Involvement of MAPKs and NF-kappaB in LPS-induced VCAM-1 expression in human tracheal smooth muscle cells

Lipopolysaccharide (LPS) has been shown to induce the expression of adhesion molecules on airway epithelial and smooth cells and contributes to inflammatory responses. Here, the roles of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappaB (NF-kappaB) pathways for LPS-induced vascular cell adhesion molecule (VCAM)-1 expression were investigated in HTSMCs. LPS-induced expression of VCAM-1 protein and mRNA in a time-dependent manner, was significantly inhibited by inhibitors of MEK1/2 (U0126), p38 (SB202190), and c-Jun-N-terminal kinase (JNK; SP600125). The involvement of p42/p44 MAPK and p38 in these responses was further confirmed by that transfection with small interference RNAs (siRNA) direct against MEK, p42, and p38 significantly attenuated LPS-induced VCAM-1 expression. Consistently, LPS-stimulated phosphorylation of p42/p44 MAPK and p38 was attenuated by pretreatment with U0126 or SB202190, and transfection with these siRNAs, respectively. In addition, LPS-induced VCAM-1 expression was significantly blocked by a specific NF-kappaB inhibitor helenalin. LPS-stimulated translocation of NF-kappaB into the nucleus and degradation of IkappaB-alpha was blocked by helenalin, U0126, SB202190, or SP600125. Moreover, the resultant enhancement of VCAM-1 expression increased the adhesion of polymorphonuclear cells to monolayer of HTSMCs which was blocked by pretreatment with helenalin, U0126, or SP600125 prior to LPS exposure. Taken together, these results suggest that in HTSMCs, activation of p42/p44 MAPK, p38, and JNK pathways, at least in part, mediated through NF-kappaB, is essential for LPS-induced VCAM-1 gene expression. These results provide new insight into the mechanisms of LPS action that bacterial toxins may promote inflammatory responses in the airway disease.     

Cigarette smoke extract regulates cytosolic phospholipase A2 expression via NADPH oxidase/MAPKs/AP-1 and p300 in human tracheal smooth muscle cells

Up-regulation of cytosolic phospholipase A(2) (cPLA(2)) by cigarette smoke extract (CSE) may play a critical role in airway inflammatory diseases. However, the mechanisms underlying CSE-induced cPLA(2) expression in human tracheal smooth muscle cells (HTSMCs) were not completely understood. Here, we demonstrated that CSE-induced cPLA(2) protein and mRNA expression was inhibited by pretreatment with the inhibitors of AP-1 (tanshinone IIA) and p300 (garcinol) or transfection with siRNAs of c-Jun, c-Fos, and p300. Moreover, CSE also induced c-Jun and c-Fos expression, which were inhibited by pretreatment with the inhibitors of NADPH oxidase (diphenyleneiodonium chloride and apocynin) and the ROS scavenger (N-acetyl-L-cysteine) or transfection with siRNAs of p47(phox) and NADPH oxidase (NOX)2. CSE-induced c-Fos expression was inhibited by pretreatment with the inhibitors of MEK1 (U0126) and p38 MAPK (SB202190) or transfection with siRNAs of p42 and p38. CSE-induced c-Jun expression and phosphorylation were inhibited by pretreatment with the inhibitor of JNK1/2 (SP600125) or transfection with JNK2 siRNA. CSE-stimulated p300 phosphorylation was inhibited by pretreatment with the inhibitors of NADPH oxidase and JNK1/2. Furthermore, CSE-induced p300 and c-Jun complex formation was inhibited by pretreatment with diphenyleneiodonium chloride, apocynin, N-acetyl-L-cysteine or SP600125. These results demonstrated that CSE-induced cPLA(2) expression was mediated through NOX2-dependent p42/p44 MAPK and p38 MAPK/c-Fos and JNK1/2/c-Jun/p300 pathways in HTSMCs.     

Induction of cytosolic phospholipase A2 by lipopolysaccharide in canine tracheal smooth muscle cells: involvement of MAPKs and NF-kappaB pathways

Cytosolic phospholipase A2 (cPLA2) plays a pivotal role in mediating agonist-induced arachidonic acid (AA) release for prostaglandins (PG) synthesis induced by bacterial lipopolysaccharide (LPS) and cytokines. However, the intracellular signaling pathways mediating LPS-induced cPLA2 expression and PGE2 synthesis in canine tracheal smooth muscle cells (TSMCs) remains unknown. LPS-induced expression of cPLA2 and release of PGE2 was attenuated by inhibitors of tyrosine kinase (genistein), phosphatidylcholine-phospholipase C (D609), phosphatidylinositol-phospholipase C (U73122), PKC (GF109203X and staurosporine), removal of Ca2+ by BAPTA/AM plus EDTA, MEK1/2 (PD98059), p38 (SB202190), JNK (SP600125), and phosphatidylinositol 3-kinase (PI3-K; LY294002 and wortmannin). The involvement of MPAKs in LPS-induced responses was further confirmed by transfection of TSMCs with dominant negative mutants of ERK2 and p38. LPS-induced cPLA2 expression and PGE2 synthesis was inhibited by a selective NF-kappaB inhibitor (helenalin) and transfection with dominant negative mutants of NF-kappaB inducing kinase (NIK), IkappaB kinase (IKK)-alpha, and IKK-beta, consistent with that LPS-stimulated both IkappaB-alpha degradation and NF-kappaB translocation into nucleus in these cells. LPS-stimulated cPLA2 phosphorylation was inhibited by PD98059, GF109203X, and staurosporine, indicating the regulation by p42/p44 MAPK and PKC. Moreover, LPS-induced up-regulation of cPLA2 and COX-2 linked to PGE2 synthesis was inhibited by AACOCF3 (a selective cPLA2 inhibitor), implying the involvement of cPLA2 in these responses. These findings suggest that phosphorylation and expression of cPLA2 correlates with the release of PGE2 from LPS-challenged TSMCs, at least in part, mediated through MAPKs and NF-kappaB signaling pathways. LPS-mediated responses were modulated by PLC, Ca2+, PKC, tyrosine kinase, and PI3-K in TSMCs.     

TLR4-NOX4-AP-1 signaling mediates lipopolysaccharide-induced CXCR6 expression in human aortic smooth muscle cells

CXCL16 is a transmembrane non-ELR CXC chemokine that signals via CXCR6 to induce aortic smooth muscle cell (ASMC) proliferation. While bacterial lipopolysaccharide (LPS) has been shown to stimulate CXCL16 expression in SMC, its effects on CXCR6 are not known. Here, we demonstrate that LPS upregulates CXCR6 mRNA, protein, and surface expression in human ASMC. Inhibition of TLR4 with neutralizing antibodies or specific siRNA interference blocked LPS-mediated CXCR6 expression. LPS stimulated both AP-1 (c-Fos, c-Jun) and NF-kappaB (p50 and p65) activation, but only inhibition of AP-1 attenuated LPS-induced CXCR6 expression. Using dominant negative expression vectors and siRNA interference, we demonstrate that LPS induces AP-1 activation via MyD88, TRAF6, ERK1/2, and JNK signaling pathways. Furthermore, the flavoprotein inhibitor diphenyleniodonium chloride significantly attenuated LPS-mediated AP-1-dependent CXCR6 expression, as did inhibition of NOX4 NADPH oxidase by siRNA. Finally, CXCR6 knockdown inhibited CXCL16-induced ASMC proliferation. These results demonstrate that LPS-TLR4-NOX4-AP-1 signaling can induce CXCR6 expression in ASMC, and suggest that the CXCL16-CXCR6 axis may be an important proinflammatory pathway in the pathogenesis of atherosclerosis.     

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

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

Rho expression and activation in vascular smooth muscle cells

Phenotypic modulation of smooth muscle cells (SMC) involves dramatic changes in expression and organization of contractile and cytoskeletal proteins, but little is known of how this process is regulated. The present study used a cell culture model to investigate the possible involvement of RhoA, a known regulator of the actin cytoskeleton. In rabbit aortic SMC seeded into primary culture at moderate density, Rho activation was high at two functionally distinct time-points, first as cells modulated to the "synthetic" phenotype, and again upon confluence and return to the "contractile" phenotype. Rho expression increased with time, such that maximal expression occurred upon return to the contractile state. Transient transfection of synthetic state cells with constitutively active RhoA (Val14RhoA) caused a reduction in cell size and reorganization of cytoskeletal proteins to resemble that of the contractile phenotype. Actin and myosin filaments were tightly packed and highly organised while vimentin localised to the perinuclear region; focal adhesions were enlarged and concentrated at the cell periphery. Conversely, inhibition of endogenous Rho by C3 exoenzyme resulted in complete loss of contractile filaments without affecting vimentin distribution; focal adhesions were reduced in size and number. Treatment of synthetic state SMC with known regulators of SMC phenotype, heparin and thrombin, caused a modest increase in Rho activation. Long-term confluence and serum deprivation induced cells to return to a more contractile phenotype and this was augmented by heparin and thrombin. The results implicate RhoA for a role in regulating SMC phenotype and further show that activation of Rho by heparin and thrombin correlates with the ability of these factors to promote the contractile phenotype.     

Receptor-dependent prorenin activation and induction of PAI-1 expression in vascular smooth muscle cells

Although elevated plasma prorenin levels are commonly found in diabetic patients and correlate with microvascular complications, the pathological role of these increases, if any, remains unclear. Prorenin/renin binding to the prorenin/renin receptor [(p)RR] enhances the efficiency of angiotensinogen cleavage by renin and unmasks prorenin catalytic activity. We asked whether plasma prorenin could be activated in local vascular tissue through receptor binding. Immunohistochemical staining showing localization of the (p)RR in the aorta to vascular smooth muscle cells (VSMCs). After cultured rat VSMCs were incubated with 10(-7) M inactive prorenin, cultured supernatant acquired the ability to generate ANG I from angiotensinogen, indicating that prorenin had been activated. Activated prorenin facilitated angiotensin generation in cultured VSMCs when exogenous angiotensinogen was added. Small interfering RNA (siRNA) against the (p)RR blocked this activation and subsequent angiotensin generation. Prorenin alone induced dose- and time-dependent increases in mRNA and protein for the profibrotic molecule plasminogen activator inhibitor (PAI)-1, effects that were blocked by siRNA, but not by the ANG II receptor antagonist saralasin. When inactive prorenin and angiotensinogen were incubated with cells, PAI-1 mRNA increased a striking 54-fold, 8-fold higher than the increase seen with prorenin alone. PAI-1 protein increased 2.75-fold. These effects were blocked by treatment with siRNA + saralasin. We conclude that prorenin at high concentration binds the (p)RR on VSMCs and is activated. This activation leads to increased expression of PAI-1 via ANG II-independent and -dependent mechanisms. These data provide a mechanism by which elevated prorenin levels in diabetes may contribute to the progression of fibrotic disease.     

ERK activation and mitogenesis in human airway smooth muscle cells

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

Differential expression of caveolin-3 in mouse smooth muscle cells in vivo

Expression of caveolin-1 and -3 in mouse smooth muscle cells in vivo was examined by immunohistochemistry. Caveolin-1 was detected in almost all smooth muscles examined, except for the pupillary dilator muscle, whereas caveolin-3 was present only in smooth muscles of some specific tissues. In the eye, the pupillary sphincter muscle was intensely positive for caveolin-3, whereas the ciliary muscle and pupillary dilator muscle were negative. In the gastrointestinal tract, caveolin-3 was detected in the inner circular layer, but not in the outer longitudinal layer. Vascular smooth muscle cells of the resistance-sized artery in the uterus and corpus cavernosum were intensely positive for caveolin-3, whereas those of the aorta were only weakly positive and those of the vena cava were negative. Caveolin-3 was also detected in smooth muscle cells of the urinary bladder, ureter, prostatic vas deferens, and seminal vesicle. The different levels of caveolin-3 expression among various smooth muscle tissues were confirmed by Western blot analysis. Even within the same muscle, the relative expression levels of caveolin-1 and -3 were variable among neighboring cells, suggesting distinct fine regulation of expression of these two caveolins. Moreover, even in the same cell, caveolin-1 and -3 showed different distributions. These results indicate that the two caveolins form distinct caveolae in smooth muscles, and that caveolin-1 and -3 serve different functions. Their differential expression may therefore be related to the functional diversity of smooth muscles. This work was supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture of the Japanese Government.     

Cyclooxygenase is regulated by ET-1 and MAPKs in peripheral lung microvascular smooth muscle cells

We examined the hypothesis that the potent vasoconstrictor endothelin (ET)-1 regulates both its own production and production of the vasodilator prostaglandins PGE(2) and prostacyclin in sheep peripheral lung vascular smooth muscle cells (PLVSMC). Confluent layers of PLVSMC were exposed to 10 nM ET-1; expression of the prepro (pp)-ET-1, cyclooxygenase (COX)-1, and COX-2 genes was examined by RT-PCR and Western analysis. Intracellular levels of ET-1 were measured by ELISA with and without addition of the protein synthesis inhibitor brefeldin A (50 microg/ml). Prostaglandin levels were measured by gas chromatography-mass spectrometry. Through use of ET(A) and ET(B) antagonists (BQ-610 and BQ-788, respectively), the contribution of the ET receptors to COX-1 and -2 expression and ppET-1 gene expression was examined. The contribution of phosphorylated p38 and p44/42 MAPK on COX-1 and COX-2 expression was also examined with MAPK inhibitors (p38, SB-203580 and p44/42, PD-98056). ET-1 resulted in transient increases in ppET-1, COX-1, and COX-2 gene and protein expression and release of 6-keto-PGF(1alpha) and PGE(2) (P < 0.05). Both internalization of ET-1 and synthesis of new peptide contributed to an increase in intracellular ET-1 (P < 0.05). Although increased ppET-1 was regulated by both ET(A) and ET(B), COX-2 expression was upregulated only by ET(A); COX-1 expression was unaffected by either antagonist. ET-1 treatment resulted in transient phosphorylation of p38 and p44/42 MAPK; inhibitors of these MAPKs suppressed expression of COX-2 but not COX-1. Our data indicate that local production of ET-1 regulates COX-2 by activation of the ET(A) receptor and phosphorylation of p38 and p44/42 MAPK in PLVSMC.