Protein kinase C in transmembrane signalling

Crosstalk between PKC and MAPK pathway activation in cardiac fibroblasts in a rat model of atrial fibrillation

OBJECTIVE

Atrial fibrillation (AF) is the most frequent form of cardiac arrhythmia and major cause of cardiac ischemia. Defective calcium homeostasis due to anomalous expression of ryanodine receptor type 2 (RyR2) or its hyperactivation by phosphorylation by serine threonine kinases has been implicated as a central mechanism of AF pathogenesis. Given the role of protein kinase C (PKC) isoforms in cardiac function we investigated role of PKC in AF using a rat model.

RESULTS

PMA induced global increase in protein synthesis in cardiac fibroblasts isolated from AF rats, but not healthy controls, and the increase was inhibited by PKC inhibition. PMA mediated activation of both PKC and ERK and either inhibition of PKC by Go6983 or ERK by the MEK inhibitor Trametinib attenuated both P-ERK and P-PKC in both cardiac fibroblasts isolated from AF rats or from healthy rats but transduced with PKC-delta. The PKC and ERK mediated induction of global protein synthesis was found to be mediated by increased phosphorylation of the ribosomal protein S6.

CONCLUSION

Our findings provide a foundation for future testing of PKC and MEK inhibitors to treat AF in pre-clinical models. It also needs to be determined if PKC and MAPK pathway activation is functioning via RyR2 or some yet undefined substrates.

Protein kinase C and cardiac dysfunction: a review

Heart failure (HF) is a physiological state in which cardiac output is insufficient to meet the needs of the body. It is a clinical syndrome characterized by impaired ability of the left ventricle to either fill or eject blood efficiently. HF is a disease of multiple aetiologies leading to progressive cardiac dysfunction and it is the leading cause of deaths in both developed and developing countries. HF is responsible for about 73,000 deaths in the UK each year. In the USA, HF affects 5.8 million people and 550,000 new cases are diagnosed annually. Cardiac remodelling (CD), which plays an important role in pathogenesis of HF, is viewed as stress response to an index event such as myocardial ischaemia or imposition of mechanical load leading to a series of structural and functional changes in the viable myocardium. Protein kinase C (PKC) isozymes are a family of serine/threonine kinases. PKC is a central enzyme in the regulation of growth, hypertrophy, and mediators of signal transduction pathways. In response to circulating hormones, activation of PKC triggers a multitude of intracellular events influencing multiple physiological processes in the heart, including heart rate, contraction, and relaxation. Recent research implicates PKC activation in the pathophysiology of a number of cardiovascular disease states. Few reports are available that examine PKC in normal and diseased human hearts. This review describes the structure, functions, and distribution of PKCs in the healthy and diseased heart with emphasis on the human heart and, also importantly, their regulation in heart failure.

Role of Protein Kinase-C in Thymocyte Apoptosis Induced by Irradiation

The role of protein kinase C in radiation-induced death of thymocytes was studied. For this purpose murine thymocytes were irradiated and incubated for 6 h at 37 degrees C and afterwards the fraction of fragmented DNA was measured. Results indicate that radiation-induced DNA fragmentation can be prevented by adding the protein kinase C inhibitor H-7 or staurosporine to the thymocytes during incubation time. Incubation of irradiated cells with HA-1004, an inhibitor of cAMP-dependent protein kinase, with a minor effect on protein kinase C did not affect the DNA fragmentation induced by irradiation. Incubation of cells with phorboldibutyrate gave a dose-dependent induction of DNA fragmentation. This effect can be inhibited by staurosporine. These results suggest that radiation-induced DNA fragmentation is an active cellular process in which protein kinase C plays an important role.

Resveratrol attenuates adenosine diphosphate-induced platelet activation by reducing protein kinase C activity

Inappropriate platelet activation is the key point of thrombogenesis. The aim of the present study was to investigate the effects of resveratrol (RESV), a compound extracted from the Chinese medicinal herb Polygonum cuspidatum sieb et Zucc, on the platelet activation induced by adenosine diphosphate (ADP) and its possible mechanism. The percentage of platelet aggregation and surface P-selectin-positive platelets, and the activity of protein kinase C (PKC) of platelet were observed with platelet aggregometer, flow cytometry and phosphorimaging system, respectively. RESV at 25, 50 and 100 microM showed anti-platelet aggregation and inhibition of surface P-selectin-positive platelets in a concentration-dependent manner. RESV (50 microM) inhibited the activity of PKC in the membrane fraction of platelets and decreased the percentage of membrane associated PKC activity in total PKC activity. Moreover, DL-erythro-1,3-Dihydroxy-2-aminooctadecane, an elective protein kinase C inhibitor (PKCI), and RESV had additive effects of inhibiting the percentage of platelet aggregation and surface P-selectin-positive platelets. It is suggested that RESV may inhibit platelet aggregation, the percentage of surface P-selectin-positive platelets and subsequent thrombus formation. The mechanisms may be partly relative to the decrease of the activity of PKC of platelets.

Total synthesis of (-)-balanol, all stereoisomers, their N-tosyl analogues, and fully protected ophiocordin: an easy route to hexahydroazepine cores from garner aldehydes

Total syntheses of (-)-balanol and all of its stereoisomers starting from easily available Garner aldehydes are described. Diastereoselective Grignard reactions on Garner aldehydes and ring-closing metatheses are the key steps for the construction of hexahydroazepine subunits. The benzophenone subunits were constructed through coupling of suitably functionalized aromatic aldehyde and bromo components. The synthetic route constitutes a convenient and scalable reaction sequence to generate all of the stereoisomers of balanol. The methodology is explored further for the synthesis of N-tosyl analogues of balanol and of fully protected ophiocordin.

Protein kinase C in the human heart: differential regulation of the isoforms in aortic stenosis or dilated cardiomyopathy

OBJECTIVES

Protein kinase C (PKC) is a central enzyme in the regulation of growth and hypertrophy. Little was known on PKC isoform regulation in human heart. Goal of this study was to characterize the isoforms of protein kinase C in human heart, their changes during ontogenesis, and their regulation in myocardial hypertrophy and heart failure.

METHODS

In left ventricular and atrial samples from adults with end-stage dilated cardiomyopathy (DCM), from adults with severe aortic stenosis (AS), from small infants undergoing repair of ventricular septal defects, and from healthy organ donors (CO), activity of protein kinase C and the expression of its isozymes were examined.

RESULTS

In the adult human heart, the isoforms PKC-alpha, PCK-beta, PKC-delta, PKC-epsilon, PKC-lambda/-iota, and PKC-zeta were detected both on protein and on mRNA level. All isozymes are subjected to downregulation during ontogenesis. No evidence, however, exists for an isoform shift from infancy to adulthood. DCM leads to a pronounced upregulation of PKC-beta. Severe left ventricular hypertrophy in AS, however, recruits a distinct isoform pattern, i.e., isoforms PKC-alpha, PKC-delta, PKC-epsilon, PKC-lambda/-iota, and PKC-zeta are upregulated, whereas PKC-beta is not changed under this condition.

CONCLUSION

This work gives evidence for a differential recruitment of human PKC isoforms in various forms of myocardial hypertrophy and heart failure.

Polyamines inhibit both platelet aggregation and glycoprotein IIb/IIIa activation

Platelet aggregation is inhibited by the polyamines putrescine, spermidine, and spermine. To date, the mechanism of action has not been clearly identified. Evidence suggests that polyamines may interact with the fibrinogen receptor (GP IIb/IIIa), interfering with platelet-platelet attachment. The effect of polyamines on human platelet aggregation and GP IIb/IIIa activation was evaluated. For the aggregation experiments, platelets were obtained from heparin- or citrate-collected blood. Our results indicate that the polyamines putrescine, spermidine, and spermine cause a dose-dependent inhibition of ADP- or collagen-mediated platelet aggregation with an order of potency spermine>spermidine>putrescine. In addition, spermine arrests or inhibits thrombin-, epinephrine-, arachidonate-, or ristocetin-induced platelet aggregation. Expression of platelet membrane glycoproteins IIb, IIIa, and IX is not reduced by polyamines. However, spermine inhibits the ADP- or thrombin-induced activation of GP IIb/IIIa. It is concluded that the final step in aggregation, common to all agonists, ie, fibrinogen binding to GP IIb/IIIa, is inhibited by spermine through inhibition of the agonist-induced activation of GP IIb/IIIa that precedes fibrinogen-ligand binding.

In vivo metabolism of [14C]ruboxistaurin in dogs, mice, and rats following oral administration and the structure determination of its metabolites by liquid chromatography/mass spectrometry and NMR spectroscopy

Ruboxistaurin (LY333531), a potent and isoform-selective protein kinase C beta inhibitor, is currently undergoing clinical trials as a therapeutic agent for the treatment of diabetic microvascular complications. The present study describes the disposition and metabolism of [14C]ruboxistaurin following administration of an oral dose to dogs, mice, and rats. The study revealed that ruboxistaurin was highly metabolized in all species. Furthermore, the results from the bile duct-cannulated study revealed that ruboxistaurin was well absorbed in rats. The primary route of excretion of ruboxistaurin and its metabolites was through feces in all species. The major metabolite detected consistently in all matrices for all species was the N-desmethyl metabolite 1, with the exception of rat bile, in which hydroxy N-desmethyl metabolite 5 was detected as the major metabolite. Other significant metabolites detected in dog plasma were 2, 3, 5, and 6 and in mouse plasma 2, 5, and 19. The structures of the metabolites were proposed by tandem mass spectrometry with the exception of 1, 2, 3, 5, and 6, which were additionally confirmed either by direct comparison with authentic standards or by nuclear magnetic resonance spectroscopy. To assist identification by nuclear magnetic resonance spectroscopy, metabolites 3 and 5 were produced via biotransformation using recombinant human CYP2D6 and, likewise, metabolite 6 and compound 4 (regioisomer of 3 which did not correlate to metabolites found in vivo) were produced using a microbe, Mortierella zonata. The unambiguous identification of metabolites enabled the proposal of clear metabolic pathways of ruboxistaurin in dogs, mice, and rats.

Activation of human T lymphocytes under conditions similar to those that occur during exposure to microgravity: A proteomics study

A number of experiments, conducted under microgravity conditions, i.e. in space shuttle biolaboratories or in ground based systems simulating the conditions occurring in microgravity, show that in hypogravity, in vitro human lymphocyte activation is severely impaired. However, very early stimulation steps of T lymphocytes are not compromised, since CD69 receptor, the earliest membrane activation marker, is expressed by T cells at a level comparable to that observed on 1 g activated lymphocytes. Since CD69 engagement, together with submitogenic doses of phorbol esters, transduces an activation signal to T lymphocytes, we undertook a comparative study on the stimulation mediated through this receptor on human CD3+ cells cultured under conditions similar to those which occur during exposure to microgravity, i.e. in clinorotation, or at 1 g. During the early hours of activation, increased levels of intracellular calcium and increased mitochondrial membrane potential were detectable in clinorotating as well as in 1 g cells. However, after 48 hours clinorotation, interleukin 2 production by T lymphocytes was significantly reduced and cell proliferation was greatly decreased. By means of a differential proteomics approach on T cells activated in clinorotation or at 1 g for 48 hours, we were able to detect statistically significant quantitative protein alterations. Seven proteins with modified expression values were identified; they are involved in nucleic acids processing, proteasome regulation and cytoskeleton structure.

Control of aldosterone secretion: a model for convergence in cellular signaling pathways

Aldosterone secretion by glomerulosa cells is stimulated by angiotensin II (ANG II), extracellular K(+), corticotrophin, and several paracrine factors. Electrophysiological, fluorimetric, and molecular biological techniques have significantly clarified the molecular action of these stimuli. The steroidogenic effect of corticotrophin is mediated by adenylyl cyclase, whereas potassium activates voltage-operated Ca(2+) channels. ANG II, bound to AT(1) receptors, acts through the inositol 1,4,5-trisphosphate (IP(3))-Ca(2+)/calmodulin system. All three types of IP(3) receptors are coexpressed, rendering a complex control of Ca(2+) release possible. Ca(2+) release is followed by both capacitative and voltage-activated Ca(2+) influx. ANG II inhibits the background K(+) channel TASK and Na(+)-K(+)-ATPase, and the ensuing depolarization activates T-type (Ca(v)3.2) Ca(2+) channels. Activation of protein kinase C by diacylglycerol (DAG) inhibits aldosterone production, whereas the arachidonate released from DAG in ANG II-stimulated cells is converted by lipoxygenase to 12-hydroxyeicosatetraenoic acid, which may also induce Ca(2+) signaling. Feedback effects and cross-talk of signal-transducing pathways sensitize glomerulosa cells to low-intensity stimuli, such as physiological elevations of [K(+)] (< or =1 mM), ANG II, and ACTH. Ca(2+) signaling is also modified by cell swelling, as well as receptor desensitization, resensitization, and downregulation. Long-term regulation of glomerulosa cells involves cell growth and proliferation and induction of steroidogenic enzymes. Ca(2+), receptor, and nonreceptor tyrosine kinases and mitogen-activated kinases participate in these processes. Ca(2+)- and cAMP-dependent phosphorylation induce the transfer of the steroid precursor cholesterol from the cytoplasm to the inner mitochondrial membrane. Ca(2+) signaling, transferred into the mitochondria, stimulates the reduction of pyridine nucleotides.

Enantioselective Total Syntheses of Several Bioactive Natural Products Based on the Development of Practical Asymmetric Catalysis

I present herewith enantioselective total syntheses of several bioactive natural products, such as (-)-strychnine, (+)-decursin, (-)-cryptocaryolone diacetate, (-)-fluoxetine, and aeruginosin 298-A, based on practical asymmetric catalyses (Michael reaction, epoxidation, and phase-transfer reaction) that I developed with co-workers in Prof. Shibasaki's group over the past 5 years. In the first part of this review, I discuss the great improvement of catalyst efficiency in an ALB-catalyzed asymmetric Michael reaction of malonate and application to the pre-manufacturing scale (greater than kilogram scale) and enantioselective total synthesis of (-)-strychnine with the development of novel domino cyclization. To broaden the substrate generality of the Michael reaction, we developed a highly stable, storable, and reusable La-O-linked-BINOL complex. Further extension of the reaction using beta-keto ester as a Michael donor was achieved with the development of a La-NR-linked-BINOL complex, thereby improving indole alkaloid syntheses. In the second section, I discuss enantioselective total synthesis of (+)-decursin using catalytic asymmetric epoxidation. To achieve the synthesis, we developed a new La-BINOL-Ph(3)As = O (1:1:1) complex catalyst system, which has much higher reactivity and broader substrate generality than the previously developed catalyst systems. This allowed us to achieve catalytic asymmetric epoxidation of alpha,beta-unsaturated carboxylic acid derivatives with high enantioselectivity and broad substrate generality for the first time by changing the lanthanide metal and reaction conditions. Among them, catalytic asymmetric epoxidation of alpha,beta-unsaturated morpholinyl amides is quite useful in terms of synthetic utility of the corresponding alpha,beta-epoxy morpholinyl amides. Highly catalyst-controlled enantio- or diastereoselective epoxidation of the alpha,beta-unsaturated morpholinyl amides, coupled with diastereoselective reduction of beta-hydroxy ketones, enabled the synthesis of all possible stereoisomers of 1,3-polyol arrays with successful enantioselective total synthesis of several 1,3-polyol natural products, such as (-)-cryptocaryolone diacetate. In addition, the development of a new regioselective epoxide-opening reaction of alpha,beta-epoxy amides to the corresponding alpha- and beta-hydroxy amides enhanced the usefulness of the present epoxidation and was applied to the enantioselective total synthesis of (-)-fluoxetine. In the final section, I report the development of a new asymmetric two-center organocatalyst (TaDiAS) and its application to the enantioselective synthesis of aeruginosin 298-A and its analogues. Because of the remarkable structural diversity of TaDiAS, a practical asymmetric phase-transfer reaction with broad substrate generality was achieved. As a result, we succeeded in developing a highly versatile synthetic method for aeruginosin 298-A and its analogues. Inhibitory activity studies of the compounds against the serine protease trypsin provided preliminary information about their structure-activity relations.

Inhibition of arterial thrombosis by polyamines in a canine coronary artery injury model

Polyamines are polycations present in all living organisms and have been shown to play an important role in various physiological functions. Previous studies have shown that various amines including polyamines inhibit platelet activation. Among the amines tested tetra-amine, spermine is the potent inhibitor of platelet aggregation. In spite of vast literature on the anti-aggregatory effect of amines, there are no definitive studies testing their efficacy in an in vivo thrombosis model. In the present study, we investigated if polyamines could inhibit in-vivo thrombosis. A partially occlusive thrombus was generated by application of electric current in canine coronary artery. In control animals, the artery was completely in 76+/-14 min after the current was discontinued. When 40 mg/kg (1.44 mM) spermine was given immediately after stopping the current blood flow remained patent for >240 min. At equimolar concentration, triamine, spermidine and diamine putrescine are also equally effective in preventing thrombus development. The anti thrombic effect of polyamines was not associated with increased bleeding tendency, as judged by the amount of blood adsorbed by a gauge pad placed in a surgical incision extending to the muscle tissue and by a standard template bleeding. These results indicate that apart from inhibiting in-vitro platelet aggregation polyamines can also inhibit in-vivo thrombus formation.

Phorbol ester-induced migration of HepG2 cells is accompanied by intensive stress fibre formation, enhanced integrin expression and transient down-regulation of p21-activated kinase 1

Previously, we observed that phorbol ester induced more intensive scattering of HepG2 human hepatoma cells than hepatocyte growth factor (HGF). Regulatory components accounting for this intensive migration were studied. Phorbol ester-activated protein kinase C induced the early appearance of a great number of actin stress fibres. Whereas in response to HGF, the activation of phosphatidylinositol 3-kinase initiates the rearrangements of the actin cytoskeleton, in phorbol ester-treated cells, the activation of this enzyme was not required to the actin polymerisation. Activation of Erk1/Erk2 MAP kinases that was essential to the migration had a key role in enhancing the adherence of cells to the extracellular matrix via the increased expression of integrins alpha2, alpha6 and beta1. Protein kinase C stimulated the activation of p21-activated kinase (PAK), as well. However, it also stimulated the selective and transient down-regulation of PAK1, which coincided with the formation of stress fibres.

Effect of polyamines on in vitro platelet aggregation and in vivo thrombus formation

INTRODUCTION

Polyamines are polycations present in all living organisms and have been shown to play an important role in various physiological functions. Previous studies have shown that various amines including polyamines inhibited platelet activation, but there were no definitive studies testing their efficacy in an in vivo thrombosis model. We carried out detailed in vitro platelet aggregation studies using various concentrations of polyamines as well as agonists.

METHODS

Platelet aggregation was measured by a turbidimetric method. Electric current induced in vivo thrombosis model is used for assessing antithrombotic effect. Incidence of bleeding was evaluated by template bleeding and incisional bleeding.

RESULTS

Polyamines inhibited agonist-induced platelet aggregation in a dose-dependent manner. The inhibitory effect of polyamines is inversely proportional to the concentration of the agonist used. Among the polyamines, spermine is the potent inhibitor of platelet aggregation. A partially occlusive thrombus was generated by application of electric current in canine coronary artery. In control animals, the artery was completely occluded in 70 +/- 11 min after the current was discontinued. Blood flow remained patent for >240 min when 2 mg/kg spermine was given immediately after stopping the current. The antithrombotic effect of spermine was not associated with increased bleeding tendency.

CONCLUSION

These results indicate that apart from inhibiting in vitro platelet aggregation polyamines can also inhibit in vivo thrombus formation. To our knowledge, this is the first study demonstrating this phenomenon.

Synthesis and protein kinase inhibitory activity of balanol analogues with modified benzophenone subunits

A series of analogues of the protein kinase C (PKC) inhibitory natural product balanol which bear modified benzophenone subunits are described. The analogues were designed with the goal of uncovering structure-activity features that could be used in the development of PKC inhibitors with a reduced polar character compared to balanol itself. The results of these studies suggest that most of the benzophenone features found in the natural product are important for obtaining potent PKC inhibitory compounds. However, several modifications were found to lead to selective inhibitors of the related enzyme protein kinase A (PKA), and several specific modifications to the polar structural elements of the benzophenone were found to provide potent PKC inhibitors. In particular, it was found that replacement of the benzophenone carboxylate with bioisosteric equivalents could lead to potent analogues. Further, a tolerance for lipophilic substituents on the terminal benzophenone ring was uncovered. These results are discussed in light of recently available structural information for PKA.

Protein kinase C-beta, fibronectin, alpha(5)beta(1)-integrin, and tumor necrosis factor-alpha are required for phorbol diester-induced apoptosis in human myeloid leukemia cells

The human myeloid HL-60 cell line and its cell variant HL-525 were used to study signaling events leading to apoptosis induction by phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC) enzymes. Unlike parental cells, HL-525 cells are PKC-beta deficient and resistant to PMA-induced apoptosis. These cells regain susceptibility to apoptosis induction after transfection with a PKC-beta expression vector. By using this vector and specific neutralizing monoclonal antibodies (mAbs), it was established that PMA-induced apoptosis also called for an interaction between cell-surface alpha(5)beta(1)-integrin and its deposited ligand fibronectin (FN), which is downstream of PKC-beta activation. Experiments with mAbs, the PKC-beta vector, and exogenous FN revealed that the next step entailed an interaction between secreted tumor necrosis factor-alpha and its type I receptor. By using a sphingomyelinase inhibitor, it was concluded that the subsequent step involved ceramide production. Moreover, a permeable ceramide was effective in inducing apoptosis in both HL-60 and HL-525 cells, and this induction was caspase-1 and/or -4 dependent because an inhibitor of these caspases abrogated the induced apoptosis. Based on these and related differentiation studies, we conclude that the above signaling events, the early ones in particular, are shared with PMA-induced macrophage differentiation in the HL-60 cells. It is likely that once these cells acquire their macrophage phenotype and perform their tasks, they become superfluous and are eliminated from the body by a self-triggered apoptotic process that involves our proposed signaling scheme.

PAF receptor antagonist modulates neutrophil responses with thermal injury in vivo

The role of platelet-activating factor (PAF) in Ca(2+) signaling and Ca(2+)-related enhancement of reactive oxygen intermediate (ROI) generation in neutrophils of burn-injured rats was ascertained by evaluating the effect of treatment of the rats with a PAF receptor antagonist. The treatment of rats with the antagonist also allowed us to evaluate the role of PAF in the priming of neutrophil ROI response with burn in vivo. A full skin thickness burn injury was produced in anesthetized rats by exposing 30% of total body surface area to 98 degrees C water for 10 s. Sham and burn rats were killed 1 day later, and their blood was collected to obtain neutrophils. Fluorescence-activated cell sorter analysis was used to quantify ROI production by the neutrophils. Cytosolic-free Ca(2+) concentration ([Ca(2+)](i)) imaging technique was employed to measure neutrophil [Ca(2+)](i) in individual cells and microfluorometry for the assessment of [Ca(2+)](i) responses in suspensions of neutrophils. There was an overt enhancement of ROI generation by burn rat neutrophils. ROI release was accompanied by a marked elevation of [Ca(2+)](i) signaling. The treatment of rats with PAF receptor antagonist before burn prevented the upregulation of both [Ca(2+)](i) and ROI generation in neutrophils. These studies indicate that enhanced ROI production in neutrophils in the early stages after burn injury results from a PAF-mediated priming of the [Ca(2+)](i) signaling pathways in vivo.

On the mechanism of the spermine-exerted inhibition on alpha-thrombin-induced platelet activation

Previous reports have shown that various amines inhibited platelet activation, but no definitive conclusions on their action mechanism were drawn. We have further investigated the action of spermine on platelet responses evoked by alpha-thrombin and other agonists. Spermine inhibited in a concentration-dependent manner (1-10 mM), and more efficiently than spermidine and putrescine, the alpha-thrombin-induced (1.5 nM) platelet activation. Spermine added at a concentration that inhibited completely aggregation only partially affected the thrombin-induced increase in cytosolic Ca(2+) concentration, protein phosphorylation, and ATP secretion. The polyamine had little effect on the morphology of resting platelets, as measured by electron microscopy, thrombin hydrolytic activity, and fibrinogen clotting capacity but decreased the thrombin binding to platelets and isolated glycocalicin. Spermine partially inhibited the aggregation elicited by ADP, vasopressin, platelet-activating factor, thrombin receptor-activating peptide, fluoroaluminate, ionomycin, and dioctanoylglycerol but did not affect the cytosolic Ca(2+) increase induced by these agonists. The polyamine bound to both glycocalicin and platelets, and it inhibited the fibrinogen binding to stimulated platelets. The amount of 14C-spermine bound to resting cells decreased in the presence of the glycoprotein GPIb-antibody LJIB1, whereas the polyamine bound to activated platelets, which was higher than that tied to resting cells, was markedly reduced by LJCP8 or decorsin, a GPIIb/IIIa antibody and antagonist-peptide, respectively. These results indicate that spermine specifically inhibits the thrombin binding to GPIb of resting platelets and the fibrinogen binding to GPIIb/IIIa (integrin alpha(IIb)beta(3)) of activated platelets.

Gender influences the effect of perinatal copper deficiency on cerebellar PKC gamma content

Change in cerebellar protein kinase C gamma (PKCgamma) content caused by perinatal copper (Cu) deficiency was determined in 22-day old rats. The offspring of dams with low Cu intake during gestation and lactation exhibited signs characteristic of Cu deficiency including anemia, greater than 90% reduction in liver Cu concentration, and undetectable serum ceruloplasmin. In addition, brain Cu concentrations were reduced 80%. No differences in the signs of Cu deficiency were observed between female and male offspring. However, cerebellar PKCgamma content was reduced 54% (P < 0.05, Tukey's test) in female offspring but only 18% (P > 0.05) in male offspring. Following 6 weeks of Cu supplementation, brain Cu concentrations remained depressed in female and male rats that experienced perinatal Cu deficiency, but cerebellar PKCgamma content was completely restored to control levels. Postnatal expression of PKCgamma in the cerebellum coincides with and regulates cerebellar maturation. The results of the present study indicate perinatal Cu deficiency may impair cerebellar maturation to a greater extent in females than in males. However, it is not clear whether suppression of PKCgamma by perinatal Cu deficiency produces permanent neuropathology in the cerebellum because the effects were reversed by Cu supplementation.

Stimulation of expression for the adenosine A2A receptor gene by hypoxia in PC12 cells. A potential role in cell protection

The purpose of this study was to examine the regulation of adenosine A2A receptor (A2AR) gene expression during hypoxia in pheochromocytoma (PC12) cells. Northern blot analysis revealed that the A2AR mRNA level was substantially increased after a 3-h exposure to hypoxia (5% O2), which reached a peak at 12 h. Immunoblot analysis showed that the A2AR protein level was also increased during hypoxia. Inhibition of de novo protein synthesis blocked A2AR induction by hypoxia. In addition, removal of extracellular free Ca2+, chelation of intracellular free Ca2+, and pretreatment with protein kinase C inhibitors prevented A2AR induction by hypoxia. Moreover, depletion of protein kinase C activity by prolonged treatment with phorbol 12-myristate 13-acetate significantly inhibited the hypoxic induction of A2AR. A2AR antagonists led to a significant enhancement of A2AR mRNA levels during hypoxia, whereas A2AR agonists caused down-regulation of A2AR expression during hypoxia. This suggests that A2AR regulates its own expression during hypoxia by feedback mechanisms. We further found that activation of A2AR enhances cell viability during hypoxia and also inhibits vascular endothelial growth factor expression in PC12 cells. Thus, increased expression of A2AR during hypoxia might protect cells against hypoxia and may act to inhibit hypoxia-induced angiogenic activity mediated by vascular endothelial growth factor.

Intracellular free calcium regulates the onset of the respiratory burst of human neutrophils activated by phorbol myristate acetate

Thapsigargin was used to study the regulation of different static calcium level ([Ca2+]i) on the respiratory hurst of human neutrophils stimulated with phorbol myristate acetate (PMA). The result showed that the onset time of the respiratory hurst was obviously reduced by elevation of static [Ca2+]i but is still much longer than that stimulated with N-formylmethionylleucylphenylalanine (fMLP). To find the reason, the onset times of the respiratory burst stimulated with fMLP, 1,2-dioctanoyl-sn-glycerol (DiC8), and PMA were determined at different static [Ca2+]i. It turns out that although DiC8 was unable to induce the respiratory burst at low [Ca2+], the onset time of DiC8-stimulated response at high [Ca2+]i was almost the same as that stimulated with fMLP. The study revealed that the fast onset of the fMLP-stimulated respiratory burst in comparison with PMA-stimulated response is not only due to the transient rise of [Ca2+]i, but is also due to the higher efficiency of diacylglycerol (DAG) in activating protein kinase c (PKC). The determining step in governing the onset of a respiratory burst is the activation of PKC.

Inhibition of calcium channels by neurokinin receptor and signal transduction in hamster submandibular ganglion cells

Both substance P (SP) and neurokinin A (NKA) are known as neurotransmitters of the submandibular ganglion (SMG) neurons. SP released from collaterals of the sensory nerves also regulates the excitability of SMG neurons. It has recently been shown that neurokinins (NK) inhibit calcium channels in various neurons. In this study, the effects of NK on voltage-dependent calcium channel current (I(Ca)) in SMG cells were investigated using the whole-cell patch-clamp recording method. NK-1 receptor agonist and SP caused inhibition of I(Ca) in SMG cells in a dose-dependent manner. NK-1 receptor agonist inhibited L-, N- and P/Q-type I(Ca) components. GDP-beta-S included in the pipette solution reduced the NK-1 receptor agonist-induced inhibition of I(Ca). In addition, NK-1 receptor agonist-induced inhibition of I(Ca) was reduced by stimulation of protein kinase C (PKC) but not cyclic AMP-dependent protein kinase (PKA). The results provided evidence for a signal transduction pathway in which calcium channel inhibition by NK receptors required activation of G-protein and PKC-affected step phosphorylation in SMG neurons.

Crystal structure of the potent natural product inhibitor balanol in complex with the catalytic subunit of cAMP-dependent protein kinase

Endogenous protein kinase inhibitors are essential for a wide range of physiological functions. These endogenous inhibitors may mimic peptide substrates as in the case of the heat-stable protein kinase inhibitor (PKI), or they may mimic nucleotide triphosphates. Natural product inhibitors, endogenous to the unique organisms producing them, can be potent exogenous inhibitors against foreign protein kinases. Balanol is a natural product inhibitor exhibiting low nanomolar Ki values against serine and threonine specific kinases, while being ineffective against protein tyrosine kinases. To elucidate balanol's specific inhibitory effects and provide a basis for understanding inhibition-regulated biological processes, a 2.1 A resolution crystal structure of balanol in complex with cAMP-dependent protein kinase (cAPK) was determined. The structure reveals conserved binding regions and displays extensive complementary interactions between balanol and conserved cAPK residues. This report describes the structure of a protein kinase crystallized with a natural ATP mimetic in the absence of metal ions and peptide inhibitor.

Signaling mechanisms of elevated neutrophil O2- generation after burn injury

A full skin thickness burn injury was produced in anesthetized rats by exposing 25% of total body surface area to 98 degrees C water for 10 s. Sham (exposed to 37 degrees C water) and burn rats were killed 1, 3, 7, or 10 days later. The role of Ca2+ signaling and Ca(2+)-related protein kinase C (PKC) activation in neutrophil O2- generation was ascertained by evaluating the effect of treatment of the rats with the Ca2+ entry blocker, diltiazem. There was an overt enhancement of O2- generation by polymorphonuclear leukocytes from burn rats on days 1, 3, and 7 postburn, with the peak release occurring on day 3 postburn. O2- generation comparable to the sham was noted on day 10 after the burn. O2- releases on days 1, 3, and 7 postburn were accompanied by marked elevation of Cai2+ and PKC responses. Like the O2- release, intracellular Ca2+ concentration ([Ca2+]i) response on day 10 after burn was suppressed to levels found in the sham group. The treatment of burn rats with diltiazem prevented the upregulation of both [Ca2+]i and PKC responses as well as O2- generation in neutrophils in rats on days 1, 3, and 7 after the burn. Because previous studies have shown that increases in [Ca2+]i precede O2- generation and degranulation, our results suggest that neutrophil O2- release enhancement in the early stages after burn injury (e.g., days 1-7 postburn) results from an overactivation of the Cai2+ and PKC signaling pathways. The heightened O2- generation during the early burn injury phase might play a role in tissue damage in one or more of host organs.

The effect of UCN-01 (7-hydroxystaurosporine), a potent inhibitor of protein kinase C, on fractionated radiotherapy or daily chemotherapy of a murine fibrosarcoma

PURPOSE

To investigate the effect of UCN-01 (7-hydroxystaurosporine), a potent and selective protein kinase C inhibitor, on fractionated irradiation or daily chemotherapy; cis-diamminedichloroplatinum(II) (cis-DDP) or 5-fluorouracil (5-FU) in vivo. Radiosensitivity and chemosensitivity given in combination with UCN-01 were further studied in vitro to analyze these in vivo results.

METHODS AND MATERIALS

For in vivo studies, single-cell suspension was prepared from fourth generation FSa-II tumors and transplanted subcutaneously into the leg of 8-10-week-old C3Hf/Sed mice. Treatments were initiated when tumors reached an average diameter of 4 mm. Tumor response was studied using tumor growth and growth delay time assays. UCN-01 was given continuously for 7 days using Alzet osmotic pump (4.0 microg/microl/h or approximately 3.2 mg/kg/day). A daily gamma-ray dose of 10 Gy each was given in air for 7 days. Cis-DDP (0.7 mg/kg/day) or 5-FU (20 mg/kg/day) was given by an i.p. injection for 7 days. For in vitro studies, an established FSa-II cell line was used and cell survival was studied by colony formation assay.

RESULTS

UCN-01 acted synergistically with fractionated irradiation, though it was slightly radioprotective in vitro and had no effect on SLD repair. The surviving fraction of the FSa-II cells treated with both UCN-01 and cis-DDP in vitro was lower than the calculated additive effect; however, the sensitizing effect of UCN-01 was not found when combined with either of the chemotherapeutic agents in vivo. Possible causes of synergism of combined UCN-01 and fractionated radiation may be that a continuous UCN-01 treatment inhibited clonogen repopulation during the course of fractionated irradiation and accumulated cells in the G2-M phase where cells are most sensitive to irradiation.

CONCLUSION

UCN-01 is a promising agent that may indirectly interact with fractionated irradiation in vivo but may not with chemotherapeutic agents.

Synthesis and protein kinase C inhibitory activities of balanol analogues with modification of 4-hydroxybenzamido moiety

A series of racemic balanol analogues with modification of the benzamido moiety of balanol have been synthesized and evaluated for their inhibitory activities against human protein kinase C isozymes (PKC-alpha, -beta I, -beta II, -gamma, -delta, -epsilon, and -eta). The structural modification includes replacement of the 4-hydroxyphenyl group with variously substituted phenyl rings, substitution of the amide linkage with a sulfonamide or an ester, and replacement of the 4-hydroxyphenyl substructure with a hydroxyl substituted indole or a hydroxybenzyl group. in general, these analogues were found to be less potent than balanol, but a number of analogues were identified with improved isozyme selectivity. The structure-activity relationship studies of these analogues also indicated that (1) the optimal general PKC inhibition requires a free 4-hydroxyl group in the benzamido portion of the molecule, (2) the amide linkage of the benzamido moiety is important for PKC inhibition, and (3) the conformation associated with the benzamido moiety seems to have a profound effect on PKC inhibition. The requirement of a free 4-hydroxyl group in conjunction with an appropriate conformation of the benzamido moiety for optimal PKC inhibition suggests that the 4-hydroxyphenyl group may be involved in a specific inhibitor-enzyme interaction important for PKC inhibition.

Receptor-mediated diacylglycerol kinase translocation dependent on both transient increase in the intracellular calcium concentration and modification by protein kinase C

Diacylglycerol kinase (DG kinase) is activated by various stimuli in many types of cells. We reported earlier that carbachol (CCh) induced DG kinase translocation from the cytosolic fraction to the membrane fraction in guinea pig taenia coli (Biochem. Pharmacol., 50: 591-599, 1995). In this study, the regulation mechanisms of DG kinase translocation are reported, based on the following findings: 1) CCh sustained an increase in DG kinase in the membrane fraction and a decrease in the cytosolic fraction; 2) blocking calcium influx by removing extracellular calcium did not affect the CCh-induced sustained DG kinase translocation; 3) exposing purified protein kinase C (PKC) to DG kinase increased DG kinase affinity to octylglycoside micelles only with the enzyme extracted from the cytosolic fraction; and 4) CCh-induced DG kinase translocation was reversed by removing CCh, and the serine/threonine phosphatase inhibitor, okadaic acid, blocked the reversal of the translocation. These results suggest that CCh-induced DG kinase translocation is promoted by both a transient increase in intracellular calcium, which may be released from the intracellular store, and by DG kinase phosphorylation by PKC.

Thymosin alpha 1 antagonizes dexamethasone and CD3-induced apoptosis of CD4+ CD8+ thymocytes through the activation of cAMP and protein kinase C dependent second messenger pathways

It is well established that glucocorticoid hormones and anti-CD3 monoclonal antibodies induce apoptosis in immature developing thymocytes. This process can be modulated by soluble factors, anti-oxidants and adhesion receptors. Previously we have demonstrated that thymosin alpha 1 (T alpha 1), a 28-amino acid thymic peptide hormone, is a dose and time dependent antagonist of dexamethasone (DEX) and CD# induced DNA fragmentation of murine thymocytes in vitro. To further investigate the mechanism of T alpha 1 action we determined a T alpha 1 sensitive thymocyte population and examined some of the molecular events associated with T alpha 1 anti-apoptotic activity. Phenotypic analysis of the sub-populations of thymocytes, based on CD4 and CD8 expression, revealed that T alpha 1 exerts its effect on CD4+ CD8+ immature thymocytes. T alpha 1 treatment of thymocytes delays the production of free radicals and the subsequent consumption of glutathione, that is observed during both DEX and CD3 induced apoptosis. We further demonstrate that T alpha 1 stimulates the production of cAMP and activates PKC in thymocytes. These data suggest that T alpha 1 exerts an influence on the development of a population of immature T-cells in the thymus by effecting the sensitivity of thymocytes to apoptosis during the pre-selection stages of thymic development. Our studies also suggest that the mechanism of T alpha 1 action involves the induction of both cAMP and PKC dependent second messenger pathways.

Thrombin-induced phosphorylation of the myristoylated alanine-rich C kinase substrate (MARCKS) protein in bovine pulmonary artery endothelial cells

Myristoylated alanine-rich C kinase substrates (MARCKS) is a prominent protein kinase C (PKC) substrate that is targeted to the plasma membrane by an aminoterminal myristoyl group. In its nonphosphorylated form, MARCKS cross-links Factin and binds calmodulin (CaM) reciprocally. However, upon phosphorylation by PKC, MARCKS release the actin or CaM MARCKS may therefore act as a CaM sink in resting cells and regulate CaM availability during cell activation. We have demonstrated previously that thrombin-induced myosin light chain (MLC) phosphorylation and increased monolayer permeability in bovine pulmonary artery endothelial cells (BPAEC) require both PKC-and CaM-dependent pathways. We therefore decided to investigate the phosphorylation of MARCKS in BPAEC to ascertain whether this occurs in a temporally relevant manner to participate in the thrombin-induced events. MARCKS is phosphorylated in response to thrombin with a time course similar to that seen with MLC. As expected, MARCKS is also phosphorylated by phorbol 12-myristate 13 acetate (PMA), a PKC activator, but with a slower onset and more prolonged duration. Bradykinin also enhances MARCKS phosphorylation in BPAEC, but histamine does not. MARCKS is distributed evently between the membrane and cytosol in BPAEC, and neither thrombin nor PMA caused significant translocation of the protein. Specific PKC inhibitors attenuated MARCKS phosphorylation by either thrombin or PMA. Since thrombin-induced MLC phosphorylation is also attenuated by these inhibitors, MARCKS may be involved in MLC kinase activation and subsequent BPAEC contraction. W7, a CaM antagonist, enhances the phosphorylation of MARCKS. This was expected since CaM binding to MARCKS has been shown to decrease MARCKS phosphorylation by PKC. On the other hand, tyrosine kinase inhibitors, genistein and tyrphostin, attenuate MARCKS phosphorylation but have no effect on MLC phosphorylation, suggesting that MARCKS may be phosphorylated by kinases other than PKC. Phosphorylation of MARCKS outside the PKC phosphorylation domain would not be expected to induce the release of CaM. These data provide support for the hypothesis that MARCKS may serve as a regulator of CaM availability in BPAEC.

The renin-angiotensin system and vascular hypertrophy

In addition to its vasoconstrictor and aldosterone-stimulating action, angiotensin II also drives cell growth and replication in the cardiovascular system, which may result in myocardial hypertrophy and hypertrophy or hyperplasia of conduit and resistance vessels in certain subjects. These actions are mediated through angiotensin II receptors (subtype AT1), which activate the G protein, phospholipase C, diacylglycerol and inositol trisphosphate pathway, to increase the expression of certain protooncogenes (c-fos, c-myc and c-jun) and growth factors (platelet-derived growth factor-A-chain, transforming growth factor-beta 1 and basic fibroblast growth factor). The cellular responses to angiotensin II in vascular smooth muscle have been shown in different hypertensive vessels to be either hypertrophy alone, hypertrophy and DNA synthesis without cell division (polyploidy) or DNA synthesis with cell division (hyperplasia). In genetic hypertension, the altered structure of small arteries is due to either cellular hyperplasia or remodeling, whereas in renovascular hypertension there is hypertrophy of vascular smooth muscle cells. Angiotensin II also increases synthesis of some matrix components, activates blood monocytes and is thrombogenic. Angiotensin-converting enzyme (ACE) inhibitors prevent or reverse vascular hypertrophy in animal models of hypertension; this seems to be a class effect, shared to some extent with calcium channel blocking agents. In human hypertension, ACE inhibitors reduce the increased media/lumen ratio of large and small arteries in hypertension and increase arterial compliance. These properties are also shared by losartan, the first of the new class of angiotensin II receptor (AT1) antagonists. The clinical implications of these findings need to be tested through rigorous and prospective clinical trials.

Possible involvement of protein kinase C-epsilon in phorbol ester-induced growth inhibition of human lymphoblastic cells

Sustained activation of members of the protein kinase C (PKC) family is known to influence the growth and differentiation of various cell types, however, the specific roles for individual isoforms mediating these cellular events have yet to be elucidated. Activation of PKC by phorbol esters leads to growth inhibition in certain cell lines. The HT58 human B lymphoblastic cell may serve as a cellular model system to investigate the participation of individual isoforms in the initial events of growth arrest induced by phorbol ester. Determination of cell cycle and investigation of apoptosis were performed by flow cytometric measurements. Phorbol ester-induced translocation and down-regulation of the conventional alpha, beta and the novel epsilon isoforms of PKC were demonstrated by Western blot analysis. At lower concentrations (o.5 ng/ml) phorbol myristate acetate (PMA) stimulated a G1 arrest with retention of viability in the human HT58 B lymphoblastic cell. The protein kinase inhibitor staurosporine at a concentration of 25 nM did not significantly alter HT58 cell viability. However, staurosporine (25 nM) induced apoptosis in cells preincubated for 4 hr with 0.5-1.0 ng/ml PMA. The translocation of PKC-epsilon was observed within 39 min exposure to 0.5 ng/ml PMA. After a 4 hr treatment, evidence for down-regulation and and altered phosphorylation state of PKC-epsilon was seen. In contrast, the conventional alpha and beta isoforms were practically uneffected by this PMA treatment. At higher PMA concentrations (50 ng/ml) the alpha and beta isoforms showed a significant down-regulation. The preferential alterations in PKC-epsilon observed under the conditions required for PMA to influence the growth and survival of HT58 cells suggest a role for the Ca(2+)-independent epsilon isoform in mediating the initial events of the phorbol ester stimulated cellular responses.

Total Synthesis of (-)- and (+)-Balanol(1)

Two total syntheses of the potent protein kinase C inhibitory fungal metabolite balanol are described. In the first approach, the core aminohydroxyazepane subunit was prepared in racemic form by stereospecific functionalization of N-benzyl-epsilon-caprolactam. Resolution prior to coupling to the benzophenone subunit provided access to both enantiomers of balanol. In the second approach, an efficient silicon-mediated cyclization of (2S,3R)-3-hydroxylysine followed by reduction provided the azepane subunit in enantiomerically pure form. The sterically congested benzophenone subunit was assembled from two highly substituted aromatic precursors by way of an anionic homo-Fries rearrangement.

Modulation by protein kinase C of the enhanced responsiveness to tachykinins in ovalbumin-sensitized guinea pig alveolar macrophages

As previously reported, alveolar macrophages (AMs) from ovalbumin-sensitized guinea pigs present an enhanced responsiveness to tachykinins but not to N-formylmethionyl-leucyl-phenylalanine (fMLP). We have investigated the biochemical mechanisms underlying this varied responsiveness to tachykinins. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) induced a larger superoxide anion (O2-) production in AMs from sensitized guinea pigs, as did tachykinins. Pretreatment of AMs with pertussis toxin abolished tachykinin-evoked respiratory burst, had no effect on PMA-evoked O2- production and strongly inhibited fMLP-evoked one, with no appreciable variation between control or sensitized AMs. Staurosporine and its derivative cgp 41251, significantly decreased PMA- and tachykinin-evoked O2- production in both populations, being more potent in control AMs, but exerted little effects against fMLP. Pretreatment of AMs with PMA significantly inhibited fMLP-, PMA- and tachykinin-evoked O2- production in both control and sensitized AMs. fMLP, substance P (SP), neurokinin A (NKA) and the NK2 agonist [beta-Ala8]-NKA(4-10) dose-dependently increased [3H] phorbol 12, 13 dibutyrate (PDBu) binding to control and sensitized AMs. While fMLP exerted similar effects in both populations, dose-response curves for SP1 NKA and the NK2 receptor agonist were shifted leftwards (1, 4 and 3 orders of magnitude, respectively) in sensitized AMs. These results indicate a possible PKC involvement in the enhanced responsiveness to tachykinins in actively sensitized AMs.

Protein phosphorylation in the blood-brain barrier. Possible presence of MARCKS in brain microvessels

The protein phosphorylation in rat brain microvessels has been examined; the major phosphorylated proteins correspond to a doublet of molecular weight 134-141 kDa, and four proteins of approx. 25, 55, 80 and 200 kDa. TPA (12-O-tetradecanoylphorbol-13-acetate) enhanced, in a few minutes, the phosphorylation of three major protein substrates with apparent molecular weights of 17.5, 44.5 and 80 kDa. These effects are inhibited by staurosporine. The 80 kDa protein resulted to be myristoylated alanine-rich C kinase substrate (MARCKS). This work demonstrates that protein kinase C plays an important role in protein phosphorylation in blood-brain barrier (BBB).