The mitogen-activated protein kinase pathway can mediate growth inhibition and proliferation in smooth muscle cells. Dependence on the availability of downstream targets

Urokinase potentiates PDGF-induced chemotaxis of human airway smooth muscle cells

We investigated the chemotactic action of PDGF and urokinase on human airway smooth muscle (HASM) cells in culture. Cells were put in collagen-coated transwells with 8-micro m perforations, incubated for 4 h with test compounds, then fixed, stained, and counted as migrated nuclei by microscopy. Cells from all culture conditions showed some basal migration (migration in the absence of stimuli during the assay), but cells preincubated for 24 h in 10% FBS or 20 ng/ml PDGF showed higher basal migration than cells quiesced in 1% FBS. PDGF(BB), PDGF(AA), and PDGF(AB) were all chemotactic when added during the assay. PDGF chemotaxis was blocked by the phosphatidyl 3'-kinase inhibitor LY-294002, the MEK inhibitor U-0126, PGE(2), formoterol, pertussis toxin, and the Rho kinase inhibitor Y-27632. Urokinase alone had no stimulatory effect on migration of quiescent cells but caused a dose-dependent potentiation of chemotaxis toward PDGF. Urokinase also potentiated the elevated basal migration of cells pretreated in 10% FBS or PDGF. This potentiating effect of urokinase appears to be novel. We conclude that PDGF and similar cytokines may be important factors in airway remodeling by redistribution of smooth muscle cells during inflammation and that urokinase may be important in potentiating the response.

Role of PP2A in the regulation of p38 MAPK activation in bovine aortic endothelial cells exposed to cyclic strain

We have previously reported that cyclic strain results in rapid phosphorylation of p38 mitogen activated protein kinase (MAPKs). The aim of this study was to examine the role of protein phosphatase type 2A (PP2A) in regulating p38 MAPK activation in bovine aortic endothelial cells exposed to cyclic strain. In this study, we demonstrate that the catalytic subunit of PP2A is tyrosine phosphorylated by cyclic strain, resulting in inhibition of phosphatase activity. Okadaic acid, an inhibitor of PP2A at lower concentrations increased phosphorylation of p-38. Phospho-p38 MAPK physically associated with the catalytic subunit, PP2Ac. Phospho-p38 MAPK was dephosphorylated by purified PP2Ac in cell lysates, but if pretreated with okadaic acid, phospho-p38 MAPK was maintained. Taken together, our result suggests that PP2A plays a regulatory role in p38 MAPK activation in endothelial cells exposed to cyclic strain.

Inhibition of rat smooth muscle cell adhesion and proliferation by non-anticoagulant heparins

Heparin is a well established growth inhibitor of arterial smooth muscle cells (SMCs) both in animal models and in vitro. Even though the cellular mechanisms involved in the anti-proliferative properties of heparin are being resolved, the structural requirements for the biological effects of heparin are not known in detail. Here, we have studied the effect of chemically modified heparins of different molecular weights and anticoagulant activities on proliferation and adhesion of rat aortic SMCs in vitro. The effects of native heparin (NH) and chemically modified heparins were examined after stimulation with fetal calf serum (FCS), platelet-derived growth factor BB (PDGF BB), basic fibroblast growth factor (bFGF), and heparin-binding epidermal growth factor (hbEGF) with respect to DNA synthesis and expression of phosphorylated and activated mitogen-activated protein kinase (pERK1 and 2). In a similar manner as NH, the modified heparins were capable of inhibiting activation of ERK1 and 2 and DNA synthesis induced by FCS and hbEGF whereas the modified heparins potentiated the mitogenic effect of bFGF and no compound affected PDGF BB-induced ERK activity and SMC growth. In contrast, cell adhesion to fibronectin was inhibited by NH and modified heparins in a size-dependent manner with the lowest effect by the smallest compound. The results show that heparins with varying anticoagulant activities and molecular weights but with similar sulfate content can retain anti-proliferative properties while the effect on some other biological processes such as cell adhesion is lost. Possibly, such chemical alterations may yield useful substances for the prevention of SMC proliferation after arterial injury.

The oxygen radical scavenger pyrrolidine dithiocarbamate enhances interleukin-1beta-induced cyclooxygenase-2 expression in cerebral microvascular smooth muscle cells

Oxidative stress and inducible cyclooxygenase-2 (COX-2)-mediated prostaglandin (PG) formation have been proposed to play an important role in cytokine-induced vascular pathology. To explore the relationship between oxidative stress and COX-2 induction, cultured murine cerebral microvascular smooth muscle cells (SMCs) were stimulated with interleukin-1beta (IL-1beta) in the presence or absence of an oxygen radical scavenger, pyrrolidine dithiocarbamate (PDTC). IL-1beta increased COX-2 protein expression in a dose- and time-dependent manner, an increase that was further enhanced by PDTC in a dose-dependent manner. PDTC did not, however, affect the expression of COX-1 protein. In the presence of 100 microM PDTC, PGE(2) production induced by IL-1beta (5 ng/ml) was increased by threefold as compared with IL-1beta alone. Although PDTC enhanced COX-2 protein expression, it did not increase IL-1beta-induced expression of COX-2 mRNA, indicating that the regulatory effect occurred at the posttranscriptional level. The time course of COX-2 protein degradation indicated that PDTC also did not alter the stability of the COX-2 protein induced by IL-1beta. These results suggest that endogenous oxygen radicals may blunt COX-2 induced by IL-1beta through an effect on translation.

Adenosine up-regulates cyclooxygenase-2 in human granulocytes: impact on the balance of eicosanoid generation

Polymorphonuclear neutrophils (granulocytes; PMNs) are often the first blood cells to migrate toward inflammatory lesions to perform host defense functions. PMNs respond to specific stimuli by releasing several factors and generate lipid mediators of inflammation from the 5-lipoxygenase and the inducible cyclooxygenase (COX)-2 pathways. In view of adenosine's anti-inflammatory properties and suppressive impact on the 5-lipoxygenase pathway, we addressed in this study the impact of this autacoid on the COX-2 pathway. We observed that adenosine up-regulates the expression of the COX-2 enzyme and mRNA. Production of PGE(2) in response to exogenous arachidonic acid was also increased by adenosine and correlated with COX-2 protein levels. The potentiating effect of adenosine on COX-2 could be mimicked by pharmacological increases of intracellular cAMP levels, involving the latter as a putative second messenger for the up-regulation of COX-2 by adenosine. Specific COX-2 inhibitors were used to confirm the predominant role of the COX-2 isoform in the formation of prostanoids by stimulated PMNs. Withdrawal of extracellular adenosine strikingly emphasized the inhibitory potential of PGE(2) on leukotriene B(4) formation and involved the EP(2) receptor subtype in this process. Thus, adenosine may promote a self-limiting regulatory process through the increase of PGE(2) generation, which may result in the inhibition of PMN functions. This study identifies a new aspect of the anti-inflammatory properties of adenosine in leukocytes, introducing the concept that this autacoid may exert its immunomodulatory activities in part by modifying the balance of lipid mediators generated by PMNs.

Oncostatin M stimulates proliferation, induces collagen production and inhibits apoptosis of human lung fibroblasts

1. Oncostatin M (OSM), a member of the interleukin-6 (IL-6) cytokine family, acts on a variety of cells and elicits diversified biological responses, suggesting potential roles in the regulation of cell survival, differentiation and proliferation. 2. We have examined the effect of OSM on the regulation of human lung fibroblast proliferation, collagen production and spontaneous apoptosis. The proliferative effects of OSM (0.5 - 100 ng ml(-1)) were assessed using a MTS assay as well as [(3)H]-thymidine incorporation and cell counts at 24 and 48 h. Hydroxyproline was measured as an index of procollagen production by high pressure liquid chromotography (HPLC). Apoptosis was determined by annexin staining. 3. OSM enhanced the mitotic activity of lung fibroblasts in a time and dose dependent manner. Maximum proliferation of 57% above control was observed after incubation for 48 h with 2 ng ml(-1) OSM (P<0.05). 4. Incubation with the mitogen activated protein kinase (MAPK) kinase inhibitor, PD98059 or the tyrosine kinase inhibitor, genestein both significantly reduced the mitogenic effect of OSM (P<0.05). 5. In contrast, proliferation in response to OSM was not regulated by induction of cyclo-oxygenase and subsequent prostaglandin E(2) (PGE(2)) release or by IL-6. 6. OSM also stimulated fibroblasts to synthesize pro-collagen by a maximum of 35% above control levels after 48 h (P<0.05). 7. OSM significantly inhibited the spontaneous apoptosis of fibroblasts at 24 and 48 h. 8. These results provide evidence that OSM has pro-fibrotic properties and suggest that it may play a role in normal lung wound repair and fibrosis.

Activation of Raf-1/MEK-1/2/p42/44(MAPK) cascade alone is sufficient to uncouple LDL receptor expression from cell growth

Our previous observation that induction of low density lipoprotein (LDL) receptor expression by a variety of extracellular signals is blocked by PD98059, a specific mitogen-activated protein kinase kinase inhibitor, led to the suggestion that the growth-responsive p42/44(MAPK) cascade plays a critical role in regulating LDL receptor transcription. To analyze the specific contribution of the p42/44(MAPK) cascade in regulating cell growth and LDL receptor induction, we established a HepG2-derived cell line that stably expresses an inducible form of oncogenic human Raf-1 kinase. Using this system, we provide direct evidence that specific activation of this cascade alone is not only required but is sufficient to fully induce LDL receptor expression. Interestingly, degree of p42/44(MAPK) activation determines the extent of LDL receptor induction. However, activation of p42/44(MAPK) in the above cells led to the inhibition of DNA synthesis, caused growth arrest, decrease in cyclin A and upregulation of p21(Cip) expression in a time-dependent manner. These results suggest that each of these two processes can be regulated independently of each other in response to p42/44(MAPK) activation. Thus, extent of p42/44(MAPK) activation may be important in transducing divergent cellular responses in human cells with implications for altered signaling resulting in hypercholesterolemia.

Stimulation of DNA synthesis, activation of mitogen-activated protein kinase ERK2 and nuclear accumulation of c-fos in human aortic smooth muscle cells by ketamine

Proliferation of vascular smooth muscle cells is known to be regulated by autocrine and paracrine stimuli, including extracellular matrix, reactive oxygen species, lipids, and biomechanical forces. The effect of many pharmacological agents to which smooth muscle cells may be exposed, however, is widely unexplored. Ketamine, an intravenous anaesthetic and a phencyclidine derivative, regulates diverse intracellular signalling pathways in smooth muscle cells, several of which are known to affect cell proliferation. The effect of ketamine on proliferative response of smooth muscle cells, however, is not determined. We tested the hypothesis that ketamine may regulate proliferation of smooth muscle cells, and investigated the effects of pharmacological doses of ketamine on their proliferative capacity by measuring DNA synthesis and activation of mitogen-activated protein (MAP) kinase signalling pathway in human aortic smooth muscle cells. DNA synthesis, as determined by incorporation of 3H-thymidine into DNA, was enhanced by 73% (P < 0.0001) and 130% (P < 0.0001) with 10 and 100 microm ketamine, respectively. Ketamine-induced DNA synthesis was dependent on de novo protein synthesis, as it was abolished by an inhibitor of protein synthesis, cycloheximide. A synthetic inhibitor of MAP kinase pathway, PD98059, decreased 50% (P < 0.0001) of ketamine-induced DNA synthesis, suggesting that the activation of MAP kinase pathway was partially responsible for ketamine-induced effects. Consistently, in-gel kinase assay and in vitro kinase assay of cell lysates showed ketamine-induced MAP kinase activation and expression of ERK2 (extracellular signal-regulated kinase) in smooth muscle cells. This effect of ketamine was not dependent on de novo protein synthesis. Immunofluorescent light microscopy showed ketamine-induced nuclear accumulation of c-fos, a downstream effect of MAP kinase activation, in smooth muscle cells. In conclusion, these data support the hypothesis of the study and demonstrate that ketamine, by stimulating DNA synthesis in human aortic smooth muscle cells, may have an impact on proliferative capacity of these cells. The present results also demonstrate that ketamine induces the activation of MAP kinase pathway and nuclear accumulation of transcription factor c-fos in smooth muscle cells. They further demonstrate that the activation of MAP kinases is partially responsible for ketamine-induced DNA synthesis in human aortic smooth muscle cells. Together, these findings suggest that ketamine may play a role as a pharmacological regulator of mechanisms involved in proliferation of smooth muscle cells.

CaM kinase II-dependent activation of tyrosine kinases and ERK1/2 in vascular smooth muscle

In vascular smooth muscle (VSM) and many other cells, G protein receptor-coupled activation of mitogen-activated protein kinases has been linked, in part, to increases in free intracellular Ca(2+). Previously, we demonstrated that ionomycin-, angiotensin II-, and thrombin-induced activation of extracellular signal-regulated kinase (ERK)1/2 in VSM cells was attenuated by pretreatment with KN-93, a selective inhibitor of the multifunctional Ca(2+)/calmodulin-dependent protein kinase (CaM kinase II). In the present study, we show that the Ca(2+)-dependent pathway leading to activation of ERK1/2 is preceded by nonreceptor proline-rich tyrosine kinase (PYK2) activation and epidermal growth factor (EGF) receptor tyrosine phosphorylation and is attenuated by inhibitors of src family kinases or the EGF receptor tyrosine kinase. Furthermore, we demonstrate that pretreatment with KN-93 or a CaM kinase II inhibitor peptide inhibits Ca(2+)-dependent PYK2 activation and EGF receptor tyrosine phosphorylation in response to ionomycin, ATP, and platelet-derived growth factor but has no effect on phorbol 12,13-dibutyrate- or EGF-induced responses. The results implicate CaM kinase II as an intermediate in the Ca(2+)/calmodulin-dependent activation of PYK2.

Many actions of cyclooxygenase-2 in cellular dynamics and in cancer

Cyclooxygenase-2 (COX-2) is the inducible isoform of cyclooxygenase, the enzyme that catalyzes the rate-limiting step in prostaglandin synthesis from arachidonic acid. Various prostaglandins are produced in a cell type-specific manner, and they elicit cellular functions via signaling through G-protein coupled membrane receptors, and in some cases, through the nuclear receptor PPAR. COX-2 utilization of arachidonic acid also perturbs the level of intracellular free arachidonic acid and subsequently affects cellular functions. In a number of cell and animal models, induction of COX-2 has been shown to promote cell growth, inhibit apoptosis and enhance cell motility and adhesion. The mechanisms behind these multiple actions of COX-2 are largely unknown. Compelling evidence from genetic and clinical studies indicates that COX-2 upregulation is a key step in carcinogenesis. Overexpression of COX-2 is sufficient to cause tumorigenesis in animal models and inhibition of the COX-2 pathway results in reduction in tumor incidence and progression. Therefore, the potential for application of non-steroidal anti-inflammatory drugs as well as the recently developed COX-2 specific inhibitors in cancer clinical practice has drawn tremendous attention in the past few years. Inhibition of COX-2 promises to be an effective approach in the prevention and treatment of cancer, especially colorectal cancer.

Cyclooxygenase isozyme expression and intimal hyperplasia in a rat model of balloon angioplasty

Prostaglandin formation is enhanced in vascular disease, in part through induction of cyclooxygenase (COX-2) in vascular smooth muscle cells. Because COX regulates cell growth and migration, we examined whether the COX expression plays a role in the development of intimal hyperplasia after vascular injury. Rats undergoing balloon angioplasty of the carotid artery were randomized to receive a selective COX-2 inhibitor (SC-236), a selective COX-1 inhibitor (SC-560) or a combination of the two. Normal, uninjured vessels showed COX-1, but no COX-2 expression. Fourteen days after balloon injury, both COX-1 and COX-2 were expressed in the neointima. Balloon angioplasty resulted in a marked increase in the urinary excretion of prostaglandin (PG) E(2,) PGF(2alpha), and thromboxane (TX) B(2). Both the COX-1 inhibitor SC-560 and the COX-2 inhibitor SC-236 suppressed the generation of PGE(2) and PGF(2alpha), particularly when combined, suggesting a role for both isozymes in the generation of prostaglandins in this model. In contrast, TXA(2) was markedly suppressed by the COX-1 inhibitor SC-560. COX-2 inhibition with SC-236 had no effect on intimal hyperplasia at day 14 (0 versus 8.5%; n = 7 in controls). In contrast, intimal hyperplasia was reduced by SC-560 when administered alone (by 42%; n = 7, p < 0.05) or in combination with SC-236 (by 40%; n = 7, p < 0.05). COX-1 may play a role in the development of intimal hyperplasia, potentially through the inhibition of platelet TXA(2). Despite being expressed in the neointima, COX-2 does not play a role in the development of intimal hyperplasia after vascular injury.

The involvement of NF-kappaB in the constitutive overexpression of cyclooxygenase-2 in cyclooxygenase-1 null cells

We recently reported that there was enhanced cyclooxygenase (COX)-2 expression and prostaglandin E(2) biosynthesis in COX-1 deficient (COX-1(-/-)) cells. We also observed that the growth of COX-1(-/-) cells was significantly retarded compared to wild-type (WT) and COX-2 deficient (COX-2(-/-)) cells. In this study, COX-2 expression and its promoter activity were compared in immortalized, nontransformed fibroblasts from WT, COX-1(-/-) or COX-2(-/-) mice in the context of the role of COX-2 as a growth regulator. When compared with WT cells expressing both COX isoenzymes, constitutive COX-2 protein and promoter activity were significantly higher in COX-1(-/-) cells as determined by Western blotting and luciferase assays using a 5'-flanking promoter construct of the murine COX-2 gene. The luciferase assay using a series of luciferase-linked COX-2 promoter deletions transfected into COX-1(-/-) cells indicated that a region involving NF-kappaB plays a significant role in regulating constitutive COX-2 expression. Data from electrophoretic mobility shift assays showed that COX-1(-/-) cells contained higher levels of activated NF-kappaB than either WT or COX-2(-/-) cells. Furthermore, COX-2 promoter activity was significantly inhibited by the oligonucleotides (ODNs) containing the NF-kappaB element (NF-kappaB decoy ODNs) but not by the scrambled control ODNs, as examined by the luciferase assay. These findings indicate that constitutive COX-2 promoter activity and protein expression are enhanced in COX-1(-/-) fibroblasts and that signaling via the NF-kappaB pathway is involved in the transcriptional control of constitutive COX-2 expression.

Cyclooxygenase-2 in myocardium stimulation by angiotensin-II in cultured cardiac fibroblasts and role at acute myocardial infarction

Myocardial infarction is followed by a complex repair process that includes a significant role for inflammatory cells. Cyclooxygenase-2 (COX-2) plays a key role in mediating inflammation. Contribution of COX-2 to inflammatory response following myocardial infarction is less certain. In an effort to evaluate the function of COX-2 and prostaglandin E(2)(PGE(2)) in myocardial infarction, we examined the role of COX-2 after angiotensin II (Ang II) stimulation in cardiac fibroblasts and in rats with experimental myocardial infarction (MI). We combined Western blot analysis and enzyme immunoassay to demonstrate COX-2 expression and PGE(2)release in cardiac fibroblasts. Isolated cardiac fibroblasts were stimulated with Ang II. Unstimulated fibroblasts showed no COX-2 protein expression. Fibroblasts stimulated with Ang II showed a strong time-dependent expression of COX-2 protein. The p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 but not the p42/44 MAPK-inhibitor PD98059 suppressed Ang II-induced COX-2 protein expression. COX-2 expression correlated with a significantly increased PGE(2)release from cardiac fibroblasts. The COX-2 specific inhibitor NS-398 suppressed the Ang II-stimulated PGE(2)production. We then investigated COX-2 expression and inflammatory cell infiltration in our rat model of myocardial infarction. MI was produced by coronary artery ligation in adult female Wistar rats. The period of coronary artery occlusion was 96 h. The selective COX-2 inhibitor rofecoxib (3 mg/kg/d), administered orally, was given one day before MI and continued for four days. Western blotting showed expression of COX-2 protein in the area of necrosis and the infarct border zone. Immunofluorescence analysis showed macrophage infiltration as well as fibroblast proliferation in the infarct border zone of 4-d infarcted tissue and a significantly reduced cell invasion and fibroblast proliferation in infarcted tissue of rats treated with rofecoxib. MI size at day 4 was comparable in untreated and treated rats. In conclusion, we demonstrate that pharmacological interference with prostaglandin synthesis in myocardial infarction is associated with reduced myocardial invasion of inflammatory cells.

Modulation of COX-2 expression by statins in human aortic smooth muscle cells. Involvement of geranylgeranylated proteins

Cyclooxygenase (COX)-2 and COX-1 play an important role in prostacyclin production in vessels and participate in maintaining vascular homeostasis. Statins are inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, which is crucial in cholesterol biosynthesis. Recently, cholesterol-independent effects of statins have been described. In this study, we evaluated the effect of two inhibitors of HMG CoA reductase, mevastatin and lovastatin, on the production of prostacyclin and the expression of COX in human aortic smooth muscle cells. Treatment of cells with 25 microm mevastatin or lovastatin resulted in the induction of COX-2 and increase in prostacyclin production. Mevalonate, the direct metabolite of HMG CoA reductase, and geranylgeranyl-pyrophosphate reversed this effect. GGTI-286, a selective inhibitor of geranylgeranyltransferases, increased COX-2 expression and prostacyclin formation, thus indicating the involvement of geranylgeranylated proteins in the down-regulation of COX-2. Furthermore, Clostridium difficile toxin B, an inhibitor of the Rho GTP-binding protein family, the Rho selective inhibitor C3 transferase, and Y-27632, a selective inhibitor of the Rho-associated kinases, targets of Rho A, increased COX-2 expression whereas the activator of the Rho GTPase, the cytotoxic necrotizing factor 1, blocked interlukin-1alpha-dependent COX-2 induction. These results demonstrate that statins up-regulate COX-2 expression and subsequent prostacyclin formation in human aortic smooth muscle cells in part through inhibition of Rho.

Diabetes-related changes in cAMP response element-binding protein content enhance smooth muscle cell proliferation and migration

We hypothesized that diabetes and glucose-induced reactive oxygen species lead to depletion of cAMP response element-binding protein (CREB) content in the vasculature. In primary cultures of smooth muscle cells (SMC) high medium glucose decreased CREB function but increased SMC chemokinesis and entry into the cell cycle. These effects were blocked by pretreatment with the antioxidants. High glucose increased intracellular reactive oxygen species detected by CM-H(2)DCFA. SMC exposed to oxidative stress (H(2)O(2)) demonstrated a 3.5-fold increase in chemokinesis (p < 0.05) and accelerated entry into cell cycle, accompanied by a significant decrease in CREB content. Chronic oxidative challenge similar to the microenvironment in diabetes (glucose oxidase treatment) decreases CREB content (40-50%). Adenoviral-mediated expression of constitutively active CREB abolished the increase in chemokinesis and cell cycle progression induced by either high glucose or oxidative stress. Analysis of vessels from insulin resistant or diabetic animals indicates that CREB content is decreased in the vascular stroma. Treatment of insulin-resistant animals with the insulin sensitizer rosiglitazone restores vessel wall CREB content toward that observed in normal animals. In summary, high glucose and oxidative stress decrease SMC CREB content increase chemokinesis and entry into the cell cycle, which is blocked by antioxidants or restoration of CREB content. Thus, decreased vascular CREB content could be one of the molecular mechanisms leading to increased atherosclerosis in diabetes.

Dipyridamole inhibits PDGF-stimulated human peritoneal mesothelial cell proliferation

BACKGROUND

It has been proposed that proliferation of human peritoneal mesothelial cells (HPMCs) accompanied by collagen synthesis may contribute to the development of peritoneal fibrosis (PF) in patients of long-term continuous ambulatory peritoneal dialysis (CAPD). However, the precise molecular mechanism regulating HPMC proliferation has never been reported. Dipyridamole has been reported to have potential as an antiproliferative and antifibrotic agent. We investigated the mechanism and effect of dipyridamole in regulation of HPMC proliferation.

METHODS

HPMCs were cultured from human omentum by an enzyme digestion

METHOD

Cell proliferation was measured by the methyltetrazolium assay and intracellular cAMP was measured using an enzyme immunoassay kit. Cell-cycle distribution of HPMC was analyzed by flow cytometry. Extracellular signal-regulated protein kinase (p44/p42 ERK) activity and expressions of cell-cycle proteins (cyclin D(1), CDK4, pRB and p27(Kip1)) were determined by Western blotting.

RESULTS

The addition of DP suppressed PDGF-stimulated HPMC proliferation by cell-cycle arrest at the G1 phase. The antimitogenic effect of dipyridamole was mediated through the cAMP pathway. PDGF (25 ng/mL) increased the ERK1/2 activity of HPMC within 15 minutes, which maximized at 30 minutes, and the pretreatment with dipyridamole (17 microg/mL) substantially reduced the ERK response to PDGF by approximately 78.5%. PDGF induced elevated protein levels of cyclin D(1), but the CDK4 protein level did not change. Dipyridamole and DBcAMP had no effect on the levels of cyclin D(1) and CDK4 in PDGF-stimulated HPMC. PDGF decreased p27(Kip1) and induced pRB phosphorylation of HPMC. In contrast, dipyridamole prevented PDGF-induced p27(Kip1) degradation and attenuated PDGF-stimulated pRB phosphorylation.

CONCLUSION

Dipyridamole appears to inhibit PDGF-stimulated HPMC proliferation through attenuated ERK activity, preservation of p27(Kip1), and decreased pRB phosphorylation. Thus, dipyridamole may have therapeutic efficacy to prevent or alleviate PF.

Cell adhesion and signaling on the fibronectin 1st type III repeat; requisite roles for cell surface proteoglycans and integrins

BACKGROUND

The first type III repeat of fibronectin is known to be involved in fibronectin matrix assembly, and recombinant proteins from this type III repeat can inhibit cell proliferation, tumor metastasis and angiogenesis. We have analyzed the way rat aortic smooth muscle cells (RASMCs) interact with a recombinant protein encompassing a C-terminal portion of the first type III repeat of fibronectin (protein III1-C).

RESULTS

Cells are able to adhere to and spread on III1-C coated on a dish. Both beta1 integrins and cell surface heparan sulfate proteoglycans serve as receptors for III1-C. For example, cell attachment to III1-C is partially inhibited by agents that block beta1 integrins or by heparin. Complete inhibition of cell attachment is seen only when integrin blocking agents are combined with heparin. Affinity chromatography revealed the binding of proteins that likely represent the integrin beta1 and alpha5 submits to a III1-C column. Cell adhesion to III1-C results in robust ERK1/2 activation that is blocked by integrin-blocking agents. In addition, cell adhesion to III1-C and ERK1/2 activation by III1-C are both inhibited by heparan sulfate but not by chondroitin sulfate. Moreover, heparitinase treatment, but not chondroitinase treatment of RASMCs results in reduced cell adhesion and ERK1/2 activation. Affinity chromatography experiments demonstrated that 35SO4-labeled cell surface heparan sulfate proteoglycans bound specifically to III1-C.

CONCLUSIONS

The results suggest that the 1st type III repeat of fibronectin contains a previously unrecognized cell adhesion domain that stimulates robust ERK1/2 activation in RASMCs. Cells interact with this domain through cell surface heparan sulfate proteoglycans and integrins, and both classes of receptors are required for optimal cell adhesion and ERK1/2 activation.

β-Migrating Very Low Density Lipoprotein (βVLDL) Activates Smooth Muscle Cell Mitogen-activated Protein (MAP) Kinase via G Protein-coupled Receptor-mediated Transactivation of the Epidermal Growth Factor (EGF) Receptor

This study examined the premise that the atherogenic lipoprotein, beta-migrating very low density lipoprotein (betaVLDL), might activate the mitogen-activated protein (MAP) kinases ERK1/ERK2, thereby contributing to the induction of smooth muscle cell proliferation in atherosclerosis. The data show that betaVLDL activates rabbit smooth muscle cell ERK1/ERK2. Interestingly, ERK1/ERK2 activation is mediated by G protein-coupled receptors that transactivate the epidermal growth factor (EGF) receptor. betaVLDL-induced MAP kinase activation depends on Ras and Src activity as well as protein kinase C. The inhibition of lysosomal degradation of betaVLDL has no effect on ERK1/ERK2 activation. The contribution of betaVLDL-induced activation of ERK1/ERK2 to smooth muscle cell proliferation was also explored. betaVLDL induces expression of egr-1 and c-fos mRNA. Despite its ability to stimulate early gene expression, betaVLDL alone is unable to inspire quiescent cells into S phase. When added in conjunction with EGF, however, stimulation of [(3)H]thymidine incorporation into DNA and an increase in histone gene expression are observed. Moreover, betaVLDL plus EGF synergistically induce cyclin D1 expression and down-regulate p27(KIP1) expression. The addition of either betaVLDL or EGF stimulates a robust activation of ERK1/ERK2, but the addition of both agents simultaneously sustains the activation for a longer time period. Inhibition of MAP kinase kinase, pertussis toxin-sensitive G proteins, the EGF receptor, or protein kinase C blocks betaVLDL plus EGF-induced proliferation, demonstrating that activation of the betaVLDL-induced signaling pathway results in smooth muscle cell proliferation.

Endothelin-1 induces cyclooxygenase-2 expression via nuclear factor of activated T-cell transcription factor in glomerular mesangial cells

Nuclear factor of activated T cells (NFAT) originally was identified as a T-cell-specific transcription factor whose activity is regulated by calcineurin, one of the serine-threonine phosphatases. Recent studies have shown that NFAT also is expressed in nonlymphoid cells and plays an important role in various cell functions. It is widely known that treatment with cyclosporin A (CsA), which can inhibit calcineurin/NFAT signaling, results in glomerular dysfunction characterized by a decrease of GFR or glomerulosclerosis, suggesting that NFAT might regulate the glomerular function. However, the precise function of NFAT in glomerular cells remains to be clarified. Herein, evidence has been produced that NFAT2/NFATc, one of five known NFAT isoforms, is expressed in glomerular mesangial cells. Stimulation of mesangial cells with endothelin-1 caused translocation of NFAT2 into the nucleus with a concomitant increase in NFAT2 DNA-binding activity, both of which were inhibited by CsA. Furthermore, CsA inhibited endothelin-1-induced cyclooxygenase-2 (COX-2) expression in mesangial cells. NFAT2 bound directly to the GGAAA sequence, which is the minimal consensus sequence for NFAT binding, in a promoter region of rat COX-2 gene, and it enhanced the reporter activity of rat COX-2 promoter in mesangial cells. These findings provide the first evidence that NFAT2 is expressed and regulates COX-2 gene expression in mesangial cells. These results will contribute to evaluation of the precise roles of NFAT in glomerular functions and the CsA-induced nephrotoxicity.

Cyclooxygenase-2 deficiency results in a loss of the anti-proliferative response to transforming growth factor-beta in human fibrotic lung fibroblasts and promotes bleomycin-induced pulmonary fibrosis in mice

Prostaglandin E(2) (PGE(2)) inhibits fibroblast proliferation and collagen production. Its synthesis by fibroblasts is induced by profibrotic mediators including transforming growth factor (TGF)-beta(1). However, in patients with pulmonary fibrosis, PGE(2) levels are decreased. In this study we examined the effect of TGF-beta(1) on PGE(2) synthesis, proliferation, collagen production, and cyclooxygenase (COX) mRNA levels in fibroblasts derived from fibrotic and nonfibrotic human lung. In addition, we examined the effect of bleomycin-induced pulmonary fibrosis in COX-2-deficient mice. We demonstrate that basal and TGF-beta(1)-induced PGE(2) synthesis is limited in fibroblasts from fibrotic lung. Functionally, this correlates with a loss of the anti-proliferative response to TGF-beta(1). This failure to induce PGE(2) synthesis is because of an inability to up-regulate COX-2 mRNA levels in these fibroblasts. Furthermore, mice deficient in COX-2 exhibit an enhanced response to bleomycin. We conclude that a decreased capacity to up-regulate COX-2 expression and COX-2-derived PGE(2) synthesis in the presence of increasing levels of profibrotic mediators such as TGF-beta(1) may lead to unopposed fibroblast proliferation and collagen synthesis and contribute to the pathogenesis of pulmonary fibrosis.

Thrombin-stimulated DNA synthesis in human cultured airway smooth muscle occurs independently of products of cyclo-oxygenase or 5-lipoxygenase

Arachidonic acid (AA) liberation and metabolism via cyclo-oxygenase or lipoxygenases may be an important regulatory pathway for mitogenic signalling in human cultured airway smooth muscle (ASM) cells. In cytokine-treated cells, thrombin markedly enhances production of the anti-mitogenic arachidonic acid metabolite, PGE(2). In this study, in the absence of cytokines, we examined the role of endogenous AA metabolism in thrombin-stimulated ASM DNA synthesis. Selective inhibitors of cyclo-oxygenase of 5-lipoxygenase metabolism had no significant effect on 0.3 U/ml thrombin-stimulated DNA synthesis. However, the non-selective, redox-active lipoxygenase inhibitors NDGA and BWA4C inhibited thrombin-stimulated DNA synthesis. Under basal conditions, and following stimulation by thrombin, the levels of the AA metabolites PGE(2), TxA(2), and LTC(4), remained below assay detection limits. Exogenous addition of AA, LTD(4), or 5-, 12-, and 15-HETE and HpETE metabolites had no consistent or substantial stimulatory effect on either basal or thrombin-stimulated DNA synthesis. These data suggest that the non-selective lipoxygenase inhibitors influence DNA synthesis via effects unrelated to lipoxygenase inhibition. The lack of detection of AA metabolites, the lack of influence of selective antagonists/inhibitors of the AA pathway, and the failure of selected AA metabolites to either enhance or directly stimulate DNA synthesis suggest that in the absence of cytokines, cyclo-oxygenase and lipoxygenase metabolism has little role in signalling of human ASM DNA synthesis by thrombin.

C1q arrests the cell cycle progression of fibroblasts in G(1) phase: role of the cAMP/PKA-I pathway

C1q may participate in the loss of connective tissue occurring in chronic inflammatory lesions. The hypothesis of a detrimental role of C1q on cell proliferation was tested on primary cultures of human fibroblasts (HFs). C1q suppressed the DNA synthesis of HF in response to platelet-derived growth factor (PDGF) with an IC(50) of 20 microg/ml, and blocked 78% of the cycling cells in G(1) phase. The C1q block did not involve production of inhibitory prostaglandin by the cells. Given that C1q elicits signals of the adenylyl cyclase pathway in HF, we examined cAMP-dependent mechanisms to understand how C1q inhibited the PDGF response. Whereas the C1q block was enhanced by agonist dibutyryl-adenosine 3', 5'-cyclic mono-phosphate (db-cAMP), antagonist adenosine 3', 5'-cyclic monophosphorotioate triethylammonium salt (Rp-cAMP) minimized it. C1q increased the level of cAMP-dependent protein kinase I (PKA-I) 4.5-fold, without altering the activation of the extracellular-regulated protein kinase (ERK) pathway. These results demonstrate that the interactions of C1q with HF cause growth arrest at the G(1) phase through mechanisms associated with a PKA-I dependent pathway.

Inhibitory effect of pentalenolactone on vascular smooth muscle cell proliferation

The effect of pentalenolactone, an inhibitor of glyceraldehyde-3-phosphate dehydrogenase, on rat vascular smooth muscle cell proliferation was studied. Addition of pentalenolactone together with serum to quiescent cells dose-dependently inhibited cell proliferation and DNA synthesis. This inhibition was not associated with cell death. When quiescent cells were stimulated with serum and then treated with pentalenolactone, the inhibitory effect on the DNA synthesis declined gradually. A similar result was obtained when PD 98059 (2'-amino-3'-methoxyflavone), an inhibitor of extracellular signal-regulated kinase1/2 (ERK1/2) kinase (MEK1/2), was added to the cells after serum stimulation. Pentalenolactone inhibited serum or protein kinase C activator (phorbol 12,13-dibutyrate)-induced phosphorylation of ERK1/2 and MEK1/2. In contrast, pentalenolactone had little effect on platelet-derived growth factor receptor autophosphorylation. Taken together, these results indicate that pentalenolactone inhibits vascular smooth muscle cell proliferation, and that this inhibition appears to be mediated by inhibition of the ERK1/2 cascade.

Shape-dependent control of cell growth, differentiation, and apoptosis: switching between attractors in cell regulatory networks

Development of characteristic tissue patterns requires that individual cells be switched locally between different phenotypes or "fates;" while one cell may proliferate, its neighbors may differentiate or die. Recent studies have revealed that local switching between these different gene programs is controlled through interplay between soluble growth factors, insoluble extracellular matrix molecules, and mechanical forces which produce cell shape distortion. Although the precise molecular basis remains unknown, shape-dependent control of cell growth and function appears to be mediated by tension-dependent changes in the actin cytoskeleton. However, the question remains: how can a generalized physical stimulus, such as cell distortion, activate the same set of genes and signaling proteins that are triggered by molecules which bind to specific cell surface receptors. In this article, we use computer simulations based on dynamic Boolean networks to show that the different cell fates that a particular cell can exhibit may represent a preprogrammed set of common end programs or "attractors" which self-organize within the cell's regulatory networks. In this type of dynamic network model of information processing, generalized stimuli (e.g., mechanical forces) and specific molecular cues elicit signals which follow different trajectories, but eventually converge onto one of a small set of common end programs (growth, quiescence, differentiation, apoptosis, etc.). In other words, if cells use this type of information processing system, then control of cell function would involve selection of preexisting (latent) behavioral modes of the cell, rather than instruction by specific binding molecules. Importantly, the results of the computer simulation closely mimic experimental data obtained with living endothelial cells. The major implication of this finding is that current methods used for analysis of cell function that rely on characterization of linear signaling pathways or clusters of genes with common activity profiles may overlook the most critical features of cellular information processing which normally determine how signal specificity is established and maintained in living cells.

Antiproliferative properties of sphingosine 1-phosphate in human hepatic myofibroblasts. A cyclooxygenase-2 mediated pathway

Proliferation of hepatic myofibroblasts (hMF) is central for the development of fibrosis during liver injury, and factors that may limit their growth are potential antifibrotic agents. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid with growth-regulating properties, either via Edg receptors or through intracellular actions. In this study, we examined the effects of S1P on the proliferation of human hMF. Human hMF expressed mRNAs for the S1P receptors Edg1, Edg3, and Edg5. These receptors were functional at nanomolar concentrations and coupled to pertussis toxin-sensitive and -insensitive G proteins, as demonstrated in guanosine 5'-3-O-(thio)triphosphate binding assays. S1P potently inhibited hMF growth (IC(50) = 1 microm), in a pertussis toxin-insensitive manner. Analysis of the mechanisms involved in growth inhibition revealed that S1P rapidly increased prostaglandin E(2) production and in turn cAMP, two growth inhibitory messengers for hMF; C(2)-ceramide and sphingosine, which inhibited hMF proliferation, did not affect cAMP levels. Production of cAMP by S1P was abolished by NS-398, a selective inhibitor of COX-2. Also, S1P potently induced COX-2 protein expression. Blocking COX-2 by NS-398 blunted the antiproliferative effect of S1P. We conclude that S1P inhibits proliferation of hMF, probably via an intracellular mechanism, through early COX-2-dependent release of prostaglandin E(2) and cAMP, and delayed COX-2 induction. Our results shed light on a novel role for S1P as a growth inhibitory mediator and point out its potential involvement in the negative regulation of liver fibrogenesis.

Fucoidan inhibits smooth muscle cell proliferation and reduces mitogen-activated protein kinase activity

OBJECTIVES AND DESIGN

fucoidan has previously been shown to inhibit the proliferation of arterial smooth muscle cells both in animal models and in vitro. However, the mechanisms behind the anti-proliferative effects of this polysulfated polysaccharide are not known in detail. Here, the inhibitory effect of fucoidan on rat aortic smooth muscle cell proliferation was examined and compared with the effects of heparin after stimulation with fetal calf serum, platelet-derived growth factor BB, basic fibroblast growth factor, heparin-binding epidermal growth factor, and angiotensin II.

MATERIALS AND METHODS

the cultures were analysed with respect to cell proliferation and DNA synthesis by cell counting and measurement of(3)H-thymidine incorporation. Phosphorylation of mitogen-activated protein kinase and nuclear translocation of phosphorylated mitogen-activated protein kinase were studied by immunoblotting and immunocytochemistry.

RESULTS

fucoidan was shown to be a more potent inhibitor of smooth muscle cell proliferation than heparin. Fucoidan also reduced growth factor-induced activation of mitogen-activated protein kinase and prevented nuclear translocation of phosphorylated mitogen-activated protein kinase.

CONCLUSION

fucoidan is a more potent anti-proliferative polysulphated polysaccharide than heparin and may mediate its effects through inhibition of the mitogen-activated protein kinase pathway in a similar manner as heparin.

15-Deoxy-Delta(12,14)-prostaglandin J(2) induces G(1) arrest and differentiation marker expression in vascular smooth muscle cells

In search of substances useful for the treatment of atherosclerotic vascular diseases, we studied the effects of 15-deoxy-Delta(12, 14)-prostaglandin J(2) (15d-PGJ(2)), a natural ligand for peroxisome proliferator-activated receptor gamma, on the proliferation and differentiation of vascular smooth muscle cells (VSMCs). 15d-PGJ(2) but not WY14643, an agonist for peroxisome proliferator-activated receptor alpha, dose-dependently inhibited VSMC proliferation; the effect was maximal at 12 microM. This compound strongly suppressed the activities of cyclin-dependent kinases (Cdk) 4, 6, and 2, thereby preventing the phosphorylation of the retinoblastoma protein. These Cdks seemed to be inhibited through two mechanisms: the down-regulation of cyclin D1 and the up-regulation of Cdk inhibitor p21(Cip1/Waf1/Sdi1). 15d-PGJ(2) was found to inhibit the phosphatidylinositol 3-kinase/protein kinase B signaling pathway, which mediates cyclin D1 expression. Mitogenic stimulation of quiescent cells decreased the level of mRNA for the smooth muscle-specific myosin heavy-chain SM1, whereas this reduction was prevented by 15d-PGJ(2). A long-term treatment of exponentially growing VSMCs with 15d-PGJ(2) markedly elevated the mRNA level of SM1 and, moreover, induced SM2, another isoform expressed exclusively in mature VSMCs. 15d-PGJ(2) also increased the expression levels of calponin-h1 and smooth muscle alpha-actin. These results suggest that 15d-PGJ(2) induces G(1) arrest by two distinct mechanisms and promotes VSMC differentiation.

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.

Induction of cyclooxygenase-2 by overexpression of the human catalase gene in cerebral microvascular endothelial cells

Prostaglandin (PG) formation by the inducible (type 2) cyclooxygenase (COX-2) and reactive oxygen species (ROS) have been proposed to play important roles in cerebrovascular pathological processes. To explore the relationship between ROS and COX-2 expression, adenovirus (Ad) vectors containing cDNA for human antioxidant enzymes including catalase (AdCAT:), copper/zinc superoxide dismutase (AdCu/ZnSOD), and manganese superoxide dismutase (AdMnSOD) were transferred into murine cerebral microvascular endothelial cells. AdCAT: (100 multiplicity of infection) infection increased the content and enzymatic activity of cellular Cat threefold and decreased the intracellular peroxide level. The expression of COX-2 mRNA and protein in cell lysates was up-regulated, and the amount of PGE(2) formed from exogenous arachidonic acid increased following AdCAT: infection in a dose-dependent manner, paralleling the expression of COX-2 protein. The AdCAT:-induced increase in PGE(2) formation was inhibited by NS-398, a selective inhibitor of COX-2 enzymatic activity. AdCAT: infection did not change the expression of the constitutive (type 1) COX protein. Although AdCu/ZnSOD and AdMnSOD infection increased the expression of superoxide dismutase proteins, COX-2 expression was not induced. An in vitro nuclear transcription assay indicated that overexpression of the Cat gene increases the transcription of the COX-2 gene. Furthermore, the stability of COX-2 mRNA induced by lipopolysaccharide was increased after AdCAT: gene transfer. These results indicate that AdCAT: gene transfer induces the transcriptional activation of the COX-2 gene and increases COX-2 mRNA stability. Therefore, peroxide may have regulatory effect on COX-2 function in the cerebral microcirculation.

Fibrinogen interactions with ICAM-1 (CD54) regulate endothelial cell survival

We tested hypothesis that the interaction of fibrinogen (Fg) with intercellular adhesion molecule 1 (ICAM-1) mediates cellular adhesion and cell proliferation. Our results demonstrate that Fg : ICAM-1 ligation mediates endothelial cell survival and has an anti-apoptotic effect via activation of the MAP kinase pathway. Fg : ICAM-1 ligation in endothelial cells treated with tumor necrosis factor (TNF)alpha resulted in the hyperphosphorylation of extracellular signal-regulated kinase (ERK)-1/2 (eightfold to 10-fold) at 5-30 min. The specificity of ERK-1/2 phosphorylation was verified using the recognition peptides Fg-gamma-(117-133) and ICAM-1(8-22). ERK-1/2 hyperphosphorylation was dependent on intact cytoskeleton, as treatment with cytochalasin B and nocodazole blocked this activity. The attachment of TNFalpha-treated endothelial cells to fibrinogen or Fg-gamma-(117-133) resulted in cell survival, as assessed by an annexin V binding assay. ICAM-1(8-22) blocked the survival process. The MEK-1 inhibitor PD 98059 blocked ERK-1/2 phosphorylation, and treatment of endothelial cells with PD 98059 resulted in apoptosis even upon Fg : ICAM-1 ligation. Cells transfected with dominant-negative ERK-1/2 underwent apoptosis upon Fg : ICAM-1 ligation. Cell survival factor A1 was specifically upregulated upon adhesion of TNFalpha-stimulated endothelial cells to Fg. A1 expression was blocked by ICAM-1(8-22) and PD 98059. The Fg : ICAM-1 endothelial cell survival pathway appears to be mediated via the activation and upregulation of ERK-1/2 and A1.

Reactive oxygen species stimulate p44/42 mitogen-activated protein kinase and induce p27(Kip1): role in angiotensin II-mediated hypertrophy of proximal tubular cells

Angiotensin II (AngII) induces G(1) phase arrest and hypertrophy of cultured renal proximal tubular cells. In previous studies, it was shown that these effects depend on oxygen radical-mediated induction of p27(Kip1), an inhibitor of cyclin-dependent kinases. The present study was undertaken to investigate whether mitogen-activated protein (MAP) kinases serve as signaling intermediates between AngII-induced oxidative stress and induction of p27(Kip1). AngII (10(-7) M) induces a biphasic phosphorylation pattern of p44/42 MAP kinase with an early phosphorylation after 2 min and a later, second phosphorylation peak after prolong incubation (12 h) in cultured proximal tubular cells from two different species (MCT and LLC-PK(1) cells). Total protein expression of MAP kinase was not changed by AngII. These phosphorylation patterns of p44/42 MAP kinase caused activation of the enzyme, as detected by phosphorylated MAP substrate Elk-1 after immuno-precipitation of MAP kinase. Exogenous H(2)O(2) also stimulates a biphasic phosphorylation of p44/42 MAP kinase. The flavoprotein inhibitor diphenylene iodinium, as well as the antioxidant N-acetylcysteine, prevented AngII-induced p44/42 MAP kinase phosphorylation, indicating involvement of reactive oxygen species generated by membrane-bound NAD(P)H oxidase. The MAP kinase kinase inhibitor PD98059 completely inhibits AngII-induced p27(Kip1) expression and (3)[H]leucine incorporation into proteins as a previously established marker of cell hypertrophy. PD98059 did not attenuate AngII-stimulated intracellular synthesis of oxygen radicals. Transient transfection with p44/42 MAP kinase antisense, but not sense, phosphorothioate-modified oligonucleotides also prevented AngII-induced MAP kinase phosphorylation, p27(Kip1) expression, and cell hypertrophy. Furthermore, induction of p27(Kip1) by H(2)O(2) was also abolished in the presence of PD98059. Although AngII induces phosphorylation of the stress-activated p38 MAP kinase, inhibition of this enzyme with SB203580 failed to attenuate induced p27(Kip1) expression and hypertrophy. These data provide evidence that AngII- mediated oxygen stress leads to the phosphorylation of p44/42 MAP kinase in proximal tubular cells. Activation of this enzyme is essential for p27(Kip1) expression, G(1) phase arrest, and hypertrophy of proximal tubular cells. These findings may lead to new concepts concerning interference of the development of proximal tubular hypertrophy, which may eventually turn into a maladaptive process in vivo leading ultimately to tubular atrophy and tubulointerstitial fibrosis.

Enhanced expression of cyclooxygenase (COX)-2 in human skin epidermal cancer cells: evidence for growth suppression by inhibiting COX-2 expression

Cyclooxygenase (COX)-2 is one of the rate-limiting enzymes in the conversion of arachidonic acid to prostaglandins and other eicosanoids. Recent studies have shown enhanced expression of COX-2 in cancer cells of several tissues. We investigated the expression of COX-2 and prostaglandin (PG) E((2)) production in two human skin epidermal cancer cell lines: cutaneous squamous cell carcinoma, HSC-5, and eccrine carcinoma, EcCa. Both COX-2 expression and PGE((2)) production were significantly enhanced in cancer cell lines compared with the non-tumorigenic human keratinocyte cell line, HaCaT. In order to determine the role of COX-2 in the proliferation of HSC-5 and EcCa, the growth of untreated cells and cells transfected with COX-2 antisense oligonucleotide was compared using the MTT assay. Transfection with the antisense oligonucleotide suppressed COX-2 protein expression and significantly inhibited cell growth. The effect of a selective inhibitor of COX-2, NS398, was compared with the effect of the antisense oligonucleotide in order to see whether COX-2 expression and prostaglandins have selective effects on cell growth. COX-2 expression was unchanged by NS398 treatment, whereas NS398 inhibited cell growth to a certain extent. The degree of growth inhibition was greater with the antisense oligonucleotide than with NS398. Our findings indicate that COX-2 protein expression is enhanced in skin epidermal cancer cells and that COX-2 plays a pivotal role in regulating cell growth. Furthermore, inhibition of COX-2 expression had a more significant effect on growth suppression than inhibition of COX-2 catalytic activity, suggesting the existence of two different signal pathways via COX-2 in regulating cell growth.

Cyclooxygenase-2 is required for tumor necrosis factor-alpha- and angiotensin II-mediated proliferation of vascular smooth muscle cells

Tumor necrosis factor-alpha (TNF-alpha) and angiotensin II (Ang II) induced a transient increase in vascular smooth muscle cell (VSMC) cyclooxygenase-2 (COX-2) mRNA accumulation, without affecting COX-1 mRNA levels. The kinetics of COX-2 mRNA accumulation were similar in VSMCs challenged with either TNF-alpha or Ang II; mRNA accumulation peaked at 2 hours and decreased to control levels by approximately 6 hours. Accumulation of COX-2 mRNA was associated with a time-dependent increase of COX-2 protein expression that displayed similar kinetics in response to either TNF-alpha or Ang II. Both the increase in COX-2 mRNA accumulation and protein expression in response to either TNF-alpha or Ang II were inhibited by the mitogen-activated protein/extracellular signal-regulated kinase (MEK) inhibitor PD098059. In addition, the AT(1)-selective receptor antagonist losartan attenuated the Ang II-mediated increase in COX-2 mRNA accumulation; the AT(2)-selective antagonist PD123319 had no effect. Prostacyclin I(2) synthesis was tightly coupled to expression of COX-2, whereas prostaglandin E(2) and thromboxane A(2) (TXA(2)) synthesis may be associated with differential usage of COX-1 and COX-2. The COX-2-selective inhibitors NS-398 and nimesulide and the TXA(2) receptor antagonist BMS 180,291 inhibited TNF-alpha- and Ang II-mediated increases in DNA content and cell number by approximately 95%. These findings suggest that a prostanoid derived from COX-2, possibly TXA(2), may contribute to VSMC hyperplasia in vessel injury or pathophysiological conditions associated with elevated levels of either TNF-alpha or Ang II.

Nitric oxide increases p21(Waf1/Cip1) expression by a cGMP-dependent pathway that includes activation of extracellular signal-regulated kinase and p70(S6k)

Nitric oxide (NO) regulates the expression of p21(Waf1/Cip1) in several cell types. The present study examined the role of both the extracellular signal-regulated kinase (ERK) and p70 S6 kinase (p70(S6k)) in the NO-induced increase in p21 expression that occurred in adventitial fibroblasts during the cell cycle. Both ERK and p70(S6k) were phosphorylated in response to the NO donor S-nitroso-N-acetylpenicillamine (SNAP) and the activation was rapid, transient, and preceded increased p21 expresion under defined conditions where serum was present. Addition of a selective inhibitor of ERK phosphorylation (PD98059) prevented the subsequent phosphorylation of p70(S6k) and the increase in p21 protein. Both cGMP and cAMP activated both ERK and p70(S6k), whereas only selective inhibitors of protein kinase G prevented the activation of the kinases by SNAP. A complex between ERK and p70(S6k) was documented by immunoprecipitation procedures. Rapamycin blocked p70(S6k) phosphorylation induced by NO and also inhibited p53 phosphorylation and p21 expression whereas PD98059 only prevented the NO-induced increase in p21 protein without influencing either p53 activation or p21 mRNA expression. The studies show a unique relationship between NO, ERK, and p70(S6k) and also provide evidence for a novel role of p70(S6k) in the activation of p53.

beta-arrestin-dependent endocytosis of proteinase-activated receptor 2 is required for intracellular targeting of activated ERK1/2

Recently, a requirement for beta-arrestin-mediated endocytosis in the activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) by several G protein-coupled receptors (GPCRs) has been proposed. However, the importance of this requirement for function of ERK1/2 is unknown. We report that agonists of Galphaq-coupled proteinase-activated receptor 2 (PAR2) stimulate formation of a multiprotein signaling complex, as detected by gel filtration, immunoprecipitation and immunofluorescence. The complex, which contains internalized receptor, beta-arrestin, raf-1, and activated ERK, is required for ERK1/2 activation. However, ERK1/2 activity is retained in the cytosol and neither translocates to the nucleus nor causes proliferation. In contrast, a mutant PAR2 (PAR2deltaST363/6A), which is unable to interact with beta-arrestin and, thus, does not desensitize or internalize, activates ERK1/2 by a distinct pathway, and fails to promote both complex formation and cytosolic retention of the activated ERK1/2. Whereas wild-type PAR2 activates ERK1/2 by a PKC-dependent and probably a ras-independent pathway, PAR2(deltaST363/6A) appears to activate ERK1/2 by a ras-dependent pathway, resulting in increased cell proliferation. Thus, formation of a signaling complex comprising PAR2, beta-arrestin, raf-1, and activated ERK1/2 might ensure appropriate subcellular localization of PAR2-mediated ERK activity, and thereby determine the mitogenic potential of receptor agonists.

Hypoxia induces cell-specific changes in gene expression in vascular wall cells: implications for pulmonary hypertension

Mammals respond to reduced oxygen concentrations (hypoxia) in many different ways at the systemic, local, cellular and molecular levels. Within the pulmonary circulation, exposure to chronic hypoxia has been demonstrated to illicit increases in pulmonary artery pressure as well as dramatic structural changes in both large and small vessels. It has become increasingly clear that the response to hypoxia in vivo is differentially regulated at the level of specific cell types within the vessel wall. For instance, in large pulmonary blood vessels there is now convincing evidence to suggest that the medial layer is made up of many different subpopulations of smooth muscle cells. In response to hypoxia there are remarkable differences in the proliferative and matrix producing responses of these cells to the hypoxic environment. Some cell populations proliferate and increase matrix protein synthesis, while in other cell populations no apparent change in the proliferative or differentiation state of the cell takes place. In more peripheral vessels, the predominant proliferative changes in response to hypoxia in the pulmonary circulation occur in the adventitial layer rather than in the medial layer. Here again, specific increases in proliferation and matrix protein synthesis take place. Accumulating evidence suggests that the unique responses exhibited by specific cell types of hypoxia in vivo can be modeled in vitro. We have isolated, in culture, specific medial cell populations which demonstrate significant increases in proliferation in response to hypoxia, and others which exhibit no change or, in fact, a decrease in proliferation under hypoxic conditions. We have also isolated and cloned several unique populations of adventitial fibroblasts. There is good evidence that only certain fibroblast populations are capable of responding to hypoxia with an increase in proliferation. We have begun to elucidate the signaling pathways which are activated in those cell populations that exhibit proliferative responses to hypoxia. We show that hypoxia, in the absence of serum or mitogens, specifically activates select members of the protein kinase C isozyme family, as well as members of the mitogen-activated protein kinase (MAPK) family of proteins. This selective activation appears to take place in response to hypoxia only in those cells exhibiting a proliferative response, and antagonists of this pathway inhibit the response. Thus, there appear to be cells within each organ that demonstrate unique responses to hypoxia. A better understanding of why these cells exist and how they specifically transduce hypoxia-mediated signals will lead to a better understanding of how the changes in the pulmonary circulation take place under conditions of chronic hypoxia.

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.

Induction of cyclooxygenase-2 by angiotensin II in cultured rat vascular smooth muscle cells

Angiotensin II (Ang II) stimulates the release of prostaglandins (PGs) in various cells and tissues. Recently, cyclooxygenase-2 (COX-2) emerged as a new key regulator for PG synthesis. In the present study, we investigated whether Ang II regulates COX-2 expression in cultured rat vascular smooth muscle cells (VSMCs). Ang II markedly increased the expression of COX-2 mRNA in a time- and dose-dependent manner. This effect was completely blocked by the Ang II type 1 receptor antagonist losartan but not by the Ang II type 2 receptor antagonist PD123319. The p42/44 mitogen-activated protein kinase (MAPK) kinase-1 inhibitor PD98059 and the p38 MAPK inhibitor SB203580 significantly suppressed Ang II-induced COX-2 mRNA and protein expression. Ang II did not increase transcription of the COX-2 gene, as examined with a COX-2 promoter/luciferase chimeric plasmid construct. Instead, it suppressed the degradation of COX-2 mRNA. PD98059 and SB203580 markedly enhanced the decay of COX-2 mRNA induced by Ang II, implying that p42/44 and p38 MAPK activated by Ang II play a role in the regulation of COX-2 through stabilization of its mRNA. The COX-2-specific inhibitor NS-398 attenuated Ang II-stimulated DNA and protein synthesis, as well as PGE(2) production by VSMCs. These results suggest that Ang II regulates COX-2 expression and PG production and modulates cell proliferation through MAPK-mediated signaling pathways in rat VSMCs.

Subendothelial cells from normal bovine arteries exhibit autonomous growth and constitutively activated intracellular signaling

The arterial media is comprised of heterogeneous smooth muscle cell (SMC) subpopulations with markedly different growth responses to pathophysiological stimuli. Little information exists regarding the intracellular signaling pathways that contribute to these differences. Therefore, we investigated the growth-related signaling pathways in a unique subset of subendothelial SMCs (L1 cells) from normal, mature, bovine arteries and compared them with those in "traditional" SMCs derived from the middle media (L2 SMCs). Subendothelial L1 cells exhibited serum-independent autonomous growth, not observed in L2 SMCs. Autonomous growth of L1 cells was driven largely by the constitutively activated extracellular signal-regulated kinase (ERK-1/2) cascade. Inhibition of upstream activators of ERKs (MAP kinase kinase-1, p21(ras), receptor tyrosine kinases, and Gi protein-coupled receptors) led to suppression of autonomous growth in these cells. L1 cells also exhibited constitutive activation of important downstream targets of ERKs (cytosolic phospholipase A(2), cyclooxygenase-2) and secreted large amounts of prostaglandins. Importantly, L1 cells secreted potent mitogenic factor(s), which could potentially contribute in an autocrine fashion to the constitutive activation of these cells. Our data suggest that unique arterial cells with autonomous growth potential and constitutively activated signaling pathways exist in normal arteries and may contribute selectively to the pathogenesis of vascular diseases.

Early intracellular signalling pathway of ethanol in vascular smooth muscle cells

1. ERKs belong to MAP kinase family and are activated by several growth and stress factors. Although ethanol has been shown to modulate ERK1 and ERK2 (p44(mapk) and p42(mapk)) activity, it can also act as an antiproliferative agent in various mammalian cells. Since the nature of the antiproliferative effect of ethanol in VSMCs has not been defined, we examined its effects on growth and on early intracellular events normally induced by growth factors in VSMCs. 2. Measurement of cytosolic Ca(2+) and pH in cell monolayers was performed using fura-2/AM and BCECF/AM, respectively. The effect of ethanol on VSMCs growth was assessed by [(3)H]-thymidine incorporation, by cell counting and by determination of the caspase 3 activity. Stimulation of ERK1 and ERK2 was examined by the chemiluminescence Western blotting method. The expression of c-fos was quantitated by Northern blotting. Determination of inositolphosphates was performed after labelling of VSMCs with myo-[2-(3)H]-inositol and separation of inositolphosphates by HPLC. 3. Ethanol (0.3 - 1.0% v v(-1), 17 - 170 mM) induced a dose-dependent maximal stimulation of p44(mapk)/p42(mapk) at 30 min and expression of c-fos mRNA with a maximum at 120 min. Intracellular events upstream to MAP kinase, like an increase in [Ca(2+)](i), activation of the Na(+)/H(+) exchanger and formation of phosphoinositol metabolites were also markedly activated by ethanol. Treatment of VSMCs with ethanol for 3 - 5 min induced an increase in DNA synthesis whereas treatment of the cells for more than 30 min was toxic. Caspase 3 activity was not modulated by ethanol treatment of VSMCs. 4. We may postulate that the activation of these mitogenic signals including the elevation of DNA synthesis reflects a cell effort to protect itself against the toxic effects of ethanol.

Distinct role of cAMP and cGMP in the cell cycle control of vascular smooth muscle cells: cGMP delays cell cycle transition through suppression of cyclin D1 and cyclin-dependent kinase 4 activation

cAMP and cGMP are known to suppress vascular smooth muscle cell (SMC) proliferation. In this study, our aim was to delineate the molecular mechanism underlying cAMP and cGMP suppression of cell cycle transition in human SMCs. cAMP inhibits both platelet-derived growth factor-stimulated cyclin-dependent kinase (cdk) 2 and cdk4 activation through upregulation of the cdk2 inhibitor p27(Kip1) and downregulation of cyclin D1 expression, which leads to a complete arrest of the cells in phase G(1). In contrast, cGMP inhibits cyclin D1 expression, inhibits cdk4 activation, and delays platelet-derived growth factor-mediated cdk2 activation, resulting in a delay in G(1)/S transition. A transient increase in p27(Kip1) in cdk2 immunoprecipitates, without changes in total cellular p27(Kip1) levels, correlates with the delay in cdk2 activation caused by cGMP. Thus, cAMP and cGMP differentially affect cell cycle through distinct regulation of cell cycle molecules in human SMCs.

Increase in prostaglandin E(2) production by interleukin-1beta in arterial smooth muscle cells derived from patients with moyamoya disease

Moyamoya disease is a progressive cerebrovascular occlusive disease that primarily affects children. The cause is unknown. We examined the production of prostanoids and the expression of cyclooxygenase-2 (COX-2) in cultured arterial smooth muscle cells (SMCs) derived from patients with moyamoya disease. Twelve moyamoya and 8 control cell strains were examined. The steady-state levels of prostanoids in the culture medium did not differ between moyamoya and control SMCs. When the cells were stimulated with interleukin-1beta (IL-1beta), prostaglandin E(2) (PGE(2)) release into the medium was significantly greater from moyamoya SMCs than from control SMCs, whereas the amounts of prostacyclin and thromboxane B(2) did not differ. IL-1beta-induced PGE(2) production by moyamoya SMCs was completely blocked by the addition of indomethacin or NS-398. IL-1beta significantly stimulated cell migration and DNA synthesis in control SMCs but had an inhibitory effect on moyamoya SMCs. The inhibitory effects on the growth and migration of moyamoya SMCs were caused by excessive secretion of PGE(2) and was reversed with indomethacin treatment. Immunofluorescence studies and Western blot analysis showed greater amounts of COX-2 protein expression in IL-1beta-stimulated moyamoya SMCs. These findings suggest that moyamoya SMCs respond to inflammatory stimuli to produce excess amounts of PGE(2) through the activation of COX-2, which increases vascular permeability and decreases vascular tone. This facilitates the exposure of vessels to blood constituents and promotes the development of intimal thickening in moyamoya disease.

Role of ERK MAP kinases in responses of cultured human airway smooth muscle cells to IL-1beta

We have previously reported that interleukin (IL)-1beta causes beta-adrenergic hyporesponsiveness in cultured human airway smooth muscle cells by increasing cyclooxygenase-2 (COX-2) expression and prostanoid formation. The purpose of this study was to determine whether extracellular signal-regulated kinases (ERKs) are involved in these events. Levels of phosphorylated ERK (p42 and p44) increased 8.3- and 13-fold, respectively, 15 min after treatment with IL-1beta (20 ng/ml) alone. Pretreating cells with the mitogen-activated protein kinase kinase inhibitor PD-98059 or U-126 (2 h before IL-1beta treatment) decreased ERK phosphorylation. IL-1beta (20 ng/ml for 22 h) alone caused a marked induction of COX-2 and increased basal PGE(2) release 28-fold (P < 0.001). PD-98059 (100 microM) and U-126 (10 microM) each decreased COX-2 expression when administered before IL-1beta treatment. In control cells, PD-98059 and U-126 had no effect on basal or arachidonic acid (AA; 10 microM)-stimulated PGE(2) release, but both inhibitors caused a significant decrease in bradykinin (BK; 1 microM)-stimulated PGE(2) release, consistent with a role for ERK in the activation of phospholipase A(2) by BK. In IL-1beta-treated cells, prior administration of PD-98059 caused 81, 92 and 40% decreases in basal and BK- and AA-stimulated PGE(2) release, respectively (P < 0.01), whereas administration of PD-98059 20 h after IL-1beta resulted in only 38 and 43% decreases in basal and BK-stimulated PGE(2) release, respectively (P < 0.02) and had no effect on AA-stimulated PGE(2) release. IL-1beta attenuated isoproterenol-induced decreases in human airway smooth muscle stiffness as measured by magnetic twisting cytometry, and PD-98059 or U-126 abolished this effect in a concentration-dependent manner. These results are consistent with the hypothesis that ERKs are involved early in the signal transduction pathway through which IL-1beta induces PGE(2) synthesis and beta-adrenergic hyporesponsiveness and that ERKs act by inducing COX-2 and activating phospholipase A(2).

Extracellular signal-regulated kinase activation differentially regulates platelet-derived growth factor's actions in hepatic stellate cells, and is induced by in vivo liver injury in the rat

Upon liver injury, hepatic stellate cells (HSC) show increased proliferation, motility, and extracellular matrix (ECM) production. The extracellular signal-regulated kinases (ERK) control different functions in a cell-specific manner. In this study, we evaluated the role of ERK activation in cultured HSC stimulated with platelet-derived growth factor (PDGF) and after induction of liver injury in vivo. HSC were isolated from normal human liver tissue, cultured on plastic, and used in their myofibroblast-like phenotype. In in vivo experiments, HSC were isolated from normal rats or at different time points after a single intragastric administration of CCl(4). Nontoxic concentrations of PD98059, a specific inhibitor of ERK activation, reduced PDGF-induced activation of ERK in a dose-dependent fashion. Suppression of ERK activation was associated with complete inhibition of HSC proliferation and with a 57% reduction in chemotaxis. In the presence of the ERK inhibitor, binding of the AP-1 complex and of STAT1 to the related regulatory elements was inhibited. The inhibition of the DNA binding activity of STAT1 was mediated by a reduction in PDGF-induced tyrosine phosphorylation. Expression of c-fos in response to PDGF was also reduced, but not suppressed, by treatment with PD98059. In HSC isolated from CCl(4)-treated rats, ERK activity increased as early as 6 hours following liver damage, and declined thereafter. The results of this study indicate that ERK activation regulates proliferation and chemotaxis of HSC, and modulates nuclear signaling. Acute liver damage in vivo leads to activation of ERK in HSC.

Endothelins stimulate expression of cyclooxygenase 2 in rat cultured astrocytes

Endothelin (ET) is one of the active endogenous substances regulating the functions of astrocytes. In the present study, we examined effects of ET on cyclooxygenase (COX) expression in cultured astrocytes. ET-3 (100 nM) caused transient increases in the expression of both COX2 mRNA and protein, but not those of COX1, in cultured astrocytes. ET-induced COX2 mRNA expression was suppressed by 5 microg/ml actinomycin D, 30 microM BAPTA/AM, inhibitors of protein kinase C (1-100 nM staurosporin and 100 microM H-7), 2 microM dexamethasone, and prolonged treatment with 100 nM phorbol 12-myristate 13-acetate. ET-3 stimulated production of prostaglandin (PG) E2 in cultured astrocytes. The effect of ET-3 on the PGE2 production was diminished by actinomycin D. Indomethacin and NS398, a selective COX2 inhibitor, comparably decreased both the basal and the ET-stimulated PGE2 production. Proliferation of cultured astrocytes was stimulated by 100 nM ET-3, and the increased proliferation was reduced by co-addition of 1 microM PGE2. Treatment with 1 microM PGE2 caused astrocytic morphological changes accompanied by disappearance of stress fibers, a prominent structure of organized cytoskeletal actin in cultured astrocytes. In the presence of 10 nM ET-3, PGE2 did not show an effect on astrocytic actin organization. The present study shows that ET is an inducer of astrocytic COX2 and suggests that ET-induced PGE2 production through COX2 may be involved in the regulation of astrocytic functions.

Differential regulation of extracellular signal-regulated protein kinases (ERKs) 1 and 2 by cAMP and dissociation of ERK inhibition from anti-mitogenic effects in rabbit vascular smooth muscle cells

The inhibition of extracellular signal-regulated protein kinases (ERKs) is implicated in the negative regulation of vascular smooth muscle cell (VSMC) mitogenesis by cAMP-elevating agents and transforming growth factor beta(1) (TGF-beta(1)). These factors inhibited rabbit aortic VSMC mitogenesis induced by platelet-derived growth factor (PDGF)-BB by preventing the entry of cells into S-phase. cAMP-elevating agents partly inhibited the late phase (1-4 h) of activation of ERKs 1 and 2 induced by PDGF-BB without inhibiting the early phase of activity (5-15 min) and had no effect on activity induced by basic fibroblast growth factor (bFGF). In contrast, cAMP elevation caused a marked inhibition of early ERK activation induced by angiotensin II and thrombin. TGF-beta(1) had no inhibitory effect on ERK activation induced by PDGF-BB or bFGF. The inhibition of PDGF-BB-stimulated DNA synthesis by either forskolin/3-isobutyl-1-methylxanthine (IBMX) or TGF-beta(1) was not decreased when the agents were added up to 8 h after growth factor. In contrast, the selective ERK kinase inhibitor PD98059 was a weak inhibitor of DNA synthesis; a combination of PD98059 and forskolin/IBMX had an additive inhibitory effect on DNA synthesis. Forskolin/IBMX inhibited the growth factor-induced expression of c-myc mRNA and cyclin D(1) protein, and enhanced the protein expression of p27(kip1). TGF-beta(1) had no effect on the expression of c-myc or p27(kip1) and weakly attenuated the expression of cyclin D(1). These findings support the conclusion that the suppression of VSMC mitogenesis by cAMP and TGF-beta(1) is independent of ERK inhibition. Anti-mitogenic effects of cAMP might be primarily mediated by events in late G(1).

Effects of dehydroepiandrosterone on mitogen-activated protein kinase in human aortic smooth muscle cells

The objective of the present study was to determine whether dehydroepiandrosterone (DHEA) modifies growth factor-induced mitogen-activated protein kinase (MAPK) activation, based on our previous study demonstrating that DHEA attenuates fetal calf serum-induced proliferation in human male aortic smooth muscle cells (human male aortic SMCs). Human male aortic SMCs were used for this study. Platelet-derived growth factor-BB (PDGF-BB), epidermal growth factor (EGF), and basic fibroblast growth factor (bFGF), but not insulin-like growth factor-1 (IGF-1), stimulated MAPK activity. Only MAPK activation induced by PDGF-BB was reduced by pretreatment with DHEA, although DHEA did not affect the MAPK activation induced by EGF or bFGF. The basal and PDGF-stimulated MAPK activity were decreased by two types of cyclic AMP (cAMP) elevating agents and increased by cAMP-dependent protein kinase (PKA) inhibitor in human male aortic SMCs, suggesting that cAMP regulates MAPK negatively. The intracellular cAMP was increased by PDGF-BB. The increase of cAMP by PDGF-BB was augmented by pretreatment with DHEA, although DHEA alone did not affect cAMP. Neither EGF nor bFGF affected cAMP with and without DHEA pretreatment. Secretion of PGE2 induced by PDGF was augmented by pretreatment with DHEA. Stimulatory effects of DHEA on the production of PGE2 and cAMP were partially canceled by aromatase inhibitor and completely canceled by indomethacin or selective inhibitor of cyclooxygenase-2. These results suggest that DHEA inhibited MAPK activation induced by PDGF-BB via PGE2 overproduction and subsequent cAMP-dependent pathway in human male aortic SMCs.