Lysophosphatidic acid stimulates p21-activated kinase in vascular smooth muscle cells

The Autotaxin-LPA Axis Emerges as a Novel Regulator of Smooth Muscle Cell Phenotypic Modulation during Intimal Hyperplasia

Neointimal hyperplasia is characterized by a loss of the contractile phenotype of vascular smooth muscle cells (VSMCs). Our group has recently shown that VSMC proliferation and migration are mediated by lysophosphatidic acid (LPA) during restenosis, but the role of autotaxin (ATX; lysophospholipase D), which produces LPA, remains unclear. Endothelial denudation of the mouse carotid artery was performed to induce neointimal hyperplasia, and the extent of damage caused by the ATX-LPA axis was assessed in VSMCs. We observed the upregulation of ATX activity (p < 0.0002) in the injured carotid artery using an AR2 probe fluorescence assay. Further, the tissue carotid LPA levels were elevated 2.7-fold in carotid vessels, augmenting neointimal hyperplasia. We used an electrical cell-substrate impedance sensor (ECIS) to measure VSMC proliferation and migration. Treatment with an ATX inhibitor (PF8380) or LPA receptor inhibitor (Ki16425) attenuated VSMC proliferation (extracellular signal-regulated kinases) activity and migration in response to recombinant ATX. Indeed, PF8380 treatment rescued the aggravated post-wire injury neointima formation of carotid arteries. The upregulation of ATX following vessel injury leads to LPA production in VSMCs, favoring restenosis. Our observations suggest that inhibition of the ATX-LPA axis could be therapeutically targeted in restenosis to minimize VSMC phenotypic modulation and inflammation after vascular injury.

Integrative Analysis of Metabolomic and Transcriptomic Data Reveals the Antioxidant Potential of Dietary Lutein in Chickens

Lutein can increase the body's skin color and has antioxidant potential. However, how it affects lipid metabolism and oxidative stress in chickens remains unknown. In this study, 74-day-old male chickens raised on feed supplemented with lutein had higher hip, back, breast, leg, shin and abdominal fat yellowness than the control group, and the livers of chickens in the lutein group had higher superoxide dismutase and glutathione peroxidase and lower malondialdehyde activities. To clarify the potential regulatory network regulated by lutein, we used RNA-seq and nontargeted metabolomics to detect changes in the male chicken liver and plasma, respectively. A total of 243 differentially expressed genes were significantly enriched in cytokine–cytokine receptor interaction signaling pathways, among others. A total of 237 significantly different metabolites were enriched in lysine biosynthesis and degradation and glycerophospholipid metabolism signaling pathways, among others. Finally, we comprehensively analyzed metabolome and transcriptome data and found that many differentially expressed genes and significantly different metabolites play crucial roles in lipid metabolism and oxidative stress. In summary, dietary lutein can improve male chicken skin yellowness and antioxidant indices and affect liver gene expression and plasma metabolites and may help improve the health of chickens.

Molecular Regulation of Lysophosphatidic Acid Receptor 1 Maturation and Desensitization

Lysophosphatidic acid receptor 1 (LPA1) belongs to the G protein-coupled receptor family. The ligand for LPA1 is LPA, the simplest lysophospholipid. LPA is considered a growth factor and induces cell proliferation, anti-apoptosis, and cell migration. The pro-inflammatory and pro-fibrotic roles of LPA have also been well-demonstrated. Most of the biological functions of LPA are mostly executed through LPA1. The mature form of LPA1 is glycosylated and localized on the plasma membrane. LPA1 is bound to heterotrimetric G proteins and transduces intracellular signaling in response to ligation to LPA. Desensitization of LPA1 negatively regulates LPA1-mediated signaling and the resulting biological functions. Phosphorylation and ubiquitination are well-demonstrated posttranslational modifications of GPCR. In this review, we will discuss our knowledge of LPA1 glycosylation, maturation, and trafficking from the endoplasmic reticulum (ER)/Golgi to the plasma membrane. Moreover, in light of recent findings, we will also discuss molecular regulation of LPA1 internalization and stability.

Lysophosphatidic acid receptor LPA3 prevents oxidative stress and cellular senescence in Hutchinson-Gilford progeria syndrome

Hutchinson–Gilford progeria syndrome (HGPS) is a rare laminopathy that produces a mutant form of prelamin A, known as Progerin, resulting in premature aging. HGPS cells show morphological abnormalities of the nuclear membrane, reduced cell proliferation rates, accumulation of reactive oxygen species (ROS), and expression of senescence markers. Lysophosphatidic acid (LPA) is a growth factor‐like lipid mediator that regulates various physiological functions via activating multiple LPA G protein‐coupled receptors. Here, we study the roles of LPA and LPA receptors in premature aging. We report that the protein level of LPA₃ was highly downregulated through internalization and the lysosomal degradation pathway in Progerin‐transfected HEK293 cells. By treating Progerin HEK293 cells with an LPA₃ agonist (OMPT, 1‐Oleoyl‐2‐O‐methyl‐rac‐glycerophosphothionate) and performing shRNA knockdown of the Lpa3r transcript in these cells, we showed that LPA₃ activation increased expression levels of antioxidant enzymes, consequently inhibiting ROS accumulation and ameliorating cell senescence. LPA₃ was shown to be downregulated in HGPS patient fibroblasts through the lysosomal pathway, and it was shown to be crucial for ameliorating ROS accumulation and cell senescence in fibroblasts. Moreover, in a zebrafish model, LPA₃ deficiency was sufficient to cause premature aging phenotypes in multiple organs, as well as a shorter lifespan. Taken together, these findings identify the decline of LPA₃ as a key contributor to the premature aging phenotypes of HGPS cells and zebrafish.

The phospholipase A2 activity of peroxiredoxin 6 modulates NADPH oxidase 2 activation via lysophosphatidic acid receptor signaling in the pulmonary endothelium and alveolar macrophages

Peroxiredoxin 6 (Prdx6) is essential for activation of NADPH oxidase type 2 (NOX2) in pulmonary microvascular endothelial cells (PMVECs), alveolar macrophages (AMs), and polymorphonuclear leukocytes. Angiotensin II and phorbol ester increased superoxide/H2O2 generation in PMVECs, AMs, and isolated lungs from wild-type (WT) mice, but had much less effect on cells or lungs from Prdx6-null or Prdx6-D140A-knock-in mice that lack the phospholipase A2 activity (PLA2) of Prdx6; addition of either lysophosphatidylcholine (LPC) or lysophosphatidic acid (LPA) to cells restored their oxidant generation. The generation of LPC by PMVECs required Prdx6-PLA2 We propose that Prdx6-PLA2 modulates NOX2 activation by generation of LPC that is converted to LPA by the lysophospholipase D activity of autotaxin (ATX/lysoPLD). Inhibition of lysoPLD with HA130 (cells,10 μM; lungs, 20 μM; IC50, 29 nM) decreased agonist-induced oxidant generation. LPA stimulates pathways regulated by small GTPases through binding to G-protein-coupled LPA receptors (LPARs). The LPAR blocker Ki16425 (cells, 10 μM; lungs, 25 μM; Ki, 0.34 μM) or cellular knockdown of LPAR type 1 decreased oxidant generation and blocked translocation of rac1 to plasma membrane. Thus, Prdx6-PLA2 modulates NOX2 activation through generation of LPC for conversion to LPA; binding of LPA to LPAR1 signals rac activation.-Vázquez-Medina, J. P., Dodia, C., Weng, L., Mesaros, C., Blair, I. A., Feinstein, S. I., Chatterjee, S., Fisher, A. B. The phospholipase A2 activity of peroxiredoxin 6 modulates NADPH oxidase 2 activation via lysophosphatidic acid receptor signaling in the pulmonary endothelium and alveolar macrophages.

Biophysical induction of vascular smooth muscle cell podosomes

Vascular smooth muscle cell (VSMC) migration and matrix degradation occurs with intimal hyperplasia associated with atherosclerosis, vascular injury, and restenosis. One proposed mechanism by which VSMCs degrade matrix is through the use of podosomes, transient actin-based structures that are thought to play a role in extracellular matrix degradation by creating localized sites of matrix metalloproteinase (MMP) secretion. To date, podosomes in VSMCs have largely been studied by stimulating cells with phorbol esters, such as phorbol 12,13-dibutyrate (PDBu), however little is known about the physiological cues that drive podosome formation. We present the first evidence that physiological, physical stimuli mimicking cues present within the microenvironment of diseased arteries can induce podosome formation in VSMCs. Both microtopographical cues and imposed pressure mimicking stage II hypertension induce podosome formation in A7R5 rat aortic smooth muscle cells. Moreover, wounding using a scratch assay induces podosomes at the leading edge of VSMCs. Notably the effect of each of these biophysical stimuli on podosome stimulation can be inhibited using a Src inhibitor. Together, these data indicate that physical cues can induce podosome formation in VSMCs.

Nox family NADPH oxidases: Molecular mechanisms of activation

NADPH oxidases of the Nox family are important enzymatic sources of reactive oxygen species (ROS). Numerous homologue-specific mechanisms control the activity of this enzyme family involving calcium, free fatty acids, protein-protein interactions, intracellular trafficking, and posttranslational modifications such as phosphorylation, acetylation, or sumoylation. After a brief review on the classic pathways of Nox activation, this article will focus on novel mechanisms of homologue-specific activity control and on cell-specific aspects which govern Nox activity. From these findings of the recent years it must be concluded that the activity control of Nox enzymes is much more complex than anticipated. Moreover, depending on the cellular activity state, Nox enzymes are selectively activated or inactivated. The complex upstream signaling aspects of these events make the development of "intelligent" Nox inhibitors plausible, which selectively attenuate disease-related Nox-mediated ROS formation without altering physiological signaling ROS. This approach might be of relevance for Nox-mediated tissue injury in ischemia-reperfusion and inflammation and also for chronic Nox overactivation as present in cancer initiation and cardiovascular disease.

Lysophosphatidic acid induces integrin activation in vascular smooth muscle and alters arteriolar myogenic vasoconstriction

In vascular smooth muscle cells (VSMC) increased integrin adhesion to extracellular matrix (ECM) proteins, as well as the production of reactive oxygen species (ROS) are strongly stimulated by lysophosphatidic acid (LPA). We hypothesized that LPA-induced generation of ROS increases integrin adhesion to the ECM. Using atomic force microscopy (AFM) we determined the effects of LPA on integrin adhesion to fibronectin (FN) in VSMC isolated from rat (Sprague-Dawley) skeletal muscle arterioles. In VSMC, exposure to LPA (2 μM) doubled integrin-FN adhesion compared to control cells (P < 0.05). LPA-induced integrin-FN adhesion was reduced by pre-incubation with antibodies against β1 and β3 integrins (50 μg/ml) by 66% (P < 0.05). Inhibition of LPA signaling via blockade of the LPA G-protein coupled receptors LPAR1 and LPAR3 with 10 μM Ki16425 reduced the LPA-enhanced adhesion of VSCM to FN by 40% (P < 0.05). Suppression of ROS with tempol (250 μM) or apocynin (300 μM) also reduced the LPA-induced FN adhesion by 47% (P < 0.05) and 59% (P < 0.05), respectively. Using confocal microscopy, we observed that blockade of LPA signaling, with Ki16425, reduced ROS by 45% (P < 0.05), to levels similar to control VSMC unexposed to LPA. In intact isolated arterioles, LPA (2 μM) exposure augmented the myogenic constriction response to step increases in intraluminal pressure (between 40 and 100 mm Hg) by 71% (P < 0.05). The blockade of LPA signaling, with Ki16425, decreased the LPA-enhanced myogenic constriction by 58% (P < 0.05). Similarly, blockade of LPA-induced ROS release with tempol or gp91 ds-tat decreased the LPA-enhanced myogenic constriction by 56% (P < 0.05) and 55% (P < 0.05), respectively. These results indicate that, in VSMC, LPA-induced integrin activation involves the G-protein coupled receptors LPAR1 and LPAR3, and the production of ROS, and that LPA may play an important role in the control of myogenic behavior in resistance vessels through ROS modulation of integrin activity.

Role of small GTPase protein Rac1 in cardiovascular diseases: development of new selective pharmacological inhibitors

A pathway-based genome-wide association analysis has recently identified Rac1 as one of the biologically important gene in coronary heart diseases. The role of the small GTPase Rac1 in cardiac hypertrophy and atherosclerosis has also been documented in clinical studies with the HMG-CoA reductase inhibitors and in in vitro and in vivo settings using transgenic and knockout mice. Thus, Rac1 has emerged as a new pharmacological target for the treatment of cardiovascular diseases. The activation state of Rac1 depends on the release of guanosine diphosphate and the binding of guanosine triphosphate. This cycling is regulated by the guanine nucleotide exchange factors, as activators, and by the GTPase-activating proteins. Three categories of selective Rac1 inhibitors have been developed affecting different steps of this pathway: antagonists of Rac1-guanine nucleotide exchange factor interaction, allosteric inhibitors of nucleotide binding to Rac1, and antagonists of Rac1-mediated NADPH oxidase activity. These chemical compounds have shown to selectively inhibit Rac1 activation in cultured cell lines without affecting the homologous proteins RhoA and Cdc42. Moreover, pioneer studies have been conducted with Rac1 inhibitors in in vivo experimental models of cardiovascular diseases with encouraging results. The present review summarizes the current knowledge of the role of Rac1 in cardiovascular diseases and the pharmacological approaches that have been developed to selectively inhibit its function.

Lysophosphatidic acid in atherosclerotic diseases

Lysophosphatidic acid (LPA) is a potent bioactive phospholipid. As many other biological active lipids, LPA is an autacoid: it is formed locally on demand, and it acts locally near its site of synthesis. LPA has a plethora of biological activities on blood cells (platelets, monocytes) and cells of the vessel wall (endothelial cells, smooth muscle cells, macrophages) that are all key players in atherosclerotic and atherothrombotic processes. The specific cellular actions of LPA are determined by its multifaceted molecular structures, the expression of multiple G-protein coupled LPA receptors at the cell surface and their diverse coupling to intracellular signalling pathways. Numerous studies have now shown that LPA has thrombogenic and atherogenic actions. Here, we aim to provide a comprehensive, yet concise, thoughtful and critical review of this exciting research area and to pinpoint potential pharmacological targets for inhibiting thrombogenic and atherogenic activities of LPA. We hope that the review will serve to accelerate knowledge of basic and clinical science, and to foster drug development in the field of LPA and atherosclerotic/atherothrombotic diseases.

Lipid phosphate phosphatase 3 negatively regulates smooth muscle cell phenotypic modulation to limit intimal hyperplasia

OBJECTIVE

The lipid phosphate phosphatase 3 (LPP3) degrades bioactive lysophospholipids, including lysophosphatidic acid and sphingosine-1-phosphate, and thereby terminates their signaling effects. Although emerging evidence links lysophosphatidic acid to atherosclerosis and vascular injury responses, little is known about the role of vascular LPP3. The goal of this study was to determine the role of LPP3 in the development of vascular neointima formation and smooth muscle cells (SMC) responses.

METHODS AND RESULTS

We report that LPP3 is expressed in vascular SMC after experimental arterial injury. Using gain- and loss-of-function approaches, we establish that a major function of LPP3 in isolated SMC cells is to attenuate proliferation (extracellular signal-regulated kinases) activity, Rho activation, and migration in response to serum and lysophosphatidic acid. These effects are at least partially a consequence of LPP3-catalyzed lysophosphatidic acid hydrolysis. Mice with selective inactivation of LPP3 in SMC display an exaggerated neointimal response to injury.

CONCLUSIONS

Our observations suggest that LPP3 serves as an intrinsic negative regulator of SMC phenotypic modulation and inflammation after vascular injury, in part, by regulating lysophospholipid signaling. These findings may provide a mechanistic link to explain the association between a PPAP2B polymorphism and coronary artery disease risk.

MicroRNA-195 regulates vascular smooth muscle cell phenotype and prevents neointimal formation

AIMS

Proliferation and migration of vascular smooth muscle cells (VSMCs) can cause atherosclerosis and neointimal formation. MicroRNAs have been shown to regulate cell proliferation and phenotype transformation. We discovered abundant expression of microRNA-195 in VSMCs and conducted a series of studies to identify its function in the cardiovascular system.

METHODS AND RESULTS

MicroRNA-195 expression was initially found to be altered when VSMCs were treated with oxidized low-density lipoprotein (oxLDL) in a non-replicated microRNA array experiment. Using cellular studies, we found that microRNA-195 reduced VSMC proliferation, migration, and synthesis of IL-1β, IL-6, and IL-8. Using bioinformatics prediction and experimental studies, we showed that microRNA-195 could repress the expression of Cdc42, CCND1, and FGF1 genes. Using a rat model, we found that the microRNA-195 gene, introduced by adenovirus, substantially reduced neointimal formation in a balloon-injured carotid artery. In situ hybridization confirmed the presence of microRNA-195 in the treated arteries but not in control arteries. Immunohistochemistry experiments showed abundant Cdc42 in the neointima of treated arteries.

CONCLUSIONS

We showed that microRNA-195 plays a role in the cardiovascular system by inhibiting VSMC proliferation, migration, and proinflammatory biomarkers. MicroRNA-195 may have the potential to reduce neointimal formation in patients receiving stenting or angioplasty.

Lysophosphatidic acid effects on atherosclerosis and thrombosis

Lysophosphatidic acid (LPA) has been found to accumulate in high concentrations in atherosclerotic lesions. LPA is a bioactive phospholipid produced by activated platelets and formed during the oxidation of LDL. Accumulating evidence suggests that this lipid mediator may serve as an important risk factor for development of atherosclerosis and thrombosis. The role of LPA in atherogenesis is supported by the evidence that LPA: stimulates endothelial cells to produce adhesion molecules and chemoattractants; induces smooth muscle cells to produce inflammatory cytokines; stimulates smooth muscle cell dedifferentiation, proliferation, and migration; increases monocyte migration and decreases monocyte-derived cell emigration from the vessel wall; induces hypertension and vascular neointimal formation in vivo; and promotes plaque progression in a mouse atherosclerosis model. The role of LPA in thrombogenesis is supported by the evidence that LPA markedly induces the aggregation of platelets and the expression of tissue factor, which is the principal initiator of blood coagulation. Recent experimental data indicate that LPA is produced by specific enzymes and that LPA binds to and activates multiple G-protein-coupled receptors, leading to intracellular signaling. Therapeutics targeting LPA biosynthesis, metabolism and signaling pathways could be viable for prevention and treatment of atherosclerosis and thrombosis.

Lysophosphatidic acid induces MDA-MB-231 breast cancer cells migration through activation of PI3K/PAK1/ERK signaling

Background

Enhanced motility of cancer cells is a critical step in promoting tumor metastasis. Lysophosphatidic acid (LPA), representing the major mitogenic activity in serum, stimulates migration in various types of cancer cells. However, the underlying signaling mechanisms for LPA-induced motility of cancer cells remain to be elucidated.

Methodology/Principal Findings

In this study, we found that LPA dose-dependently stimulated migration of MDA-MB-231 breast cancer cells, with 10 µM being the most effective. LPA also increased ERK activity and the MEK inhibitor U0126 could block LPA-induced ERK activity and cell migration. In addition, LPA induced PAK1 activation while ERK activation and cell migration were inhibited by ectopic expression of an inactive mutant form of PAK1 in MDA-MB-231 cells. Furthermore, LPA increased PI3K activity, and the PI3K inhibitor LY294002 inhibited both LPA-induced PAK1/ERK activation and cell migration. Moreover, in the breast cancer cell, LPA treatment resulted in remarkable production of reactive oxygen species (ROS), while LPA-induced ROS generation, PI3K/PAK1/ERK activation and cell migration could be inhibited by N-acetyl-L-Cysteine, a scavenger of ROS.

Conclusions/Significance

Taken together, this study identifies a PI3K/PAK1/ERK signaling pathway for LPA-stimulated breast cancer cell migration. These data also suggest that ROS generation plays an essential role in the activation of LPA-stimulated PI3K/PAK1/ERK signaling and breast cancer cell migration. These findings may provide a basis for designing future therapeutic strategy for blocking breast cancer metastasis.

p21-activated kinase 1 participates in vascular remodeling in vitro and in vivo

Vascular smooth muscle cell hypertrophy, proliferation, or migration occurs in hypertension, atherosclerosis, and restenosis after angioplasty, leading to pathophysiological vascular remodeling. Angiotensin II and platelet-derived growth factor are well-known participants of vascular remodeling and activate a myriad of downstream protein kinases, including p21-activated protein kinase (PAK1). PAK1, an effector kinase of small GTPases, phosphorylates several substrates to regulate cytoskeletal reorganization. However, the exact role of PAK1 activation in vascular remodeling remains to be elucidated. Here, we have hypothesized that PAK1 is a critical target of intervention for the prevention of vascular remodeling. Adenoviral expression of dominant-negative PAK1 inhibited angiotensin II-stimulated vascular smooth muscle cell migration. It also inhibited vascular smooth muscle cell proliferation induced by platelet-derived growth factor. PAK1 was activated in neointima of the carotid artery after balloon injury in the rat. Moreover, marked inhibition of the neointima hyperplasia was observed in a dominant-negative PAK1 adenovirus-treated carotid artery after the balloon injury. Taken together, these results suggest that PAK1 is involved in both angiotensin II and platelet-derived growth factor-mediated vascular smooth muscle cell remodeling, and inactivation of PAK1 in vivo could be effective in preventing pathophysiological vascular remodeling.

Pak protein kinases and their role in cancer

Some of the characteristics of cancer cells are high rates of cell proliferation, cell survival, and the ability to invade surrounding tissue. The cytoskeleton has an essential role in these processes. Dynamic changes in the cytoskeleton are necessary for cell motility and cancer cells are dependent on motility for invasion and metastasis. The signaling pathways behind the reshaping and migrating properties of the cytoskeleton in cancer cells involve a group of Ras-related small GTPases and their effectors, including the p21-activated kinases (Paks). Paks are a family of serine/threonine protein kinases comprised of six isoforms (Pak 1-6), all of which are direct targets of the small GTPases Rac and Cdc42. Besides their role in cytoskeletal dynamics, Paks have recently been shown to regulate various other cellular activities, including cell survival, mitosis, and transcription. Paks are overexpressed and/or hyperactivated in several human tumors and their role in cell transformation makes them attractive therapeutic targets. Pak-targeted therapeutics may efficiently inhibit certain types of tumors and efforts to identify selective Pak-inhibitors are underway.

Lysophosphatidic acid signaling in airway epithelium: role in airway inflammation and remodeling

Lysophosphatidic acid (LPA), a potent bioactive phospholipid, induces diverse cellular responses, including cell proliferation, migration, and cytokine release. LPA can be generated intracellularly and extracellularly through multiple synthetic pathways by action of various enzymes, such as phospholipase A(1/2) (PLA(1/2)), phospholipase D (PLD), acylglycerol kinase (AGK), and lysophospholipase D (lysoPLD). Metabolism of LPA is regulated by a family of lipid phosphate phosphatases (LPPs). Significant amounts of LPA have been detected in various biological fluids, including serum, saliva, and bronchoalveolar lavage fluid (BALF). The most significant effects of LPA appear to be through activation of the G-protein-coupled receptors (GPCRs), termed LPA(1-6). LPA regulates gene expression through activation of several transcriptional factors, such as nuclear factor-kappaB (NF-kappaB), AP-1, and C/EBPbeta. In addition to GPCRs, cross-talk between LPA receptors and receptor tyrosine kinases (RTKs) partly regulates LPA-induced intracellular signaling and cellular responses. Airway epithelial cells participate in innate immunity through the release of cytokines, chemokines, lipid mediators, other inflammatory mediators and an increase in barrier function in response to a variety of inhaled stimuli. Expression of LPA receptors has been demonstrated in airway epithelial cells. This review summarizes our recent observations of the role of LPA/LPA-Rs in regulation of airway epithelium, especially in relation to the secretion of pro- and anti-inflammatory mediators and regulation of airway barrier function.

Role of Src tyrosine kinase in the atherogenic effects of the 12/15-lipoxygenase pathway in vascular smooth muscle cells

OBJECTIVE

The 12/15-Lipoxygenase (12/15-LO) and its metabolite 12(S)-Hydroxyeicosatetraenoic acid [12(S)-HETE] mediate proatherogenic responses in vascular smooth muscle cells (VSMCs). We examined the role of the nonreceptor tyrosine kinase Src in the signaling and epigenetic chromatin mechanisms involved in these processes.

METHODS AND RESULTS

Rat VSMCs (RVSMCs) were stimulated with 12(S)-HETE (0.1 micromol/L) in the presence or absence of the Src inhibitor PP2 (10 micromol/L). Src activation and downstream signaling events including inflammatory gene expression and chromatin histone H3-Lys-9/14 acetylation were examined by immunoblotting, RT-PCR, and chromatin immunoprecipitation assays, respectively. 12(S)-HETE significantly activated Src, focal adhesion kinase, Akt, p38MAPK, and CREB. Expression of monocyte chemoattractant protein-1 and interleukin-6 genes and histone H3-Lys-9/14 acetylation on their promoters were also increased by 12(S)-HETE. PP2 inhibited these responses as well as 12(S)-HETE-induced VSMC migration. Furthermore, dominant negative mutants of Src, CREB, and a histone acetyltransferase p300 significantly blocked 12(S)-HETE-induced inflammatory gene expression. In addition, growth factor induced Src signaling and downstream events including H3-Lys-9/14 acetylation and migration were significantly attenuated in VSMCs derived from 12/15-LO(-/-) mice relative to WT.

CONCLUSIONS

Src kinase signaling plays a central role in the proatherogenic responses mediated by 12/15-LO and its oxidized lipid metabolite 12(S)-HETE in VSMCs.

Lysophosphatidic acid receptors 1 and 2 play roles in regulation of vascular injury responses but not blood pressure

Phenotypic modulation of vascular smooth muscle cells (SMCs) is essential for the development of intimal hyperplasia. Lysophosphatidic acid (LPA) is a serum component that can promote phenotypic modulation of cultured SMCs, but an endogenous role for this bioactive lipid as a regulator of SMC function in vivo has not been established. Ligation injury of the carotid artery in mice increased levels in the vessel of both autotaxin, the lysophospholipase D enzyme responsible for generation of extracellular LPA, and 2 LPA responsive G protein-coupled receptors 1 (LPA1) and 2 (LPA2). LPA1(-/-)2(-/-) mice were partially protected from the development of injury-induced neointimal hyperplasia, whereas LPA1(-/-) mice developed larger neointimal lesions after injury. Growth in serum, LPA-induced extracellular signal-regulated protein kinase activation, and migration to LPA and serum were all attenuated in SMCs isolated from LPA1(-/-)2(-/-) mice. In contrast, LPA1(-/-) SMCs exhibited enhanced migration resulting from an upregulation of LPA3. However, despite their involvement in intimal hyperplasia, neither LPA1 nor LPA2 was required for dedifferentiation of SMCs following vascular injury or dedifferentiation of isolated SMCs in response to LPA or serum in vitro. Similarly, neither LPA1 nor LPA2 was required for LPA to elicit a transient increase in blood pressure following intravenous administration of LPA to mice. These results identify a role for LPA1 and LPA2 in regulating SMC migratory responses in the context of vascular injury but suggest that additional LPA receptor subtypes are required for other LPA-mediated effects in the vasculature.

The p21-activated kinase is required for neuronal migration in the cerebral cortex

The normal formation and function of the mammalian cerebral cortex depend on the positioning of its neurones, which occurs in a highly organized, layer-specific manner. The correct morphology and movement of neurones rely on synchronized regulation of their actin filaments and microtubules. The p21-activated kinase (Pak1), a key cytoskeletal regulator, controls neuronal polarization, elaboration of axons and dendrites, and the formation of dendritic spines. However, its in vivo role in the developing nervous system is unclear. We have utilized in utero electroporation into mouse embryo cortices to reveal that both loss and gain of Pak1 function affect radial migration of projection neurones. Overexpression of hyperactivated Pak1 predominantly caused neurones to arrest in the intermediate zone (IZ) with apparently misoriented and disorganized leading projections. Loss of Pak1 disrupted the morphology of migrating neurones, which accumulated in the IZ and deep cortical layers. Unexpectedly, a significant number of neurones with reduced Pak1 expression aberrantly entered into the normally cell-sparse marginal zone, suggesting their inability to cease migrating that may be due to their impaired dissociation from radial glia. Our findings reveal the in vivo importance of temporal and spatial regulation of the Pak1 kinase during key stages of cortical development.

Roles of lysophosphatidic acid in cardiovascular physiology and disease

The bioactive lipid mediator lysophosphatidic acid (LPA) exerts a range of effects on the cardiovasculature that suggest a role in a variety of critical cardiovascular functions and clinically important cardiovascular diseases. LPA is an activator of platelets from a majority of human donors identifying a possible role as a regulator of acute thrombosis and platelet function in atherogenesis and vascular injury responses. Of particular interest in this context, LPA is an effective phenotypic modulator of vascular smooth muscle cells promoting the de-differentiation, proliferation and migration of these cells that are required for the development of intimal hyperplasia. Exogenous administration of LPA results in acute and systemic changes in blood pressure in different animal species, suggesting a role for LPA in both normal blood pressure regulation and hypertension. Advances in our understanding of the molecular machinery responsible for the synthesis, actions and inactivation of LPA now promise to provide the tools required to define the role of LPA in cardiovascular physiology and disease. In this review we discuss aspects of LPA signaling in the cardiovasculature focusing on recent advances and attempting to highlight presently unresolved issues and promising avenues for further investigation.

Distinct effects of contraction agonists on the phosphorylation state of cofilin in pulmonary artery smooth muscle

We hypothesized that agonist-induced contraction correlates with the phospho-cofilin/cofilin (P-CF/CF) ratio in pulmonary artery (PA) rings and cultured smooth muscle cells (PASMCs). PA rings were used for isometric contractions and along with PASMCs for assay of P-CF/CF by isoelectric focusing and immunoblotting. The P-CF/CF measured 22.5% in PA and differentiated PASMCs, but only 14.8% in undifferentiated PASMCs. With comparable contraction responses in PA, endothelin-1 (100 nM) and norepinephrine (1 μM) induced a 2-fold increase of P-CF/CF, while angiotensin II (1 μM) induced none. All agonists activated Rho-kinase and LIMK2, and activation was eliminated by inhibition of Rho-kinase. Microcystin LF (20 nM) potentiated the angiotensin II, but not the 5-hydroxytryptamine (1 μM)-mediated increase of P-CF/CF. In conclusion, all tested agonists activate the Rho-kinase-LIMK pathway and increase P-CF/CF. Angiotensin II activates PP2A and counteracts the LIMK-mediated CF phosphorylation. CF phosphorylation stabilizes peripheral actin structures and may contribute to the maximal contraction of PA.

Autophosphorylation-dependent degradation of Pak1, triggered by the Rho-family GTPase, Chp

The Paks (p21-activated kinases) Pak1, Pak2 and Pak3 are among the most studied effectors of the Rho-family GTPases, Rac, Cdc42 (cell division cycle 42) and Chp (Cdc42 homologous protein). Pak kinases influence a variety of cellular functions, but the process of Pak down-regulation, following activation, is poorly understood. In the present study, we describe for the first time a negative-inhibitory loop generated by the small Rho-GTPases Cdc42 and Chp, resulting in Pak1 inhibition. Upon overexpression of Chp, we unexpectedly observed a T-cell migration phenotype consistent with Paks inhibition. In line with this observation, overexpression of either Chp or Cdc42 caused a marked reduction in the level of Pak1 protein in a number of different cell lines. Chp-induced degradation was accompanied by ubiquitination of Pak1, and was dependent on the proteasome. The susceptibility of Pak1 to Chp-induced degradation depended on its p21-binding domain, kinase activity and a number of Pak1 autophosphorylation sites, whereas the PIX- (Pak-interacting exchange factor) and Nck-binding sites were not required. Together, these results implicate Chp-induced kinase autophosphorylation in the degradation of Pak1. The N-terminal domain of Chp was found to be required for Chp-induced degradation, although not for Pak1 activation, suggesting that Chp provides a second function, distinct from kinase activation, to trigger Pak degradation. Collectively, our results demonstrate a novel mechanism of signal termination mediated by the Rho-family GTPases Chp and Cdc42, which results in ubiquitin-mediated degradation of one of their direct effectors, Pak1.

p21-Activated kinase-1 and its role in integrated regulation of cardiac contractility

We review here a novel concept in the regulation of cardiac contractility involving variations in the activity of the multifunctional enzyme, p21-activated kinase 1 (Pak1), a member of a family of proteins in the small G protein-signaling pathway that is activated by Cdc42 and Rac1. There is a large body of evidence from studies in noncardiac tissue that Pak1 activity is key in regulation of a number of cellular functions, including cytoskeletal dynamics, cell motility, growth, and proliferation. Although of significant potential impact, the role of Pak1 in regulation of the heart has been investigated in only a few laboratories. In this review, we discuss the structure of Pak1 and its sites of posttranslational modification and molecular interactions. We assemble an overview of the current data on Pak1 signaling in noncardiac tissues relative to similar signaling pathways in the heart, and we identify potential roles of Pak1 in cardiac regulation. Finally, we discuss the current state of Pak1 research in the heart in regard to regulation of contractility through functional myofilament and Ca(2+)-flux modification. An important aspect of this regulation is the modulation of kinase and phosphatase activity. We have focused on Pak1 regulation of protein phosphatase 2A (PP2A), which is abundant in cardiac muscle, thereby mediating dephosphorylation of sarcomeric proteins and sensitizing the myofilaments to Ca(2+). We present a model for Pak1 signaling that provides a mechanism for specifically affecting cardiac cellular processes in which regulation of protein phosphorylation states by PP2A dephosphorylation predominates.

The signaling mechanism of ROS in tumor progression

Reactive oxygen species (ROS) are recently proposed to be involved in tumor metastasis which is a complicated processes including epithelial-mesenchymal transition (EMT), migration, invasion of the tumor cells and angiogenesis around the tumor lesion. ROS generation may be induced intracellularly, in either NADPH oxidase- or mitochondria-dependent manner, by growth factors and cytokines (such as TGFbeta and HGF) and tumor promoters (such as TPA) capable of triggering cell adhesion, EMT and migration. As a signaling messenger, ROS are able to oxidize the critical target molecules such as PKC and protein tyrosine phosphates (PTPs), which are relevant to tumor cell invasion. PKC contain multiple cysteine residues that can be oxidized and activated by ROS. Inactivation of multiple PTPs by ROS may relieve the tyrosine phosphorylation-dependent signaling. Two of the down-stream molecules regulated by ROS are MAPK and PAK. MAPKs cascades were established to be a major signal pathway for driving tumor cell metastasis, which are mediated by PKC, TGF-beta/Smad and integrin-mediated signaling. PAK is an effector of Rac-mediated cytoskeletal remodeling that is responsible for cell migration and angiogenesis. There are several transcriptional factors such as AP1, Ets, Smad and Snail regulating a lot of genes relevant to metastasis. AP-1 and Smad can be activated by PKC activator and TGF-beta1, respectively, in a ROS dependent manner. On the other hand, Est-1 can be upregulated by H2O2 via an antioxidant response element in the promoter. The ROS-regulated genes relevant to EMT and metastasis include E-cahedrin, integrin and MMP. Comprehensive understanding of the ROS-triggered signaling transduction, transcriptional activation and regulation of gene expressions will help strengthen the critical role of ROS in tumor progression and devising strategy for chemo-therapeutic interventions.

Epidermal growth factor stimulates Rac1 and p21-activated kinase in vascular smooth muscle cells

Epidermal growth factor (EGF) has been shown to be a potent mitogen for vascular smooth muscle cells (VSMC) both in vitro and in vivo, thus contributing to the development of atherosclerosis and hypertension. Stimulation of Rho-family GTPases Rac/Cdc42 exerts pleiotropic cellular effects and have been demonstrated to contribute to EGF-induced proliferation in other cell systems. However, the effect of EGF on Rac/Cdc42 activation is unknown for VSMC. In the present report, we evaluated stimulation of Rac/Cdc42 by EGF in VSMC performing PAK-PBD binding assay. EGF treatment of VSMC induced time and concentration dependent binding of GTP-bound Rac1 to PAK-PBD peaking at 1 min and showing sustained activation up to 15 min. However, stimulation of Cdc42 could not be demonstrated. To further evaluate downstream effectors of Rac1 stimulation of p21-activated kinase (PAK) and c-Jun N-terminal kinase (JNK) by EGF was determined. In VSMC, EGF sequentially stimulated PAK, peaking at 5 min, and JNK, peaking at 15 min. Pretreatment of VSMC by EGF receptor specific tyrosine kinase inhibitor AG1478 and non-specific tyrosine kinase inhibitor genistein inhibited EGF-induced activation of Rac1, PAK and JNK, whereas tyrosine kinase inhibitors specific for Src (PP1) and specific for platelet-derived growth factor (AG1296) had no effect. Specific inhibition or Rac1 by NSC23766 attenuated EGF-induced [(3)H] thymidine incorporation in VSMC. Our data provide evidence for EGF-induced Rac1 activation and implicate PAK and JNK as downstream targets of Rac1 in EGF signal transduction in VSMC.

Lysophosphatidic acid stimulation of platelets rapidly induces Ca2+-dependent dephosphorylation of cofilin that is independent of dense granule secretion and aggregation

Cofilin is an actin dynamizing protein and inactivated after Ser3 phosphorylation by LIM-kinases (LIMKs). We studied whether in platelets stimulated by lysophosphatidic acid (LPA), Rho-kinase or p21-activated kinase (PAK) mediates LIMK-1 activation leading to subsequent phosphorylation and inactivation of cofilin and the increase of F-actin. During LPA (0.1 microM)-induced shape change, a rapid Rho-kinase activation and a slower activation of PAK were observed. Rho-kinase activation led to rapid LIMK-1 (Thr508) phosphorylation. Despite of LIMK-1 activation, cofilin net phosphorylation was not increased. Cofilin rapidly associated with F-actin and preceded the F-actin increase. Pretreatment with the Rho-kinase inhibitor Y-27632 inhibited LIMK-1 phosphorylation, unmasked cofilin dephosphorylation and inhibited the reversible F-actin increase during shape change. In the presence of fibrinogen, LPA (10 microM) induced ATP-secretion from dense granules and aggregation, and cofilin was rapidly dephosphorylated and then rephosphorylated in a Rho-kinase/LIMK-1-dependent manner. In the absence of fibrinogen, cofilin de- and rephosphorylation after LPA (10 microM) was unchanged, but secretion and aggregation were absent. Cofilin dephosphorylation was completely blocked by BAPTA-AM indicating that it was mediated by an increase of cytosolic Ca(2+). We conclude that in LPA-stimulated platelets, Rho-kinase-dependent LIMK-1 activation mediates the F-actin increase during shape change without enhancing cofilin net phosphorylation. However, a rapid dephosphorylation of cofilin occurs during secretion and aggregation, which is Ca(2+)-dependent, upstream of secretion and aggregation and might regulate these platelet responses.

Reactive oxygen species signaling in vascular smooth muscle cells

Reactive oxygen species (ROS) have been shown to function as important signaling molecules in the cardiovascular system. Vascular smooth muscle cells (VSMCs) contain several sources of ROS, among which the NADPH oxidases are predominant. In VSMCs, ROS mediate many pathophysiological processes, such as growth, migration, apoptosis and secretion of inflammatory cytokines, as well as physiological processes, such as differentiation, by direct and indirect effects at multiple signaling levels. Therefore, it becomes critical to understand the different roles ROS play in the physiology and pathophysiology of VSMCs.

Regulation of lysophosphatidic acid-induced epidermal growth factor receptor transactivation and interleukin-8 secretion in human bronchial epithelial cells by protein kinase Cdelta, Lyn kinase, and matrix metalloproteinases

We have demonstrated earlier that lysophosphatidic acid (LPA)-induced interleukin-8 (IL-8) secretion is regulated by protein kinase Cdelta (PKCdelta)-dependent NF-kappaB activation in human bronchial epithelial cells (HBEpCs). Here we provide evidence for signaling pathways that regulate LPA-mediated transactivation of epidermal growth factor receptor (EGFR) and the role of cross-talk between G-protein-coupled receptors and receptor-tyrosine kinases in IL-8 secretion in HBEpCs. Treatment of HBEpCs with LPA stimulated tyrosine phosphorylation of EGFR, which was attenuated by matrix metalloproteinase (MMP) inhibitor (GM6001), heparin binding (HB)-EGF inhibitor (CRM 197), and HB-EGF neutralizing antibody. Overexpression of dominant negative PKCdelta or pretreatment with a PKCdelta inhibitor (rottlerin) or Src kinase family inhibitor (PP2) partially blocked LPA-induced MMP activation, proHB-EGF shedding, and EGFR tyrosine phosphorylation. Down-regulation of Lyn kinase, but not Src kinase, by specific small interfering RNA mitigated LPA-induced MMP activation, proHB-EGF shedding, and EGFR phosphorylation. In addition, overexpression of dominant negative PKCdelta blocked LPA-induced phosphorylation and translocation of Lyn kinase to the plasma membrane. Furthermore, down-regulation of EGFR by EGFR small interfering RNA or pretreatment of cells with EGFR inhibitors AG1478 and PD158780 almost completely blocked LPA-dependent EGFR phosphorylation and partially attenuated IL-8 secretion, respectively. These results demonstrate that LPA-induced IL-8 secretion is partly dependent on EGFR transactivation regulated by PKCdelta-dependent activation of Lyn kinase and MMPs and proHB-EGF shedding, suggesting a novel mechanism of cross-talk and interaction between G-protein-coupled receptors and receptor-tyrosine kinases in HBEpCs.

[Rho/Rho kinase signal transduction pathway in cardiovascular disease and cardiovascular remodeling]

The small guanosine triphosphatase Rho and its target, Rho kinase, play important roles in both blood pressure regulation and vascular smooth muscle contraction. Rho is activated by agonists of receptors coupled to cell membrane G protein, such as angiotensin II and phenylephrine. Once Rho is activated, it translocates to the cell membrane where it, in turn, activates Rho kinase. Activated Rho kinase phosphorylates myosin light chain phosphatase, which is then inhibited. This sequence stimulates vascular smooth muscle contraction, stress fiber formation,and cell migration. In this way, Rho and Rho kinase activation have important effects on several cardiovascular diseases. Currently available substances that specifically inhibit this signaling pathway could offer clinical benefits in several cardiovascular, as well as noncardiovascular diseases, such as arterial hypertension, pulmonary hypertension, cerebral or coronary spasm, post-angioplasty restenosis, and erectile dysfunction.

Role of atrial natriuretic peptide in the suppression of lysophosphatydic acid-induced rat aortic smooth muscle (RASM) cell growth

Lysophosphatidic acid (LPA) is a lipid mediator with multiple biological functions. In the present study we investigated the possible role of atrial natriuretic peptide (ANP), a hormone affecting cardiovascular homeostasis and inducing antimitogenic effects in different cell types, on LPA-induced cell growth and reactive oxygen species (ROS) production in rat aortic smooth muscle (RASM) cells. Both LPA effects on cell growth and levels of ROS were totally abrogated by physiological concentrations of ANP, without modifying the overexpression of LPA-receptors. These effects were also affected by cell pretreatment with wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K). Moreover, the LPA-induced activation of Akt, a downstream target of PI3K, was completely inhibited by physiological concentrations of ANP, which were also able to inhibit p42/p44 phosphorylation. Taken together, our data suggest that PI3K may represent an important step in the LPA signal transduction pathway responsible for ROS generation and DNA synthesis in RASM cells. At same time, the enzyme could also represent an essential target for the antiproliferative effects of ANP.

Human bronchial smooth muscle cell proliferation via thromboxane A2 receptor

Thromboxane A2 receptor (TP) mediates bronchial smooth muscle cell (BSMC) contraction, airway hyperresponsiveness, and airway inflammation in patients with asthma. In the present study, a pathogenic role of TP activation in airway remodeling was examined using primary cultures of human BSMC. A TP agonist, I-BOP, concentration-dependently enhanced not only bromodeoxyuridine (BrdU) uptake but also cell proliferation of BSMC. A TP-selective antagonist, AA-2414, blocked the effects of I-BOP on both BrdU uptake and cell proliferation. I-BOP-induced BrdU uptake was significantly blocked by two non-selective tyrosine kinase inhibitors, genistein and herbimycin A, or a Src family tyrosine kinase inhibitor, PP2, but not by an inhibitor of epidermal growth factor (EGF) receptor-associated tyrosine kinase, AG1478. In conclusion, TP receptor activation causes DNA synthesis and cell proliferation of human BSMC by activating tyrosine kinases including Src, but not by EGF receptor transactivation.

Rho kinase-induced nuclear translocation of ERK1/ERK2 in smooth muscle cell mitogenesis caused by serotonin

There is now considerable evidence supporting a mitogenic action of serotonin (5-HT) on vascular smooth muscle cells (SMC) that might participate in pulmonary hypertension (PH). Our previous studies have demonstrated that 5-HT-induced proliferation depends on the generation of reactive oxygen species and activation of extracellular signal-regulated kinase (ERK) 1/ERK2. Activation of Rho kinase (ROCK) in SMC also may be important in PH. We undertook the present study to assess the role of Rho A/ROCK and its possible relation to ERK1/ERK2 in 5-HT-induced pulmonary artery SMC proliferation. We found that this stimulation of SMC proliferation requires Rho A/ROCK as inhibition with Y27632, a ROCK inhibitor, or dominant negative (DN) mutant Rho A blocks 5-HT-induced proliferation, cyclin D1 expression, phosphorylation of Elk, and the DNA binding of transcription factors, Egr-1 and GATA-4. 5-HT activated ROCK, and the activation was blocked by GR 55562 and GR127935, 5-HT 1B/1D receptor antagonists, but not by serotonin transport (SERT) inhibitors. Activation of Rho kinase by 5-HT was independent of activation of ERK1/ERK2, and 5-HT activated ERK1/ERK2 independently of ROCK. Treatment of SMC with Y27632 and expression of DNRho A in cells blocked translocation of ERK1/ERK2 to the cellular nucleus. Depolymerization of actin with cytochalasin D (CD) and latrunculin B (latB) failed to block the translocation of ERK, suggesting that the actin cytoskeleton does not participate in the translocation. The studies show for the first time to our knowledge combinational action of SERT and a 5-HT receptor in SMC growth and Rho A/ROCK participation in 5-HT receptor 1B/1D-mediated mitogenesis of vascular SMCs through an effect on cytoplasmic to nuclear translocation of ERK1/ERK2.

Cell surface receptors activate p21-activated kinase 1 via multiple Ras and PI3-kinase-dependent pathways

p21-activated kinases (PAKs) were the first identified mammalian members of a growing family of Ste20-like serine-threonine protein kinases. In this study, we show that PAK1 can be stimulated by carbachol, lysophosphatidic acid (LPA), epidermal growth factor (EGF), and phorbol 12-myristate 13-acetate (PMA) by multiple independent and overlapping pathways. Dominant-negative Ras, Rac, and Cdc42 inhibited PAK1 activation by all of these agonists, while active Rac1 and Cdc42 were sufficient to maximally activate PAK1 in the absence of any treatment. Active Ras induced only a weak activation of PAK1 that could be potentiated by muscarinic receptor stimulation. Studies using inhibitors of the EGF receptor tyrosine kinase, phosphatidylinositol 3-kinase (PI3-kinase) and protein kinase C (PKC) revealed that all of the cell surface agonists could activate PAK1 through pathways independent of PKC, that EGF stimulated a PI3-kinase dependent pathway to stimulate PAK1, and that muscarinic receptor stimulation of PAK1 was predominantly mediated through this EGF-R-dependent mechanism. Activation of PAK1 by LPA was independent of PI3-kinase and the EGF receptor, but was inhibited by dominant-negative RhoA. These results identify multiple Ras-dependent pathways to activation of PAK1.

Activation of p21-activated kinase 1 is required for lysophosphatidic acid-induced focal adhesion kinase phosphorylation and cell motility in human melanoma A2058 cells

Lysophosphatidic acid (LPA), one of the naturally occurring phospholipids, stimulates cell motility through the activation of Rho family members, but the signaling mechanisms remain to be elucidated. In the present study, we investigated the roles of p21-activated kinase 1 (PAK1) on LPA-induced focal adhesion kinase (FAK) phosphorylation and cell motility. Treatment of human melanoma cells A2058 with LPA increased phosphorylation and activation of PAK1, which was blocked by treatment with pertussis toxin and by inhibition of phosphoinositide 3-kinase (PI3K) with an inhibitor LY294002 or by overexpression of catalytically inactive mutant of PI3Kgamma, indicating that LPA-induced PAK1 activation was mediated via a Gi protein and the PI3Kgamma signaling pathway. In addition, we demonstrated that Rac1/Cdc42 signals acted as upstream effector molecules of LPA-induced PAK activation. However, Rho-associated kinase, MAP kinase kinase 1/2 or phospholipase C might not be involved in LPA-induced PAK1 activation or cell motility stimulation. Furthermore, PAK1 was necessary for FAK phosphorylation by LPA, which might cause cell migration, as transfection of the kinase deficient mutant of PAK1 or PAK auto-inhibitory domain significantly abrogated LPA-induced FAK phosphorylation. Taken together, these findings strongly indicated that PAK1 activation was necessary for LPA-induced cell motility and FAK phosphorylation that might be mediated by sequential activation of Gi protein, PI3Kgamma and Rac1/Cdc42.

Phosphoinositide-dependent kinase 1 and p21-activated protein kinase mediate reactive oxygen species-dependent regulation of platelet-derived growth factor-induced smooth muscle cell migration

Smooth muscle cell migration in response to platelet-derived growth factor (PDGF) is a key event in several vascular pathologies, including atherosclerosis and restenosis. PDGF increases intracellular levels of reactive oxygen species (ROS) in vascular smooth muscle cells (VSMCs), but the ROS sensitivity of migration and of the signaling pathways leading to migration are largely unknown. In VSMCs, PDGF dose-dependently increased migration compared with nonstimulated cells, with a maximum increase at 10 ng/mL. Pretreatment with the antioxidant N-acetyl-cysteine, the flavin-containing enzyme inhibitor diphenylene iodonium, or the glutathione peroxidase mimetic ebselen significantly attenuated migration (PDGF alone, 5.0+/-1.1-fold; NAC, 1.8+/-0.2-fold; diphenylene iodonium, 1.4+/-0.3-fold migration; and ebselen, 2.0+/-0.5-fold migration), as did overexpression of catalase. Pretreatment of VSMCs with the Src inhibitor PP1 or dominant-negative Rac adenovirus significantly inhibited migration, but only Src activation was attenuated by ROS inhibitors. Phosphorylation of the Src- and Rac-effector p21-activated protein kinase (PAK) 1 on Thr423 (the phosphoinositide-dependent kinase-1 [PDK1] site) was attenuated by ROS inhibition, and infection of VSMCs with dominant-negative PAK1 adenovirus attenuated migration. Moreover, kinase-inactive K111N-PDK1 inhibited PAK1 phosphorylation on Thr423, and both K111N-PDK1 and Y9F-PDK1 significantly inhibited VSMC migration. PDK1 tyrosine phosphorylation was also ROS dependent. These data indicate that PDGF-induced VSMC migration is ROS dependent and identify the Src/PDK1/PAK1 signaling pathway as an important ROS-sensitive mediator of migration. Such information is critical to understanding the role of ROS in vascular diseases in which migration of VSMCs is an important component.

Biology of the p21-activated kinases

The p21-activated kinases (PAKs) 1-3 are serine/threonine protein kinases whose activity is stimulated by the binding of active Rac and Cdc42 GTPases. Our understanding of the regulation and biology of these important signaling proteins has increased tremendously since their discovery in the mid-1990s. PAKs 1-3 are activated by a variety of GTPase-dependent and -independent mechanisms. This complexity reflects the contributions of PAK function in many cellular signaling pathways and the need to carefully control PAK action in a highly localized manner. PAKs serve as important regulators of cytoskeletal dynamics and cell motility, transcription through MAP kinase cascades, death and survival signaling, and cell-cycle progression. Consequently, PAKs have also been implicated in a number of pathological conditions and in cell transformation. We propose here a key role for PAK action in coordinating the dynamics of the actin and microtubule cytoskeletons during directional motility of cells, as well as in other functions requiring cytoskeletal polarization.

Edaravone, a Radical Scavenger, May Enhance or Produce Antiproliferative Effects of Fluvastatin, Amlodipine, Ozagrel, GF109203X, Y27632 on Cultured Basilar Artery Smooth Muscle Cells

Proliferation of vascular smooth muscle cells stimulated by reactive oxygen species (ROS) may play a pivotal role in the pathogenesis of atherosclerosis. To clarify mechanisms by which ROS promote vascular atherogenesis, effects of fluvastatin, amlodipine, ozagrel (thromboxane synthetase inhibitor), GF109203X (a protein kinase C inhibitor) and Y27632 (a ROCK inhibitor) on the proliferation of guinea-pig basilar artery smooth muscle cells (GBa-SM3) in a 5% FBS culture medium were studied over 3 d in the presence or absence of a free radical scavenger, edaravone. Viability of cells at the end of incubation was measured by the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) test. Results demonstrated that fluvastatin and amlodipine by themselves possess antiproliferative effects on the GBa-SM3 cells at 10-100 microM and 0.1-1 microM, respectively. While edaravone possessed no antiproliferative effect by itself at 100 microM, it significantly (p<0.05) augmented the antiproliferative effects of fluvastatin and amlodipine. In addition, ozagrel, GF109203X and Y27632 possessed no appreciable effects on the cell growth by themselves. However, coincubation of edaravone at 100 microM with these agents elicited significant antiproliferative effects for ozagrel, GF109203X and Y27632 at 10-100 microM, 1-10 microM and 0.1-1 microM, respectively. In conclusion, edaravone may have clinically beneficial interactions with fluvastatin, amlodipine and ozagrel regarding the prevention of vascular atherosclerosis. The interactions between edaravone and the inhibitors of protein kinase C and ROCK were suggestive of possible contributions of ROS-triggered intracellular signals associated with these enzymes to vascular atherogenesis, but further studies are required for confirmation.

Ligand-specific control of src-suppressed C kinase substrate gene expression

The src-suppressed C-kinase substrate, SSeCKS, is now recognized as a key regulator of cell signaling and cytoskeletal dynamics. However, few ligands that control SSeCKS expression have been identified. We report that platelet-derived growth factor-BB (PDGF-BB), lysophosphatidic acid (LPA), and eicosapentaenoic acid (EPA) potently modulate SSeCKS gene expression in cultured smooth muscle (RASM) cells relative to other bioactive ligands tested. In addition, EPA-dependent regulation of SSeCKS expression correlates with distinct changes in cell morphology and adhesion in RASM cells. Independent evidence that ligand-specific control of SSeCKS expression links to the regulation of cell adhesion and morphology was obtained using ras-transformed fibroblasts, KNRK. Sodium butyrate (NaB) upregulates SSeCKS mRNA and protein expression corresponding to increased cell-spreading and adhesion. In addition, ectopic expression of recombinant SSeCKS recapitulates attributes of NaB-induced morphogenesis in KNRK cells. The data provide novel evidence that SSeCKS functions in PDGF-BB-, LPA-, EPA-, and NaB-mediated cell signaling.