1 (mitogen-activated ERK kinase) inhibitor, PD 98059 (30 microM), inhibited both ERK phosphorylation and activity, and either prevented (thrombin 0.3 and 3 u ml(-1), bFGF 300 pM) or attenuated (bFGF 3 nM) DNA synthesis. Thrombin and bFGF increased both cyclin D1 mRNA and protein levels. PD 98059 decreased cyclin D1 protein levels stimulated by the lower but not higher thrombin concentrations. Moreover, increases in cyclin D1 mRNA levels were unaffected by PD 98059 pretreatment, irrespective of the mitogen or its concentration, suggesting that inhibition of cyclin D1 protein levels occurred by a post-transcriptional mechanism. These findings indicate that the control of cyclin D1 protein levels may occur independently of the MEK1/ERK signalling pathways. The inhibition of S phase entry by PD 98059 at higher thrombin concentrations appears to result from effects on pathways downstream or parallel to those regulating cyclin D1 protein levels. These findings suggest heterogeneity in the signalling of DNA synthesis in human cultured airway smooth muscle.

Desensitisation of protease-activated receptor-1 (PAR-1) in rat astrocytes: evidence for a novel mechanism for terminating Ca2+ signalling evoked by the tethered ligand

Protease-activated receptor-1 (PAR-1), a G-protein-coupled receptor, is activated when thrombin cleaves its N-terminal exodomain, thereby regulating morphology, growth and survival of neurones and astrocytes. We have investigated the mechanism of PAR-1 desensitisation and resensitisation after proteolytic or non-proteolytic stimulation with thrombin or thrombin receptor agonist peptide (TRag), respectively. In rat primary astrocytes, short-term stimulation with thrombin resulted in a single [Ca2+]i transient and a dose-dependent de- and resensitisation, as assessed by single-cell Ca2+ imaging of fura-2-loaded astrocytes. An initial proteolytic activation of astrocyte PAR-1 by exposure to thrombin strongly decreased the response elicited by subsequent application of a second dose of thrombin or of TRag. In contrast, after an initial non-proteolytic activation of astrocyte PAR-1 by TRag, the subsequent response to thrombin, but not to an additional application of TRag, was strongly attenuated, and the time course for desensitisation was slower. Based on this finding we hypothesised that after PAR-1 activation, the 'tethered ligand' is proteolytically destroyed. As a consequence, the receptor becomes unresponsive to a subsequent thrombin stimulus but is still capable of responding to TRag. This hypothesis was supported by applying thermolysin, which is known to cleave PAR-1 within its tethered-ligand domain, and was confirmed by incubation with soybean trypsin inhibitor. PAR-1 resensitisation occurs via new PAR-1 synthesis since resensitisation was inhibited by cycloheximide and brefeldin A. From these results, we derive a novel model wherein activation of PAR-1, in addition to initiating signal transduction, activates a protease mechanism that cleaves the N-terminus of the receptor, thus terminating the signal and probably inducing receptor internalisation.

Thrombin inhibits tumor cell growth in association with up-regulation of p21(waf/cip1) and caspases via a p53-independent, STAT-1-dependent pathway

Thrombin, a multifunctional protein, has been found to be involved in cellular mitogenesis, tumor growth, and metastasis, in addition to its well known effects on the initiation of platelet aggregation and secretion and the conversion of fibrinogen to fibrin to form blood clots. These properties of thrombin rely on its action as a serine protease, which cleaves the N-terminal region of a 7-transmembrane G protein receptor (protease-activated receptor, PAR-1), thus exposing a tethered end hexapeptide sequence capable of activating its receptor. Little is known about its effect on genes that regulate the cell cycle. This study was undertaken to investigate the possible mechanisms by which thrombin regulates tumor cell growth in several tumor cell lines: human CHRF megakaryocyte, DU145 prostate, MDAMB231 and MCF7 breast, U3A fibrosarcoma, and 2 murine fibroblast cell lines, MEFp53(-/-) and CD STAT(-/-). We have found that thrombin under the conditions of culture employed inhibits cell growth by both up-regulation of p21(waf/cip1) and induction of caspases via its PAR-1 receptor. The increased expression of p21(waf/cip1) by thrombin was p53 independent, STAT1 dependent, and protein synthesis independent. This was associated with tyrosine phosphorylation of JAK2 and STAT1, and nuclear translocation of STAT1. Induction of apoptosis is also PAR-1-specific, STAT1-dependent, and associated with up-regulation of caspases 1, 2, and 3. Our study establishes, for the first time, a link between PAR-1 receptor activation with the STAT signal pathway, which leads to cell cycle control and apoptosis. This observation broadens our understanding of the mechanism of PAR-1 activation and its effect on cell growth, and could possibly lead to therapeutic approaches for the treatment of cancer.

Requirement for protein-tyrosine phosphatase SHP-2 in insulin-induced activation of c-Jun NH(2)-terminal kinase

Mitogen-activated protein kinases, including extracellular signal-regulated kinases and c-Jun NH(2)-terminal kinases (JNKs), are activated by insulin. Although the mechanism by which the insulin receptor activates extracellular signal-regulated kinases is relatively well defined, the pathway that leads to JNK activation is poorly understood. Overexpression of a catalytically inactive mutant (SHP-2C/S) of the protein-tyrosine phosphatase SHP-2 in Rat-1 fibroblasts that also express human insulin receptors has now revealed that activation of JNKs by insulin and epidermal growth factor, but not that by anisomycin or sorbitol, requires SHP-2. A dominant negative mutant (RasN17) of Ha-Ras blocked insulin-induced JNK activation, whereas a dominant negative mutant (RacN17) of Rac1 or a specific inhibitor (LY294002) of phosphoinositide 3-kinase did not, indicating a role for Ras, but not for Rac or phosphoinositide 3-kinase, in this effect. SHP-2C/S markedly inhibited Ras activation in response to insulin without affecting insulin-induced tyrosine phosphorylation of cellular substrates or the dissociation of the Crk-p130(Cas) complex. In contrast, SHP-2C/S did not inhibit activation of JNKs induced by a constitutively active mutant (RasV12) of Ha-Ras. Furthermore, expression of myristoylated SOS, which functions as a potent activator of Ras, induced JNK activation even when SHP-2 was inactivated. These results suggest that SHP-2 contributes to JNK activation in response to insulin by positively regulating the Ras signaling pathway at the same level as, or upstream from, SOS.

Regulation of vascular smooth muscle cell proliferation by nuclear factor-kappaB and its inhibitor, I-kappaB

Proliferation of vascular smooth muscle cells (SMC) is a crucial event in the formation of atherosclerotic tissues and is regulated by nuclear transcriptional factors including nuclear factor-kappaB (NF-kappaB). We constructed a reporter gene assay to measure NF-kappaB-dependent transcriptional activity in SMC. Thrombin receptor-activating peptide (TRAP) and basic fibroblast growth factor (bFGF) stimulated SMC proliferation and rapidly enhanced the NF-kappaB transcriptional activity in a dose-dependent manner. 4-Cyano-5,5-bis-(methoxyphenyl)4-pentenoic acid (E5510) significantly inhibited SMC proliferation and also suppressed NF-kappaB transcription stimulated by TRAP and bFGF. In contrast, although tumor necrosis factor (TNF)-alpha activated NF-kappaB transcription, E5510 had no effect on TNF-alpha-induced activation. NF-kappaB was activated after the stimulation of TRAP, bFGF, and TNF-alpha in electrophoretic mobility shift assay, and E5510 suppressed the NF-kappaB activation induced by TRAP and bFGF but not the activation by TNF-alpha. Western blot analysis of I-kappaBalpha and I-kappaBbeta, inhibitors of NF-kappaB, indicated that I-kappaBalpha degradation, rather than I-kappaBbeta degradation, was important in NF-kappaB activation after the stimulation of TRAP and bFGF. PD98059, an inhibitor of extracellular signal-regulated kinase (ERK) kinase, suppressed NF-kappaB transcriptional activity and SMC proliferation. The phosphorylation of ERK1/2 was rapidly induced by TRAP and bFGF but not by TNF-alpha. These results indicate that TRAP and bFGF induced I-kappaB degradation and NF-kappaB activation through a distinct pathway from TNF-alpha and that ERK1/2 may play an important role in NF-kappaB activation induced by TRAP and bFGF.

Autocrine production of matrix metalloproteinase-2 is required for human airway smooth muscle proliferation

Airway smooth muscle proliferation is important in asthma and is dependent on pro- and antimitogenic factors and cell-matrix interactions. Here we show an antiproliferative effect of protease inhibitors on human airway smooth muscle due to inhibition of autocrine-derived matrix metalloproteinase (MMP)-2. Proliferation in response to fetal bovine serum, thrombin, and platelet-derived growth factor was inhibited by the broad-spectrum protease inhibitor Complete and the MMP inhibitors EDTA and Ro-31-9790 but not by cysteine or serine protease inhibitors. Conditioned medium from airway smooth muscle cells contained 72-kDa gelatinase that was secreted by growth-arrested cells and increased by fetal bovine serum but not by thrombin or platelet-derived growth factor. Immunostaining of cultured human airway smooth muscle cells and normal lung biopsies confirmed this gelatinase to be MMP-2. Our results suggest a novel role for MMP-2 as an important autocrine factor required for airway smooth muscle proliferation. Inhibition of MMPs could provide a target for the prevention of smooth muscle hyperplasia and airway remodeling in asthma.

MAPK superfamily activation in human airway smooth muscle: mitogenesis requires prolonged p42/p44 activation

Asthma is frequently associated with abnormal airway smooth muscle (ASM) growth that may contribute to airway narrowing and hyperresponsiveness to contractile agents. Although numerous hormones and cytokines have been shown to induce human ASM (HASM) proliferation, the cellular and molecular mechanisms underlying HASM hyperplasia are largely unknown. Here we characterize the roles of the mitogen-activated protein kinase (MAPK) superfamily [p42/p44 MAPK, c-Jun amino-terminal kinase/stress-activated protein kinase (JNK/SAPK), and p38] in mediating hormone- and cytokine-induced HASM proliferation. Significant enhancement of [(3)H]thymidine incorporation in HASM cultures was observed only by treatment with agents (epidermal growth factor, platelet-derived growth factor, thrombin, and phorbol 12-myristate 13-acetate) that promoted a strong and sustained activation of p42/p44 MAPK. Significant activation of the JNK/SAPK and p38 pathways was only observed on stimulation with interleukin (IL)-1beta and tumor necrosis factor-alpha, agents that did not appreciably stimulate HASM proliferation. Two different inhibitors of MAPK/extracellular signal-regulated kinase kinase (MEK), PD-98059 and U-0126, inhibited mitogen-induced [3H]thymidine incorporation in a manner consistent with their ability to inhibit p42/p44 activation. Elk-1 and activator protein-1 reporter activation by mitogens was similarly inhibited by inhibition of MEK, suggesting a linkage between p42/p44 activation, transcription factor activation, and HASM proliferation. These findings establish a fundamental role for p42/p44 activation in regulating HASM proliferation and provide insight into species-specific differences observed among studies in ASM mitogenesis.

Changes in the balance of phosphoinositide 3-kinase/protein kinase B (Akt) and the mitogen-activated protein kinases (ERK/p38MAPK) determine a phenotype of visceral and vascular smooth muscle cells

The molecular mechanisms behind phenotypic modulation of smooth muscle cells (SMCs) remain unclear. In our recent paper, we reported the establishment of novel culture system of gizzard SMCs (Hayashi, K., H. Saga, Y. Chimori, K. Kimura, Y. Yamanaka, and K. Sobue. 1998. J. Biol. Chem. 273: 28860-28867), in which insulin-like growth factor-I (IGF-I) was the most potent for maintaining the differentiated SMC phenotype, and IGF-I triggered the phosphoinositide 3-kinase (PI3-K) and protein kinase B (PKB(Akt)) pathway. Here, we investigated the signaling pathways involved in de-differentiation of gizzard SMCs induced by PDGF-BB, bFGF, and EGF. In contrast to the IGF-I-triggered pathway, PDGF-BB, bFGF, and EGF coordinately activated ERK and p38MAPK pathways. Further, the forced expression of active forms of MEK1 and MKK6, which are the upstream kinases of ERK and p38MAPK, respectively, induced de-differentiation even when SMCs were stimulated with IGF-I. Among three growth factors, PDGF-BB only triggered the PI3-K/PKB(Akt) pathway in addition to the ERK and p38MAPK pathways. When the ERK and p38MAPK pathways were simultaneously blocked by their specific inhibitors or an active form of either PI3-K or PKB(Akt) was transfected, PDGF-BB in turn initiated to maintain the differentiated SMC phenotype. We applied these findings to vascular SMCs, and demonstrated the possibility that the same signaling pathways might be involved in regulating the vascular SMC phenotype. These results suggest that changes in the balance between the PI3-K/PKB(Akt) pathway and the ERK and p38MAPK pathways would determine phenotypes of visceral and vascular SMCs. We further reported that SMCs cotransfected with active forms of MEK1 and MKK6 secreted a nondialyzable, heat-labile protein factor(s) which induced de-differentiation of surrounding normal SMCs.

Cell cycle arrest and reversion of Ras-induced transformation by a conditionally activated form of mitogen-activated protein kinase kinase kinase 3

Signal-induced proliferation, differentiation, or stress responses of cells depend on mitogen-activated protein kinase (MAPK) cascades, the core modules of which consist of members of three successively acting kinase families (MAPK kinase kinase [MAP3K], MAPK kinase, and MAPK). It is demonstrated here that the MEKK3 kinase inhibits cell proliferation, a biologic response not commonly associated with members of the MAP3K family of kinases. A conditionally activated form of MEKK3 stably expressed in fibroblasts arrests these cells in early G1. MEKK3 critically blocks mitogen-driven expression of cyclin D1, a cyclin which is essential for progression of fibroblasts through G1. The MEKK3-induced block of cyclin D1 expression and of cell cycle progression may be mediated via p38 MAPK, a downstream effector of MEKK3. The MEKK3-mediated block of proliferation also reverses Ras-induced cellular transformation, suggesting possible tumor-suppressing functions for this kinase. Together, these results suggest an involvement of the MEKK3 kinase in negative regulation of cell cycle progression, and they provide the first insights into biologic activities of this kinase.