Role of protein kinase C in attachment, spreading, and migration of human endothelial cells

Mechanosensitive Pathways Involved in Cardiovascular Development and Homeostasis in Zebrafish

Cardiovascular diseases such as coronary heart disease, myocardial infarction, and cardiac arrhythmia are the leading causes of morbidity and mortality in developed countries and are steadily increasing in developing countries. Fundamental mechanistic studies at the molecular, cellular, and animal model levels are critical for the diagnosis and treatment of these diseases. Despite being phylogenetically distant from humans, zebrafish share remarkable similarity in the genetics and electrophysiology of the cardiovascular system. In the last 2 decades, the development and deployment of innovative genetic manipulation techniques greatly facilitated the application of zebrafish as an animal model for studying basic biology and diseases. Hemodynamic shear stress is intimately involved in vascular development and homeostasis. The critical mechanosensitive signaling pathways in cardiovascular development and pathophysiology previously studied in mammals have been recapitulated in zebrafish. In this short article, we reviewed recent knowledge about the role of mechanosensitive pathways such as Notch, PKCε/PFKFB3, and Wnt/Ang2 in cardiovas-cular development and homeostasis from studies in the -zebrafish model.

An Overview of VEGF-Mediated Signal Transduction

Vascular endothelial growth factor (VEGF) plays a fundamental role in angiogenesis and endothelial cell biology, and has been the subject of intense study as a result. VEGF acts via a diverse and complex range of signaling pathways, with new targets constantly being discovered. This review attempts to summarize the current state of knowledge regarding VEGF cell signaling in endothelial and cardiovascular biology, with a particular emphasis on its role in angiogenesis.

PKCδ regulates force signaling during VEGF/CXCL4 induced dissociation of endothelial tubes

Wound healing requires the vasculature to re-establish itself from the severed ends; endothelial cells within capillaries must detach from neighboring cells before they can migrate into the nascent wound bed to initiate angiogenesis. The dissociation of these endothelial capillaries is driven partially by platelets' release of growth factors and cytokines, particularly the chemokine CXCL4/platelet factor-4 (PF4) that increases cell-cell de-adherence. As this retraction is partly mediated by increased transcellular contractility, the protein kinase c-δ/myosin light chain-2 (PKCδ/MLC-2) signaling axis becomes a candidate mechanism to drive endothelial dissociation. We hypothesize that PKCδ activation induces contractility through MLC-2 to promote dissociation of endothelial cords after exposure to platelet-released CXCL4 and VEGF. To investigate this mechanism of contractility, endothelial cells were allowed to form cords following CXCL4 addition to perpetuate cord dissociation. In this study, CXCL4-induced dissociation was reduced by a VEGFR inhibitor (sunitinib malate) and/or PKCδ inhibition. During combined CXCL4+VEGF treatment, increased contractility mediated by MLC-2 that is dependent on PKCδ regulation. As cellular force is transmitted to focal adhesions, zyxin, a focal adhesion protein that is mechano-responsive, was upregulated after PKCδ inhibition. This study suggests that growth factor regulation of PKCδ may be involved in CXCL4-mediated dissociation of endothelial cords.

Molecular mediators of angiogenesis

Angiogenesis, or the formation of new blood vessels from the preexisting vasculature, is a key component in numerous physiologic and pathologic responses and has broad impact in many medical and surgical specialties. In this review, we discuss the key cellular steps that lead to the neovascularization of tissues and highlight the main molecular mechanisms and mediators in this process. We include discussions on proteolytic enzymes, cell-matrix interactions, and pertinent cell signaling pathways and end with a survey of the mechanisms that lead to the stabilization and maturation of neovasculatures.

Induction of apoptosis of detached oral squamous cell carcinoma cells by safingol. Possible role of Bim, focal adhesion kinase and endonuclease G

The protein kinase C (PKC) inhibitor safingol increased rounding and detachment of human oral squamous cell carcinoma (SCC) cells in monolayer cultures. When dissociated cells were incubated in the presence of safingol, cell adhesion was prevented and cell viability was lost gradually, while most cells survived in the absence of safingol even if their attachment was blocked by coating the culture plates with polyhydroxyethyl methacrylate. Flow cytometric analysis and agarose gel electrophoresis of cellular DNA revealed an increase in the proportion of sub-G(1) cells and DNA fragmentation, indicating that safingol induced apoptosis of dissociated cells. During the induction of apoptosis in cell suspensions by safingol, there was an increase of the pro-apoptotic BH-3 only protein Bim and decrease of pro-survival Bcl-2 family proteins Bcl-xL and mitochondrial pro-apoptogenic factor endonuclease G translocated to the nucleus. The level of phosphorylated focal adhesion kinase (FAK) required for cell survival also rapidly decreased, followed by a decrease in the protein level. The introduction of siRNA against PKCalpha into SAS cells resulted in an increase of Bim, a decrease of Bcl-xL, the translocation of endonuclease G, and a decrease in the phosphorylation of FAK. These results suggest that Bim, Bcl-xL, FAK and endonuclease G are involved in safingol-induced apoptosis of detached oral SCC cells. Safingol can be used to induce apoptosis with cell detachment, anoikis, of oral SCC cells.

Transplantation of human neural stem cells protect against ischemia in a preventive mode via hypoxia-inducible factor-1alpha stabilization in the host brain

Hypoxia-inducible factor-1 (HIF-1) plays important roles in the prevention of cerebral ischemia. Deferoxamine (DFX), an iron chelator stabilizes the HIF-1alpha and activates target genes involved in compensation for ischemia. In this study, we are to investigate whether HIF-1alpha can be stabilized in human neural stem cells (NSCs) by DFX, and pre-transplantation of NSCs with HIF-1alpha stabilization can induce prolonged ischemic tolerance. In the DFX-treated NSCs, the HIF-1alpha protein expression was increased about 100-fold time-dependently, and subsequent transcriptional activation (VEGF, BDNF and CXCR4) was also observed. To test an ability to induce ischemic prevention in vivo, DFX-treated NSCs or naïve NSCs were transplanted in the striatum of adult rats. Seven days following the transplantation, focal cerebral ischemia was done. Infarct volumes were reduced in both NSCs-transplanted groups, compared with ischemia-only, but more reduced in DFX-treated NSCs group. The protective effects of NSCs were ablated when HIF-1alpha was silenced. HIF-1alpha protein levels were increased in both NSCs-transplanted groups, but more increased in DFX-treated NSCs group. RT-PCR analysis manifested a downregulation of mRNA expression of TNF-alpha, IL-6 and MMP-9 in both NSCs groups, but further decrease in DFX-treated NSCs group. These findings provide evidence that HIF-1alpha stabilization in human NSCs can be achieved effectively by DFX, and HIF-1alpha-stabilized NSCs protect against ischemia in a preventive mode.

Lipid phosphate phosphatase-1 regulates lysophosphatidic acid- and platelet-derived-growth-factor-induced cell migration

LPPs (lipid phosphate phosphatases) are members of a family of enzymes that catalyse the dephosphorylation of lipid phosphates. The only known form of regulation of this family of enzymes is via de novo expression of LPP isoforms in response to growth factors. In this respect, we evaluated the effect of moderate increases in the expression of recombinant LPP1 on signal transduction by both G-protein-coupled receptors and receptor tyrosine kinases. We present evidence for a novel role of LPP1 in reducing PDGF (platelet-derived growth factor)- and lysophosphatidic acid-induced migration of embryonic fibroblasts. We demonstrate that the overexpression of LPP1 inhibits cell migration by reducing the PDGF-induced activation of p42/p44 MAPK (mitogen-activated protein kinase). This appears to occur via a mechanism that involves the LPP1-induced down-regulation of typical PKC (protein kinase C) isoform(s), which are normally required for PDGF-induced activation of p42/p44 MAPK and migration. In this regard, DAG (diacylglycerol) levels are high and sustained in cells overexpressing LPP1, suggesting a dynamic interconversion of phosphatidic acid into DAG by LPP1. This may account for the effects of LPP1 on cell migration, as sustained DAG is known to down-regulate PKC isoforms in cells. Therefore the physiological changes in the expression levels of LPP1 might represent a heterologous desensitization mechanism for attenuating PKC-mediated signalling and regulation of cell migration.

Angiotensin II induces focal adhesion kinase/paxillin phosphorylation and cell migration in human umbilical vein endothelial cells

In the present study, we demonstrated that Ang II provokes a transitory enhancement of focal adhesion kinase (FAK) and paxillin phosphorylation in human umbilical endothelial cells (HUVEC). Moreover, Ang II induces a time- and dose-dependent augmentation in cell migration, but does not affect HUVEC proliferation. The effect of Ang II on FAK and paxillin phosphorylation was markedly attenuated in cells pretreated with wortmannin and LY294002, indicating that phosphoinositide 3-kinase (PI3K) plays an important role in regulating FAK activation. Similar results were observed when HUVEC were pretreated with genistein, a non-selective tyrosine kinases inhibitor, or with the specific inhibitor PP2 for Src family kinases, demonstrating the involvement of protein tyrosine kinases, and particularly Src family of tyrosine kinases, in the downstream signalling pathway of Ang II receptors. Furthermore, FAK and paxillin phosphorylation was markedly blocked after treatment of HUVEC with AG1478, a selective inhibitor of epidermal growth factor receptor (EGFR) phosphorylation. Pretreatment of cells with inhibitors of PI3K, Src family tyrosine kinases, and EGFR also decreased HUVEC migration. In conclusion, these results suggest that Ang II mediates an increase in FAK and paxillin phosphorylation and induces HUVEC migration through signal transduction pathways dependent on PI3K and Src tyrosine kinase activation and EGFR transactivation.

Gene regulation of a novel angiogenesis inhibitor, vasohibin, in endothelial cells

We recently reported that vasohibin is a negative feedback regulator of angiogenesis, and it is specifically expressed in endothelial cells. Here, we characterize the regulation of vasohibin expression. Two possible splicing variants were found, and the longer isoform was preferentially expressed. VEGF induced the expression of vasohibin, and this induction was abrogated by anti-VEGFR2 mAb but not by anti-VEGFR1 mAb. Pharmacological analysis revealed that the downstream targets of VEGFR2 were PKCs, especially PKCdelta. Actinomycin D did not alter the kinetics of vasohibin mRNA induction upon VEGF treatment, whereas cycloheximide completely abolished its induction. We tested the effect of various inflammatory cytokines on vasohibin expression. TNFalpha, IL1 and IFNgamma decreased VEGF-stimulated vasohibin expression. Actinomycin D did not alter the kinetics of vasohibin mRNA induction upon TNFalpha treatment. These results indicate that the expression of vasohibin in endothelial cells is regulated either positively or negatively by certain factors at the transcriptional level.

Basic Fibroblast Growth Factor Coating and Endothelial Cell Seeding of a Decellularized Heparin-coated Vascular Graft

The objective of this study was to determine the effect of basic fibroblast growth factor (bFGF) coating on endothelial cell seeding and proliferation on a decellularized heparin coated vascular graft and to determine the retention of seeded cells on the graft under flow conditions. Disks of heparin coated decellularized grafts were incubated for 24 h as controls or with bFGF. Human microvascular endothelial cells (HMECs) or canine peripheral blood endothelial progenitor cells (CEPC) were seeded onto the disks and incubated for 96 h or 48 h, respectively. HMECs were also seeded onto the luminal surfaces of two heparin-coated decellularized grafts for 3 h. One graft was placed in a perfusion culture system and cultured for an additional 6 h with flow and pressure. After culturing, there were 4.7 +/- 1.4 cells/mm(2) HMECs on control grafts and 11.4 +/- 1.4 cells/mm(2) in bFGF treated grafts (P < 0.05). Likewise, with CEPCs, there were 14.8 +/- 4.8 cells/mm(2) in control grafts and 33.3 +/- 7.3 cells/mm(2) in bFGF treated grafts. After only 3 h of cell attachment, 60% of HMECs were retained in the intact graft exposed flow relative to the static control graft, which is an acceptable level. These data demonstrate that bFGF coating on the heparin bound decellularized grafts significantly increases both HMEC and dog EPC proliferation and that seeded cells are stable under perfusion conditions.

Actin microdomains on endothelial cells: association with CD44, ERM proteins, and signaling molecules during quiescence and wound healing

During studies of the actin cytoskeleton in cultured endothelial cells we have observed that the luminal side of many cells contains F-actin microdomains that are rich in the hyaluronan receptor CD44 and in ezrin-radixin-moesin (ERM) proteins. A small subpopulation of the domains are also enriched in tyrosine phosphorylated proteins and signaling molecules. Confocal microscopy of rat aortic endothelial cells in situ demonstrated that similar microdomains occur in vivo. During healing of endothelial wounds, characteristic alterations of the actin cytoskeleton occurred. Thus, in many cells close to the wound, focal F-actin branching points appeared. The branching points were similar to the microdomains in that they colocalized with CD44 and ERM proteins, but, in addition, they formed centers for actin filament branching and were associated with phosphorylated protein kinase C alpha/betaII. These colocalization data are consonant with the view that activated PKC is responsible for activating ERM-mediated crosslinking between CD44 and the actin cytoskeleton. Importantly, inhibition of PKC activity decreased staining for phosphorylated ERM proteins, decreased the frequency of F-actin branching points, and inhibited monolayer wound healing. Together, our data show that endothelial cells contain a novel actin cytoskeletal structure, the F-actin microdomain, and suggest that during wound healing such structures become associated with activated signaling molecules and thereby enhance actin cytoskeletal remodeling.

Pharmacologically activated migration of aortic endothelial cells is mediated through p38 SAPK

Impairment in endothelial cell (EC) function plays a central role in vascular diseases (e.g. atherosclerosis, restenosis, diabetic angiopathies, microvascular angina, peripheral arterial disease). BRX-235 (a novel small molecule synthesized by Biorex, Hungary) has a potent vasculoprotective activity in different in vivo and in vitro studies. Since the importance of the p38 pathway in EC homeostasis and migration in particular is well documented, we have carried out studies to address the role of the p38 stress activated protein kinase (p38 SAPK) in the mode of action of BRX-235. In this study, Bovine aortic endothelial cells were used in a wounding migration assay (WMA) and for Western-blot analysis to study the effect and molecular mechanism of BRX-235-induced EC migration. The bovine aortic endothelial (BAE) cells were shown to be good models for EC migration. Both endothelial cell growth factor (ECGF)- and BRX-235-induced BAE cell migration were shown to be inhibited by SB 203580, a specific inhibitor of p38 SAPK. It was also shown that, BRX-235 induces phosphorylation of p38 SAPK without affecting p38 SAPK protein levels. Thus, BRX-235 acts upstream of p38 SAPK. In summary, we have shown that p38 SAPK is a potential pharmacological mediator for candidate drugs that target the endothelium.

Inhibition of protein kinase Calpha prevents endothelial cell migration and vascular tube formation in vitro and myocardial neovascularization in vivo

Although protein kinase C (PKC) activation is required for endothelial cell (EC) growth, migration, adhesion, and vessel formation, the role of individual PKC isoenzymes in these events is not defined. Because PKCalpha has been previously linked with enhanced EC migration and response to angiogenic growth factors, we characterized a specific phosphorothioate-modified 21-mer antisense PKCalpha (AS-PKCalpha). AS-PKCalpha (500 nmol/L) prevented the expression of PKCalpha protein by 90% in human ECs and did not reduce the expression of any other PKC isoenzyme. AS-PKCalpha reduced human EC migration by 64% compared with its control oligonucleotide in a "scratch" wounding assay, and AS-PKCalpha reduced human EC adhesion to the extracellular matrix protein vitronectin by 18%. Phosphorylation of mitogen-activated protein kinase (extracellular signal-regulated kinase 1/2) induced by vascular endothelial growth factor was inhibited by 30% in human ECs transfected with AS-PKCalpha. Compared with control, AS-PKCalpha also reduced the number of EC tubes formed in a 3D type I collagen gel assay by 37.5%. Finally, using an osmotic minipump, we infused AS-PKCalpha into mice in which myocardial infarction was induced by coronary ligation and found that the oligonucleotide was primarily taken up by intramyocardial blood vessels. Compared with the results with control oligonucleotide, AS-PKCalpha oligonucleotide inhibited the number of anti-PKCalpha-stained blood vessels by 48% and reduced the total vessel number by 72% as well. In conclusion, the expression of PKCalpha is required for full EC migration, adhesion to vitronectin, vascular endothelial growth factor-induced extracellular signal-regulated kinase activation, and tube formation and is likely to be of importance in myocardial angiogenesis in vivo after ischemia.

Update on pulmonary edema: the role and regulation of endothelial barrier function

Discovery of the pathophysiologic mechanisms leading to pulmonary edema and identification of effective strategies for prevention remain significant clinical concerns. Endothelial barrier function is a key component for maintenance of the integrity of the vascular boundary in the lung, particularly since the gas exchange surface area of the alveolar-capillary membrane is large. This review is focused on new insights in the pulmonary endothelial response to injury and recovery, reversible activation by edemagenic agents, and the biochemical/structural basis for regulation of endothelial barrier function. This information is discussed in the context of fundamental concepts of lung fluid balance and pulmonary function.

Involvement of the muscarinic acetylcholine receptor in inhibition of cell migration

Activation of G protein-coupled receptors is known to stimulate cell migration, but receptor-mediated signals inhibiting cell migration have not been identified. We investigated the ability of transfected human M(3) muscarinic acetylcholine receptors (mAChR) to regulate the migration of Chinese hamster ovary (CHO) cells. Single cells migrated on colloidal gold applied to fibronectin-coated plates, and videomicroscopy was used to measure cell spreading and migration. Activation of M(3) mAChR with the agonist carbachol was found to inhibit cell migration, whereas direct activation of protein kinase C (PKC) with PMA was found to stimulate migration. The amount of cell adhesion and spreading was found to be equivalent for carbachol- and PMA-treated cells. Selective inactivation of conventional PKC isoforms with Go6976 (C(24)H(18)N(4)O) abolished the PMA-mediated increase in cell migration. In contrast, the mAChR-mediated decrease in migration was not altered by Go6976, but was abolished when both novel and conventional PKC isoforms were inactivated by calphostin C or chelerythrine. These findings suggest involvement of conventional PKC isoforms in the stimulation of migration and of novel PKC isoforms in the inhibition of migration. Carbachol- but not PMA-treated cells exhibited an elongated morphology reminiscent of migrating cells that cannot detach their trailing edges from the substratum. Similarly, carbachol-treated cells detached less readily from fibronectin than control or PMA-treated cells when integrin activity was diminished by the chelation of Ca(2+) and Mg(2+). Finally, the carbachol-induced diminution of cell detachment was preserved after inhibition of the conventional PKC isoforms with Go6976, but was abrogated by treatment with either calphostin C or chelerythrine. These findings suggest that mAChR activation diminishes the ability of cells to detach from the substratum, resulting in diminished migration. This is in contrast to the direct activation of PKC with PMA, which stimulates migration.

High efficiency transient transfection of genes in human umbilical vein endothelial cells by electroporation

Endothelial cells derived from the human umbilical vein (HUVEC) are used to study the mechanisms involved in EC response to various stimuli as well as to investigate the basis of pathological conditions of the vascular system such as altered endothelium permeability, tumor-induced angiogenesis, atherosclerosis and leukocyte extravasation in chronic inflammatory responses. However, investigations of gene involvement related to these conditions have progressed slowly because of the difficulty of transfecting HUVEC with high efficiency. Whereas several technical approaches have been described, they usually result in low levels of transfected cells or they require several steps or sophisticated instrumentation. We describe here a straightforward protocol of transfection of freshly isolated HUVEC that is based on the simple technique of electroporation. Efficiencies of gene transfection greater than 40% were routinely obtained by using a combination of optimized conditions of HUVEC isolation, composition of the electroporation medium and homogeneity of the plasmids. The protocol has been applied to the functional transient transfection of functional genes in HUVEC as illustrated in the case of the cDNA encoding GFP, protein kinase C (alpha and epsilon isotypes) and beta-galactosidase.

Anti-angiogenic activities of gliotoxin and its methylthioderivative, fungal metabolites

In the search for new naturally occurring angiogenic inhibitor, we found that culture broths from two unidentified fungal strains exerted potent inhibitory activities on capillary-like tube formation of human umbilical vein endothelial cells (HUVEC) in vitro. Two active compounds were isolated by bioassay-guided separation and their structures were identified as gliotoxin (1) and its derivative methylthiogliotoxin (2) by spectroscopic analyses. These compounds significantly inhibited the migration of HUVEC assessed by in vitro wounding migration assay and exhibited at least 10 times more potent inhibition of proliferation of HUVECs as compared with that of cancer cell lines such as HeLa, MCF-7, and KB 3-1 cells. Especially, gliotoxin having disulfide group exerted more potent activities than methylthiogliotoxin, suggesting that gliotoxin could be a useful compound for further study as an anti-angiogenic agent.

Differential effects of protein kinase C on human vascular smooth muscle cell proliferation and migration

Vascular smooth muscle cell (SMC) migration and proliferation contribute to intimal hyperplasia, and protein kinase C (PKC) may be required for both events. In this report, we investigated the role of PKC in proliferation and migration of SMC derived from the human saphenous vein. Activation of PKC by phorbol-12,13-dibutyrate (PDBu) or (-)-indolactam [(-)-ILV] increases SMC proliferation. Downregulation of PKC activity by prolonged incubation with phorbol ester or inhibition of PKC with chelerythrine in SMC diminished agonist-stimulated proliferation. In contrast, stimulation of PKC with PDBu or (-)-ILV inhibited basal and agonist-induced SMC chemotaxis. Moreover, downregulation of PKC or inhibition with chelerythrine accentuated migration. We postulated that the inhibitory effect of PKC on SMC chemotaxis was mediated through cAMP-dependent protein kinase (protein kinase A, PKA). In support of this hypothesis, we found that activation of PKC in SMC stimulated PKA activity. The cAMP agonist forskolin significantly inhibited SMC chemotaxis. Furthermore, the inhibitory effect of PKC on SMC chemotaxis was completely reversed by cAMP or PKA inhibitors. In search of the PKC isotype(s) underlying these differential effects of PKC in SMC, we identified eight isotypes expressed in human SMC. Only PKC-alpha, -beta I, -delta, and -epsilon were eliminated by downregulation, suggesting that one or more of these four enzymes facilitate the observed phorbol ester-dependent effects of PKC in SMC. In summary, we found that PKC activation enhances proliferation but inhibits migration of human vascular SMC. These differential effect of PKC on vascular cells appears to be mediated through PKC-alpha, -beta I, -delta, and/or -epsilon.

Associations of PKC isoforms with the cytoskeleton of B16F10 melanoma cells

Although PKC plays a major role in regulating the morphology and function of the cytoskeleton, little is known about in situ associations of specific isoforms with the cytoskeleton. We demonstrate that seven PKC isoforms are expressed in B16F10 melanoma cells and show different levels of induction by serum. Using cell cytoskeleton preparations (CSKs), confocal microscopy, and immunocytochemistry, all isoforms show specific patterns of localization to focal contact-like structures (alpha, delta), very small cytoplasmic granules/vesicles (all isoforms), dense ordered arrays of small granules in the perinuclear region (alpha, delta), granules/vesicles associated with a homogeneous framework in the cytoplasm adjacent to the nucleus (gamma), or irregular-shaped patches of granules at or near the nuclear perimeter (eta, theta). In addition, several isoforms are present as cytoplasmic granules/ vesicles in linear or curvilinear arrays (alpha, delta, epsilon, theta). When isoform localization is examined using 3.7% formaldehyde or methanol:acetone, the patterns of localization in CSKs are often difficult or impossible to detect, and many are described here for the first time. Double-labeling experiments with CSK demonstrate that PKC actin co-localizes with punctate alpha-rich particles above the nucleus, granules of epsilon throughout the cytoplasm, and with theta in irregular-shaped aggregates associated with the nucleus. Vimentin co-localizes with perinuclear granules of delta and beta(2), and alpha-tubulin co-localizes with theta in structures at or near the nuclear surface and in microtubules associated with the microtubule organizing center (MTOC). In summary, the present study demonstrates that seven PKC isoforms are endogenously expressed in B16F10 melanoma cells. These isoforms show various levels of induction by serum and specific patterns of association with various components of the detergent-resistant cell cytoskeleton.

Regulation of adenosine transport by D-glucose in human fetal endothelial cells: involvement of nitric oxide, protein kinase C and mitogen-activated protein kinase

The effects of elevated D-glucose on adenosine transport were investigated in human cultured umbilical vein endothelial cells isolated from normal pregnancies. Elevated D-glucose resulted in a time- (8-12 h) and concentration-dependent (half-maximal at 10+/-2 mM) inhibition of adenosine transport, which was associated with a reduction in the Vmax for nitrobenzylthioinosine (NBMPR)-sensitive (es) saturable nucleoside with no significant change in Km. d-Fructose (25 mM), 2-deoxy-D-glucose (25 mM) or D-mannitol (20 mM) had no effect on adenosine transport. Adenosine transport was inhibited following incubation of cells with the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA; 100 nM, 30 min to 24 h). D-Glucose-induced inhibition of transport was abolished by calphostin C (100 nM, an inhibitor of PKC), and was not further reduced by PMA. Increased PKC activity in the membrane (particulate) fraction of endothelial cells exposed to D-glucose or PMA was blocked by calphostin C but was unaffected by NG-nitro-L-arginine methyl ester (L-NAME; 100 microM, an inhibitor of nitric oxide synthase (NOS)) or PD-98059 (10 microM, an inhibitor of mitogen-activated protein kinase kinase 1). D-Glucose and PMA increased endothelial NOS (eNOS) activity, which was prevented by calphostin C or omission of extracellular Ca2+ and unaffected by PD-98059. Adenosine transport was inhibited by S-nitroso-N-acetyl-l, d-penicillamine (SNAP; 100 microM, an NO donor) but was increased in cells incubated with L-NAME. The effect of SNAP on adenosine transport was abolished by PD-98059. Phosphorylation of mitogen-activated protein kinases p44mapk (ERK1) and p42mapk (ERK2) was increased in endothelial cells exposed to elevated D-glucose (25 mM for 30 min to 24 h) and the NO donor SNAP (100 microM, 30 min). The effect of D-glucose was blocked by PD-98059 or L-NAME, which also prevented the inhibition of adenosine transport mediated by elevated D-glucose. Our findings provide evidence that D-glucose inhibits adenosine transport in human fetal endothelial cells by a mechanism that involves activation of PKC, leading to increased NO levels and p42-p44mapk phosphorylation. Thus, the biological actions of adenosine appear to be altered under conditions of sustained hyperglycaemia.

Omega-3 fatty acids enhance ligament fibroblast collagen formation in association with changes in interleukin-6 production

Altering dietary ratios of n-3 and n-6 polyunsaturated fatty acids (PUFA) represents an effective nonpharmaceutical means to improve systemic inflammatory conditions. An effect of PUFA on cartilage and bone formation has been demonstrated, and the purpose of this study was to determine the potential of PUFA modulation to improve ligament healing. The effects of n-3 and n-6 PUFA on the in vitro healing response of medial collateral ligament (MCL) fibroblasts were investigated by studying the cellular coverage of an in vitro wound and the production of collagen, PGE2, IL-1, IL-6, and TNF. Cells were exposed to a bovine serum albumin (BSA) control or either eicosapentaenoic acid (EPA, 20:5n-3) or arachidonic acid (AA, 20:4n-6) in the form of soaps loaded onto BSA for 4 days and wounded on Day 5. AA and EPA improved the healing of an in vitro wound over 72 hr. EPA increased collagen synthesis and the overall percentage of collagen produced, but AA reduced collagen production and total protein. PGE2 production was increased in the AA-treated group and decreased in the EPA-treated group, but was not affected by wounding. IL-1 was not produced at the time point evaluated, but TNF and IL-6 were both produced, and their levels varied relative to the PUFA or wounding treatment. There was a significant linear correlation (r2 = 0.57, P = 0.0045) between IL-6 level and collagen production. These results demonstrate that n-3 PUFA (represented by EPA in this study) positively affect the healing characteristics of MCL cells and therefore may represent a possible noninvasive treatment to improve ligament healing. Additionally, these results show that MCL fibroblasts produce PGE2, IL-6, and TNF and that IL-6 production is related to MCL collagen synthesis.

Protein kinase C mediates basic fibroblast growth factor-induced proliferation through mitogen-activated protein kinase in coronary smooth muscle cells

Proliferation of coronary smooth muscle cells (cSMCs) contributes to the pathogenesis of arteriosclerosis and restenosis after angioplasty, and basic fibroblast growth factor (bFGF) is a powerful mitogen for cSMCs. In this study, we investigated the involvement of mitogen-activated protein kinase (MAPK), protein kinase C (PKC), and the transcription factor c-myc in bFGF-stimulated mitogenesis, as well as the functional relationship between these factors. cSMC stimulation with bFGF resulted in phosphorylation of p42 MAPK, as well as the phosphorylation and increased expression of c-myc. The MAPK kinase (MEK) inhibitor PD98059 blocked bFGF-stimulated MAPK phosphorylation and resulted in both a decrease of c-myc expression and inhibition of bFGF-stimulated DNA synthesis in cSMCs. bFGF also increased PKC activity in cSMCs in a time-dependent manner. The inhibition of PKC by chelerythrine or its downregulation by phorbol 12-myristate 13-acetate (PMA) inhibited bFGF-induced DNA synthesis and blocked the phosphorylation of MAPK and c-myc expression in response to bFGF. This indicates an involvement of phorbol ester-sensitive PKC isoforms in MAPK activation and mitogenic signaling by bFGF. Western blot analysis revealed the presence of the phorbol ester-sensitive isoforms PKC alpha, epsilon, and gamma as well as the PKC isoforms iota, lambda, micro, and zeta in cSMCs. In this study, we show that the MAPK cascade is required for bFGF-induced proliferation and that phorbol ester-sensitive PKC isoforms contribute to the bFGF-induced cSMC mitogenesis in cSMCs.

SPARC inhibits endothelial cell adhesion but not proliferation through a tyrosine phosphorylation-dependent pathway

SPARC, a counteradhesive matricellular protein, inhibits endothelial cell adhesion and proliferation, but the pathways through which these activities are blocked are not known. In this study, we used inhibitors of major signaling proteins to identify mediators through which SPARC exerts its counteradhesive and antiproliferative functions. Pretreatments with the general protein tyrosine kinase (PTK) inhibitors, herbimycin A and genistein, protected against the inhibitory effect of SPARC on bovine aortic endothelial (BAE) cell spreading by more than 60%. Similar pretreatments with PTK inhibitors significantly blocked the diminishment of focal adhesions by SPARC in confluent BAE cell monolayers, as determined by the formation of actin stress-fibers and the distribution of vinculin in focal adhesion plaques. Inhibition of endothelial cell cycle progression by SPARC and a calcium-binding SPARC peptide, however, was not affected by PTK inhibitors. Inhibition of DNA synthesis by SPARC was not reversed by inhibitors of the activity of protein kinase C (PKC), or of cAMP-dependent protein kinase (PKA), but was sensitive to pertussis (and to a lesser extent, cholera) toxin. The counteradhesive effect of SPARC on endothelial cells is, therefore, mediated through a tyrosine phosphorylation-dependent pathway, whereas its antiproliferative function is dependent, in part, on signal transduction via a G protein-coupled receptor.

Induction of in vitro angiogenesis in the endothelial-derived cell line, EA hy926, by ethanol is mediated through PKC and MAPK

We have previously shown that ethanol-induced injury to the gastric mucosa triggers increased expression of the angiogenic factors, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) and angiogenesis. To further investigate ethanol-induced angiogenesis, we used an in vitro angiogenesis model which employs the ability of an endothelial-derived cell line (EA hy926) to form tubelike structures resembling capillaries when plated on the matrix material, Matrigel. We report that serum-starved EA hy926 cells, incubated for as little as 5 minutes with ethanol concentrations of 1.0-2.5%, formed tubelike structures reflecting in vitro angiogenesis. Control cells, not incubated with ethanol, did not form tubelike structures. Incubation for 5 minutes with 2.5% ethanol resulted in increased activities of PKC and MAP kinase (ERK2) by 1.6-fold (p < 0.05) and 2.3-fold (P < 0.001), respectively. Furthermore, inhibitors of the MAPK kinase, MEK (PD98059) and PKC (GF 109203X) prevented the induction of in vitro angiogenesis by ethanol.

New perspectives on PKCtheta, a member of the novel subfamily of protein kinase C

Members of the protein kinase C (PKC) family of serine/threonine protein kinases have been implicated in numerous cellular responses in a large variety of cell types. Expression patterns of individual members and differences in their cofactor requirements and potential substrate specificity suggest that each isoenzyme may be involved in specific regulatory processes. The PKCtheta isoenzyme exhibits a relatively restricted expression pattern with high protein levels found predominantly in hematopoietic cells and skeletal muscle. PKCtheta was found to be expressed in T, but not B lymphocytes, and to colocalize with the T-cell antigen receptor (TCR) at the site of contact between the antigen-responding T cell and the antigen-presenting cell (APC). Colocalization of PKCtheta with the TCR was selective for this isoenzyme and occurred only upon antigen-mediated responses leading to T-cell activation and proliferation. PKCtheta was found to be involved in the regulation of transcriptional activation of early-activation genes, predominantly AP-1, and its cellular distribution and activation were found to be regulated by the 14-3-3 protein. Other findings indicated that PKCtheta can associate with the HIV negative factor (Nef) protein, suggesting that altered regulation of PKCtheta by Nef may contribute to the T-cell impairments that are characteristic of infection by HIV. PKCtheta is expressed at relatively high levels in skeletal muscle, where it is suggested to play a role in signal transduction in both the developing and mature neuromuscular junction. In addition, PKCtheta appears to be involved in the insulin-mediated response of intact skeletal muscle, as well as in experimentally induced insulin resistance of skeletal muscle. Further studies suggest that PKCtheta is expressed in endothelial cells and is involved in multiple processes essential for angiogenesis and wound healing, including the regulation of cell cycle progression, formation and maintenance of actin cytoskeleton, and formation of capillary tubes. Here, we review recent progress in the study of PKCtheta and discuss its potential role in various cellular responses.

Human melanoma metastasis is inhibited following ex vivo treatment with an antisense oligonucleotide to protein kinase C-alpha

To determine whether alteration of PKC alpha expression would affect the metastatic potential of human melanoma cells, replicate cultures of C8161 cells were treated in vitro with a phosphorothioate antisense oligodeoxynucleotide (ODN) that specifically inhibits PKC alpha expression (ISIS-3521). Control C8161 cultures were treated with a scrambled sequence ODN, cationic liposomes or were left untreated. Northern blots demonstrated 70% inhibition of PKC alpha mRNA in ISIS-3521-treated cells compared to controls. Metastasis was suppressed by 75% when ISIS-3521-treated cells were injected intravenously into athymic mice. These results show that PKC alpha expression is important in the regulation of human melanoma metastasis.

A peptide fraction from factor VIII reduces PKC activity in cultured endothelial cells

A peptide fraction of low molecular weight (Vueffe) prepared from bovine Factor VIII by enzymatic hydrolysis with trypsin, reduces significantly (p<0.05) membrane bound protein kinase C (PKC) activity in cultured bovine pulmonary artery endothelial cells grown with enhanced glucose levels (22.2 mM) or stimulated by phorbol 12-myristate 13-acetate (PMA). The activation of PKC is a common pathway by which mediators increase transendothelial permeability during tissue inflammation and in the development of diabetic vascular complications. Our results suggest that the antihaemorrhagic properties of Vueffe could be related to a decrease in endothelial permeability mediated by PKC.