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

Crosstalk Between Signaling Pathways Involved in the Regulation of Airway Smooth Muscle Cell Hyperplasia

Increased ASM mass, primarily due to ASM hyperplasia, has been recognized as a hallmark of airway remodeling in asthma. Increased ASM mass is the major contributor to the airway narrowing, thus worsening the bronchoconstriction in response to stimuli. Inflammatory mediators and growth factors released during inflammation induce increased ASM mass surrounding airway wall via increased ASM proliferation, diminished ASM apoptosis and increased ASM migration. Several major pathways, such as MAPKs, PI3K/AKT, JAK2/STAT3 and Rho kinase, have been reported to regulate these cellular activities in ASM and were reported to be interrelated at certain points. This article aims to provide an overview of the signaling pathways/molecules involved in ASM hyperplasia as well as the mapping of the interplay/crosstalk between these major pathways in mediating ASM hyperplasia. A more comprehensive understanding of the complexity of cellular signaling in ASM cells will enable more specific and safer drug development in the control of asthma.

Involvement of ERK1/2, p38 MAPK, and PI3K/Akt signaling pathways in the regulation of cell cycle progression by PTHrP in colon adenocarcinoma cells

Parathyroid hormone-related peptide (PTHrP) is distributed in most fetal and adult tissues, and its expression correlates with the severity of colon carcinoma. Recently we obtained evidence that in Caco-2 cells, a cell line from human colorectal adenocarcinoma, exogenous PTHrP increases the number of live cells, via ERK1/2, p38 MAPK, and PI3-kinase and induces the expression of cyclin D1, a cell cycle regulatory protein. In this study, we further investigated the role of PTHrP in the regulation of the cell cycle progression in these intestinal cells. Flow cytometry analysis revealed that PTHrP treatment diminishes the number of cells in the G0/G1 phase and increases the number in both S and G2/M phases. The hormone increases the expression of CDK6 and diminishes the amount of negative cell cycle regulators p27Kip1, p15INK4B, and p53. However, PTHrP does not modify the expression of cyclin D3, CDK4, and p16INK4A. In addition, inhibitors of ERK1/2 (PD98059), p38 MAPK (SB203580), and PI3Kinase (LY294002) reversed PTHrP response in Caco-2 cells. Taken together, our results suggest that PTHrP positively modulates cell cycle progression and changes the expression of proteins involved in cell cycle regulation via ERK1/2, p38 MAPK, and PI3K signaling pathways in Caco-2 cells.

M2 Muscarinic acetylcholine receptor modulates rat airway smooth muscle cell proliferation

Airways chronic inflammatory conditions in asthma and COPD are characterized by tissue remodeling, being smooth muscle hyperplasia, the most important feature. Non-neuronal and neuronal Acetylcholine acting on muscarinic receptors (MAChRs) has been postulated as determinant of tissue remodeling in asthma and COPD by promoting proliferation and phenotypic changes of airway smooth muscle cells (ASMC). The objective was to evaluate proliferative responses to muscarinic agonist as carbamylcholine (Cch) and to identify the MAchR subtype involved. ASMC were isolated from tracheal fragments of Sprague-Dawley rats by enzymatic digestion. Proliferation assays were performed by MTS-PMS method. Viability was confirmed by trypan blue exclusion method. Mitogens as, epidermal growth factor (EGF), Tumor necrosis factor-alpha (TNF-α) and fetal bovine serum (FBS) increased ASMC proliferation (p < 0.05, n = 5). Cch alone increased ASMC proliferation at 24 and 48 hrs. However, combination of Cch with other mitogens exhibited a dual effect, synergistic proliferation effect in the presence of EGF (5 ng/mL) and 5% FBS and inhibiting the proliferation induced by 10% FBS, EGF (10 ng/mL) and TNF-α (10 ng/mL). To determine the MAChR subtype involved in these biological responses, a titration curve of selective muscarinic antagonists were performed. The Cch stimulatory and inhibitory effects on ASCM proliferation was blocked by AF-DX-116 (M2AChR selective antagonist), in greater proportion than 4-DAMP (M3AChR selective antagonist), suggesting that the modulation of muscarinic agonist-induced proliferation is M2AChR mediated responses. Thus, M2AChR can activate multiple signal transduction systems and mediate both effects on ASMC proliferation depending on the plethora and variable airway microenvironments existing in asthma and COPD.

The ω-3 epoxide of eicosapentaenoic acid inhibits endothelial cell proliferation by p38 MAP kinase activation and cyclin D1/CDK4 down-regulation

BACKGROUND AND PURPOSE

Dietary intake of ω-3 polyunsaturated fatty acids (ω-3 PUFAs) like eicosapentaenoic acid (EPA) decreases cancer risk, while arachidonic acid and other ω-6 PUFAs increase risk, but the underlying mechanisms are unclear. Cytochrome P450 (CYP)-derived epoxides contribute to enhanced tumourigenesis due to ω-6 PUFA intake. Thus, ω-6 arachidonic acid epoxides (EETs) inhibit apoptosis and stimulate proliferation by up-regulating cyclin D1 expression in cells. The present study evaluated the corresponding ω-3 PUFA epoxides and assessed their role in the regulation of cell proliferation.

EXPERIMENTAL APPROACH

Four chemically stable EPA epoxides (formed at the 8,9-, 11,12-, 14,15- and 17,18-olefinic bonds) were synthesized and tested against growth-related signalling pathways in brain microvascular endothelial bEND.3 cells. Cell cycle distribution was determined by flow cytometry and cyclin gene expression by immunoblotting and real-time PCR. The role of the p38 mitogen-activated protein (MAP) kinase in cyclin D1 dysregulation was assessed using specific inhibitors and dominant-negative expression plasmids.

KEY RESULTS

The ω-3 17,18-epoxide of EPA decreased cell proliferation, interrupted the cell cycle in S-phase and down-regulated the cyclin D1/cyclin-dependent kinase (CDK)-4 complex, whereas the 8,9-, 11,12- and 14,15-epoxides were either inactive or enhanced proliferation. Cyclin D1 down-regulation by 17,18-epoxy-EPA was mediated by activation of the growth-suppressing p38 MAP kinase, but the alternate EPA-epoxides were inactive.

CONCLUSIONS AND IMPLICATIONS

The present findings suggest that the epoxide formed by CYP enzymes at the ω-3 olefinic bond may contribute to the beneficial effects of ω-3 PUFA by down-regulating cyclin D1 and suppressing cell proliferation.

Activation of the p38 MAPK/Akt/ERK1/2 signal pathways is required for the protein stabilization of CDC6 and cyclin D1 in low-dose arsenite-induced cell proliferation

Arsenic trioxide (ATO) is a first-line anti-cancer agent for acute promyelocytic leukemia, and induces apoptosis in other solid cancer cell lines including breast cancer cells. However, as with arsenites found in drinking water and used as raw materials for wood preservatives, insecticides, and herbicides, low doses of ATO can induce carcinogenesis after long-term exposure. At 24 h after exposure, ATO (0.01-1 µM) significantly increased cell proliferation and promoted cell cycle progression from the G1 to S/G2 phases in the non-tumorigenic MCF10A breast epithelial cell line. The expression of 14 out of 96 cell-cycle-associated genes significantly increased, and seven of these genes including cell division cycle 6 (CDC6) and cyclin D1 (CCND1) were closely related to cell cycle progression from G1 to S phase. Low-dose ATO steadily increased gene transcript and protein levels of both CDC6 and cyclin D1 in a dose- and time-dependent manner. Low-dose ATO produced reactive oxygen species (ROS), and activated the p38 MAPK, Akt, and ERK1/2 pathways at different time points within 60 min. Small molecular inhibitors and siRNAs inhibiting the activation of p38 MAPK, Akt, and ERK1/2 decreased the ATO-increased expression of CDC6 protein. Inhibiting the activation of Akt and ERK1/2, but not p38 MAPK, decreased the ATO-induced expression of cyclin D1 protein. This study reports for the first time that p38 MAPK/Akt/ERK1/2 activation is required for the protein stabilization of CDC6 in addition to cyclin D1 in ATO-induced cell proliferation and cell cycle modulation from G1 to S phase.

p38 MAPK regulates G1-S transition in hypoxic cardiac fibroblasts

Cardiac fibroblast hyperplasia associated with augmented matrix production is central to wound healing following myocardial injury. Regulation of the cardiac fibroblast cell cycle by factors in the diseased myocardium that can potentially modify the hyperplastic response of cardiac fibroblasts has, however, not been investigated. We examined the regulation of the cardiac fibroblast cell cycle by hypoxia, a major constituent of myocardial ischemia. Significant reductions in DNA synthesis and cell number, and flow cytometry indicated decreased G1/S progression in hypoxic adult rat cardiac fibroblasts. Western blot analysis showed reduced levels of cyclin D and cyclin A, induction of p27 and hypophosphorylation of Rb under hypoxia. Skp2, which targets p27 for degradation, was significantly lower and inversely related to p27 protein levels in hypoxic cells. Marked p38 MAPK activation was observed under hypoxia and its inhibition using SB203580 reversed the effects of hypoxia on DNA synthesis, cell cycle phase distribution, p27, and cyclin D1 but not cyclin A. Interestingly, a 2-fold increase in p27 mRNA in hypoxic cells, demonstrated by real-time PCR, was unaffected by SB203580, which, however, reversed the hypoxic inhibition of Skp2. In summary, p38 MAPK is an important determinant of hypoxia-induced G0/G1 block in cardiac fibroblasts. p27 induction in hypoxic cardiac fibroblasts may involve direct transcriptional regulation, independent of p38 MAPK, and post-translational regulation via p38 MAPK-dependent suppression of its degradation by Skp2. The study identifies Skp2 as a potential downstream target of p38 MAPK, suggesting a novel mechanism of G1-S regulation in cardiac fibroblasts exposed to stress conditions.

The elements of human cyclin D1 promoter and regulation involved

Cyclin D1 is a cell cycle machine, a sensor of extracellular signals and plays an important role in G1-S phase progression. The human cyclin D1 promoter contains multiple transcription factor binding sites such as AP-1, NF-қB, E2F, Oct-1, and so on. The extracellular signals functions through the signal transduction pathways converging at the binding sites to active or inhibit the promoter activity and regulate the cell cycle progression. Different signal transduction pathways regulate the promoter at different time to get the correct cell cycle switch. Disorder regulation or special extracellular stimuli can result in cell cycle out of control through the promoter activity regulation. Epigenetic modifications such as DNA methylation and histone acetylation may involved in cyclin D1 transcriptional regulation.

Evidence that age-related changes in p38 MAP kinase contribute to the decreased steroid production by the adrenocortical cells from old rats

The current studies were initiated to investigate whether excessive oxidative stress exerts its antisteroidogenic action through modulation of oxidant-sensitive mitogen-activated protein kinase (MAPK) signaling pathways. Western blot analysis indicated that aging caused increased phosphorylation and activation of rat adrenal p38 MAPK, but not the ERK1/2 or JNK1/2. Lipid peroxidation measurements (an index of cellular oxidative stress) indicated that adrenal membranes from young animals contained only minimal levels of endogenous thiobarbituric acid-reactive substances (TBARS), and exposure of membranes to enzymatic and non-enzymatic pro-oxidants enhanced TBARS formation approximately 12- and 20-fold, respectively. The adrenal membranes from old animals showed much more susceptibility to lipid peroxidation and exhibited roughly 4- to 6-fold higher TBARS formation than young controls both under basal conditions and in response to pro-oxidants. Qualitatively similar results were obtained when lipid peroxide formation was measured using a sensitive FOXRS (ferrous oxidation-xylenol orange-reactive substances) technique. We next tested whether aging-induced excessive oxidative insult alters steroidogenesis through modulation of MAPK signaling pathway. Treatment of adrenocortical cells from old rats with specific p38 MAPK inhibitors restored Bt(2)cAMP-stimulated steroidogenesis approximately 60-70% of the value seen in cells of young animals. Likewise, pretreatment of cells with reactive oxygen species (ROS) scavengers MnTMPyP and N-acetyl cysteine also partially rescued age-induced loss of steroid production. In contrast, simultaneous treatment of cells with ROS scavengers and p38 MAPK inhibitor did not produce any additional effect suggesting that both types of inhibitors exert their stimulatory action through inhibition of p38 MAPK activation. Collectively, these results indicate that p38 MAPK functions as a signaling effector in oxidative stress-induced inhibition of steroidogenesis during aging.

Mechanisms of induction of airway smooth muscle hyperplasia by transforming growth factor-beta

Airway smooth muscle (ASM) hyperplasia is a characteristic feature of the asthmatic airway, but the underlying mechanisms that induce ASM hyperplasia remain unknown. Because transforming growth factor (TGF)-beta is a potent regulator of ASM cell proliferation, we determined its expression and mitogenic signaling pathways in ASM cells. We obtained ASM cells by laser capture microdissection of bronchial biopsies and found that ASM cells from asthmatic patients expressed TGF-beta1 mRNA and protein to a greater extent than nonasthmatic individuals using real-time RT-PCR and immunohistochemistry, respectively. TGF-beta1 stimulated the growth of nonconfluent and confluent ASM cells either in the presence or absence of serum in a time- and concentration-dependent manner. The mitogenic activity of TGF-beta1 on ASM cells was inhibited by selective inhibitors of TGF-beta receptor I kinase (SD-208), phosphatidylinositol 3-kinase (PI3K, LY-294002), ERK (PD-98059), JNK (SP-600125), and NF-kappaB (AS-602868). On the other hand, p38 MAPK inhibitor (SB-203580) augmented TGF-beta1-induced proliferation. To study role of the Smads, we transduced ASM cells with an adenovirus vector-expressing Smad4, Smad7, or dominant-negative Smad3 and found no involvement of these Smads in TGF-beta1-induced proliferation. Dexamethasone caused a dose-dependent inhibition in TGF-beta1-induced proliferation. Our findings suggest that TGF-beta1 may act in an autocrine fashion to induce ASM hyperplasia, mediated by its receptor and several kinases including PI3K, ERK, and JNK, whereas p38 MAPK is a negative regulator. NF-kappaB is also involved in the TGF-beta1 mitogenic signaling, but Smad pathway does not appear important.

Altered cell adhesion and cell viability in a p38alpha mitogen-activated protein kinase-deficient mouse embryonic stem cell line

p38 mitogen-activated protein (MAP) kinase alpha (p38alpha) is a broadly expressed protein kinase that regulates growth and development. Most studies of p38alpha have been in somatic cells. Little is known about its function in embryonic stem (ES) cells. Using a ES cell line isolated from p38alpha knockout mouse embryos (p38alpha (-/-) ES cells), we investigated roles of p38alpha in the regulation of ES cell activities. p38alpha (-/-) ES cells displayed several altered features different from wild-type cells. The major findings are that p38alpha (-/-) ES cells have significantly increased cell adhesion to several extracelluar matrix proteins, correlating with elevated phosphorylation of focal adhesion kinase and paxillin. p38alpha (-/-) ES cells also showed increased cell viability, correlating with increased expression of survivin and activation of AKT (protein kinase B), two molecules that are known to improve cell viability. p38alpha (-/-) ES cells reach confluence faster than wild-type cells in routine cell culture. However, this is not due to a higher cell proliferation rate in p38alpha (-/-) ES cells, but rather is likely a result of improved cell adhesion and/or cell viability. Together our results indicated that p38alpha may negatively regulate mouse ES cell adhesion and viability.

Ethanol reduces p38 kinase activation and cyclin D1 protein expression after partial hepatectomy in rats

BACKGROUND/AIMS

Chronic ethanol consumption inhibits liver regeneration. We examined the effects of chronic ethanol consumption on two mitogen-activated protein kinases in relation to induction of cell cycle proteins after partial hepatectomy (PH).

METHODS

Male Wistar rats were ethanol-fed (EF) or pair-fed (PF) for 16 weeks before PH. Hepatic activation of extracellular signal regulated kinase (ERK)1/2, p38 kinase and expression of cyclinD1, cyclin-dependent kinase-4 (cdk4) and proliferating cell nuclear antigen (PCNA) were studied.

RESULTS

In PF rats, PH-induced p38 activation was evident at 2h and was maximal at 12h. There was a close temporal relationship between p38 activation, cyclin D1 and PCNA expression. Alcohol exposure reduced p38 activation, cyclin D1 and PCNA, each by approximately 50%. ERK1/2 activation occurred during the first 2h post-PH in both EF and PF rats, and there was no later increase in PF rats. In vivo inhibition of p38 suppressed PCNA expression whereas the effect of ERK1/2 inhibition was inconsistent.

CONCLUSIONS

p38 kinase activation is linked temporally with cyclin D1 expression after PH and appears to exert cell cycle control in the adult liver. p38 signaling also appears to be a target for the inhibitory effect of chronic alcohol on liver regeneration.

Constitutive activation of MKK6 in chondrocytes of transgenic mice inhibits proliferation and delays endochondral bone formation

Accumulating in vitro evidence suggests that the p38 mitogen-activated protein kinase (MAPK) pathway is involved in endochondral ossification. To investigate the role of this pathway in endochondral ossification, we generated transgenic mice with expression in chondrocytes of a constitutively active mutant of MKK6, a MAPK kinase that specifically activates p38. These mice had a dwarf phenotype characterized by reduced chondrocyte proliferation, inhibition of hypertrophic chondrocyte differentiation, and a delay in the formation of primary and secondary ossification centers. Histological analysis with in situ hybridization showed reduced expression of Indian hedgehog, PTH/PTH-related peptide receptor (PTH, parathyroid hormone), cyclin D1, and increased expression of p21 in chondrocytes. In addition, both in vivo and in transfected cells, p38 signaling increased the transcriptional activity of Sox9, a transcription factor essential for chondrocyte differentiation. In agreement with this observation, transgenic mice that express a constitutively active mutant of MKK6 in chondrocytes showed phenotypes similar to those of mice that overexpress SOX9 in chondrocytes. These observations are consistent with the notion that increased activity of Sox9 accounts at least in part for the phenotype caused by constitutive activation of MKK6 in chondrocytes. Therefore, our study provides in vivo evidence for the role of p38 in endochondral ossification and suggests that Sox9 is a likely downstream target of the p38 MAPK pathway.

YC-1-inhibited proliferation of rat mesangial cells through suppression of cyclin D1-independent of cGMP pathway and partially reversed by p38 MAPK inhibitor

This study was designed to investigate the effect of 1-benzyl-3-(5'-hydroxymethyl-2'-furyl) indazole (YC-1), a guanylate cyclase activator, upon the proliferation of rat mesangial cells and its underlying mechanism. YC-1 inhibited cell proliferation and DNA synthesis in a dose- and time-dependent manner. Flow cytometry cell-cycle studies revealed that YC-1 prevented the entry of cells from G1 into S phase. The expression of cyclin D1 and the kinase activity of cyclin D1/cyclin-dependent kinase (CDK)4 were lower within YC-1-treated cells, revealed by Western blotting, Northern blotting and kinase assays. YC-1 did not increase the intracellular cGMP concentration in mesangial cells. Inhibitors of soluble guanylate cyclase, protein kinase G, or protein kinase A also did not reverse the inhibitory effect elicited by YC-1, while co-treatment with p38 mitogen-activated protein kinase (MAPK) inhibitor could partially reverse the suppressive effect. YC-1 inhibited proliferation of mesangial cells and induced cell-cycle arrest by the reduction of cyclin D1 synthesis and cyclin D1/CDK4 kinase activity. This effect acts partially through p38 MAPK signal transduction activation and is independent of cGMP-signaling pathways.

Role of TNF-{alpha} signaling in regeneration of cardiotoxin-injured muscle

Recent data suggest a physiological role for the proinflammatory cytokine TNF-alpha in skeletal muscle regeneration. However, the underlying mechanism is not understood. In the present study, we analyzed TNF-alpha-activated signaling pathways involved in myogenesis in soleus muscle injured by cardiotoxin (CTX) in TNF-alpha receptor double-knockout mice (p55(-/-)p75(-/-)). We found that activation of p38MAPK, which is critical for myogenesis, was blocked in CTX-injured p55(-/-)p75(-/-) soleus on day 3 postinjury when myogenic differentiation was being initiated, while activation of ERK1/2 and JNK MAPK, as well as transcription factor NF-kappaB, was not reduced. Consequently, the phosphorylation of transcription factor myocyte enhancer factor-2C, which is catalyzed by p38 and crucial for the expression of muscle-specific genes, was blunted. Meanwhile, expression of p38-dependent differentiation marker myogenin and p21 were suppressed. In addition, expression of cyclin D1 was fivefold that in wild-type (WT) soleus. These results suggest that myogenic differentiation is blocked or delayed in the absence of TNF-alpha signaling. Histological studies revealed abnormalities in regenerating p55(-/-)p75(-/-) soleus. On day 5 postinjury, new myofiber formation was clearly observed in WT soleus but not in p55(-/-)p75(-/-) soleus. To the contrary, p55(-/-)p75(-/-) soleus displayed renewed inflammation and dystrophic calcification. On day 12 postinjury, the muscle architecture of WT soleus was largely restored. Yet, in p55(-/-)p75(-/-) soleus, multifocal areas of inflammation, myofiber death, and myofibers with smaller cross-sectional area were observed. Functional studies demonstrated an attenuated recovery of contractile force in injured p55(-/-)p75(-/-) soleus. These data suggest that TNF-alpha signaling plays a critical regulatory role in muscle regeneration.

Stress-activated protein kinases mediate cell migration in human airway epithelial cells

Airway epithelial cell (AEC) repair immediately after injury requires coordinated cell spreading and migration at the site of injury. Stress-activated protein kinases such as p38 MAPK and c-Jun N-terminal Protein Kinase (JNK) modulate several responses to cell stress and injury, but their role in AEC migration is not clear. We examined migration in confluent 16HBE14o(-) human AEC lines and in primary AEC grown on collagen-IV. Wounds were created by mechanical abrasion and followed to closure using digital microscopy. Inhibitors of either p38 extracellular signal-regulated kinase (ERK)1/2 (PD98059), mitogen-activated protein kinase (MAPK) (SB203580), or JNK (SP600125) could block cell migration substantially. Inhibiting JNK but not p38 MAPK or ERK1/2 blocked extension of cells into the wound region from the original line of injury. Initial migration was associated with phosphorylation of ERK, p38 MAPK, and JNK within 5-15 min. The downstream effector of p38, heat shock protein 27, also was phosphorylated rapidly after injury; phosphorylation could be blocked by prior treatment with SB203580 but not SP600125. The downstream effector of JNK, c-Jun, likewise was phosphorylated rapidly after injury and could be blocked by inhibiting JNK. Our data demonstrate that p38 MAPK, JNK, and ERK1/2 participate in the early stages of AEC migration.

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.

Methodologic advancements in the study of airway smooth muscle

The study of isolated airway myocytes has provided important information relative to specific processes that regulate contraction, proliferation, and synthetic properties of airway smooth muscle (ASM). To place this information in physiological context, however, improved methods to examine airway biology in vivo are needed. Advances in genetic, biochemical, and optical methods provide unprecedented opportunities to improve our understanding of in vivo physiology and pathophysiology. This article describes 4 important methodologic advances in the study of ASM: (1) the development of transgenic mice that could be used to investigate ASM proliferation and phenotype switching during the development of hypersensitivity, and to investigate excitation-contraction coupling; (2) the use of CD38-deficient mice to confirm the role of CD38-dependent, cyclic adenosine diphosphate-ribose-mediated calcium release in airway responsiveness; (3) investigation of the role of actin filament length and p38 mitogen-activated protein kinase activity in regulating the mechanical plasticity-elasticity balance in contracted ASM; and (d) the use of bronchial biopsies to study ASM structure and phenotype in respiratory science.

Contribution of the p38MAPK signalling pathway to proliferation in human cultured airway smooth muscle cells is mitogen-specific

We have investigated the role of p38MAPK in human airway smooth muscle (HASM) proliferation in response to thrombin and bFGF. The regulation of cyclin D1 mRNA, cyclin D1, cyclin E and p21Cip1 protein levels, and the extent of retinoblastoma protein (pRb) phosphorylation in response to activation of p38MAPK have also been examined. Two distinct inhibitors of p38MAPK, SB 203580 (10 microm) and SB 202190 (10 microm), prevented bFGF (0.3-3 nm)-stimulated cell proliferation, but had no effect on the response to thrombin (0.3-3 U ml(-1)). In cells incubated with thrombin or bFGF for 20 h, there was an increase in p38MAPK phosphorylation in response to bFGF, but not to thrombin. Thrombin and bFGF-stimulated increases in ERK phosphorylation and cyclin D1 mRNA and protein levels were not influenced by SB 203580 pre-treatment. Similarly, cyclin E and p21Cip1 protein levels, measured after 20 h incubation with mitogen, did not appear to be regulated by SB 203580 (10 microm). Although both thrombin and bFGF significantly increased levels of pRb phosphorylation, SB 203580 (10 microm) inhibited only bFGF-stimulated pRb phosphorylation. In addition, SB 203580 (10 microm) selectively inhibited bFGF-stimulated DNA synthesis, suggesting that the antimitogenic actions of SB 203580 on pRb phosphorylation cause cell cycle arrest at late G1 phase. In conclusion, these results indicate that p38MAPK is involved in bFGF-, but not in thrombin-stimulated HASM proliferation. The activation of the p38MAPK pathway by bFGF, but not by thrombin, regulates the phosphorylation of pRb without influencing cyclin D1 expression.

Fungal immunomodulatory protein from Flammulina velutipes induces interferon-gamma production through p38 mitogen-activated protein kinase signaling pathway

FIP-fve is a fungal immunomodulatory protein purified from Flammulina velutipes, an edible golden needle mushroom thought to possess potent immunomodulatory properties. When examined for its effects on lymphocytes, FIP-fve exhibited potent mitogenic effects on human peripheral blood lymphocytes, inducing G1/G0 to S phase proliferation. T cells activated by FIP-fve show significant production and secretion of interferon-gamma (IFN-gamma) associated with intercellular adhesion molecule 1 expression but low detectable levels of interleukin-4 in vitro or in vivo. However, SB203580, the p38 mitogen-activated protein kinase (p38 MAPK) inhibitor, can fully abolish the production of IFN-gamma induced by FIP-fve. At the same time, SB203580 only partially prevents the lymphocytes from progressing from G1 to S phase of the cell cycle. These findings demonstrate that FIP-fve is a potent T-cell activator, mediating its effects via cytokine regulation of p38 MAPK. The immunoprophylatic effects of FIP-fve in Th2-mediated allergic anaphylaxis are believed to be associated with the ability of FIP-fve to enhance activation of IFN-gamma-releasing Th1 cells.

Force-independent expression of c-fos mRNA by endothelin-1 in rat intact small mesenteric arteries

AIM

Wall stress-independent signalling pathways were studied for endothelin-1 (ET-1)-induced c-fos expression in rat intact mesenteric small arteries.

METHODS

Arteries were kept unmounted in Krebs buffer, equilibrated for 1 h and stimulated with vasoactive substances for 15-60 min. The c-fos mRNA expression was determined by real-time polymerase chain reaction.

RESULTS

Stimulation with fetal bovine serum (FBS), phorbol 12-myristate 13-acetate (PMA) and ET-1 caused about a doubling of c-fos mRNA. The ET-1-induced c-fos expression was steady (15-60 min) and was inhibited by the inhibitor of the ET(A) receptor, BQ-123. Platelet-derived growth factor-B, angiotensin II and U46619 did not cause increased c-fos mRNA levels. The broad specificity inhibitor staurosporine inhibited the response to ET-1, but inhibitors of Rho-A kinase and phosphatidylinositol 3-kinase had no effect. However, inhibitors to tyrosine kinases, the MAP kinases [extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun amino-terminal kinase, p38], and to conventional protein kinase C showed no inhibition. Consistent with these findings, ET-1 did not cause activation of ERK1/2, a finding also seen in vessels held under pressure. In contrast, ET-1-induced c-fos expression was inhibited by the calcium chelator BAPTA, suggesting a role for intracellular calcium. This possibility was supported by the finding that raising the extracellular K(+) concentration caused increased expression of c-fos in a concentration-dependent manner.

CONCLUSION

The results suggest that in the absence of wall stress, ET-1 is able to induce increased expression of c-fos independent of traditional growth pathways, such as MAP kinase. The mechanism appears to be calcium-dependent.

Induction of early growth-response factor 1 by platelet-derived growth factor in human airway smooth muscle

Platelet-derived growth factors (PDGF) may contribute to the activation and growth of smooth muscle that is characteristic of airway remodeling in asthmatic patients. Early growth response 1 (EGR-1) is a transcription factor that is induced in several cell types by PDGF and may mediate some of the effects of PDGF. We show that human airway smooth muscle cells in cell culture express EGR-1 1 h after addition of PDGF. Analysis of the EGR-1 promoter indicates that a serum response element located between 663 and 654 bp 5' to the ATG start site is essential for this induction. Serum response factor, E26 transcription factor-like protein 1, and serum protein 1 bind to this region. PDGF causes phosphorylation of ERK1/2 and is temporally associated with E26 transcription factor-like protein 1 phosphorylation. Finally, the specific ERK1/2 inhibitor U-0126 abolishes PDGF-induced expression of EGR-1 in these cells. On the basis of these data, we speculated that EGR-1 would be increased in airway smooth muscle of asthmatic patients compared with nonasthmatic controls. Using immunohistochemistry, we found that EGR-1 protein was expressed in airway smooth muscle cells and epithelial cells of asthmatic patients and nonasthmatic controls; however, there was no significant difference in the intensity of staining between groups. EGR-1 was similarly expressed in the lungs of mice with and without ovalbumin-induced airway inflammation; however, there was no difference between groups by immunohistochemistry and quantitative PCR. Although EGR-1 is induced by PDGF in human airway smooth muscle cells in cell culture, the role of EGR-1 in airway remodeling and asthma remains to be established.

Long-term effect of heat shock protein 60 from Actinobacillus actinomycetemcomitans on epithelial cell viability and mitogen-activated protein kinases

Our previous studies showed that bacterial heat shock protein 60 (hsp60) induces cultured epithelial cell proliferation within 24 h. Here we investigated the long-term effects of heat shock protein 60 isolated from Actinobacillus actinomycetemcomitans on skin keratinocyte (HaCaT cell line) viability and the cell signaling involved. Prolonged incubation in the presence of hsp60 increased the rate of epithelial cell death. The number of viable cells in hsp60-treated culture was 37% higher than the number in the control at 24 h but 27% lower at 144 h. A kinetics study of the effect of hsp60 on the phosphorylation of mitogen-activated protein kinases (MAPKs) involving Western blotting with phospho-specific antibodies showed that in addition to a transient early increase in p38 levels, a second peak appeared in keratinocytes 24 h after the addition of hsp60. In contrast, prolonged incubation with hsp60 caused a decrease in the level of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) compared with that in the controls, possibly as a result of protein phosphatase activity. We found that hsp60 increased the levels of several phosphatases, including MAP-2, which strongly dephosphorylates ERK1/2. Moreover, hsp60 increased the level of tumor necrosis factor alpha (TNF-alpha) in culture medium in a dose-dependent manner. TNF-alpha added to culture showed a cytotoxic effect on epithelial cells, particularly with longer incubation periods. TNF-alpha also induced the phosphorylation of p38. Finally, our results show that bacterial hsp60 inhibited stress-induced synthesis of cellular hsp60. Therefore, several cell behavior changes caused by long-term exposure to bacterial hsp60 may lead to impaired epithelial cell viability.

Inhibitors of p38 mitogen-activated protein kinase: potential as anti-inflammatory agents in asthma?

Asthma is an inflammatory disease of the airways, which in patients with mild to moderate symptoms is adequately controlled by either beta(2)-adrenoceptor agonists or corticosteroids, or a combination of both. Despite this, there are classes of patients that fail to respond to these treatments. In addition, there is a general trend towards increasing morbidity and mortality due to asthma, which suggests that there is a need for new and improved treatments. The p38 mitogen-activated protein kinases (MAPKs) represent a point of convergence for multiple signalling processes that are activated in inflammation and that impact on a diverse range of events that are important in inflammation. Small molecule pyridinyl imidazole inhibitors of p38 MAPK have proved to be highly effective in reducing various parameters of inflammation, in particular cytokine expression. Like corticosteroids, inhibitors of p38 MAPK appear to be able to repress gene expression at multiple levels, for example, by transcriptional, posttranscriptional and translational repression, and this raises the possibility of a similarly broad spectrum of anti-inflammatory activities. Indeed these molecules have proved to be effective in numerous in vitro and in vivo models of inflammation and septicaemia, which suggests that such compounds may be effective as therapeutic agents against inflammatory disorders. Despite these very promising indications of the possible therapeutic use of p38 MAPK inhibitors, a number of events that are p38-dependent are in fact also beneficial to the resolution or modulation of diseases such as asthma. We conclude that the overall effect of p38 MAPK inhibition would be beneficial in inflammatory diseases such as rheumatoid arthritis and asthma. However, these drugs may result in a complex phenotype that will require careful evaluation. Currently, a number of second or third generation inhibitors of p38 MAPK are being tested in phase I and phase II clinical trials.

Different roles of ERK and p38 MAP kinases during tube formation from endothelial cells cultured in 3-dimensional collagen matrices

In a two-dimensional (2D) culture dish, the major activity of endothelial cells is proliferation with limited morphological change. When cultured in a three-dimensional (3D) collagen gel matrix, endothelial cells undergo a series of morphological changes starting with development of intracellular vacuoles and followed by cell elongation. Adjacent cells then coalesce to form tube-like structures. This process mimics the steps of capillary formation during angiogenesis. Using this model, we investigated the roles of extracellular signal-regulated kinase (ERK) and p38 MAP kinase (p38) in the tube formation from human umbilical vein endothelial cells (HUVEC). Proliferating HUVEC gradually lost their ability to divide after being transferred to 3D collagen matrices, where differentiation became the dominant cellular activity. The transition from proliferation to the differentiation state was accompanied by a drastic reduction of cyclin-dependent kinases CDC2, CDK4, and retinoblastoma (Rb) protein, but the expression of cyclin-dependent kinase inhibitor, p27kip1, was increased. Inhibition of p38 by SB203580 partially prevented these changes and increased the proliferation rate of HUVEC. However, cells under this condition exhibited unusually elongated cell bodies, and they were unable to coalesce to form tube structures. Inhibition of ERK neither affected the cell proliferation rate nor the expression levels of cell cycle regulators, but it completely blocked tube formation by inducing apoptosis, a finding different from the best-known role of ERK in cell proliferation in the 2D cell culture systems. We conclude that the major function of ERK is to maintain cell viability while p38 plays multiple roles in controlling cell proliferation, viability, and morphogenesis during tube formation.

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.

MAPK regulation of gene expression in airway smooth muscle

Mitogen-activated protein kinases (MAPK) are important components of signaling modules activated by neurotransmitters, cytokines, and growth factors, as well as chemical and mechanical stressors. In the airway, these external signals produce acute responses that modify smooth muscle contraction and may also induce chronic responses that modify airway structure. Both acute and chronic events in airway remodeling result from altered expression of multiple genes encoding protein mediators of cell-cell signaling, extracellular matrix remodeling, cell cycle control and intracellular signaling pathways. This review will focus on inflammatory and growth factor mediators of cell-cell signaling regulated by the ERK and p38 MAPK pathways in airway smooth muscle (ASM). These signaling mediators affect ASM tissue mechanics, cell migration, and gene expression patterns in a paracrine and autocrine fashion, although the relative importance of each MAPK pathway varies with the stimulus. These events thereby contribute to normal airway function and participate in pathological changes in ASM that accompany symptoms of asthma.

Mechanisms of inflammation-mediated airway smooth muscle plasticity and airways remodeling in asthma

Recent evidence points to progressive structural change in the airway wall, driven by chronic local inflammation, as a fundamental component for development of irreversible airway hyperresponsiveness. Acute and chronic inflammation is orchestrated by cytokines from recruited inflammatory cells, airway myofibroblasts and myocytes. Airway myocytes exhibit functional plasticity in their capacity for contraction, proliferation, and synthesis of matrix protein and cytokines. This confers a principal role in driving different components of the airway remodeling process, and mediating constrictor hyperresponsiveness. Functional plasticity of airway smooth muscle (ASM) is regulated by an array of environmental cues, including cytokines, which mediate their effects through receptors and a number of intracellular signaling pathways. Despite numerous studies of the cellular effects of cytokines on cultured airway myocytes, few have identified how intracellular signaling pathways modulate or induce these cellular responses. This review summarizes current understanding of these concepts and presents a model for the effects of inflammatory mediators on functional plasticity of ASM in asthma.

Differential inhibition of thrombin- and EGF-stimulated human cultured airway smooth muscle proliferation by glucocorticoids

The present study compared the effects of glucocorticoids on thrombin- and EGF-stimulated proliferation in human cultured airway smooth muscle (ASM) to identify pathways that may be differentially regulated by glucocorticoids. Mitogenic responses to thrombin were inhibited by extracellular-regulated kinase (ERK 1/2) and phosphoinositide 3-kinase (PI3K) inhibitors, whereas mitogenic responses to EGF were inhibited by ERK 1/2 and PI3K inhibitors as well as by the p38 mitogen activated protein kinase inhibitor, SB203580 (10 microM). Mitogenic responses to thrombin were more sensitive to inhibition by dexamethasone (Dex) or fluticasone propionate (FP) than were those to EGF. Elevated cyclin D1 protein and mRNA levels induced by thrombin and EGF were attenuated equally by glucocorticoids. The protein or mRNA levels of the cyclin-dependent kinase inhibitors (cdki) p21(Cip1), p27(Kip1) were unaffected by Dex treatment of ASM cells treated with mitogens. The resistance of EGF-induced proliferation to inhibition by glucocorticoids is not associated with a failure to regulate cyclin D1 induction, nor does it appear to be explained by differential regulation of the levels of the cdki's, p21(Cip1) and p27(Kip1).

IFN-gamma inhibits human airway smooth muscle cell proliferation by modulating the E2F-1/Rb pathway

Elucidating the factors that inhibit the increase in airway smooth muscle (ASM) mass may be of therapeutic benefit in asthma. Here, we investigated whether interferon-gamma (IFN-gamma), a potent inducer of growth arrest in various cell types, regulates mitogen-induced ASM cell proliferation. IFN-gamma (1-100 U/ml) was found to markedly decrease both DNA synthesis and ASM cell number induced by the mitogens epidermal growth factor (EGF) and thrombin. Interestingly, IFN-gamma had no effect on mitogen-induced activation of three major mitogenic signaling pathways, phosphatidylinositol 3-kinase, p70(S6k), or mitogen-activated protein kinases. Mitogen-induced expression of cell cycle regulator cyclin D1 was increased by IFN-gamma, whereas no effect was observed on degradation of p27(Kip1). Expression array analysis of 23 cell cycle-related genes showed that IFN-gamma inhibited EGF-induced increases in E2F-1 expression, whereas induction of c-myc, cyclin D2, Egr-1, and mdm2 were unaffected. Induction of E2F-1 protein and Rb hyperphosphorylation after mitogen stimulation was also suppressed by IFN-gamma. In addition, IFN-gamma decreased activation of cdk2 and expression of cyclin E, upstream signaling molecules responsible for Rb hyperphosphorylation in the late G1 phase. IFN-gamma also increased levels of IFI 16 protein, whose mouse homolog p202 has been associated with growth inhibition. Together, our data indicate that IFN-gamma is an effective inhibitor of ASM cell proliferation by blocking transition from G1-to-S phase by acting at two different levels: modulation of cdk2/cyclin E activation and inhibition of E2F-1 gene expression.

Signaling intermediates required for NF-kappa B activation and IL-8 expression in CF bronchial epithelial cells

Ligation of the asialoGM1 Pseudomonas aeruginosa pilin receptor has been demonstrated to induce IL-8 expression in airway epithelial cells via an NF-kappaB-dependent pathway. We examined the signaling pathways required for asialoGM1-mediated NF-kappaB activation in IB3 cells, a human bronchial epithelial cell line derived from a cystic fibrosis (CF) patient, and C-38 cells, the rescued cell line that expresses a functional CF transmembrane regulator. Ligation of the asialoGM1 receptor with specific antibody induced greater IL-8 expression in IB3 cells than C-38 cells, consistent with the greater density of asialoGM1 receptors in CF phenotype cells. AsialoGM1-mediated activation of NF-kappaB, IkappaB kinase (IKK), and ERK was also greater in IB3 cells. With the use of genetic inhibitors, we found that IKK-beta and NF-kappaB-inducing kinase are required for maximal NF-kappaB transactivation and transcription from the IL-8 promoter. Finally, although ERK activation was required for maximal asialoGM1-mediated IL-8 expression, inhibition of ERK signaling had no effect on IKK or NF-kappaB activation, suggesting that ERK regulates IL-8 expression in an NF-kappaB-independent manner.

p38 mitogen-activated protein kinase regulates growth factor-induced mitogenesis of rat pulmonary myofibroblasts

Myofibroblast proliferation is a central feature of pulmonary fibrogenesis. Several growth factors, including platelet-derived growth factor (PDGF) and epidermal growth factor (EGF), stimulate myofibroblast growth by activating extracellular signal regulated kinases 1 and 2 (ERK1/2). In this report, we demonstrate that PDGF-BB and EGF also activate the p38 mitogen-activated protein (MAP) kinase. Inhibition of p38 activity with the pyridinylimidazole compound SB203580 enhanced both PDGF-BB and EGF-stimulated DNA synthesis in rat lung myofibroblasts. ERK1/2 phosphorylation in response to either PDGF-BB or EGF treatment was significantly increased by pretreatment of cells with SB203580. We also demonstrated that ERK1/2-induced phosphorylation of PHAS-1 substrate was enhanced by inhibition of p38 MAP kinase with SB203580. However, SB203580 did not significantly increase growth factor-induced activation of MEK, the upstream kinase that phosphorylates ERK1/2. p38 MAP kinase was co-immunoprecipitated with ERK-1/2 following growth factor stimulation. Collectively, these data demonstrate that p38 MAP kinase activation negatively regulates PDGF- and EGF-mediated growth responses by directly interacting with ERK1/2 and suppressing its phosphorylation.

Effects of extracellular triphosphate nucleotides and nucleosides on airway smooth muscle cell proliferation

Extracellular ATP and uridine triphosphate (UTP) have a range of effects on a wide variety of cells through the activation of P(2) receptors. The aim of this work was to establish if stimulation with ATP and UTP enhances airway smooth muscle (ASM) cell proliferation and to determine the type of receptor mediating this effect. Proliferation of rat ASM cells was assessed through bromodeoxyuridine (BrdU) uptake and by cell counting. At concentrations of 10(-6) and 10(-5) M, ATP and UTP induced significant increases in BrdU incorporation. ATP analogs specific for the P(2X) and P(2Y1) receptor subtypes had no effect. UDP (a P(2Y6) receptor agonist) produced significant decreases in BrdU incorporation and cell counts. Adenosine, the metabolite of ATP, produced an increase in cell proliferation through stimulation of the A(1) receptor. A(2) and A(3) receptor stimulation had no effect. Reverse transcription and polymerase chain reaction analysis showed that mRNA transcripts for the P(2Y2), P(2Y4), P(2Y6), A(1), A(2), and A(3) receptor subtypes were present in cultured ASM cells. These data show that extracellular UTP, ATP, and their metabolites may affect airway remodeling by increasing or by reducing (P(2Y6) receptor) ASM cell proliferation.

Regulation of airway smooth muscle cyclin D1 transcription by protein kinase C-delta

The precise mechanism by which protein kinase C-delta (PKCdelta) inhibits cell cycle progression is not known. We investigated the regulation of cyclin D1 transcription by PKCdelta in primary bovine airway smooth muscle cells. Overexpression of the active catalytic subunit of PKCdelta attenuated platelet-derived growth factor (PDGF)-mediated transcription from the cyclin D1 promoter, whereas overexpression of a dominant-negative PKCdelta increased promoter activity. A PKCdelta-specific pseudosubstrate increased cyclin D1 protein abundance. To determine the transcriptional mechanism by which PKCdelta negatively regulates cyclin D1 expression, we transiently transfected cells with cDNAs encoding cyclin D1 promoter 5' deletions and site mutations in the context of a -66 promoter fragment. We found that the -57 to -52 CRE/ATF2 site functions as a basal level and PDGF enhancer, whereas the -39 to -30 nuclear factor-kappaB site functions as a basal level suppressor. Further, PDGF and PKCdelta responsiveness of the cyclin D1 promoter was maintained following 5' deletion to the Ets-containing -22 minimal promoter. Finally, using electrophoretic mobility gel shift and reporter assays, we determined that PKCdelta inhibits CRE/ATF2 binding and transactivation, activates nuclear factor-kappaB binding and transactivation, and attenuates Ets transactivation. These data suggest that PKCdelta attenuates cyclin D1 promoter activity via the regulation of three distinct cis-acting regulatory elements.

Vav is required for cyclin D2 induction and proliferation of mouse B lymphocytes activated via the antigen Receptor

B lymphocytes from mice null for the Rho-family guanine-nucleotide exchange factor, Vav, are defective in their ability to proliferate in response to BCR cross-linking, but are able to proliferate normally in response to LPS. In addition, they have a depletion of CD5(+) (B1) lymphocytes and defective IgG class switching. This phenotype is reminiscent of that observed in mice null for the cell cycle regulatory protein, cyclin D2. We demonstrate here that the inability of vav(-/-) B cells to proliferate in response to BCR ligation is due to an inability to induce cyclin D2. In addition, we show that the proliferative defect of these cells occurs after the cells have entered early G1 phase. Analyses of potential down-stream signaling intermediates revealed differential activation of the stress-activated MAP kinases in the absence of Vav, normal activation of the ERK, MAPK, and phosphatidylinositol 3-kinase pathways, and defective intracellular calcium mobilization. We further demonstrate that intracellular calcium homeostasis is required for cyclin D2 induction, implicating a possible link with the defective calcium response of vav(-/-) B cells and their inability to induce cyclin D2.

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.