'Crosstalk': a pivotal role for protein kinase C in modulating relationships between signal transduction pathways

Role of PKCζ-NADPH oxidase signaling axis in PKCα-mediated Giα2 phosphorylation for inhibition of adenylate cyclase activity by angiotensin II in pulmonary artery smooth muscle cells

We sought to determine the mechanism by which angiotensin II (AngII) inhibits isoproterenol induced increase in adenylate cyclase (AC) activity and cyclic adenosine monophosphate (cAMP) production in bovine pulmonary artery smooth muscle cells (BPASMCs). Treatment with AngII stimulates protein kinase C-ζ (PKC-ζ), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and PKC-α activities, and also inhibits isoproterenol induced increase in AC activity and cAMP production in the cells. Pertussis toxin pretreatment eliminates AngII caused inhibition of isoproterenol induced increase in AC activity without a discernible change in PKC-ζ, NADPH oxidase, and PKC-α activities. Treatment of the cells with AngII increases α2 isoform of Gi (Giα2) phosphorylation; while pretreatment with chemical and genetic inhibitors of PKC-ζ and NADPH oxidase attenuate AngII induced increase in PKC-α activity and Giα2 phosphorylation, and also reverse AngII caused inhibition of isoproterenol induced increase in AC activity. Pretreatment of the cells with chemical and genetic inhibitors of PKC-α attenuate AngII induced increase in Giα2 phosphorylation and inhibits isoproterenol induced increase in AC activity without a discernible change in PKC-ζ and NADPH oxidase activities. Overall, PKCζ-NADPH oxidase-PKCα signaling axis plays a crucial role in Giα2 phosphorylation resulting in AngII-mediated inhibition of isoproterenol induced increase in AC activity in BPASMCs.

Evaluating the effects on steroidogenesis of estragole and trans-anethole in a feto-placental co-culture model

In this study, we determined whether estragole and its isomer trans-anethole interfered with feto-placental steroidogenesis in a human co-culture model composed of fetal-like adrenocortical (H295R) and placental trophoblast-like (BeWo) cells. Estragole and trans-anethole are considered the biologically active compounds within basil and fennel seed essential oils, respectively. After a 24 h exposure of the co-culture to 2.5, 5.2 and 25 μM estragole or trans-anethole, hormone concentrations of estradiol, estrone, dehydroepiandrosterone, androstenedione, progesterone and estriol were significantly increased. Using RT-qPCR, estragole and trans-anethole were shown to significantly alter the expression of several key steroidogenic enzymes, such as those involved in cholesterol transport and steroid hormone biosynthesis, including StAR, CYP11A1, HSD3B1/2, SULT2A1, and HSD17B1, -4, and -5. Furthermore, we provided mechanistic insight into the ability of estragole and trans-anethole to stimulate promoter-specific expression of CYP19 through activation of the PKA pathway in H295R cells and the PKC pathway in BeWo cells, in both cases associated with increased cAMP levels. Moreover, we show new evidence suggesting a role for progesterone in regulating steroid hormone biosynthesis through regulation of the StAR gene.

Pharmacologic rationale, efficacy and safety of the fixed-dose co-formulation of indacaterol and glycopyrronium

Chronic obstructive pulmonary disease (COPD) is a widespread respiratory disorder, usually characterized by progressive and poorly reversible airflow limitation. Inhaled long-acting bronchodilators, namely LABA (long-acting β2-adrenergic agonists) and LAMA (long-acting muscarinic receptor antagonists) are the mainstay of COPD treatment. Because the symptoms of many patients with COPD do not satisfactorily improve by using a single, either LABA or LAMA bronchodilator, the synergism of action resulting from the combination of the different bronchodilating mechanisms activated by LABA and LAMA, respectively, can significantly contribute to a better disease control. Based on these clinical and pharmacological considerations, several LABA/LAMA fixed-dose combinations have been developed and experimentally evaluated. Within such a context, the drug co-formulation containing indacaterol and glycopyrronium is probably the LABA/LAMA association which has been most extensively studied during the last few years.

Role of PKC-ζ in NADPH oxidase-PKCα-Giα axis dependent inhibition of β-adrenergic response by U46619 in pulmonary artery smooth muscle cells

Treatment of bovine pulmonary artery smooth muscle cells (BPASMCs) with U46619 attenuated isoproterenol caused stimulation of adenyl cyclase activity and cAMP production. Pretreatment with SQ29548 (Tp receptor antagonist), apocynin (NADPH oxidase inhibitor) and Go6976 (PKC-α inhibitor) eliminated U46619 caused attenuation of isoproterenol stimulated adenyl cyclase activity. Pretreatment with SQ29548 and apocynin prevented U46619 induced increase in NADPH oxidase activity, PKC-α activity and Giα phosphorylation. However, pretreatment with CZI, a PKC-ζ inhibitor, markedly, but not completely, inhibited U46619 induced increase in NADPH oxidase activity, PKC-α activity, Giα phosphorylation and also significantly eliminated U46619 caused attenuation of isoproterenol stimulated adenyl cyclase activity. Pretreatment with Go6976 inhibited U46619 induced increase in Giα phosphorylation, but not PKC-ζ activity and NADPH oxidase activity. Pretreatment with pertussis toxin eliminated U46619 caused attenuation of isoproterenol stimulated adenyl cyclase activity without any discernible change in PKC-ζ, NADPH oxidase and PKC-α activities. Transfection of the cells with Tp, PKC-ζ and PKC-α siRNA duplexes corroborate the findings observed with their respective pharmacological inhibitors on the responses produced by U46619. Taken together, we suggest involvement of PKC-ζ in U46619 caused attenuation of isoproterenol stimulated β-adrenergic response, which is regulated by NADPH oxidase-PKCα-Giα axis in pulmonary artery smooth muscle cells.

Evaluation of novel acyclic nucleoside phosphonates against human and animal gammaherpesviruses revealed an altered metabolism of cyclic prodrugs upon Epstein-Barr virus reactivation in P3HR-1 cells

Acyclic nucleoside phosphonates (ANPs), such as (S)-1-[(3-hydroxy-2-phosphonomethoxy)propyl)]cytosine (HPMPC), are an important group of broad-spectrum antiviral agents with activity against DNA viruses. In this report, we present the in vitro potencies of novel ANPs against gammaherpesviruses, including Kaposi's sarcoma-associated herpesvirus, Epstein-Barr virus (EBV), and three animal gammaherpesviruses. 1-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]-5-azacytosine (HPMP-5-azaC), (S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]-3-deazaadenine (3-deaza-HPMPA), and their cyclic derivatives have emerged as highly potent antigammaherpesvirus agents. Interestingly, cyclic prodrugs of ANPs exhibited reduced activities against EBV strain P3HR-1, but not against EBV strain Akata. Cell culture metabolism studies with HPMPC and cyclic HPMPC revealed that these differences were attributable to an altered drug metabolism in P3HR-1 cells after EBV reactivation and, more specifically, to a reduced hydrolysis of cyclic HPMPC by cyclic CMP phosphodiesterase. We did not correlate this effect with phosphodiesterase downregulation, or to functional mutations. Instead, altered cyclic AMP levels in P3HR-1 cells indicated a competitive inhibition of the phosphodiesterase by this cyclic nucleotide. Finally, both HPMPC and HPMP-5-azaC emerged as highly effective inhibitors in vivo through significant inhibition of murine gammaherpesvirus replication and dissemination. With the current need for potent antigammaherpesvirus agents, our findings underline the requirement of appropriate surrogate viruses for antiviral susceptibility testing and highlight HPMP-5-azaC as a promising compound for future clinical development.

Role of PKCα-p38 MAPK-Giα axis in peroxynitrite-mediated inhibition of β-adrenergic response in pulmonary artery smooth muscle cells

In the context of cross-talk between transmembrane signaling pathways, we studied the loci within the β-adrenergic receptor/G protein/adenyl cyclase system at which PKC exerts regulatory effects of peroxynitrite (ONOO(-)) on isoproterenol stimulated adenyl cyclase activity in pulmonary artery smooth muscle cells. Treatment of the cells with ONOO(-) stimulated PKC-α activity and that subsequently increased p(38)MAPK phosphorylation. Pretreatment with Go6976 (PKC-α inhibitor) and SB203580 (p(38)MAPK inhibitor) eliminated ONOO(-) caused inhibition on isoproterenol stimulated adenyl cyclase activity. Pretreatment with Go6976, but not SB203580, prevented ONOO(-) induced increase in PKC-α activity. Studies using genetic inhibitors of PKC-α (PKC-α siRNA) and p(38)MAPK (p(38)MAPK siRNA) also corroborated the findings obtained with their pharmacological inhibitors in eliminating the attenuation of ONOO(-) effect on isoproterenol stimulated adenyl cyclase activity. This inhibitory effect of ONOO(-) was found to be eliminated upon pretreatment of the cells with pertussis toxin thereby pointing to a G(i) dependent mechanism. This hypothesis was reinforced by G(i)α phosphorylation as well as by the observation of the loss of the ability of Gpp(NH)p (a measure of G(i) mediated response) to stimulate adenyl cyclase activity upon ONOO(-) treatment to the cells. We suggest the existence of a pertussis toxin sensitive G protein (G(i))-mediated mechanism in isoproterenol stimulated adenyl cyclase activity, which is regulated by PKCα-p(38)MAPK axis dependent phosphorylation of its α-subunit (G(i)α) in the pulmonary artery smooth muscle cells.

Muscarinic receptors on airway mesenchymal cells: novel findings for an ancient target

Since ancient times, anticholinergics have been used as a bronchodilator therapy for obstructive lung diseases. Targets of these drugs are G-protein-coupled muscarinic M(1), M(2) and M(3) receptors in the airways, which have long been recognized to regulate vagally-induced airway smooth muscle contraction and mucus secretion. However, recent studies have revealed that acetylcholine also exerts pro-inflammatory, pro-proliferative and pro-fibrotic actions in the airways, which may involve muscarinic receptor stimulation on mesenchymal, epithelial and inflammatory cells. Moreover, acetylcholine in the airways may not only be derived from vagal nerves, but also from non-neuronal cells, including epithelial and inflammatory cells. Airway smooth muscle cells seem to play a major role in the effects of acetylcholine on airway function. It has become apparent that these cells are multipotent cells that may reversibly adopt (hyper)contractile, proliferative and synthetic phenotypes, which are all under control of muscarinic receptors and differentially involved in bronchoconstriction, airway remodeling and inflammation. Cholinergic contractile tone is increased by airway inflammation associated with asthma and COPD, resulting from exaggerated acetylcholine release as well as increased expression of contraction related proteins in airway smooth muscle. Moreover, muscarinic receptor stimulation promotes proliferation of airway smooth muscle cells as well as fibroblasts, and regulates cytokine, chemokine and extracellular matrix production by these cells, which may contribute to airway smooth muscle growth, airway fibrosis and inflammation. In line, animal models of chronic allergic asthma and COPD have recently demonstrated that tiotropium may potently inhibit airway inflammation and remodeling. These observations indicate that muscarinic receptors have a much larger role in the pathophysiology of obstructive airway diseases than previously thought, which may have important therapeutic implications.

Modularity analysis based on predicted protein-protein interactions provides new insights into pathogenicity and cellular process of Escherichia coli O157:H7

Background

With the development of experimental techniques and bioinformatics, the quantity of data available from protein-protein interactions (PPIs) is increasing exponentially. Functional modules can be identified from protein interaction networks. It follows that the investigation of functional modules will generate a better understanding of cellular organization, processes, and functions. However, experimental PPI data are still limited, and no modularity analysis of PPIs in pathogens has been published to date.

Results

In this study, we predict and analyze the functional modules of E. coli O157:H7 systemically by integrating several bioinformatics methods. After evaluation, most of the predicted modules are found to be biologically significant and functionally homogeneous. Six pathogenicity-related modules were discovered and analyzed, including novel modules. These modules provided new information on the pathogenicity of O157:H7. The modularity of cellular function and cooperativity between modules are also discussed. Moreover, modularity analysis of O157:H7 can provide possible candidates for biological pathway extension and clues for discovering new pathways of cross-talk.

Conclusions

This article provides the first modularity analysis of a pathogen and sheds new light on the study of pathogens and cellular processes. Our study also provides a strategy for applying modularity analysis to any sequenced organism.

Characterization of oxidative stress status during diabetic bone healing

Early events associated with bone healing in patients with type 2 diabetes mellitus appear to be delayed. Hyperglycaemia and an associated increase in oxidative stress are cited as potential factors leading to a change in cellular behaviour. Using an in vivo model monitoring bone formation around implants placed into rat mandibles, we have previously identified that the onset of cell proliferation and osteoblast differentiation are delayed and subsequently prolonged compared with normal bone. This study used the same implant model to characterize oxidative stress biomarkers and primary antioxidant enzyme profiles during diabetic bone healing in vivo. Implants were placed into the sockets of incisors extracted from the mandibles of normal Wistar and diabetic Goto-Kakizaki rats for 3 and 9 weeks after implant insertion. Histochemical analysis confirmed a delay in bone healing around implants in diabetic animals. Immunohistochemical localization of peri-cellular staining for protein carbonyl groups, as a biomarker of oxidized protein content, was slightly higher in diabetic granulation tissue compared with normal tissue. However, no differences were observed in the staining patterns of advanced glycation end products. Minimal differences were observed in the number of cells positive for cytoplasmic superoxide dismutase (SOD)1 or mitochondrial SOD2. Significantly, catalase was absent in diabetic tissues. The results suggest that the oxidative environment in healing bone is differentially affected by hyperglycaemia, particularly in relation to catalase. The significance of these observations for diabetic bone healing is discussed.

The diagnostic significance of the induced acrosome reaction

In trying to discern potential causes of male infertility, little investigation has been done to determine if there is predictive value in assessing acrosome reaction inducibility of human spermatozoa for clinical interpretation and application. The purpose of this review is to outline what is currently known in terms of the diagnostic significance of the induced acrosome reaction and to discuss what might be anticipated for the future. In constructing this review, every effort has been made to provide a comprehensive literature review for the reader and a number of review articles have been cited to serve as sources for additional related material. Regarding the aforementioned, it is essential to qualify that, with the exception of the Section entitled: ‘General characteristics of capacitation and the acrosome reaction’, only characteristics, properties and areas relevant to human spermatozoa will be addressed. Thus, in total, this review will: (1) provide a general description of capacitation and the acrosome reaction; (2) briefly characterize the acrosome and its properties; (3) address the signalling mechanism(s) by which the acrosome reaction occurs; (4) outline various methods for detecting the acrosome reaction; (5) definein vitroculture conditions that facilitate the acrosome reaction; (6) define agents, i.e., biological and chemical, that induce the reaction; (7) discuss the association of the acrosome reaction with fertilization; (8) discuss the clinical implications of the induced acrosome reaction; (9) discuss the relevance of sperm function assays in general; and lastly, (10) discuss future application of acrosome reaction assessment for the clinical diagnosis of male infertility.

Effect of preischemic beta-adrenoceptor stimulation on postischemic contractile dysfunction

AIMS

Short periods of preischemic beta-adrenoceptor stimulation protect hearts against postischemic left ventricular dysfunction. It was the aim of this study to decide whether this procedure mimics ischemic preconditioning by the generation of preischemic hemodynamic and energetic stress or whether it represents an endogenous phenomenon and to investigate the influence of age and hypertension.

MAIN METHODS

Isolated rat hearts were investigated ex vivo by Langendorff perfusion and exposed to an established ischemia/reperfusion protocol (45 min no-flow ischemia and 90 min reperfusion). Left ventricular developed pressure (LVDP), rate pressure product, and +/-dP/dt were analyzed.

KEY FINDINGS

Isoprenaline concentration dependently increased LVDP up to 40+/-15 mm Hg (approximately EC(50) of 9.9+/-0.5 nM). Isoprenaline given prior to ischemia attenuated the subsequent postischemic ventricular dysfunction (approximately EC(50) of 1.4+/-0.2 pM). However, concentrations high enough to improve LVDP in normoxic hearts did not improve postischemic recovery albeit a significant reduction of hypercontraction-induced cell damage. The effect on functional recovery was attenuated by atenolol, H89, and wortmannin suggesting that beta-adrenoceptor stimulation, protein kinase A, and PI 3-kinase activation are involved. The effect was conserved in hearts from 13 month old rats but lost in age-matched spontaneously hypertensive rats.

SIGNIFICANCE

The study identifies preischemic beta-adrenoceptor stimulation as a pharmacological preconditioning protocol that does not simply mimic classical ischemic preconditioning by induction of hemodynamic or energetic stress prior to a prolonged ischemic period. The observed loss of effectiveness in hypertensives may contribute to the reduced ischemic tolerance of hypertensives.

Oxidative stress induces actin-cytoskeletal and tight-junctional alterations in hepatocytes by a Ca2+ -dependent, PKC-mediated mechanism: protective effect of PKA

Oxidative stress elevates Ca2+ and, presumably, activates Ca2+ -dependent PKCs. We analyzed the participation of Ca2+ -dependent PKCs in actin disorganization and tight-junctional impairment induced by the pro-oxidant tert-butylhydroperoxide (tBOOH) in isolated rat hepatocyte couplets. tBOOH (100 microM) augmented radical oxygen species (ROS), as indicated by increased lipid peroxidation (+217%, p < 0.05) and intracellular production of 2',7'-dichlorofluorescein (+36%, p < 0.05). Cytosolic Ca2+ and PKCalpha translocation to membrane, an indicator of PKCalpha activation, were also elevated by tBOOH (+100 and +79%, respectively, p < 0.05). tBOOH increased the number of couplets displaying membrane blebs (+278%, p < 0.001) and caused redistribution of F-actin. tBOOH induced tight-junctional impairment, as indicated by a reduction in the percentage of couplets retaining presecreted cholyllysylfluorescein in their canalicular vacuoles (-54%, p < 0.001). tBOOH induced redistribution of the tight-junctional-associated protein ZO-1. All these events were prevented by the panspecific PKC inhibitors H7 and staurosporine, the Ca2+ -dependent PKC inhibitor Gö6976, the intracellular Ca2+ chelator BAPTA/AM, and the PKA activator dibutyryl-cyclic AMP. Furthermore, PKC inhibition and PKA activation not only prevented but also fully reversed tBOOH-induced blebbing. Conversely, tBOOH-induced ROS formation and Ca2+ elevation remained unchanged. We conclude that ROS induce hepatocellular actin-cytoskeleton rearrangement and tight-junctional impairment by a PKC-mediated, Ca2+ -dependent mechanism, which is counteracted by PKA.

Protein kinase A and Ca(v)1 (L-Type) channels are common targets to facilitatory adenosine A2A and muscarinic M1 receptors on rat motoneurons

At the rat motor endplate, pre-synaptic facilitatory adenosine A2A and muscarinic M1 receptors are mutually exclusive. We investigated whether these receptors share a common intracellular signalling pathway. Suppression of McN-A-343-induced M1 facilitation of [3H]ACh release was partially recovered when CGS21680C (an A2A agonist) was combined with the cyclic AMP antagonist Rp-cAMPS. Forskolin, rolipram and 8-bromo-cyclic AMP mimicked CGS21680C blockade of M1 facilitation. Both Rp-cAMPs and nifedipine reduced augmentation of [3H]ACh release by McN-A-343 and CGS21680C. Activation of M1 and A2A receptors enhanced Ca2+ recruitment through nifedipine-sensitive channels. Nifedipine inhibition revealed by McN-A-343 was prevented by chelerythrine (a PKC inhibitor) and Rp-cAMPS, suggesting that Ca(v)1 (L-type) channels phosphorylation by PKA and PKC is required. Rp-cAMPS inhibited [3H]ACh release in the presence of phorbol 12-myristate 13-acetate, but PKC inhibition by chelerythrine had no effect on release in the presence of 8-bromo-cyclic AMP. This suggests that the involvement of PKA may be secondary to M1-induced PKC activation. In conclusion, competition of M1 and A2A receptors to facilitate ACh release from motoneurons may occur by signal convergence to a common pathway involving PKA activation and Ca2+ influx through Ca(v)1 (L-type) channels.

Oxidant-mediated activation of cytosolic phospholipase a(2) in pulmonary endothelium: role of protein kinase C alpha and a pertussis toxin-sensitive protein

The authors have previously demonstrated that the oxidant t-buOOH stimulates phospholipase A(2) (PLA(2)) activity in bovine pulmonary artery endothelial cells (S. Chakraborti et al. American Journal of Physiology, 257, L430-L437, 1989). Herein, the authors sought to investigate the mechanism by which t-buOOH stimulates PLA(2) activity and the role of protein kinase C (PKC) in this scenario. Treatment of bovine pulmonary artery endothelial cells with t-buOOH stimulated an aprotinin-sensitive protease activity, PKC activity, and PLA(2) activity in the cell membrane. Pretreatment with intracellular Ca(2+) chelator (BAPTA-AM), PKCalpha inhibitor (Go6976), cPLA(2) inhibitor (AACOCF(3)), and pertussis toxin prevented t-buOOH-stimulated PLA(2) activity. Immunoblot studies with aprotinin, cPLA(2), PKCalpha, and Gialpha antibodies revealed their presence in the endothelial membrane. Immunoblot studies of the cell membrane isolated from t-buOOH-stimulated cells with cPLA(2) and PKCalpha antibodies elicited an apparent increase in their immunoreactive protein profiles along with an additional 47-kDa immunoreactive fragment in the membrane. t-buOOH caused Gialpha phosphorylation in the membrane and pretreatment with Go6976 prevented the phosphorylation. Overall, these results suggest that t-buOOH stimulates an aprotinin-sensitive protease activity that proteolytically activates PKCalpha and that subsequently phosphorylates a pertussis toxin-sensitive protein, resulting in the stimulation of cPLA(2) activity in the cell membrane.

Protein kinase C potentiates homologous desensitization of the beta2-adrenoceptor in bovine tracheal smooth muscle

Preincubation (30 min) of bovine tracheal smooth muscle with various concentrations (0.1, 1 and 10 microM) of fenoterol decreased isoprenaline-induced maximal relaxation (E(max)) of methacholine-contracted preparations in a concentration dependent fashion, indicating desensitization of the beta(2)-adrenoceptor. Preincubation with 1 microM of the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) caused a small but significant decrease in isoprenaline-induced E(max), indicating activated PKC-mediated heterologous beta(2)-adrenoceptor desensitization. To investigate the capacity of activated PKC to regulate homologous desensitization, we incubated the smooth muscle strips with the combination of both 1 microM PMA and 1 microM fenoterol. This combined treatment synergistically decreased the isoprenaline-induced maximal relaxation, as compared to the individual effects of PMA and fenoterol alone, indicating a common pathway for heterologous and homologous desensitization. Moreover, the specific PKC-inhibitor 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl) maleimide (GF 109203X) markedly increased the potency and E(max) of isoprenaline for all conditions used, including control conditions, and the synergistic effects of PMA and fenoterol were completely prevented. In conclusion, the present study demonstrates that homologous desensitization of the beta(2)-adrenergic receptor can be enhanced by PKC activation. For the first time we have provided evidence that this concept is functionally operative in airway smooth muscle, and it may explain the reduced bronchodilator response to beta(2)-adrenoceptor agonists in patients with asthma during a severe exacerbation.

Potentiation of beta-adrenoceptor function in bovine tracheal smooth muscle by inhibition of protein kinase C

To examine the role of contractile agonist-induced activation of protein kinase C (PKC) in functional antagonism of airway smooth muscle contraction by beta-adrenoceptor agonists, we examined the effects of the specific PKC-inhibitor GF 109203X (2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl) maleimide) on isoprenaline-induced relaxation of bovine tracheal smooth muscle contracted by various concentrations of methacholine and histamine. In the absence of GF 109203X, the potency of isoprenaline (pD(2)) was gradually reduced at increasing methacholine- and histamine-induced smooth muscle tones, but the maximal relaxation (E(max)) was decreased only at higher concentrations of methacholine. In the presence of GF 109203X, pD(2) values were significantly increased for both methacholine- and histamine-induced contractions. Moreover, isoprenaline E(max) values in the presence of high concentrations of methacholine were also increased. Although both methacholine- and histamine-induced contractions were slightly reduced by GF 109203X, the changes in isoprenaline pD(2) could only partially be explained by reduced contractile tone. In contrast to isoprenaline, forskolin-induced relaxations were not affected by GF 109203X. The results indicate that PKC activation contributes to the reduced beta-adrenergic responsiveness induced by methacholine and histamine, which may involve uncoupling of the beta-adrenoceptor from the effector system. Since many mediators and neurotransmitters in allergic airway inflammation can activate PKC, this cross talk may be important in the reduced bronchodilator response of patients with severe asthma.

Modulation of beta2- and beta3-adrenoceptor-mediated relaxation of rat oesophagus smooth muscle by protein kinase C

Although a prominent role for protein kinase C (PKC) in the cross-talk between the phosphoinositide pathway and beta2-adrenoceptor signalling has been indicated, modulation of beta3-adrenoceptor function by PKC has not been studied thus far. In the present study, we have compared the relative capacity of PKC in modulating beta2- and beta3-adrenoceptor-mediated relaxation of methacholine-contracted rat oesophagus smooth muscle. To this purpose the effects of the PKC-inhibitor GF 109203X (2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimide) on relaxation induced by fenoterol, formoterol, (-)-noradrenaline, BRL 35135 (4-[2-[(2-hydroxy-2-(chlorophenyl)ethyl)amino]-propyl]-phenoxyacetic-acidmethylester) and IBMX (3-isobutyl-1-methyl-xanthine) were studied, in the absence and presence of the selective beta2-adrenoceptor antagonist ICI 118,551 (erythro-1(7-methylindan-4-yloxy)-3-(isopropylamin)-butan-2-ol). Our results show that inhibition of PKC resulted in differential augmentation of both beta2- and beta3-adrenoceptor-mediated relaxation. In contrast, relaxation induced by IBMX was not influenced at all by GF 109203X. The beta2-adrenoceptor bears phosphorylation sites for several kinases, including PKC. Since the beta3-adrenoceptor lacks these consensus sites, the results may also indicate that PKC-mediated Galphas phosphorylation is involved in the cross-talk between the muscarinic receptor-mediated phosphoinositide pathway and beta2- and, particularly, beta3-adrenoceptor signalling.

Proteolytic activation of protein kinase Calpha by peroxynitrite in stimulating cytosolic phospholipase A2 in pulmonary endothelium: involvement of a pertussis toxin sensitive protein

We sought to determine the roles of PKCalpha and G(i)alpha in regulating cPLA(2) activity in bovine pulmonary artery endothelial cell membrane under peroxynitrite (ONOO(-)) stimulation. Treatment of bovine pulmonary artery endothelial cells with ONOO(-) markedly stimulates the cell membrane associated protease activity, protein kinase C (PKC) activity, phospholipase A(2) (PLA(2)) activity, and arachidonic acid (AA) release from the cells. ONOO(-) significantly increases (Ca(2+))(i) in the cells, and pretreatment with the intracellular Ca(2+) chelator BAPTA-AM prevents the increase in (Ca(2+))(i), protease activity, PKC activity, and cPLA(2) activity in the cell membrane and AA release from the cells. Pretreatment of the cells with arachidonyl trifluoromethyl ketone (AACOCF(3)) (a cPLA(2) inhibitor) prevents ONOO(-)-stimulated cPLA(2) activity and AA release without producing a significant alteration of the protease activity. Pretreatment with vitamin E and aprotinin prevents ONOO(-)-induced increase in the protease activity, PKC activity, and cPLA(2) activity in the cell membrane and AA release from the cells. Pretreatment with the PKC inhibitor calphostin C prevents ONOO(-)-caused increase in PKC activity and cPLA(2) activity in the cell membrane and AA release from the cells. An immunoblot study of the cell membrane isolated from the ONOO(-)-treated cells with polyclonal PKCalpha antibody elicited an increase in the 80 kDa immunoreactive protein band along with an additional 47 kDa immunoreactive fragment. An immunoblot study with anti-nitrotyrosine antibody revealed that ONOO(-) induces nitration of tyrosine residues in PKCalpha. Pretreatment of the cells with aprotinin abolished the 47 kDa immunoreactive fragment in the immunoblot. An immunoblot study of the endothelial cell membrane with polyclonal cPLA(2) antibody revealed that treatment of the cells with ONOO(-) markedly increases the cPLA(2) immunoreactive protein profile in the membrane. Pretreatment of the endothelial cells with Go6976, a PKCalpha inhibitor, prevents the increase in PKC activity and cPLA(2) activity in the cell membrane under ONOO(-)-triggered condition. It, therefore, appears from the present study that treatment of the cells with ONOO(-) causes an increase in the protease activity, and that plays an important role in activating PKCalpha, which subsequently stimulates cPLA(2) activity in the cell membrane and AA release from the cells. An immunoblot assay with polyclonal G(i)alpha antibody elicited an immunoreactive band having a molecular mass of 41 kDa. Pretreatment of the cells with pertussis toxin markedly inhibits ONOO(-)-induced increase in cPLA(2) activity and AA release without significantly altering (Ca(2+))(i), protease activity, and PKC activity in the cell membrane. Treatment of the cells with ONOO(-) causes phosphorylation of G(i)alpha in the cell membrane, and pretreatment with Go6976 prevents its phosphorylation. We suggest the existence of a pertusssis toxin sensitive G protein-mediated mechanism for activation of cPLA(2) by ONOO(-) in bovine pulmonary artery endothelial cell membrane, which is regulated by PKCalpha-dependent phosphorylation and sensitive to aprotinin for its inhibition.

Role of an aprotinin-sensitive protease in protein kinase Calpha-mediated activation of cytosolic phospholipase A2 by calcium ionophore (A23187) in pulmonary endothelium

Treatment of bovine pulmonary artery endothelial cells with the calcium ionophore, A23187, stimulates the cell membrane associated protease activity, phospholipase A2 (PLA2) activity, and arachidonic acid (AA) release from the cells. Pretreatment of the cells with arachidonyl-trifluomethylketone (AACOCF3), a cPLA2 inhibitor, but not bromoenollactone (BEL), a iPLA2 inhibitor, prevents A23187 stimulated PLA2 activity and AA release without producing an appreciable alteration of the protease activity. Pretreatment of the cells with aprotinin, an ambient protease inhibitor, prevents the increase in the protease activity and cPLA2 activity in the membrane and AA release from the cells caused by both low and high doses of A23187, and also inhibits protein kinase C (PKC) activity caused by high doses of A23187. Immunoblot study of the endothelial cell membrane isolated from A23187 (10 microM)-treated cells with polyclonal PKCalpha antibody elicited an increase in the 80 kDa immunoreactive protein band along with an additional 47 kDa immunoreactive fragment. Pretreatment of the cells with aprotinin abolished the 47 kDa immunoreactive fragment in the immunoblot. Immunoblot study of the endothelial membrane with polyclonal cPLA2 antibody revealed that treatment of the cells with A23187 dose-dependently increases cPLA2 immunoreactive protein profile in the membrane. It therefore appears from the present study that treatment of the cells with a low dose of A23187 (1 microM) causes a small increase in an aprotinin-sensitive protease activity and that stimulates cPLA2 activity in the cell membrane without an involvement of PKC. By contrast, treatment of the cells with a high dose of 10 microM of A23187 causes optimum increase in the protease activity and that plays an important role in activating PKCalpha, which subsequently stimulates cPLA2 activity in the cell membrane. Although pretreatment of the cells with pertussis toxin caused ADP ribosylation of a 41 kDa protein in the cell membrane, it did not inhibit the cPLA2 activity and AA release caused by both low and high doses of A23187.

Propionic and methylmalonic acids increase cAMP levels in slices of cerebral cortex of young rats via adrenergic and glutamatergic mechanisms

We have previously described that propionic (PA) and methylmalonic (MMA) acids increased the in vitro phosphorylation of cytoskeletal proteins through cAMP-dependent protein kinase and glutamate. In the present study we investigated the in vitro effects of 1 mM glutamate, 2.5 mM MMA and 2.5 mM PA on cAMP levels in the slices of cerebral cortex of young rats. Results showed that PA, MMA and glutamate increased cAMP levels after 30 min of incubation, while the beta-adrenergic agonist epinephrine elicited a similar effect only at a shorter incubation time. Then effects were prevented by the beta-adrenergic antagonist propranolol, rather than by glutamate antagonists (AP5, CNQX and MCPG), suggesting that they were mediated by beta-adrenergic receptors. In addition, glutamate antagonists per se induced increased cAMP levels; however propranolol prevented only the effect elicited by the metabotropic glutamate antagonist MCPG. Taken together, it is feasible that PA and MMA increase cAMP synthesis via a beta-adrenergic/G protein coupled pathway, in a glutamate-dependent manner. Although additional studies will be necessary to evaluate the importance of these observations for the neuropathology of propionic and methylmalonic acidemias, it is possible that high brain cAMP levels may contribute to a certain extent to the neurological dysfunction of the affected individuals.

Age-related changes in the response of intestinal cells to parathyroid hormone

The concept of the role(s) of parathyroid hormone (PTH), has expanded from that on acting on the classical target tissues, bone and kidney, to the intestine where its actions are of regulatory and developmental importance: regulation of intracellular calcium through modulation of second messengers and, activation of mitogenic cascades leading to cell proliferation. Several causes have been postulated to modify the hormone response in intestinal cells with ageing, among them, alterations of PTH receptor (PTHR1) binding sites, reduced expression of G proteins and hormone signal transduction changes. The current review summarizes the actual knowledge regarding the molecular and biochemical basis of age-impaired PTH receptor-mediated signaling in intestinal cells. A fundamental understanding of why PTH functions are impaired with age will enhance our understanding of its importance in intestinal cell physiology.

The influence of the calcium channel blocker verapamil on experimental glaucoma

PURPOSE

To study the influence of the calcium channel blocker verapamil on the development of glaucoma in the adrenalin-induced experimental model of glaucoma.

METHODS

In the experimental model, glaucoma was induced in albino rabbits by repeated injections of small doses of adrenalin. The criteria for experimental glaucoma were (1) increased IOP, (2) decreased outflow and (3) decreased blood supply to the eye. One group with advanced glaucoma served as a control. In the other 3 groups, instillations of 0.25% verapamil were applied at different stages of the glaucomatous process.

RESULTS

Verapamil blocked the development of experimental glaucoma when applied concurrently with the adrenalin injections, and instillations at the initial or advanced stages of the disease stabilized the progression of glaucoma.

CONCLUSION

We demonstrate that mechanisms involving adrenalin and calcium are involved in glaucoma and that the use of calcium channel blockers is most effective in the early stages of the glaucomatous process.

Involvement of high-density lipoprotein in stimulatory effect of hormones supporting function of the bovine corpus luteum

The hypothesis that epinephrine (noradrenaline, NA) enhances utilisation of high-density lipoproteins (HDL) by bovine luteal cells and that this process involves phospholipase (PL) C and protein kinase (PK) C intracellular pathway was tested. Luteal cells from days 2-4, 5-10 or 11-17 of the oestrous cycle were preincubated for 20 h. Subsequently DMEM/Ham's F-12 medium was replaced by fresh medium and the cells were treated for 6 h as follows: In Experiment I with HDL (5-75 micrograms cholesterol per ml), NA, isoprenaline (ISO) or luteinising hormone (LH). In Experiment II cells were incubated for further 24 h in deficient medium (without FCS) and next treated as in Experiment I. In Experiment III cells were stimulated with NA, ISO or LH alone and together with HDL. In Experiment IV cells were treated with PLC inhibitor (U-73122) or with PKC inhibitor (staurosporine) or stimulator (phorbol 12-myristrate 13-acetate) and with either NA, insulin or LH. Only luteal cells from days 5-10 of the cycle responded on HDL and beta-mimetics (P < 0.05). LH stimulated progesterone secretion from the luteal cells during all stages of the cycle (P < 0.001). Cells incubated in deficient medium and supplemented with HDL secreted as much progesterone as those stimulated by LH in all stages of the cycle. Beta-mimetics were unable to enhance the stimulatory effect of HDL. Blockade of PLC had no influence on progesterone secretion from cells treated with either NA or LH, but this did impair the stimulatory effect of insulin (P < 0.05). Similarly, blockade of PKC by staurosporine impaired (P < 0.05) the effect of insulin only but not that observed after LH or NA treatment. We suggest that: (a) noradrenergic stimulation does not enhance utilisation of cholesterol from HDL for progesterone secretion; (b) the fasting of luteal cells seems to activate enzymes responsible for the progesterone synthesis; (c) effect of NA on progesterone secretion from luteal cells does not involve the PLC-PKC pathway.

Role of beta 1- and beta 2-adrenoceptor subtypes in preconditioning against myocardial dysfunction after ischemia and reperfusion

Using an isolated nonworking rat heart model, this study investigated the role of beta-adrenergic preconditioning (beta-PC) to attenuate myocardial dysfunction after an ischemia/reperfusion injury. After a 20-min stabilization period, the noradrenaline depleted hearts were perfused for 5 min with isoproterenol (ISO) before 40-min global ischemia (I) followed by 30-min reperfusion (R). ISO 0.02 microM provided significant protection versus unconditioned in vivo reserpinized IR control, causing a decrease of creatine kinase (CK) release (mIU/min/g wet weight) on reperfusion in coronary effluent, a preservation of the mean coronary flow (MCF) and preservation of left ventricular function assessed by the rate-pressure product (RPP). These beneficial effects were similar to those of ischemic preconditioning (I-PC) in both nonreserpinized and reserpinized rats. Propranolol (1 microM) and atenolol (10 microM) completely suppressed the ISO preconditioning. In contrast, ICI 118551 (2 microM) a highly selective beta -blocker, did not blunt the salutary effects of ISO on CK release and MCF preservation. These results indicate that ISO pretreatment provides a significant cardioprotection against prolonged ischemic myocardial injury. Although endogenous catecholamines are not necessary for I-PC in isolated rat hearts, cardioprotection provided by beta-adrenergic stimulation is quite similar to I-PC. This significant cardioprotection is mediated less by beta -adrenoceptor than by beta -adrenoceptor activation, which seems to play a crucial role in the beta-PC mechanism.

Epidermal growth factor-receptor tyrosine kinase activity regulates expansion of porcine oocyte-cumulus cell complexes in vitro

We have recently shown that epidermal growth factor (EGF) strongly stimulates expansion of porcine oocyte-cumulus complexes (OCCs) isolated from large follicles (>6 mm) and does not promote expansion of OCCs from small (3-4-mm) follicles. In order to elucidate the role of EGF in OCCs expansion, in the present study, we first examined the presence of EGF receptors (EGFRs) in cumulus cells isolated from follicles of different sizes. Surprisingly, immunoblotting showed that cumulus cells obtained from all follicular size categories contained similar amounts of EGFR protein. On the other hand, we found a dramatic difference in the pattern of protein tyrosine phosphorylation in a comparison of cumulus cells isolated from small and large follicles treated by EGF. Furthermore, tyrosine-phosphorylated EGFR was specifically immunoprecipitated with antiphosphotyrosine antibodies from EGF-treated cumulus cells isolated from the large follicles. This result strongly indicates that only OCCs from the large follicles contain mature EGFRs that are capable of becoming activated by EGF. Remarkably, preincubation of cumulus cells from small follicles (3-4 mm) with FSH strongly increased EGF-stimulated tyrosine phosphorylation to levels comparable with OCCs from large follicles. The FSH-dependent activation of EGFRs was beneficial for expansion of OCCs isolated from the small follicles since OCCs treated sequentially by FSH (3 h) and EGF (1 h) underwent expansion significantly better then OCCs cultured in FSH or EGF alone. We conclude that a FSH-dependent pathway has an important role in the maturation of the EGFR in cumulus cells and that activation of EGFR-dependent signaling is sufficient to induce expansion.

Glucose and reactive oxygen species

PURPOSE OF REVIEW

This review aims at presenting new concepts of glucose-induced damage in diabetes via an increased production of oxygen free radicals.

RECENT FINDINGS

Reactive oxygen species modulate various biological functions by stimulating transduction signals, some of which are involved in diabetes pathogenesis and complications.

SUMMARY

Diabetes is characterized by high glucose concentrations that lead, via several mechanisms (glucose autoxidation, stimulation of the polyol pathway, activation of the reduced form of nicotinamide adenine dinucleotide phosphate oxidase, and production of advanced glycation endproducts), to an increased production of reactive oxygen species. The resulting oxidative stress (the imbalance between reactive oxygen species production and the antioxidant defences) can play a key role in diabetes pathogenesis. Superoxide radicals generated by the reduced form of nicotinamide adenine dinucleotide phosphate oxidase may thus contribute to impaired endothelium-dependent vascular relaxation by the inactivation of nitric oxide, and more generally to vascular dysfunction, thereby contributing to accelerated atherosclerosis in diabetic patients. The increased production of reactive oxygen species induced by hyperglycaemia has also been suggested to be involved in platelet dysfunction, in tissue remodelling (via metalloproteinases), and in redox regulation of glucose transport in skeletal muscle. Beyond the classic treatments for diabetes, new therapeutic strategies involving antioxidants or anti-advanced glycation endproduct molecules are proposed. Future methods could take into account the signalling pathways and genes that are regulated by reactive oxygen species.

Modulatory effect of the adrenergic system upon fibroblast proliferation: participation of beta 3-adrenoceptors

1. The beta3-adrenoceptor agonist ZD 7114, like the non-selective beta-adrenoceptor agonist isoprenaline, but unlike the beta1-adrenoceptor agonist dobutamine and the beta2-adrenoceptor agonist salbutamol, produced an increment on mouse embryonic fibroblast proliferation. The half-maximal stimulation of cell growth occurred at substantially lower concentrations with the beta3-adrenoceptor agonist (EC50: 5.5 x 10(-8) m) than with isoprenaline (EC50: 1.25 x 10(-6) m). 2. The selective beta3-adrenoceptor antagonist SR 5923 OA prevented the beta3-stimulated fibroblast proliferation. Conversely, practolol and butoxamine did not prevent fibroblast growth. 3. Additionally, a decrease of cAMP was obtained in fibroblasts cells upon stimulation with isoprenaline and ZD 7114. 4. The expression of beta-adrenoreceptors on fibroblast cells was also studied by radioligand binding. The Ki values in the presence of beta1- and beta2-adrenoceptor antagonist was two-fold higher than the Ki values for beta3 adrenoceptor antagonist indicating the presence of A3-receptor subtype. 5. Inhibitors of different intracellular coupling pathways including phospholipase C (U 73122), protein kinase C (staurosporine), calcium/calmodulin (trifluoroperazine) and calcium channel (verapamil), prevented the stimulatory actions of the selective beta3-adrenoceptor agonist ZD 7114. 6. The presence of beta3-adrenoceptors on embryonic mouse fibroblast cells may play a role in the modulation of cell growth and biologic activity. The mechanism by which ZD 7114 triggers cell proliferation and function, involves the activation of phospholipase C, PKC, calcium/calmodulin and the influx of calcium.

Modulation of the beta-adrenergic receptor system of vascular smooth muscle cells in vitro and in vivo by chronically elevated endothelin-1 levels

Endothelin-1 (ET-1) levels are chronically elevated in several cardiovascular diseases and correlate with an increased mortality. However, in contrast to acute biological activities such as vasoconstriction, little is known about long-term effects of ET-1. In this study we determined the effects of ET-1 on the beta(2)-adrenergic receptor (AR) system. Incubation of smooth muscle cells with ET-1 for 72 hr led to increased beta(2)AR density as determined by radioligand binding. Experiments with inhibitors of protein and RNA synthesis as well as RT-PCR revealed that beta(2)AR upregulation required de novo synthesis. In addition, protein kinase C but neither NO nor prostaglandin metabolism were involved in this effect. The enhanced expression of beta(2)AR was associated with an increased expression of its stimulatory G-protein and the receptor's ability to stimulate adenylyl cyclase. To study chronic effects of ET-1 in vivo, rats were infused with ET-1 for 3 weeks. Similarly as in cultured cells, prolonged ET-1 exposure led to increased betaAR expression in vivo. As a consequence, beta(2)AR-induced vasodilatation was increased in aortic rings from ET-1-treated animals. Our results therefore suggest that chronically elevated ET-1 levels in vitro and in vivo induce counterregulatory mechanisms by increasing betaARs that attenuate the vasoconstrictive effects of ET-1.

High-fructose diet decreases catalase mRNA levels in rat tissues

Insulin resistance and hyperinsulinemia have recently been identified as independent determinants of several risk factors for cardiovascular disease. The generation of reactive oxygen species (ROS) may play an important role as a final common mediator by which glucose and insulin resistance might contribute to development of cardiovascular disease and hypertension. The aim of the present study was to evaluate changes on mRNA expression of antioxidant enzymes [catalase, Cu-Zn superoxide dismutase (Cu-ZnSOD), MnSOD], blood pressure and metabolic parameters in insulin resistance that follow feeding normotensive Wistar rats a high-fructose-enriched diet. In our investigation 26 normal male Wistar rats were fed a high-fructose diet for 2 weeks (no.=14) or normal chow to serve as a control group (no.=12). In vivo insulin resistance was verified in a subgroup of control and fructose-fed rats by the euglycemic hyperinsulinemic clamp technique at 2 different insulin infusion rates, 29 (submaximal stimulation) and 290 (maximal stimulation) pmol/kg/min respectively. The glucose infusion rate (GIR) was not significantly different in the two groups during the submaximal infusion of insulin (1.4 +/- 0.8 mmol/kg/min in fructose-fed rats vs 1.6 +/- 0.7 mmol/kg/min in control rats, NS) while in fructose-fed rats it was significantly lower (-29.8%) than in control rats during maximal infusion of insulin (2.6 +/- 0.3 mmol/kg/min vs 3.7 +/- 0.3 mmol/kg/min, p<0.05). Fructose feeding markedly reduced the expression of catalase mRNA and Cu-ZnSOD mRNA in the liver, catalase mRNA in the heart (p<0.05). A tendency of fructose feeding to reduce the expression of antioxidant enzymes in skeletal muscle and adipose tissue was also observed (NS). Fructose feeding also increased plasma uric acid (119.9 +/- 30.4 vs 42.1 +/- 10 pmol/l, p<0.05) and systemic blood pressure (128 +/- 4 vs 109 +/- 5 mmHg, p<0.05) respect to control animals. No significant changes were observed in plasma levels of glycemia and tryglycerides. Our study suggests that in non-hyperglycemic, fructose-fed insulin-resistant rats the expression of catalase is inhibited in liver and heart. This condition might lead to higher susceptibility to oxidative stress in insulin resistance. However, an adaptive cellular response to maintain the effectiveness of intracellular signaling pathways mediated by insulin-activated hydrogen peroxide generating systems may also be hypothesized.

Emerging therapeutic targets in bipolar mood disorder

Bipolar mood disorder is a chronic, severe and life-threatening psychiatric illness, whose underlying pathophysiology is still obscure. Lithium is the mainstay of treatment for this illness, with robust acute antimanic and long-term prophylactic effects. Over the past decade, valproate has been another medication shown to have possibly similar mood-stabilising properties to lithium, in double-blind controlled trials. Nonetheless, among patients suffering from bipolar disorder, a substantial percentage appears to respond poorly to currently available pharmacological therapies, including lithium, valproate, carbamazepine and other newer compounds, clearly demonstrating that there is a substantial need for improved therapeutic agents. Very significant effort has been made in the past several years to elucidate the cellular mechanisms by which lithium and valproate produce their therapeutic effects. The available evidence points to a modulatory action of these compounds over multiple neural biochemical pathways and most investigations have found relevant actions of mood stabilisers on intracellular signal transduction mechanisms. Moreover, it has been shown in recent years that lithium and valproate lead to long-term changes in neural plasticity, with eventual neurotrophic and neuroprotective effects. Although these actions are not fully understood, stimulation of transcription factors and effects on gene expression are potentially involved. The search for the mechanisms of action of well-established mood-stabilisers has helped to reveal promising molecular targets to test novel therapeutic approaches. This review will examine the current investigations on the diverse biochemical and molecular pathways regulated by either lithium or valproate and highlight the potential cellular targets for the development of novel mood stabilisers.

The effects of lithium on ex vivo cytokine production

BACKGROUND

Studies suggest that lithium may have profound immunomodulatory effects in animal models as well as in humans.

METHODS

In this study, whole blood cultures from normal control subjects were established for 5 days and the effects of lithium on cytokine production were investigated. Because many of lithium's actions have been postulated to be modulated through phosphoinositide (PI), protein kinase C (PKC) and cyclic adenosine monophosphate (c-AMP) signaling pathways, the effects of myo-inositol and prostaglandin E(2), alone or in combination with lithium, were also investigated.

RESULTS

We found that lithium caused an increase in interleukin-4 and interleukin-10 levels, traditionally classified as T-helper lymphocyte type-2 cytokines, and a decrease in interleukin-2 and interferon-gamma levels, traditionally classified as T-helper lymphocyte type-1 (TH-1) cytokines. This shift cannot be fully explained by lithium's actions on the PI, PKC, or c-AMP messenger systems.

CONCLUSIONS

Monocytes exposed to lithium in the presence of a mitogen for 5 days produced a shift toward the production of TH-2 cytokines and away from the production of TH-1 cytokines. The study suggests that lithium may have complex time-dependent effects on immune function.

Interplay of pituitary adenylate cyclase-activating polypeptide with a silencer element to regulate the upstream promoter of the human gonadotropin-releasing hormone receptor gene

Multiple transcription start sites were identified in the human gonadotropin releasing hormone receptor (hGnRHR) gene. Recently, an upstream promoter residing at -1727/-1674, in vicinity of a CAP site at -1673, was characterized. In this report, we elucidated the underlying mechanisms for the regulation of this promoter. Functionally, this promoter was constitutively suppressed by a silencer element (-1673/-1351) situated immediately downstream to it. On the other hand, pituitary adenylate cyclase-activating polypeptide (PACAP), via the cAMP pathway, was found to be the extracellular cue to control the upstream promoter. Following PACAP-27, PACAP-38 (30 nM) and forskolin (25 microM) treatment, there were significant increases in the reporter gene activities. By deletion analysis, the region residing at -1727 to -1577, containing the distal promoter and 97 bp of the silencer was subsequently found to be responsible for PACAP/cAMP induction. To localize the PACAP-dependent cis-acting element(s) within the silencer, block replacement scanning mutation was performed and a hGnRHR gene PACAP-responsive element (GPRE) was identified at -1676/-1648. The actions of PACAPs and forskolin on the GPRE were further evidenced by gel mobility shift assays. There was an increase in protein binding onto this element only after peptide treatment. As GnRH receptor number on gonadotrope cell surface is a key factor in regulating gonadotropin release, the present study provides an insight into the interplay between PACAP and GnRH receptors on pituitary gonadotropes to control human reproductive functions.

Protein kinase C-mediated down-regulation of beta(2)-adrenergic receptor and gene expression in rat C6 glioma cells

We investigated the regulation of beta(2)-adrenergic receptors (beta(2)AR) by protein kinase C (PKC) in rat C6 glioma cells at the levels of receptor activity, protein expression and gene expression. Cells exposed to 4beta-phorbol-12-myristate-13-acetate (PMA), a potent activator of PKC, exhibited a time- and concentration-dependent decrease in beta(2)AR binding activity. Maximum down-regulation was approximately 50% by 24 h and western blot analysis revealed a parallel decrease in beta(2)AR protein. In addition, PMA treatment resulted in an acute desensitization of beta(2)AR-stimulated cyclic AMP response prior to any reduction in receptor levels. PMA exposure also affected steady-state beta(2)AR mRNA levels in a time-dependent, biphasic manner. During the first 4 h, levels decreased by approximately 60% and then slowly recovered to approximately 75% of control by 24 h. As the reduction in receptor mRNA was not due to a decrease in its stability, we examined beta(2)AR gene transcription by nuclear run-on assays. Transcriptional activity in nuclei from C6 cells treated with PMA for 2 h was reduced by 70% compared to controls. Thus PKC can regulate beta(2)AR at least two levels: the first being an acute desensitization of receptor function, and the second being a more prolonged repression of receptor gene transcription that in turn results in decreased receptor expression.

Conventional protein kinase C isoforms and cross-activation of protein kinase A regulate cardiac Na+ current

We tested the hypothesis that specific isoforms of protein kinase C (PKC) are responsible for modulation of Na+ current (I(Na)) derived from the human cardiac Na+ channel using activators and inhibitors selective for specific PKCs. Experimental results demonstrated that I(Na) suppression was mediated by activation of conventional PKCs (cPKCs) and possibly resulted from channel internalization. In the presence of cPKC inhibition, phorbol ester application unexpectedly increased Na+ current, an effect eliminated by inhibition of protein kinase A. These findings demonstrate complex modulation of cardiac I(Na) by protein kinases and provide further evidence that PKC isoforms have distinct protein targets.

Glucagon and vasopressin V1a receptor signaling in hepatocytes from aging rats

Glucose tolerance is reduced with age. The relationship between this change in glucose homeostasis and signaling of glucagon and vasopressin V1a receptors was investigated in hepatocytes isolated from 10- and 30-month-old female WAG/Rij rats. Binding capacity of hepatocytes for 125I glucagon and 3H vasopressin increased 2- and 1.8-fold, respectively, between 10 and 30 months. Intracellular cAMP accumulation induced by glucagon was 40% greater in hepatocytes of aging rats than of adults, although EC(50) were similar in the two groups. Conversely, phosphodiesterases activity and nucleotides leakage out of the cells were unchanged with age. The rise in intracellular calcium consecutive to the stimulation of V1a receptor was comparable in adult and senescent animals. Finally, glucose release by hepatocyte suspensions was greater in senescent than in adult animals in absence as in presence of glucagon. These experiments suggest that increase in glucagon receptor expression and cAMP generation would contribute to the impaired glucose tolerance characteristic of the aging process.

Influence of nitric oxide and noradrenaline on prostaglandin F(2)(alpha)-induced oxytocin secretion and intracellular calcium mobilization in cultured bovine luteal cells

Although prostaglandin (PG) F(2alpha) released from the uterus has been shown to cause regression of the bovine corpus luteum (CL), the neuroendocrine, paracrine, and autocrine mechanisms regulating luteolysis and PGF(2alpha) action in the CL are not fully understood. A number of substances produced locally in the CL may be involved in maintaining the equilibrium between luteal development and its regression. The present study was carried out to determine whether noradrenaline (NA) and nitric oxide (NO) regulate the sensitivity of the bovine CL to PGF(2alpha) in vitro and modulate a positive feedback cascade between PGF(2alpha) and luteal oxytocin (OT) in cows. Bovine luteal cells (Days 8-12 of the estrous cycle) cultured in glass tubes were pre-exposed to NA (10(-5) M) or an NO donor (S-nitroso-N:-acetylpenicillamine [S-NAP]; 10(-4) M) before stimulation with PGF(2alpha) (10(-6) M). Noradrenaline significantly stimulated the release of progesterone (P(4)), OT, PGF(2alpha), and PGE(2) (P: < 0.01); however, S-NAP inhibited P(4) and OT secretion (P: < 0.05). Oxytocin secretion and the intracellular level of free Ca(2+) ([Ca(2+)](i)) were measured as indicators of CL sensitivity to PGF(2alpha). Prostaglandin F(2alpha) increased both the amount of OT secretion and [Ca(2+)](i) by approximately two times the amount before (both P: < 0.05). The S-NAP amplified the effect of PGF(2alpha) on [Ca(2+)](i) and OT secretion (both P: < 0.001), whereas NA diminished the stimulatory effects of PGF(2alpha) on [Ca(2+)](i) (P: < 0.05). Moreover, PGF(2alpha) did not exert any additionally effects on OT secretion in NA-pretreated cells. The overall results suggest that adrenergic and nitrergic agents play opposite roles in the regulation of bovine CL function. While NA stimulates P(4) and OT secretion, NO may inhibit it in bovine CL. Both NA and NO are likely to stimulate the synthesis of luteal PGs and to modulate the action of PGF(2alpha). Noradrenaline may be the factor that is responsible for the limited action of PGF(2alpha) on CL and may be involved in the protection of the CL against premature luteolysis. In contrast, NO augments PGF(2alpha) action on CL and it may be involved in the course of luteolysis.

Antidepressants: past, present and future

Since the discovery of first antidepressants in mid-1950's, the field has been intensively studied. Several new classes of compounds emerged and several hypotheses on the mechanism of their action were proposed. The novel antidepressants are either selective and reversible monoamine oxidase inhibitors, (e.g., moclobemide), or selective serotonin reuptake inhibitors (e.g., citalopram or paroxetine), or serotonin and noradrenaline reuptake inhibitors (e.g. , venlafaxine). Recently neuropeptides (e.g., thyrotropin-releasing hormone,TRH) or antagonists of neuropeptide receptors (e.g., tachykinin NK(1) receptor) undergo clinical tests. Several hypotheses proposed the predominant involvement of one or few neurotransmitter receptors in the mechanism of antidepressant action, but it is now assumed that several distinct receptor mechanisms' trigger different but converging intracellular signal cascades that activate transcription factors, which, in turn, promote the expression of genes encoding for proteins, that play a crucial role in restoring of neuronal functions involved in mood regulation.

Development and viability of pig oocytes matured in a protein-free medium containing epidermal growth factor

This study examined the ability of epidermal growth factor (EGF) to improve the developmental competence of pig oocytes matured in a protein-free (PF) in vitro maturation (IVM) system. Oocyte maturation was done in one of three media: 1. PF-TCM: tissue culture medium (TCM) 199 + 0.1% polyvinylalcohol (PVA); 2. PF-TCM+EGF: PF-TCM + 10 ng/ml EGF; and 3. +ve CONT: North Carolina State University (NCSU) 23 medium + 10% porcine follicular fluid. All media contained 0.57 mM cysteine. Hormonal supplements, 0.5 microg/mL LH and 0.5 microg/mL FSH, were present only for the first half (20 to 22 h) of the culture period. After maturation, oocytes were co-incubated with frozen-thawed spermatozoa for 5 to 6 h and transferred to embryo culture medium, NCSU 23 containing 0.4% BSA, for 144 h. In Experiment 1, differences in cumulus expansion were observed for oocytes matured in +ve CONT (Category 4), PF-TCM (Category 2) and PF-TCM+EGF (Category 3). However, no significant differences in nuclear maturation to metaphase II stage were observed. In Experiment 2, no differences in fertilization parameters were observed. Significant (P < 0.01) differences in cleavage rates were observed among the three media for a proportion of the oocytes matured (52, 60 and 69% in PF-TCM, PF-TCM+EGF, and +ve CONT, respectively). Oocytes matured in PF-TCM showed the lowest (P < 0.01) blastocyst development (22%). However, the same rate of blastocyst development was obtained for +ve CONT (37%) and PF-TCM+EGF (37%). Blastocyst cell numbers were significantly higher when oocytes were matured in the presence of EGF (26 vs. 37 to 41). In Experiment 3, oocytes matured in PF-TCM+EGF had a significantly (P < 0.05) higher intracellular glutathione (GSH) concentration (5.9 vs. 11.4 pmol/oocyte) compared with PF-TCM. Twenty-two of 25 embryo transfer recipients became pregnant (Experiment 4). Four animals returned to estrus in within 60 days. Six pregnant animals slaughtered at 26 to 45 days had 43 fetuses (range: 4 to 12) and the remaining 12 animals farrowed 82 piglets (range: 3 to 12). These results indicate that EGF enhances the developmental competence of pig oocytes matured in a protein-free culture medium which is correlated with higher GSH level in oocytes. Birth of piglets indicate that embryos derived from oocytes matured in the presence of EGF are viable.

Lithium regulates PKC-mediated intracellular cross-talk and gene expression in the CNS in vivo

It has become increasingly appreciated that the long-term treatment of complex neuropsychiatric disorders like bipolar disorder (BD) involves the strategic regulation of signaling pathways and gene expression in critical neuronal circuits. Accumulating evidence from our laboratories and others has identified the family of protein kinase C (PKC) isozymes as a shared target in the brain for the long-term action of both lithium and valproate (VPA) in the treatment of BD. In rats chronically treated with lithium at therapeutic levels, there is a reduction in the levels of frontal cortical and hippocampal membrane-associated PKC alpha and PKC epsilon. Using in vivO microdialysis, we have investigated the effects of chronic lithium on the intracellular cross-talk between PKC and the cyclic AMP (cAMP) generating system in vivo. We have found that activation of PKC produces an increase in dialysate cAMP levels in both prefrontal cortex and hippocampus, effects which are attenuated by chronic lithium administration. Lithium also regulates the activity of another major signaling pathway the c-Jun N-terminal kinase pathway--in a PKC-dependent manner. Both Li and VPA, at therapeutically relevant concentrations, increase the DNA binding of activator protein 1 (AP-1) family of transcription factors in cultured cells in vitro, and in rat brain ex vivo. Furthermore, both agents increase the expression of an AP-1 driven reporter gene, as well as the expression of several endogenous genes known to be regulated by AP-1. Together, these results suggest that the PKC signaling pathway and PKC-mediated gene expression may be important mediators of lithium's long-term therapeutic effects in a disorder as complex as BD.

Differential redistribution of protein kinase C isoforms by cyclic AMP in HL60 cells

In this study we have analyzed the distribution of protein kinase C isoforms in cytosol, membrane, and nucleus in HL60 cells. Furthermore, we have studied the redistribution of these isoforms after cyclic AMP treatment. Protein kinase C localization and cyclic AMP-induced translocation was demonstrated by Western blot analysis. Cytosol, membrane and nucleus in HL60 cells expressed the abundance of protein kinase C alpha, betaI, betaII, delta, lambda, and zeta isoforms. After cyclic AMP treatment, the amount of protein kinase C betaI and zeta increased only in the nucleus, while protein kinase C delta increased in the three fractions tested. These effects were dependent on the cyclic AMP concentration and duration of action. Our results suggest the existence of cross-talk between the cyclic AMP system and protein kinase C in HL60 cells. Taking into account the processes regulated by protein kinase C, these findings also suggest that cyclic AMP plays a regulatory role in various cellular responses in HL60 cells, such as differentiation and gene expression. The increase observed in PKC delta was due to cyclic AMP-dependent protein kinase C activation, and the synthesis of enzyme was probably activated by the nucleotide.

Growth hormone secretagogue actions on the pituitary gland: multiple receptors for multiple ligands?

1. Growth hormone (GH) secretion is thought to occur under the reciprocal regulation of two hypothalamic hormones, namely GH-releasing hormone (GHRH) and somatostatin (SRIF), through their engagement with specific cell-surface receptors on the anterior pituitary somatotropes. 2. In addition to GHRH and SRIF, synthetic GH-releasing peptides (GHRP) or GH secretagogue(s) (GHS) regulate GH release through the activation of a novel receptor, the GHS receptor (GHS-R). 3. The cloning of the GHS-R from human, swine and rat identifies a novel G-protein-coupled receptor involved in the control of GH secretion and supports the existence of an undiscovered hormone that may activate this receptor. 4. Varieties of intracellular signalling systems are suggested to mediate the action of GHS, which include changes in intracellular free Ca2+ ([Ca2+]i), cAMP, protein kinases A and C, phospholipase C etc. 5. With regard to the use of signalling systems by GHS, especially a new form of GHRP or GHRP-2, a clear species difference has been demonstrated, supporting the possibility of more than one type of GHS-R.

Developmental regulation of effect of epidermal growth factor on porcine oocyte-cumulus cell complexes: nuclear maturation, expansion, and F-actin remodeling

Epidermal growth factor (EGF) efficiently stimulates expansion of mouse and rat oocyte-cumulus complexes (OCC). Contradictory data have been published by several laboratories about the ability of EGF to stimulate expansion of porcine OCC. We assumed that these contradictions may have resulted from heterogeneous conditions used for isolation, culture, and assessment of OCC. The present experiments were designed to test the hypothesis that porcine OCC acquire the ability to synthesize hyaluronic acid (HA) and undergo expansion following EGF-stimulation gradually during the growth of follicles. For this reason, we isolated OCC from follicles of different sizes and assessed quantity of produced HA and proportions of expanding OCC after stimulation by EGF. In addition, we assessed in those OCC changes in morphology of cumulus cells and assembly of F-actin microfilaments, which are necessary for expansion to occur. Finally, nuclear maturation of EGF-stimulated OCC was assessed and its relationship with occurrence of expansion was evaluated. In all experiments, OCC stimulated with FSH were used as positive controls. The results showed that EGF did not stimulate production of HA, rearrangement of F-actin and expansion in OCC isolated from small follicles (<4 mm in diameter). OCC isolated from large preovulatory follicles (6-7 mm in diameter and PMSG-stimulated follicles) underwent efficient expansion when stimulated by EGF (93% and 100%, respectively). EGF dramatically stimulated total production of HA in these OCC and its retention in extracellular matrix of the expanding cumulus. Cumulus cells of the large OCC underwent essential changes of their morphology and extensive rearrangement of F-actin microfilaments following stimulation with EGF. Interestingly, EGF enhanced nuclear maturation of OCC isolated from both small and large follicles, which suggest diversity of signaling pathways controlling maturation and expansion. FSH caused cumulus expansion, F-actin remodeling, and enhancement of oocyte nuclear maturation in OCC originated from both small and large follicles. We conclude that EGF can stimulate expansion of porcine OCC in vitro; however, only of those isolated from large follicles. This indicates that EGF may have a physiological role in regulation of porcine cumulus expansion in preovulatory follicles, presumably as a mediator of signals elicited by the LH surge.

Structural determinants for post-transcriptional stabilization of lactate dehydrogenase A mRNA by the protein kinase C signal pathway

Activation of protein kinase C (PKC) and protein kinase A (PKA) in rat C6 glioma cells increases the half-life of short-lived lactate dehydrogenase (LDH)-A mRNA about 5- and 8-fold, respectively. PKA and PKC act synergistically and prolong LDH-A mRNA half-life more than 21-fold. Similar effects were observed after transfection and transcription of a globin/lactate dehydrogenase minigene consisting of a beta-globin expression vector in which the 3'-untranslated region (UTR) of beta-globin had been replaced with the LDH-A 3'-UTR. Synergism was only obtained by transcription of minigenes containing the entire 3'-UTR and did not occur when truncated 3'-UTR fragments were analyzed. Additional mutational analyses showed that a 20-nucleotide region, named PKC-stabilizing region (PCSR), is responsible for mediating the stabilizing effect of PKC. Previous studies (Tian, D., Huang, D., Short, S., Short, M. L., and Jungmann, R. A. (1998) J. Biol. Chem. 273, 24861-24866) have demonstrated the existence of a cAMP-stabilizing region in LDH-A 3'-UTR. Sequence analysis of PCSR identified a 13-nucleotide AU-rich region that is common to both cAMP-stabilizing region and PCSR. These studies identify a specific PKC-responsive stabilizing element and indicate that interaction of PKA and PKC results in a potentiating effect on LDH-A mRNA stabilization.

Effect of aging on the mechanisms of PTH-induced calcium influx in rat intestinal cells

We have investigated the effects of aging on parathyroid hormone (PTH) modulation of intracellular calcium homeostasis and their relationship to signal transduction pathways in isolated rat duodenal cells (enterocytes). PTH (10(-8)-10(-9) M) increased enterocyte (45)Ca(2+) influx and intracellular Ca(2+) concentration ([Ca(2+)](i)) to a greater extent (twofold and 50%, respectively) in aged (24 months) than in young (3 months) animals. The [Ca(2+)](i) response of old cells to the hormone was slower, lacking the early phase of changes in cytosolic Ca(2+). Ca(2+) influx induced by PTH was prevented by the protein kinase A antagonist Rp-cAMPS in both young and aged enterocytes, whereas neomycin and compound U73122, inhibitors of PLC-catalyzed phosphoinositide hydrolysis, abolished hormone-dependent Ca(2+) influx in young but had no effect on aged cells. Higher basal adenylyl cyclase (AC) activity and cAMP content were detected in old enterocytes. PTH increased the absolute levels of cAMP in aged cells and AC activity of microsomes isolated therefrom to a greater extent (>/= twofold) than in young enterocytes/membranes. In young cells, the hormone also induced a rapid and transient release of inositoltrisphosphate (IP(3)) and diacylglycerol (neomycin-sensitive) at 45 sec, and a delayed phase of DAG at 5 min (neomycin-insensitive). The early formation of IP(3) and DAG was blunted in aged animals. These results suggest that both the PLC and adenylyl cyclase cascades are involved in PTH stimulation of Ca(2+) influx in duodenal cells. During aging, however, only the cAMP pathway is operative, mediating a potentiation of the effects of the hormone. Additional studies are required to establish the relative role of PTH-dependent messenger systems in the regulation of intestinal calcium absorption and age-related abnormalities.

Protein phosphatase-protein kinase interplay modulates alpha 1b-adrenoceptor phosphorylation: effects of okadaic acid

In the present work we studied the effect of protein phosphatase inhibitors on the phosphorylation state and function of alpha(1b)-adrenoceptors. Okadaic acid increased receptor phosphorylation in a time- and concentration-dependent fashion (maximum at 30 min, EC(50) of 30 nM). Other inhibitors of protein phosphatases (calyculin A, tautomycin and cypermethrin) mimicked this effect. Staurosporine and Ro 31-8220, inhibitors of protein kinase C, blocked the effect of okadaic acid on receptor phosphorylation. Neither genistein nor wortmannin altered the effect of okadaic acid. The intense adrenoceptor phosphorylation induced by okadaic acid altered the adrenoceptor-G protein coupling, as evidenced by a small decreased noradrenaline-stimulated [(35)S]GTPgammaS binding. Okadaic acid did not alter the noradrenaline-stimulated increases in intracellular calcium or the production of inositol trisphosphate. Our data indicate that inhibition of protein phosphatases increases the phosphorylation state of alpha(1b)-adrenoceptors; this effect seems to involve protein kinase C. In spite of inducing an intense receptor phosphorylation, okadaic acid alters alpha(1b)-adrenergic actions to a much lesser extent than the direct activation of protein kinase C by phorbol myristate acetate.

Interaction of the novel GH secretagogue hexarelin with GHRH in regulating the secretion of GH by cultured human pituitary somatotrophinomas in vitro

The effects of the novel GH-releasing hexapeptide, Hexarelin, on the secretion of GH in cultured human pituitary somatotrophinomas was further investigated. Hexarelin (20 nmol/L) strongly stimulated GH secretion, which could be reduced by phloretin, but not by RP-cAMPS, an inhibitor of protein kinase A (PKA). (Ac-Tyr1,D-Arg2)-GRF(1-29)-NH2 failed to block the effects of Hexarelin but completely abolished the stimulation of GH secretion exerted by GHRH. When added alone to somatotrophinoma cell cultures, Hexarelin had no effect on cAMP levels, but it potentiated the stimulatory effects of GHRH. These results demonstrated that Hexarelin could directly stimulate GH secretion by human pituitary somatotrophs PKC-dependently, which might be contributed to the activation of the PI transduction system. In addition, Hexarelin could interact with GHRH on the adenylyl cyclase system.

Identification of G protein-coupled signaling pathways in cardiac fibroblasts: cross talk between G(q) and G(s)

Cardiac fibroblasts (CFs) are an important cellular component of myocardial responses to injury and to hypertrophic stimuli. We studied G protein-coupled receptors to understand how CFs integrate signals that activate G(q), G(s), and G(i). We predicted that the second messenger pathways present in CFs were distinct from those in cardiac myocytes and that unique signaling interactions existed in the CFs. ANG II, bradykinin, ATP, and UTP stimulated inositol phosphate (IP) production 2.2- to 7-fold. Each of these agonists elevated intracellular Ca(2+) concentration ([Ca(2+)](i)) via release from the intracellular Ca(2+) storage compartment. Endothelin-1 (ET-1), carbachol, and norepinephrine failed to increase either IP production or [Ca(2+)](i). Although agonists that activated IP and Ca(2+) transients had no effect on cAMP production when administered alone, these agents potentiated the beta(2)-adrenergic response two- to fourfold. Hormones known to inhibit adenylyl cyclase activity in cardiac myocytes, such as ET-1 and carbachol, failed to lower the beta-adrenergic response in fibroblasts. Order of potency and inhibitor data indicate that the functional receptor subtypes in these cells are beta(2), P2Y(2), and AT(1) for isoproterenol, ATP, and ANG II, respectively. We conclude that CFs express functional G protein-linked receptors that couple to G(q) and G(s), with little or no coupling to G(i). The expression of receptors and their coupling to G(q)- but not to G(i)-linked responses distinguishes the signaling in CFs from that in myocytes. Furthermore, agonists that activate G(q) in CFs potentiate stimulation of G(s), an example of signaling cross talk not observed in adult myocytes. These data suggest that G protein-mediated signaling in CFs is unique and may contribute to the specificity of hormone and drug action on individual cell types within the heart.