If I had an acute coronary syndrome...
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Angina, Unstable↗
Biomedical subjects
B C Berk
Publications and source records attributed to B C Berk.
The Gas6/Axl system: a novel regulator of vascular cell function.
Signal transduction downstream of tyrosine kinases has become an increasingly important area of study in cardiovascular biology. In this review, we consider the experimental evidence pointing to significant roles for the Axl receptor tyrosine kinase and its ligand, Gas6, in the vasculature. An introduction to the Gas6/Axl system and a discussion of its discovery is followed by a summary of the data regarding expression of Gas6/Axl in injured arteries. We conclude by discussing mechanisms by which Gas6/Axl signaling may impact on the response of blood vessels to injury, thereby contributing to the development of atherosclerosis and/or restenosis.
Animals↗
Agonist-stimulated cytoskeletal reorganization and signal transduction at focal adhesions in vascular smooth muscle cells require c-Src.
Thrombin and angiotensin II (angII) have trophic properties as mediators of vascular remodeling. Focal adhesions and actin cytoskeleton are involved in cell growth, shape, and movement and may be important in vascular remodeling. To characterize mechanisms by which thrombin and angII modulate vessel structure, we studied the effects of these G protein-coupled receptor ligands on focal adhesions in vascular smooth muscle cells (VSMCs). Both thrombin and angII stimulated bundling of actin filaments to form stress fibers, assembly of focal adhesions, and protein tyrosine phosphorylation at focal adhesions, such as p130Cas, paxillin, and tensin. To test whether c-Src plays a critical role in focal adhesion rearrangement, we analyzed cells with altered c-Src activity by retroviral transduction of wild-type (WT) and kinase-inactive (KI) c-Src into rat VSMCs, and by use of VSMCs from WT (src+/+) and Src-deficient (src-/-) mice. Tyrosine phosphorylation of Cas, paxillin, and tensin were markedly decreased in VSMCs expressing KI-Src and in src-/- VSMCs. Expression of KI-Src did not inhibit stress fiber formation by thrombin. Surprisingly, actin bundling was markedly decreased in VSMCs from src-/- mice both basally and after thrombin stimulation, compared with src+/+ mice. We also studied the effect of KI-Src and WT-Src on VSMC spreading. Expression of KI-Src reduced the rate of VSMC spreading on collagen, whereas WT-Src enhanced cell spreading. In conclusion, c-Src plays a critical role in agonist-stimulated cytoskeletal reorganization and signal transduction at focal adhesions in VSMCs. c-Src kinase activity is required for the cytoskeletal turnover that occurs in cell spreading, whereas c-Src appears to regulate actin bundling via a kinase-independent mechanism.
Angiotensin II↗
Redox signals that regulate the vascular response to injury.
Multiple enzymes may stimulate ROS production in VSMC and endothelial cells. These include NADH/NADPH oxidase, xanthine oxidase, lipoxygenases, cyclooxygenase, P-450 monooxygenases, and the enzymes of mitochondrial oxidative phosphorylation. In addition to generation of intracellular O2- by these enzymes, extracellular stimuli including lipophilic substrates, membrane permeant oxidants (e.g., H2O2), cytokines, and growth factors may modulate cellular redox state. Both intracellular and extracellular ROS act as second-messengers to activate tyrosine and serine-threonine kinases, such as the MAP kinase family. As discussed in the previous sections, regulation of the MAP kinases is one example of the complexity of ROS-dependent signal transduction. Although the complexity of ROS-mediated signal transduction is daunting, the diversity offers multiple therapeutic targets for pharmacologic intervention.
Animals↗
Angiotensin II signal transduction in vascular smooth muscle: pathways activated by specific tyrosine kinases.
In this review, the signal events regulated by angiotensin II (AngII) in vascular smooth muscle are analyzed based on activation of specific tyrosine kinases. AngII has been shown to play a critical role in the pathogenesis of hypertension, inflammation, atherosclerosis, and congestive heart failure. The expanding role of AngII indicates that multiple signal transduction pathways are likely to be activated in a tissue-specific manner. Although at least three AngII receptors have been characterized, it seems that the AngII type I receptor (AT1R) is physiologically most important since pharmacologic inhibitors of the AT1R block most AngII signal events and have beneficial effects on cardiovascular disease. The AT1R is a seven transmembrane-spanning G protein-coupled receptor that regulates intracellular signal events by activation of Gq and Gi. However, many recent data indicate that activation of tyrosine kinases by several different mechanisms contributes to AngII effects in target tissues. Tyrosine kinases activated by AngII include c-Src, focal adhesion kinase (FAK), Pyk2 (CADTK), Janus kinases (JAK2 and TYK2), and the receptor tyrosine kinases Ax1, epidermal growth factor, and platelet-derived growth factor. Finally, unknown tyrosine kinases may mediate tyrosine phosphorylation of paxillin, Shc, Raf, and phospholipase C-gamma after AngII stimulation. These AngII-regulated tyrosine kinases seem to be required for AngII effects such as vasoconstriction, proto-oncogene expression, and protein synthesis based on studies with tyrosine kinase inhibitors. Thus, understanding AngII-stimulated signaling events, especially those related to tyrosine kinase activity, may form the basis for the development of new therapies for cardiovascular diseases.
Angiotensin II↗
p38 Kinase is a negative regulator of angiotensin II signal transduction in vascular smooth muscle cells: effects on Na+/H+ exchange and ERK1/2.
Activation of the Na+/H+ exchanger isoform-1 (NHE-1) by angiotensin II is an early signal transduction event that may regulate vascular smooth muscle cell (VSMC) growth and migration. Many signal transduction events stimulated by angiotensin II are mediated by the mitogen-activated protein (MAP) kinases. To define their roles in angiotensin II-mediated NHE-1 activity, VSMCs were treated with angiotensin II and the activities of p38, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinases 1 and 2 (ERK1/2) were measured. Angiotensin II rapidly (peak, 5 minutes) activated p38 and ERK1/2, whereas JNK was activated more slowly (peak, 30 minutes). Because angiotensin II stimulated Na+/H+ exchange within 5 minutes, the effects of p38 and ERK1/2 antagonists on Na+/H+ exchange were studied. The MEK-1 inhibitor PD98059 decreased ERK1/2 activity and Na+/H+ exchange stimulated by angiotensin II. In contrast, the specific p38 antagonist SKF-86002 increased Na+/H+ exchange. Two mechanisms were identified that may mediate the effects of p38 and SKF-86002 on angiotensin II-stimulated Na+/H+ exchange. First, angiotensin II activation of ERK1/2 was increased 1. 5- to 2.5-fold (depending on assay technique) in the presence of SKF-86002, demonstrating that p38 negatively regulates ERK1/2. Second, the ability of angiotensin II-stimulated MAP kinases to phosphorylate a glutathione S-transferase fusion protein containing amino acids 625 to 747 of NHE-1 in vitro was analyzed. The relative activities of endogenous immunoprecipitated p38, ERK1/2, and JNK were 1.0, 2.0, and 0.05 versus control, respectively suggesting that p38 and ERK1/2, but not JNK, may phosphorylate NHE-1 in VSMC. These data indicate important roles for p38 and ERK1/2 in angiotensin II-mediated regulation of the Na+/H+ exchanger in VSMC.
Angiotensin II↗
Increased expression of Axl tyrosine kinase after vascular injury and regulation by G protein-coupled receptor agonists in rats.
Axl is a receptor tyrosine kinase originally identified as a transforming gene product in human myeloid leukemia cells. Cultured rat vascular smooth muscle cells also express Axl, where it has been proposed that Axl may play a role in cell proliferation. In the current study, we tested the hypotheses that Axl expression would parallel neointima formation in balloon-injured rat carotid, and that Axl expression would be regulated by growth factors present at sites of vascular injury. Ribonuclease protection assay showed dynamic increases in Axl mRNA in vessels, with peak expression 7 and 14 days after injury. Immunohistochemical analysis confirmed these results and demonstrated that Axl protein expression was localized primarily to cells of the neointima after injury. Northern blot analysis indicated increased mRNA expression for the secreted Axl ligand, Gas6, in injured carotids, with a time course paralleling that of Axl upregulation. Axl and Gas6 expression were temporally correlated with neointima formation, suggesting a role for Axl signaling in this process. Other studies, performed in cultured rat vascular smooth muscle cells, revealed positive regulation of Axl mRNA expression by thrombin or angiotensin II but not by basic fibroblast growth factor, platelet-derived growth factor-BB, or transforming growth factor-ss1. Western blot analysis confirmed these results, showing that Axl protein expression was specifically increased by thrombin or angiotensin II. Our results implicate Axl as a potential mediator of vascular smooth muscle migration and proliferation caused by vascular injury and G protein-coupled receptor agonists.
Angiotensin II↗
Angiotensin II stimulates p21-activated kinase in vascular smooth muscle cells: role in activation of JNK.
Angiotensin II (Ang II) has been previously shown to stimulate the extracellular signal-regulated kinase (ERK) 1/2 and c-Jun N-terminal kinase (JNK) mitogen-activated protein (MAP) kinase family members. Little is known regarding the upstream signaling molecules involved in Ang II-mediated JNK activation. Ang II has been shown to activate the Janus kinase/signal transducer(s) and activator(s) of transcription (JAK/STAT) pathway, suggesting similarities to cytokine signaling. In response to cytokines such as interleukin-1 and tumor necrosis factor-alpha, the p21-activated kinase (PAK) has been identified as an upstream component in JNK activation. Therefore, we hypothesized that PAK may be involved in JNK activation by Ang II in vascular smooth muscle cells (VSMCs). AlphaPAK activity was measured by myelin basic protein phosphorylation in rat aortic VSMCs. In response to Ang II, alphaPAK was rapidly stimulated within 1 minute, with a peak (5-fold increase) at 30 minutes. AlphaPAK stimulation preceded activation of JNK in VSMCs. Ang II-mediated activation of both alphaPAK and JNK was Ca2+ dependent and inhibited by downregulation of phorbol ester-sensitive protein kinase C isoforms (by pretreatment with phorbol 12,13-dibutyrate) but not by pretreatment with GF109203X. Activation of both PAK and JNK was partially inhibited by tyrosine kinase inhibitors but not by specific Src inhibitors, suggesting regulation by a tyrosine kinase other than c-Src. Finally, introduction of dominant negative PAK markedly reduced the JNK activation by Ang II in both Chinese hamster ovary and COS cells stably expressing the Ang II type 1 receptor (AT1R). Our data provide evidence for alphaPAK as an upstream mediator of JNK in Ang II signaling and extend the role of Ang II as a proinflammatory mediator for VSMCs.
Angiotensin II↗
MAP kinases and vascular smooth muscle function.
The mitogen-activated protein (MAP) kinase family members are ubiquitously expressed protein kinases activated in response to a variety of extracellular stimuli and shown to be involved in cell growth, transformation, differentiation and apoptosis. MAP kinases have been implicated in both growth and apoptosis of vascular smooth muscle cells (VSMC) which suggests that they play important roles in cardiovascular diseases such as essential hypertension, atherosclerosis, and restenosis followed angioplasty. The MAP kinases are themselves components of specific kinase cascades characterized by activation by specific stimuli, families of related serine and threonine kinases and downstream substrates that include other kinases, transcription factors, membrane receptors and other cell mediators. Cross-talk among the different MAP kinases results in direct modulation of signal transduction. In addition, increased expression and activation of MAP kinase phosphatases plays an important role in MAP kinase inactivation. Our laboratory has used angiotensin II (AngII), a potent activator of all MAP kinases in VSMC, to study mechanisms by which MAP kinases are regulated by vasoactive peptides. In this review, we describe the mechanisms by which AngII activates MAP kinases, and potential roles for MAP kinases in AngII-dependent effects on VSMC function.
Animals↗
Laminar shear stress: mechanisms by which endothelial cells transduce an atheroprotective force.
Mechanical forces are important modulators of cellular function in many tissues and are particularly important in the cardiovascular system. The endothelium, by virtue of its unique location in the vessel wall, responds rapidly and sensitively to the mechanical conditions created by blood flow and the cardiac cycle. In this study, we examine data which suggest that steady laminar shear stress stimulates cellular responses that are essential for endothelial cell function and are atheroprotective. We explore the ability of shear stress to modulate atherogenesis via its effects on endothelial-mediated alterations in coagulation, leukocyte and monocyte migration, smooth muscle growth, lipoprotein uptake and metabolism, and endothelial cell survival. We also propose a model of signal transduction for the endothelial cell response to shear stress including possible mechanotransducers (integrins, caveolae, ion channels, and G proteins), intermediate signaling molecules (c-Src, ras, Raf, protein kinase C) and the mitogen activated protein kinases (ERK1/2, JNK, p38, BMK-1), and effector molecules (nitric oxide). The endothelial cell response to shear stress may also provide a mechanism by which risk factors such as hypertension, diabetes, hypercholesterolemia, and sedentary lifestyle act to promote atherosclerosis.
Animals↗
Endothelial NO synthase is increased in regenerating endothelium after denuding injury of the rat aorta.
Endothelial nitric oxide synthase (eNOS) has been shown to be regulated both transcriptionally and posttranslationally in cultured endothelial cells, but eNOS regulatory mechanisms in vivo have not been elucidated. Because one of the strongest stimuli for eNOS expression in tissue culture is cell proliferation and because increased NO production would be beneficial in the setting of arterial injury, we hypothesized that eNOS expression should be increased in regenerating endothelium after a denuding injury. Rat aortas underwent partial endothelial denudation by passage of a deflated balloon catheter, and eNOS expression was studied 48 hours after injury. Immunohistochemistry with eNOS monoclonal antibody, NADPH diaphorase activity assay under conditions specific for eNOS, and mRNA hybridization were performed in situ on perfusion-fixed rat aortic segments. The vessels were studied en face to enhance visualization compared with cross sections. eNOS protein and mRNA expression were significantly increased in regenerating and migrating endothelial cells at the wound edge, with translocation of eNOS to the plasma membrane at the leading edge. Similar results were obtained when endothelial cells were studied in a tissue culture wound model. An important role for transforming growth factor (TGF)-beta1 in regulating eNOS expression was suggested by the ability of a TGF-beta1-neutralizing antibody to limit induction of eNOS at the wound edge. Increased eNOS expression after wounding appears to be related to signal events associated with cell migration as well as proliferation, because eNOS expression in vivo increased in nonproliferating cells and TGF-beta1-neutralizing antibody inhibited eNOS expression but stimulated proliferation. The current study is the first to suggest an important role in vivo for increased eNOS, and perhaps NO production, in the process of endothelial regeneration and wound repair.
Analysis of Variance↗
PKC-epsilon is required for mechano-sensitive activation of ERK1/2 in endothelial cells.
Mechano-sensitive regulation of endothelial cells (EC) function by shear stress is critical for flow-induced vasodilation and gene expression. Previous studies by our laboratory demonstrated that shear stress activates the 44- and 42-kDa extracellular signal-regulated kinases (ERK1/2) in EC in a time- and force-dependent manner. ERK1/2 activation was inhibited by protein kinase C (PKC) down-regulation with phorbol 12,13-dibutyrate (1 microM for 24 h) but not by calcium chelation with BAPTA-AM (acetoxymethyl ester of BAPTA) (75 microM for 30 min), suggesting that a novel PKC isoform (delta, epsilon, eta, theta) mediates shear stress-induced ERK1/2 activation. Western blotting with PKC isoform-specific antibodies demonstrated expression of PKC-alpha, -epsilon, and -zeta isoforms in EC. PKC-epsilon was specifically inhibited by transfection with antisense PKC-epsilon phosphorothioate oligonucleotides (1,000 nM for 6 h). Antisense treatment decreased PKC-epsilon protein levels by 80 +/- 13% after 72 h and completely inhibited shear stress-stimulated ERK1/2 activation. Scrambled PKC-epsilon oligonucleotides and antisense PKC-alpha and PKC-zeta oligonucleotides had no effect on ERK1/2 activity. PKC-epsilon appeared specific for mechano-sensitive ERK1/2 activation, as antisense PKC-epsilon oligonucleotides did not inhibit ERK1/2 activation by EGF or bradykinin but did inhibit ERK1/2 activation upon EC adhesion to fibronectin. These results define a pathway for shear stress-mediated ERK1/2 activation and establish a new function for PKC-epsilon as part of a mechano-sensitive signal transduction pathway in EC.
Animals↗
Vitamins C and E inhibit O2- production in the pig coronary artery.
BACKGROUND: We previously found in a pig coronary balloon injury model that vitamins C and E as well as probucol had beneficial effects on the vessel response to injury measured by morphometry These effects correlated with an inhibition in the ability to oxidize LDLs ex vivo, suggesting that the morphological response was due to the antioxidant effect of the treatments. METHODS AND RESULTS: In the present study, the production of O2- by vessels 14 days after balloon injury was determined and correlated with circulating and tissue levels of vitamins C and E. Twenty-five domestic pigs were divided into four groups: control (n=7), vitamin C (500 mg/d, group C, n=6), vitamin E (1000 IU/d, group E, n=6), and vitamins C and E (500 mg/d and 1000 IU/d, group C+E, n=6). Vitamins were administered 7 days before oversized balloon injury of the left anterior descending coronary artery (LAD) and continued for 14 days after injury. Vitamin C and E concentrations were determined in plasma and lymphocytes as an index for tissue levels. Vessels were harvested after animals were killed, and O2- production was measured by lucigenin chemiluminescence. O2- production by the injured LAD was 2.5-fold greater than O2- production by the uninjured LAD or right coronary artery (RCA). The increase in O2- was caused primarily by cells present in the media and neointima. All vitamin-treated groups showed significantly decreased O2- production in both the RCA and LAD (approximately 45% inhibition) relative to vessels in the control, untreated group. There was a significant correlation between LAD O2- production and lymphocyte vitamin E levels. CONCLUSIONS: The present study is the first to show increased O2- production in injured vessels and to demonstrate that antioxidant vitamins reduce O2- production. These results suggest that beneficial effects of antioxidant vitamins in coronary artery disease are related, in part, to alterations in vessel redox state.
Animals↗
c-Src is required for oxidative stress-mediated activation of big mitogen-activated protein kinase 1.
Big mitogen-activated kinase 1 (BMK1) or extracellular signal-regulated kinase-5 (ERK5) has recently been identified as a new member of the mitogen-activated protein kinase family. We have shown that BMK1 is activated to a greater extent by H2O2 than growth factors, suggesting that in comparison with other mitogen-activated protein kinase family members, BMK1 is a redox-sensitive kinase. Previous investigations indicate that the tyrosine kinase c-Src mediates signal transduction by reactive oxygen species, including H2O2. Therefore, the role of Src kinase family members (c-Src and Fyn) in activation of the BMK1 by H2O2 in mouse fibroblasts was studied. An essential role for c-Src was suggested by four experiments. First, H2O2 stimulated c-Src activity rapidly in fibroblasts (peak at 5 min), which preceded peak activity of BMK1 (20 min). Second, specific Src family tyrosine kinase inhibitors (herbimycin A and CP-118,556) blocked BMK1 activation by H2O2 in a concentration-dependent manner. Third, BMK1 activation in the response to H2O2 was completely inhibited in cells derived from mice deficient in c-Src, but not Fyn. Finally, BMK1 activity was much greater in v-Src-transformed NIH-3T3 cells than wild type cells. These results demonstrate an essential role for c-Src in H2O2-mediated activation of BMK1 and suggest that redox-sensitive regulation of BMK1 is a new function for c-Src.
Animals↗
A mathematical model of the cytosolic-free calcium response in endothelial cells to fluid shear stress.
Important among the responses of endothelial cells to flow stimuli are cytosolic-free calcium transients. These transients are mediated by several factors, including blood-borne agonists, extracellular calcium, and fluid-imposed shear forces. A mathematical model has been developed describing the recognition and transduction of shear stress to the second messenger cytosolic calcium. Shear stress modulates the calcium response via at least two modalities. First, mass transfer of agonist to the cell surface is enhanced by perfusion and is thus related to shear stress. Second, the permeability of the cell membrane to extracellular calcium increases upon exposure to shear stress. A mass balance for agonist in the perfusate is coupled to a previously published calcium dynamics model. Computations indicate a flow region where the transient moves from transport limited to kinetically limited. Parametric studies indicate distinct contributions to the time course by each step in the process. These steps include the time to develop the concentration boundary layer of agonist, receptor activation, and the mobilization of calcium from intracellular stores. Exogenous calcium is presumed to enter the cell via shear stress-gated ion channels. The model predicts a sigmoidal dependence of calcium influx upon shear stress. The peak value of the transient is determined largely by the agonist pathway, whereas the plateau level is governed by calcium influx. The model predicts the modulation of the calcium transient in the physiologically relevant range of flow and the associated shear stress. This implies that hemodynamics is important in regulating endothelial biology.
Animals↗
Fluid shear stress-mediated signal transduction: how do endothelial cells transduce mechanical force into biological responses?
We propose a model for signaling events induced by fluid shear stress that incorporates many of the features discussed in this paper (FIG. 4). First, heterotrimeric G-proteins, as well as a small G-proteins, are activated by flow. Indeed, a G protein appears to be required for ERK1/2 activation by flow because ERK1/2 activation is completely inhibited by GDP-beta S. Then, flow activates phospholipase C and generates IP3 and diacylglycerol (DG). IP3 releases Ca2+ from internal Ca2+ stores via IP3 receptor and DG activates PKC. Nollert and colleagues have shown that flow activates PLC and increases IP3. It is possible that several different PKC isozymes are activated by flow including both Ca(2+)-dependent and Ca(2+)-independent isozymes. These different isozymes may have specific downstream substrates. For example, PKC-epsilon may be involved in activation of ERK1/2, while the PKC isozyme responsible for activation of JNK remains unknown. It is also possible that these PKC isozymes may be important in gene transcription events. For example, PKC-zeta has been suggested to be involved in NF-kappa B-mediated gene transcription. Longer term changes in endothelial cell morphology and structure are likely to involve separate kinases. Important candidates for these changes include members of the c-Src and FAK families. c-Src is now considered to be a component of the focal adhesion complex and regulate focal adhesion formation and/or cytoskeletal rearrangement. Recently, stretch, another mechanostress, has been shown to activate c-Src in fetal rat lung cells. It has been clarified that ERK1/2 and JNK are regulated by the small G-proteins, Ras and Rac/Cdc42H, respectively, and their effectors in parallel with each other. Rac and Rho are also thought to be involved in membrane ruffling and/or cytoskeletal rearrangement. Fluid shear stress causes stress fiber formation and focal adhesion rearrangement. Recent study by Malek and Izumo suggested the importance of microtubules in shear stress-induced morphological change and actin stress fiber formation. It is clear that the focal adhesion complex plays an important role in shear stress-induced signal and it is interesting to speculate that shear stress-induced signaling has cross-talk with signaling induced by integrins. As a general model we propose that the integration between the rapid events stimulated by shear stress and the longer term events is mediated by tyrosine kinases that serve to regulate these multiple signal transduction pathways.
Animals↗
Protein kinase C-zeta mediates angiotensin II activation of ERK1/2 in vascular smooth muscle cells.
Activation of 44 and 42 kDa extracellular signal-regulated kinases (ERK)1/2 by angiotensin II (angII) plays an important role in vascular smooth muscle cell (VSMC) function. The dual specificity mitogen-actived protein (MAP) kinase/ERK kinase (MEK) activates ERK1/2 in response to angII, but the MEK activating kinases remain undefined. Raf is a candidate MEK kinase. However, a kinase other than Raf appears responsible for angII-mediated signal transduction because we showed previously that treatment with 1 microM phorbol 12, 13-dibutyrate (PDBU) for 24 h completely blocked Raf-Ras association in VSMC but did not inhibit activation of MEK and ERK1/2 by angII. We hypothesized that an atypical protein kinase C (PKC) isoform, which lacks a phorbol ester binding domain, mediated ERK1/2 activation by angII. Western blot analysis of rat aortic VSMC with PKC isoform-specific antibodies showed PKC-alpha, -beta1, -delta, -epsilon, and -zeta in relative abundance. All isoforms except PKC-zeta were down-regulated by 1 microM PDBU for 24 h suggesting that PKC-zeta was responsible for angII-mediated ERK1/2 activation. In response to angII, PKC-zeta associated with Ras as shown by co-precipitation of PKC-zeta with anti-H-Ras antibody. To characterize further the role of PKC-zeta, PKC-zeta protein was depleted specifically by transfection with antisense PKC-zeta oligonucleotides. Antisense PKC-zeta oligonucleotide treatment significantly decreased PKC-zeta protein expression (without effect on other PKC isoforms) and angII-mediated ERK1/2 activation in a concentration-dependent manner. In contrast, ERK1/2 activation by platelet-derived growth factor and phorbol ester was not significantly inhibited. These results demonstrate an important difference in signal transduction by angII compared with PDGF and phorbol ester in VSMC, and suggest a critical role for PKC-zeta and Ras in angII stimulation of ERK1/2.
Angiotensin II↗
Oxidized LDL stimulates mitogen-activated protein kinases in smooth muscle cells and macrophages.
It has been proposed that oxidized LDL is more atherogenic than native LDL. However, the mechanisms by which native LDL and oxidized LDL alter function of cells in the vessel wall remain undefined. A signal transduction pathway that mediates many changes in cell function is the mitogen-activated protein (MAP) kinase cascade. We therefore examined the effect of native LDL and oxidized LDL on MAP kinase activity in cultured vascular smooth muscle cells (VSMC), endothelial cells, and macrophages by using an in-gel-kinase assay and anti-phosphotyrosine MAP kinase antibodies. Native LDL and LDL oxidized by the addition of Cu2+ (Cu(2+)-oxidized LDL) stimulated MAP kinase in a time- and dose-dependent manner in baboon and rat VSMC but not in bovine endothelial cells. Cu(2+)-oxidized LDL stimulated MAP kinase in human monocyte-derived macrophages, but the effect was much greater in cells cultured for 7 days compared with 1 day, suggesting dynamic regulation of the cellular response to oxidized LDL. In rat VSMC, the maximal MAP kinase response to Cu(2+)-oxidized LDL was significantly greater than the response to native LDL. Cu(2+)-oxidized LDL was more potent, with half-maximal activation at 15 micrograms/mL versus 30 micrograms/mL for native LDL. Stimulation of MAP kinase appeared to involve protein kinase C, since phorbol ester pretreatment for 24 hours blocked MAP kinase activation. Oxidation of LDL by other methods showed that activation of MAP kinase was not well correlated with lipid peroxides or aldehydes, suggesting that other components present in oxidized LDL were responsible. The active moiety appeared to be lipid based on extraction of oxidized LDL with organic solvents. These data indicate that LDL stimulates MAP kinase in VSMC, oxidation of LDL potentiates the effect, a lipid moiety is involved, and Cu(2+)-oxidized LDL activation of MAP kinase is cell-type specific. These findings suggest a role for MAP kinase in the pathways by which oxidized LDL contributes to altered cellular function associated with atherogenesis.
Animals↗