Adrenergic receptor stimulation of the mitogen-activated protein kinase cascade and cardiac hypertrophy

Beta-adrenergic receptor activation inhibits keratinocyte migration via a cyclic adenosine monophosphate-independent mechanism

There is increasing evidence that G-protein-coupled receptors cross-talk with growth factor receptor-mediated signal transduction in a variety of cell types. We have investigated mechanisms by which the activation of beta-adrenergic receptors, classically GTP-binding proteins coupled receptors, influence the migration of cultured human keratinocytes. We found that iso-proterenol, a beta-adrenergic receptor-selective agonist, inhibited cell migration stimulated by either epidermal growth factor, or extracellular Ca2+ in a concentration-dependent manner. This was prevented by pretreatment of the cells with the beta-adrenergic receptor-selective antagonist timolol. Interestingly, isoproterenol, at a concentration of 1 nm, did not measurably increase intracellular cyclic adenosine monophosphate concentrations yet inhibited cell migration by 50%. To test further if isoproterenol's actions were mediated via activation of adenylyl cyclase, two inhibitors of its activity, 2'5'-dideoxyadenosine and SQ22536, were used. Both compounds significantly diminished iso-proterenol-induced increases in intracellular cyclic adenosine monophosphate concentrations but did not attenuate isoproterenol-induced inhibition of cell migration. Also, forskolin (1 microm) markedly increased intracellular cyclic adenosine monophosphate concentrations but did not significantly inhibit cell migration. As mitogen-activated protein kinases are known to signal growth factor-stimulated cell migration, we examined whether beta-adrenergic receptor-mediated inhibition of keratinocyte migration might occur via inactivation of mitogen-activated protein kinases. We found that isoproterenol inhibited phosphorylation of extracellular signal-regulated kinase mitogen-activated protein kinase in a concentration-dependent manner but had no effect on the phosphorylation of the stress mitogen-activated protein kinases c-jun N-terminal kinase and stress-activated protein kinase-2. Neither forskolin nor a membrane permeable cyclic adenosine monophosphate analog inhibited phosphorylation of any of these mitogen-activated protein kinases. These findings suggest that beta-adrenergic receptor-induced inhibition of keratinocyte migration is mediated through inhibition of the extracellular signal-regulated kinase mitogen-activated protein kinase signaling in a cyclic adenosine monophosphate-independent manner.

Aminoguanidine inhibits mitogen-activated protein kinase and improves cardiac performance and cardiovascular remodeling in failing hearts of salt-sensitive hypertensive rats

OBJECTIVES

Congestive heart failure (CHF) is associated with inducible nitric oxide synthase (iNOS) expression in the failing human heart, and recently we have also demonstrated that iNOS expression was upregulated in Dahl salt-sensitive hypertensive (DS) rats with cardiac dysfunction and vascular remodeling. Thus, we evaluated whether aminoguanidine (AG), a selective iNOS inhibitor, protects against cardiac dysfunction and vascular remodeling in DS rats receiving a high-salt diet.

METHODS

AG (DSHF-AG, 150 mg/kg per day) or vehicle (DSHF-V) were given from left ventricular hypertrophy stage (11 weeks) to CHF stage (18 weeks) for 7 weeks. The left ventricular end-systolic pressure-volume relationship (contractility: E(es)) was measured by conductance catheter.

RESULTS

Decreased E(es) in DSHF-V was significantly ameliorated by AG treatment. The iNOS mRNA and protein expression and phospho-p42/p44 extracellular signal-regulated kinase (ERK) activities in the left ventricle were significantly upregulated in DSHF-V compared with control rats, and significantly suppressed in DSHF-AG compared with DSHF-V. DSHF-V showed a significant increase of perivascular fibrosis and myocardial fibrosis, with all these parameters being significantly improved by AG treatment.

CONCLUSIONS

We demonstrated that the selective iNOS inhibitor, AG, may be at least a potential therapeutic strategy for treating CHF and cardiovascular remodeling.

Role of the local renin-angiotensin system in cardiac damage: a minireview focussing on transgenic animal models

The local generation of all components of the renin-angiotensin system (RAS) in the heart has been the basis for the postulation of a tissue RAS in this organ. Since angiotensin II is involved in the induction of cardiac hypertrophy and fibrosis the local generation of this peptide may be of highest clinical importance. Several transgenic animal models have been generated to evaluate the functional importance of the cardiac RAS. We have established a new hypertensive mouse model lacking local angiotensinogen expression in the heart. In these animals, cardiac weight and collagen synthesis are increased compared to normotensive control mice but to a lesser extent than in mice with equally enhanced blood pressure but intact cardiac angiotensinogen generation. Thus, we have shown that local synthesis of this protein is involved but not essential in the development of cardiac hypertrophy and fibrosis.

Caveolin-3 knock-out mice develop a progressive cardiomyopathy and show hyperactivation of the p42/44 MAPK cascade

A growing body of evidence suggests that muscle cell caveolae may function as specialized membrane micro-domains in which the dystrophin-glycoprotein complex and cellular signaling molecules reside. Caveolin-3 (Cav-3) is the only caveolin family member expressed in striated muscle cell types (cardiac and skeletal). Interestingly, skeletal muscle fibers from Cav-3 (-/-) knock-out mice show a number of myopathic changes, consistent with a mild-to-moderate muscular dystrophy phenotype. However, it remains unknown whether a loss of Cav-3 affects the phenotypic behavior cardiac myocytes in vivo. Here, we present a detailed characterization of the hearts of Cav-3 knock-out mice. We show that these mice develop a progressive cardiomyopathic phenotype. At four months of age, Cav-3 knock-out hearts display significant hypertrophy, dilation, and reduced fractional shortening, as revealed by gated cardiac MRI and transthoracic echocardiography. Histological analysis reveals marked cardiac myocyte hypertrophy, with accompanying cellular infiltrates and progressive interstitial/peri-vascular fibrosis. Interestingly, loss of Cav-3 expression in the heart does not change the expression or the membrane association of the dystrophin-glycoprotein (DG) complex. However, a marker of the DG complex, alpha-sarcoglycan, was specifically excluded from lipid raft domains in the absence of Cav-3. Because activation of the Ras-p42/44 MAPK pathway in cardiac myocytes can drive cardiac hypertrophy, we next assessed the activation state of this pathway using a phospho-specific antibody probe. We show that p42/44 MAPK (ERK1/2) is hyperactivated in hearts derived from Cav-3 knock-out mice. These results are consistent with previous in vitro data demonstrating that caveolins may function as negative regulators of the p42/44 MAPK cascade. Taken together, our data argue that loss of Cav-3 expression is sufficient to induce a molecular program leading to cardiac myocyte hypertrophy and cardiomyopathy.

Alpha(1)-AR-induced positive inotropic response in heart is dependent on myosin light chain phosphorylation

The possible involvement of different kinases in the alpha(1)-adrenoreceptor (AR)-mediated positive inotropic effect (PIE) was investigated in rat papillary muscle and compared with beta-AR-, endothelin receptor- and phorbol ester-induced changes in contractility. The alpha(1)-AR-induced PIE was not reduced by the inhibitors of protein kinase C (PKC), MAPK (ERK and p38), phosphatidyl inositol 3-kinase, or calmodulin kinase II. However, PKC inhibition attenuated the effect of phorbol 12-myristate 13-acetate (PMA) on contractility. alpha(1)-AR-induced PIE was reduced by approximately 90% during inhibition of myosin light chain kinase (MLCK) by 1-(5-chloronaphthalene-1-sulfonyl)1H-hexahydro-1,4-diazepine (ML-9). Endothelin-induced PIE was also reduced by ML-9, but ML-9 had no effect on beta-AR-induced PIE. The Rho kinase inhibitor Y-27632 also reduced the alpha(1)-AR-induced PIE. The alpha(1)-AR-induced PIE in muscle strips from explanted failing human hearts was also sensitive to MLCK inhibition. alpha(1)-AR induced a modest increase in (32)P incorporation into myosin light chain in isolated rat cardiomyocytes. This effect was eliminated by ML-9. The PIE of alpha(1)-AR stimulation seems to be dependent on MLCK phosphorylation.

Genistein attenuates postischemic depressed myocardial function by increasing myofilament Ca2+ sensitivity in rat myocardium

The present study investigated whether genistein, a broad-spectrum tyrosine kinase inhibitor, could increase the myofilament Ca(2+) sensitivity and partially reverse postischemic depressed myocardial function. Left ventricular papillary muscles were isolated from adult Wistar rats and loaded with the Ca2+ indicator, aequorin. The use of fluorocarbon immersion with hypoxia simulated a model of ischemia. Myofilament responsiveness to Ca2+ was evaluated from force-[Ca2+]i relationship recorded during tetani in papillary muscles. Protein levels of troponin I (TnI) were measured in postischemic papillary muscles with the Western blot technique. Isometric contraction was depressed during the period of ischemia and remained low after 60 min of reoxygenation without a corresponding significant change of peak [Ca2+]i in the control group (n = 7). In contrast, the depression of isometric contraction was ameliorated during ischemia in muscle preparations in the presence of genistein (2 micro M; n = 8), and postischemic depressed myocardial contractility partially recovered after a 60-min reperfusion. The myofilament Ca2+ responsiveness was significantly increased in papillary muscles in the presence of genistein. Protein levels of TnI were reduced in postischemic papillary muscles, whereas genistein partially restored decreased protein levels of TnI. Our results reveal that genistein produces an effective attenuation of postischemic depressed myocardial function and improves myofibrillar Ca2+ responsiveness in rat myocardium.

Beta-adrenergic receptor-mediated DNA synthesis in cardiac fibroblasts is dependent on transactivation of the epidermal growth factor receptor and subsequent activation of extracellular signal-regulated kinases

Cardiac hypertrophy often leads to heart failure and is associated with abnormal myocardial adrenergic signaling. This enlargement of myocardial mass can involve not only an increase in cardiomyocyte size, but increased proliferation of cardiac fibroblasts. A potential key player in the cardiac hypertrophic response is the ERK family of MAPKs. To gain mechanistic insight into adrenergic regulation of myocardial mitogenic signaling, we examined beta-adrenergic receptor (beta-AR) stimulation of ERK activation and DNA synthesis in cultured adult rat cardiac fibroblasts, including the involvement of tyrosine kinases in this signaling pathway. Addition of the beta-AR agonist isoproterenol (ISO) to serum-starved cells induced DNA synthesis in a dose-dependent manner, and this was inhibited by selective inhibitors of the epidermal growth factor receptor (EGFR). Importantly and in agreement with the involvement of MAPKs and the EGFR in this response in cardiac fibroblasts, the EGFR inhibitor AG1478 attenuated ISO-induced ERK phosphorylation. Moreover, pretreatment with PP2, a selective inhibitor of the Src tyrosine kinase, attenuated both ISO-mediated EGFR phosphorylation and ERK activation. Furthermore, studies in these cardiac fibroblasts showed that phosphatidylinositol 3-kinase contributed to beta-AR-mediated ERK activation, but not to EGFR activation. Finally, studies using selective inhibitors of matrix metalloproteases indicated that they and heparin-bound EGF shedding were involved in beta-AR-induced ERK activation and subsequent DNA synthesis in cardiac fibroblasts. Because these cells primarily express the beta(2)-AR subtype, our findings indicate that beta(2)-AR-mediated EGFR transactivation of intracellular tyrosine kinase signaling pathways is the major signaling pathway responsible for the adrenergic stimulation of mitogenesis of cardiac fibroblasts.

Expression of cyclin D1 and CDK4 causes hypertrophic growth of cardiomyocytes in culture: a possible implication for cardiac hypertrophy

Differentiated cardiomyocytes have little capacity to proliferate and show the hypertrophic growth in response to alpha1-adrenergic stimuli via the Ras/MEK pathway. In this study, we investigated a role of cyclin D1 and CDK4, a positive regulator of cell cycle, in cultured neonatal rat cardiomyocyte hypertrophy. D-type cyclins including cyclin D1 were induced in cells stimulated by phenylephrine. This induction was inhibited by MEK inhibitor PD98059 and the dominant negative RasN17, but mimicked by expression of the constitutive active Ras61L. Over-expression of cyclin D1 and CDK4 using adenovirus gene transfer caused the hypertrophic growth of cardiomyocytes, as evidenced by an increase of the cell size as well as the amount of cellular protein and its rate of synthesis. However, the cyclin D1/CDK4 kinase activity was not up-regulated in cells treated by hypertrophic stimuli or in cells over-expressing the cyclin D1 and CDK4. Furthermore, a CDK inhibitor, p16, did not inhibit the hypertrophic growth of cardiomyocytes. These results clearly indicated that cyclin D1 and CDK4 have a role in hypertrophic growth of cardiomyocytes through a novel mechanism(s) which appears not to be related to its activity required for cell cycle progression.

Phosphorylation and activation of mitogen- and stress-activated protein kinase-1 in adult rat cardiac myocytes by G-protein-coupled receptor agonists requires both extracellular-signal-regulated kinase and p38 mitogen-activated protein kinase

G-protein-coupled receptor agonists are powerful stimulators of mitogen-activated protein kinase (MAPK) cascades in cardiac myocytes. However, little is known regarding the physiological activation of enzymes downstream of MAPKs. We examined the activation of mitogen- and stress-activated protein kinase-1 (MSK1), a downstream target of MAPKs, in adult rat cardiac myocytes by phenylephrine and endothelin-1. Both agonists induced the phosphorylation of MSK1 at Thr-581 and Ser-376 but not at Ser-360. Maximal phosphorylation was observed at 10-15 min after stimulation and it correlated with increased activity. Maximal activation of MSK1 in adult cardiomyocytes temporally coincided with maximal p38 MAPK activation while activation of the extracellular-signal-regulated kinase (ERK) cascade was more rapid. Phosphorylation and activation of MSK1 was completely inhibited by either PD98059 (ERK1/2 pathway inhibitor) or SB203580 (p38 MAPK inhibitor) alone. These data demonstrate that MSK1 activation in adult rat cardiac myocytes by G-protein-coupled receptor agonists requires the simultaneous activation of both the ERK and p38 MAPK pathways. However, the lack of phosphorylation at Ser-360, an identified phosphorylation site targeted by MAPKs, may indicate that MSK1 is not a direct substrate of ERK1/2 and p38 MAPK in adult rat cardiomyocytes.

Norepinephrine enhances fibrosis mediated by TGF-beta in cardiac fibroblasts

Cardiac fibrosis results from proliferation of interstitial fibroblasts and concomitant increased biosynthesis of extracellular matrix (ECM) components and is often complicated by cardiac hypertrophy. This study was conducted to investigate whether norepinephrine (NE) potentiates transforming growth factor-beta (TGF-beta)-induced cardiac fibrosis. The expression of the cardiac ECM proteins, plasminogen activator inhibitor-1 (PAI-1), fibronectin, and collagen type I, was examined by Western blotting using extracts from neonatal rat primary cardiac fibroblasts. In cardiac fibroblasts, treatment with a combination of NE and TGF-beta1 increased cell proliferation and ECM expression. Luciferase assays were conducted to clarify the effect of NE on TGF-beta signaling. TGF-beta1 (1 ng/mL) increased the specific signaling activity 2-fold, whereas the combination of NE (10 micro mol/L) and TGF-beta1 (1 ng/mL) resulted in an approximate 10-fold increase in specific signaling activity. We confirmed that treatment with NE markedly enhances TGF-beta-induced phosphorylation of activating transcription factor 2 (ATF-2). These results indicated that NE has a synergistic effect on TGF-beta signaling. To determine whether this activation by NE was mediated by the TGF-beta1 receptor, we used a dominant negative vector of the TGF-beta1 type II receptor, and the synergistic effects were inhibited. Furthermore, this synergistic effect was attenuated by a specific inhibitor of p38, SB203680. These data indicate that NE enhances cardiac fibrosis through TGF-beta1 post-receptor signaling, predominantly via the p38 MAP kinase pathway.

Phenylephrine promotes phosphorylation of Bad in cardiac myocytes through the extracellular signal-regulated kinases 1/2 and protein kinase A

Studies in non-cardiomyocytic cells have shown that phosphorylation of the Bcl-2 family protein Bad on Ser-112, Ser-136 and Ser-155 decreases its pro-apoptotic activity. Both phenylephrine (100 microM) and the cell membrane-permeating cAMP analog, 8-(4-chlorophenylthio)-cAMP (100 microM), protected against 2-deoxy-D-glucose-induced apoptosis in neonatal rat cardiac myocytes as assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). In cardiac myocytes, phenylephrine primarily stimulates the alpha-adrenoceptor, but, at high concentrations (100 microM), it also increases the activity of the cAMP-dependent protein kinase, protein kinase A (PKA) through the beta-adrenoceptor. Phenylephrine (100 microM) promoted rapid phosphorylation of Bad(Ser-112) and Bad(Ser-155), though we were unable to detect phosphorylation of Bad(Ser-136). Phosphorylation of Bad(Ser-112) was antagonized by either prazosin or propranolol, indicating that this phosphorylation required stimulation of both alpha(1)- and beta-adrenoceptors. Phosphorylation of Bad(Ser-155) was antagonized only by propranolol and was thus mediated through the beta-adrenoceptor. Inhibitor studies and partial purification of candidate kinases by fast protein liquid chromatography showed that the p90 ribosomal S6 kinases, p90RSK2/3 [which are activated by the extracellular signal-regulated kinases 1 and 2 (ERK1/2)] directly phosphorylated Bad(Ser-112), whereas the PKA catalytic subunit directly phosphorylated Bad(Ser-155). However, efficient phosphorylation of Bad(Ser-112) also required PKA activity. These data suggest that, although p90RSK2/3 phosphorylate Bad(Ser-112) directly, phosphorylation of this site is enhanced by phosphorylation of Bad(Ser-155). These phosphorylations potentially diminish the pro-apoptotic activity of Bad and contribute to the cytoprotective effects of phenylephrine and 8-(4-chlorophenylthio)-cAMP.

From the sarcomere to the nucleus: role of genetics and signaling in structural heart disease

The identification of genetic mutations underlying familial structural heart disease has provided exciting new insights into how alterations in structural components of the cardiomyocyte lead to different forms of cardiomyopathy. Specifically, mutations in components of the sarcomere are frequently associated with hypertrophic cardiomyopathy, whereas mutations in cytoskeletal proteins lead to dilated cardiomyopathy. In addition, extrinsic stresses such as hypertension and valvular disease can produce myocardial remodeling that is very similar to that observed in genetic cardiomyopathy. For myocardial remodeling to occur, changes in gene expression must occur; therefore, changes in contractile function or wall stress must be communicated to the nucleus via signal transduction pathways. The identity of these signaling pathways has become a key question in molecular biology. Numerous signaling molecules have been implicated in the development of hypertrophy and failure, including the beta-adrenergic receptor, G alpha(q) and downstream effectors, mitogen-activated protein kinase pathways, and the Ca(2+)-regulated phosphatase, calcineurin. In the past it has been difficult to discern which signaling molecules actually contributed to disease progression in vivo; however, the development of numerous transgenic and knockout mouse models of cardiomyopathy is now allowing the direct testing of stimulatory and inhibitory molecules in the mouse heart. From this work it has been possible to identify signaling molecules and pathways that are required for different aspects of disease progression in vivo. In particular, a number of signaling pathways have now been identified that may be key regulators of changes in myocardial structure and function in response to mutations in structural components of the cardiomyocyte. Myocardial structure and signal transduction are now merging into a common field of research that will lead to a more complete understanding of the molecular mechanisms that underly heart disease.

Molecular and cellular mechanisms of mechanical stress-induced cardiac hypertrophy

Congestive heart failure is one of the major issues for cardiologists. Since cardiac hypertrophy deteriorates into heart failure, it is important to elucidate the mechanisms of cardiac hypertrophy. Hemodynamic overload, namely mechanical stress, is a major cause for cardiac hypertrophy. Mechanical stress induces various hypertrophic responses such as activation of phosphorylation cascades of many protein kinases, expression of specific genes and an increase in protein synthesis. During this process, secretion and production of vasoactive peptides such as angiotensin II and endothelin-1, are increased and play critical roles in the induction of these hypertrophic responses. Recently, a Ca2+ dependent protein kinase, CaMK, and a Ca2+ dependent protein phosphatase, calcineurin, have attracted great attention as critical molecules that induce cardiac hypertrophy. In this review, we described the mechanisms by which mechanical stress induces cardiac hypertrophy, especially focusing on the role of calcineurin in the development of cardiac hypertrophy.

The transcriptional co-activators CBP and p300 are activated via phenylephrine through the p42/p44 MAPK cascade

The CBP and p300 co-activators play a key role in many aspects of gene regulation being recruited to the DNA via transcription factors that are targets for specific signaling pathways. It has previously been demonstrated that in neuronal cells the ability of CBP and p300 to activate transcription can be directly stimulated by nerve growth factor or calcium-activated signaling pathways. Here we demonstrate that, in cardiac cells, the activity of CBP and p300 is stimulated by phenylephrine (PE) treatment and that they are required for the activation of atrial naturetic factor (ANF) gene expression by PE. Activation of CBP/p300 by PE involves the p42/p44 MAPK pathway and targets primarily the N terminus of p300 and the C terminus of CBP, which are not homologous to one another. To our knowledge, this is the first report of a specific stimulus modulating the activity of CBP and p300 in cardiac cells and it suggests that these factors play an important role in the hypertrophic effect of PE.

Activation of p38 mitogen-activated protein kinases by endothelin and noradrenaline in small arteries, regulation by calcium influx and tyrosine kinases, and their role in contraction

Small-artery responses to vasoconstrictor agonists are important for vascular function. To investigate the signaling pathways involved in contraction, we studied the activation and regulation of p38 mitogen-activated protein kinases (p38MAPKs) and heat shock protein (HSP) kinase by endothelin and noradrenaline in rat mesenteric arteries. Both vasoconstrictors activated p38alpha and/or p38beta but not p38gamma or p38delta, leading to increased HSP kinase activity. p38MAPK activation by noradrenaline was maximum between 2 and 10 minutes and was wholly dependent on calcium influx but insensitive to the tyrosine kinase inhibitor herbimycin A. In contrast, endothelin induced a biphasic response, with activation at 2 and 10 minutes. The early activity was wholly dependent on calcium influx and inhibited by herbimycin A. The later activity was only 50% calcium dependent, was insensitive to herbimycin A, but was 50% inhibited by genistein, a nonselective tyrosine kinase inhibitor. With both agonists, p38MAPK activity returned to basal by 30 minutes. SB203580, a p38MAPK inhibitor, blocked agonist-induced HSP kinase activity, and herbimycin A inhibited activation by endothelin but not by noradrenaline. In addition, SB203580 inhibited noradrenaline-induced contraction but had little effect on contraction to endothelin. These data show that vasoconstrictors use different upstream activators of p38MAPK in vascular tissue and that the p38MAPK pathway is selectively implicated in the contractile response to noradrenaline in small arteries.

Role of protein kinase C in the signal pathways that link Na+/K+-ATPase to ERK1/2

We have shown before that Na(+)/K(+)-ATPase acts as a signal transducer, through protein-protein interactions, in addition to being an ion pump. Interaction of ouabain with the enzyme of the intact cells causes activation of Src, transactivation of EGFR, and activation of the Ras/ERK1/2 cascade. To determine the role of protein kinase C (PKC) in this pathway, neonatal rat cardiac myocytes were exposed to ouabain and assayed for translocation/activation of PKC from cytosolic to particulate fractions. Ouabain caused rapid and sustained stimulation of this translocation, evidenced by the assay of Ca(2+)-dependent and Ca(2+)-independent PKC activities and by the immunoblot analysis of the alpha, delta, and epsilon isoforms of PKC. Dose-dependent stimulation of PKC translocation by ouabain (1-100 microm) was accompanied by no more than 50% inhibition of Na(+)/K(+)-ATPase and doubling of [Ca(2+)](i), changes that do not affect myocyte viability and are known to be associated with positive inotropic, but not toxic, effects of ouabain in rat cardiac ventricles. Ouabain-induced activation of ERK1/2 was blocked by PKC inhibitors calphostin C and chelerythrine. An inhibitor of phosphoinositide turnover in myocytes also antagonized ouabain-induced PKC translocation and ERK1/2 activation. These and previous findings indicate that ouabain-induced activation of PKC and Ras, each linked to Na(+)/K(+)-ATPase through Src/EGFR, are both required for the activation of ERK1/2. Ouabain-induced PKC translocation and ERK1/2 activation were dependent on the presence of Ca(2+) in the medium, suggesting that the signal-transducing and ion-pumping functions of Na(+)/K(+)-ATPase cooperate in activation of these protein kinases and the resulting regulation of contractility and growth of the cardiac myocyte.

Allosteric effects of G protein overexpression on the binding of beta-adrenergic ligands with distinct inverse efficacies

Allosteric models of G protein-coupled receptors predict that G protein influences the spontaneous isomerization between inactive (R) and active (R*) conformations. Since inverse agonists have been proposed to preferentially bind to the inactive and uncoupled form(s), changes in the G protein content should influence the binding properties of these ligands. To test this hypothesis, we systematically assessed the effect of G proteins on the binding of beta(2)-adrenergic ligands with distinct levels of inverse efficacy. Recombinant baculoviruses encoding the human beta(2)-adrenoreceptor (beta(2)AR) were expressed alone or in combination with G protein subunits in Sf9 cells. Coexpression with the G protein alpha s beta 1 gamma 2 did not influence the relative efficacy of the ligands to inhibit the adenylyl cyclase but induced considerable decrease in number of sites detected by [(3)H]ICI 118551, [(3)H]propranolol, and (125)I-cyanopindolol. This loss was proportional to the inverse efficacy of the ligand used as the radiotracer in the assay. The addition of Gpp(NH)p inhibited the effects of G protein overexpression indicating that the G proteins acted allosterically. Consistent with this notion, Western blot analysis revealed that coexpression with the G proteins was not accompanied by a loss of immunoreactive beta(2)AR. Such allosteric effects of the G proteins were also observed in mammalian cells expressing endogenous level of G proteins indicating that the phenomenon is not unique to overexpression systems. Taken together, these results demonstrate that the apparent receptor number detected by radiolabeled inverse agonists is affected by the content in G proteins as a result of their influence on R/R* isomerization.

Signal-transducing function of Na+-K+-ATPase is essential for ouabain's effect on [Ca2+]i in rat cardiac myocytes

We showed before that Na+-K+-ATPase is also a signal transducer in neonatal rat cardiac myocytes. Binding of ouabain to the enzyme activates multiple signal pathways that regulate cell growth. The aims of this work were to extend such studies to adult cardiac myocytes and to determine whether the signal-transducing function of Na+/K+-ATPase regulates the well-known effects of ouabain on intracellular Ca2+ concentration ([Ca2+]i). In adult myocytes, ouabain activated protein tyrosine phosphorylation and p42/44 mitogen-activated protein kinases (MAPKs), increased production of reactive oxygen species (ROS), and raised both systolic and diastolic [Ca2+]i. Pretreatment of myocytes with several Src kinase inhibitors, or overexpression of a dominant negative Ras, antagonized ouabain-induced activation of MAPKs and increases in [Ca2+]i. Treatment with PD-98059 (a MAPK kinase inhibitor) or overexpression of a dominant negative MAPK kinase 1 also ablated the effect of ouabain on MAPKs and [Ca2+]i. N-acetyl-cysteine, which blocks the effect of ouabain on ROS, did not prevent the ouabain-induced rise in [Ca2+]i. Clearly, the activation of the Ras/MAPK cascade, but not ROS generation, is necessary for ouabain-induced increases in [Ca2+]i in rat cardiac myocytes.

Cross-talk between the ERK and p70 S6 kinase (S6K) signaling pathways. MEK-dependent activation of S6K2 in cardiomyocytes

The alpha(1)-adrenergic agonist phenylephrine (PE) and insulin each stimulate protein synthesis in cardiomyocytes. Activation of protein synthesis by PE is involved in the development of cardiac hypertrophy. One component involved here is p70 S6 kinase 1 (S6K1), which lies downstream of mammalian target of rapamycin, whose regulation is thought to involve phosphatidylinositol 3-kinase and protein kinase B (PKB). S6K2 is a recently identified homolog of S6K1 whose regulation is poorly understood. Here we demonstrate that in adult rat ventricular cardiomyocytes, PE and insulin each activate S6K2, activation being 3.5- and 5-fold above basal, respectively. Rapamycin completely blocked S6K2 activation by either PE or insulin. Three different inhibitors of MEK1/2 abolished PE-induced activation of S6K2 whereas expression of constitutively active MEK1 activated S6K2, without affecting the p38 mitogen-activated protein kinase and JNK pathways, indicating that MEK/ERK signaling plays a key role in regulation of S6K2 by PE. PE did not activate PKB, and expression of dominant negative PKB failed to block activation of S6K2 by PE, indicating PE-induced S6K2 activation is independent of PKB. However, this PKB mutant did partially block S6K2 activation by insulin, indicating PKB is required here. Another hypertrophic agent, endothelin 1, also activated S6K2 in a MEK-dependent manner. Our findings provide strong evidence for novel signaling connections between MEK/ERK and S6K2.

Targeted overexpression of ornithine decarboxylase enhances beta-adrenergic agonist-induced cardiac hypertrophy

These studies were designed to determine the consequences of constitutive overexpression of ornithine decarboxylase (ODC) in the heart. Induction of ODC is known to occur in response to agents that induce cardiac hypertrophy. However, it is not known whether high ODC levels are sufficient for the development of a hypertrophic phenotype. Transgenic mice were generated with cardiac-specific expression of a stable ODC protein using the alpha-myosin heavy-chain promoter. Founder lines with >1000-fold overexpression of ODC in the heart were established, resulting in a 50-fold overaccumulation of putrescine, 4-fold elevation in spermidine, a slight increase in spermine and accumulation of large amounts of cadaverine compared with littermate controls. Despite these significant alterations in polyamines, myocardial hypertrophy, as measured by ratio of heart to body weight, did not develop, although atrial natriuretic factor RNA was slightly elevated in transgenic ventricles. However, stimulation of beta-adrenergic signalling by isoproterenol resulted in severe hypertrophy and even death in ODC-overexpressing mice without further altering polyamine levels, compared with only a mild hypertrophy in littermates. When beta1-adrenergic stimulation was blocked by simultaneous treatment with isoproterenol and the beta1 antagonist atenolol, a significant, although reduced, hypertrophy was still present in the hearts of transgenic mice, suggesting that both beta1 and beta2 adrenergic receptors contribute to the hypertrophic phenotype. Therefore these mice provide a model to study the in vivo co-operativity between high ODC activity and activation of other pathways leading to hypertrophy in the heart.

Isoproterenol activates extracellular signal-regulated protein kinases in cardiomyocytes through calcineurin

BACKGROUND

Extracellular signal-regulated kinases (ERKs) and calcineurin have been reported to play important roles in the development of cardiac hypertrophy. We examined here the relation between calcineurin and ERKs in cardiomyocytes.

METHODS AND RESULTS

Isoproterenol activated ERKs in cultured cardiomyocytes of neonatal rats, and the activation was abolished by chelation of extracellular Ca(2+) with EGTA, blockade of L-type Ca(2+) channels with nifedipine, or depletion of intracellular Ca(2+) stores with thapsigargin. Isoproterenol-induced activation of ERKs was also significantly suppressed by calcineurin inhibitors in cultured cardiomyocytes as well as in the hearts of mice. Isoproterenol failed to activate ERKs in either the cultured cardiomyocytes or the hearts of mice that overexpress the dominant negative mutant of calcineurin. Isoproterenol elevated intracellular Ca(2+) levels at both systolic and diastolic phases and dose-dependently activated calcineurin. Inhibition of calcineurin also attenuated isoproterenol-stimulated phosphorylation of Src, Shc, and Raf-1 kinase. The immunocytochemistry revealed that calcineurin was localized in the Z band, and isoproterenol induced translocation of calcineurin and ERKs into the nucleus.

CONCLUSIONS

Calcineurin, which is activated by marked elevation of intracellular Ca(2+) levels by the Ca(2+)-induced Ca(2+) release mechanism, regulates isoproterenol-induced activation of ERKs in cardiomyocytes.

Obesity is associated with impaired ventricular protein kinase C-MAP kinase signaling and altered ANP mRNA expression in the heart of adult Zucker rats

BACKGROUND

In the obesity model of the Zucker rat, myocardial protein kinase C (PKC) activation by phorbol ester is impaired. The influence of obesity on myocardial cell signaling was investigated by studying the activation of PKC isozymes and MAP kinases (MAPK) p38 and p42/44 as well as the induction of ANP mRNA.

METHODS

Isolated hearts obtained from 17-week-old lean and obese Zucker rats were perfused with 200 nM phorbol 12-myristate 13-acetate (PMA) at different time periods. Immunodetectable PKC isozymes, phosphorylated-MAPK, and ANP mRNA were determined by Western and Northern blots, respectively.

RESULTS

PMA promoted a marked transient translocation of ventricular PKCalpha from the cytosol to the membranes within 10 minutes in lean rats, whereas it had a much weaker effect in obese rats. Moreover, PMA induced a significant activation of PKCdelta in lean but not in obese rat hearts. After PKC activation, increases in phosphorylation levels of myocardial p38 and p42 MAPK were approximately 3-fold higher in lean rats than in obese animals. Concerning the induction of ANP, PMA transiently tripled ANP mRNA within 60 minutes in lean but not in obese rats.

CONCLUSIONS

In the genetically obese Zucker rat, the myocardial signal transduction cascade PKC-MAPK-ANP mRNA seems to be markedly impaired. It can be speculated that this abnormal cardiac cell signaling in obese rats reflects an early phase in the cardiac pathogenesis accompanying obesity.

Effects of cilnidipine on nitric oxide and endothelin-1 expression and extracellular signal-regulated kinase in hypertensive rats

We evaluated the effects of cilnidipine, a long-acting Ca(2+) channel antagonist, on endothelial nitric oxide synthase (eNOS), preproendothelin-1 and endothelin ETA receptor expression in the left ventricle, and evaluated the relations between these effects and coronary microvascular remodeling and extracellular signal-regulated kinases belonging to one subfamily of mitogen-activated protein kinases in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Cilnidipine (DOCA-cilnidipine, 1 mg/kg/day, subdepressor dose) or vehicle (DOCA-vehicle) was given after induction of DOCA-salt hypertension for 5 weeks. The eNOS mRNA and protein expression in the left ventricle was significantly lower in DOCA-vehicle than in control rats and significantly higher in DOCA-cilnidipine than in DOCA-vehicle rats. Preproendothelin-1 and endothelin ETA receptor expression levels and phospho-p42/p44 extracellular signal-regulated kinase activities were significantly increased in DOCA-vehicle compared with control rats and significantly suppressed in DOCA-cilnidipine compared with DOCA-vehicle rats. DOCA-vehicle rats showed a significant increase in the wall-to-lumen ratio, perivascular fibrosis and myocardial fibrosis, with all these parameters being significantly improved by cilnidipine. These results led us to conclude that phospho-p42/p44 extracellular signal-regulated kinase activities may contribute to the coronary microvascular remodeling of DOCA rats and that protective effects of cilnidipine on cardiovascular remodeling may be at least in part mediated by an increased eNOS expression and a decreased endothelin-1 and endothelin ETA receptor expression in the left ventricle.

The molecular physiology of the cardiac transient outward potassium current (I(to)) in normal and diseased myocardium

G. Y. Oudit, Z. Kassiri, R. Sah, R. J. Ramirez, C. Zobel and P. H. Backx. The Molecular Physiology of the Cardiac Transient Outward Potassium Current (I(to)) in Normal and Diseased Myocardium. Journal of Molecular and Cellular Cardiology (2001) 33, 851-872. The Ca(2+)-independent transient outward potassium current (I(to)) plays an important role in early repolarization of the cardiac action potential. I(to)has been clearly demonstrated in myocytes from different cardiac regions and species. Two kinetic variants of cardiac I(to)have been identified: fast I(to), called I(to,f), and slow I(to), called I(to,s). Recent findings suggest that I(to,f)is formed by assembly of K(v4.2)and/or K(v4.3)alpha pore-forming voltage-gated subunits while I(to,s)is comprised of K(v1.4)and possibly K(v1.7)subunits. In addition, several regulatory subunits and pathways modulating the level and biophysical properties of cardiac I(to)have been identified. Experimental findings and data from computer modeling of cardiac action potentials have conclusively established an important physiological role of I(to)in rodents, with its role in large mammals being less well defined due to complex interplay between a multitude of cardiac ionic currents. A central and consistent electrophysiological change in cardiac disease is the reduction in I(to)density with a loss of heterogeneity of I(to)expression and associated action potential prolongation. Alterations of I(to)in rodent cardiac disease have been linked to repolarization abnormalities and alterations in intracellular Ca(2+)homeostasis, while in larger mammals the link with functional changes is far less certain. We review the current literature on the molecular basis for cardiac I(to)and the functional consequences of changes in I(to)that occur in cardiovascular disease.

Oligomerization of G-protein-coupled transmitter receptors

Examples of G-protein-coupled receptors that can be biochemically detected in homo- or heteromeric complexes are emerging at an accelerated rate. Biophysical approaches have confirmed the existence of several such complexes in living cells and there is strong evidence to support the idea that dimerization is important in different aspects of receptor biogenesis and function. While the existence of G-protein-coupled-receptor homodimers raises fundamental questions about the molecular mechanisms involved in transmitter recognition and signal transduction, the formation of heterodimers raises fascinating combinatorial possibilities that could underlie an unexpected level of pharmacological diversity, and contribute to cross-talk regulation between transmission systems. Because G-protein-coupled receptors are major pharmacological targets, the existence of dimers could have important implications for the development and screening of new drugs. Here, we review the evidence supporting the existence of G-protein-coupled-receptor dimerization and discuss its functional importance.

Beta-adrenergic cardiac hypertrophy is mediated primarily by the beta(1)-subtype in the rat heart

Myocardial beta-adrenergic receptors (beta -ARs) consist of beta(1)- and beta(2)-subtypes, which mediate distinct signaling mechanisms. We examined which beta-AR subtype mediates cardiac hypertrophy. The beta(2)-subtype is predominant in neonatal rat cardiac myocytes (beta(1), 36%vbeta(2), 64%), while the beta(1)-subtype predominates in the adult rat heart (59%v 41%). Stimulation of cultured cardiac myocytes in vitro with isoproterenol (ISO), an agonist for beta(1)- and beta(2)-ARs, caused hypertrophy of myocytes along with increases in transcription of atrial natriuretic factor (ANF) and actin reorganization. All of these ISO-mediated myocyte responses in vitro were inhibited by a beta(1)-AR antagonist, betaxolol, but not by a beta(2)-AR antagonist, ICI 118551. Pertussis toxin failed to affect ISO-induced increases in total protein/DNA content and ANF transcription in vitro. ISO increased LV weight/body weight and ANF transcription in the adult rat in vivo, which were also inhibited by betaxolol but not by ICI 118551. These results suggest that beta -AR stimulated hypertrophy is mediated by the beta(1)-subtype and by a pertussis toxin-insensitive mechanism

Reactive oxygen species mediate alpha-adrenergic receptor-stimulated hypertrophy in adult rat ventricular myocytes

Norepinephrine (NE) causes hypertrophic growth of cardiac myocytes via stimulation of alpha1-adrenergic receptors (alpha1-AR). Reactive oxygen species (ROS) can act as signaling molecules for cell growth. Accordingly, we tested the hypothesis that ROS mediate alpha1-AR-stimulated hypertrophic growth in adult rat ventricular myocytes (ARVM). NE increased the level of intracellular ROS as assessed by lucigenin chemiluminescence or cytochrome c reduction, and this effect was prevented by the superoxide dismutase (SOD)-mimetic MnTMPyP. NE also caused the induction of MnSOD mRNA. alpha1-AR stimulation with NE (1 microM) in the presence of propranolol (2 microM) for 48-96 h caused a hypertrophic growth phenotype characterized by a 36+/-3% increase in 3H-leucine incorporation, a 49+/-14% increase in protein accumulation, a six-fold induction of atrial natriuretic peptide mRNA, actin filament reorganization, and the induction of MnSOD mRNA. These responses were all prevented by pretreatment with the alpha1-AR-selective antagonist prazosin (100 n M) or the SOD-mimetics MnTMPyP (50 microM) and Euk-8 (100 microM). MnTMPyP had no effect on alpha1-AR-stimulated 3H-inositol phosphate turnover or the hypertrophic phenotype caused by the protein kinase C activator phorbol-12-myristate-13-acetate. Thus, ROS play a critical role in mediating the hypertrophic growth response to alpha1-AR-stimulation in ARVM.

Low catecholamine concentrations protect adult rat ventricular myocytes against apoptosis through cAMP-dependent extracellular signal-regulated kinase activation

Catecholamines have complex effects on cardiac myocyte growth and survival, including the triggering of apoptosis at high concentration. Here, we examined whether at a lower concentration, catecholamine protected adult rat ventricular myocytes from apoptosis in vitro. Myocytes were exposed to staurosporine (ST, 10 microM) for 18 h, with or without epinephrine (0.1 or 10 microM) or fetal calf serum (10%). Apoptosis was assessed after 48 h of culture in terms of DNA fragmentation (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling method, DNA gel electrophoresis). Epinephrine (0.1 microM) and serum reduced ST-induced myocyte apoptosis by approximately 50% (n = 12 cultures, P <.001), whereas epinephrine and serum alone did not influence the low apoptotic rate in control cultures. In contrast, 10 microM epinephrine induced marked apoptosis in ST-free conditions. The protective effects of 0.1 microM epinephrine and serum were blunted by the tyrosine kinase inhibitor genistein (n = 12 cultures, P <. 001). Extracellular signal-regulated kinase (ERK) activity was stimulated by 0.1 microM epinephrine but not by 10 microM epinephrine. Furthermore, the protective effect of epinephrine was mimicked by isoproterenol (1 microM) and forskolin (1 microM) but not by phenylephrine (10 microM) and was blunted by propranolol (10 microM) but not by prazozin (10 microM). Finally, isoproterenol and forskolin activated ERK, an effect that was blunted by propranolol. In conclusion, low epinephrine concentrations attenuate ST-induced apoptosis of adult cardiac myocytes in vitro, an effect mediated by coupling between the cAMP pathway and ERK activation. This suggests that a minimal adrenergic tone is essential for myocyte survival in conditions of unusual stress.

Tyrosine kinase signaling in action potential shortening and expression of HSP72 in late preconditioning

We investigated the role of tyrosine kinase (TK) signaling in the opening of the ATP-sensitive K(+) (K(ATP)) channel and 72-kDa heat shock protein (HSP72) expression during late preconditioning. Rabbits were subjected to surgical operation (sham) or were preconditioned (PC) with four cycles of 5 min of ischemia and 10 min of reperfusion. Twenty-four hours later, animals were subjected to 30 min of ischemia and 180 min of reperfusion. Genistein (1 mg/kg ip) was used to block the receptor TK. Six groups were studied: control, sham, genistein-sham, PC, genistein-PC, and vehicle-PC group (1% dimethyl sulfoxide). Genistein or vehicle was given 30 min before the surgical procedure. Genistein pretreatment decreased the expression of HSP72 in PC hearts and suppressed action potential duration shortening during ischemia in sham and PC groups. Infarct size (%risk area) was reduced in the PC (11.6 +/- 1.0%) and vehicle-PC (19.3 +/- 2.0%) compared with the control (40.0 +/- 3.8%) or sham (46.0 +/- 2.0%) groups (P < 0.05). Genistein pretreatment increased infarct size to 46.4 +/- 4.1% in the PC hearts. We conclude that TK signaling is involved in K(ATP) channel opening and HSP72 expression during late PC.

Phosphorylation of elk-1 by MEK/ERK pathway is necessary for c-fos gene activation during cardiac myocyte hypertrophy

Cardiac hypertrophy is associated with specific alterations in myocardial gene expression; however, the exact mechanisms responsible for altered gene expression are poorly defined. The goal of this study was to investigate whether signaling kinases that are activated during cardiac hypertrophy directly modulate transcription factor activity and regulate gene expression. In an effort to understand this process, we focused our studies on the transcriptional activation of c-fos gene through the serum response element (SRE)/ternary complex factor (TCF) element, during phenylephrine-induced myocyte hypertrophy. In this study, we show that phosphorylated Elk-1, a TCF, binds to c-fos SRE and its binding to SRE is increased upon phenylephrine stimulation. Phenylephrine treatment activates phosphorylation of Elk-1 in the nucleus within five minutes and Elk-1-dependent transcriptional activation is abolished by inhibitors selective for MEK/ERK kinases. These studies implicate that phosphorylation of Elk-1 by ERK kinase pathway is important for early gene activation during phenylephrine-induced myocyte hypertrophy.

Beta 3- and alpha1-adrenergic Erk1/2 activation is Src- but not Gi-mediated in Brown adipocytes

A novel signaling pathway for mediation of beta(3)-adrenergic activation of the mitogen-activated protein kinases Erk1/2 (associated with proliferation, differentiation, and apoptosis) has recently been proposed, which implies mediation via constitutively coupled G(i)-proteins and Gbetagamma-subunits, distinct from the classical cAMP pathway of beta-adrenergic stimulation. To verify the significance of this pathway in cells in primary cultures that entopically express beta(3)-adrenoreceptors, we examined the functionality of this pathway in cultured brown adipocytes. Norepinephrine activated Erk1/2 via both beta(3) receptors and alpha(1) receptors but not via alpha(2) receptors. Forskolin induced Erk1/2 activation similarly to beta(3) activation, indicating cAMP-mediation; this induction could be inhibited with H89, implying protein kinase A mediation. The G(i)-pathway was functional in these cells, as pertussis toxin increased agonist-induced cAMP accumulation. However, pertussis toxin was unable to affect adrenergically induced Erk1/2 activation. Also, wortmannin was without effect, implying that Gbetagamma activation of the phosphatidylinositol 3-kinase pathway was not involved. PP1/2, which inhibits Src, abolished both beta(3)- and alpha(1)-induced Erk1/2 activation. Thus, the proposed novel G(i) pathway for beta(3) mediation is not universal, because it is not functional in the untransformed primary cell culture system with entopically expressed beta(3) receptors examined here. Here, the beta(3) signal is mediated classically via cAMP/protein kinase A. beta(3) and alpha(1) signals converge at Src, which thus mediates Erk1/2 activation in both pathways.

Cardioprotective mechanism of ischemic preconditioning is impaired by postinfarct ventricular remodeling through angiotensin II type 1 receptor activation

BACKGROUND

Activation of protein kinase C-linked receptors and subsequent opening of the mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channel are crucial in preconditioning (PC). This study examined whether postinfarct ventricular remodeling interferes with the PC mechanism.

METHODS AND RESULTS

Two weeks before isolation of hearts, rabbits underwent a sham operation or coronary ligation (COL) to induce remodeling. Isolated buffer-perfused hearts were subjected to 30-minute global ischemia/2-hour reperfusion, and infarct size was expressed as a percentage of the left ventricle (%I/LV), from which the scarred infarct by COL was excluded. Although %I/LV was similar in sham-operated and remodeled hearts (52.9+/-6.5% versus 45.8+/-5.2%), PC with 2 episodes of 5-minute ischemia protected sham-operated but not remodeled hearts (%I/LV=18.1+/-2.5% versus 54.8+/-2.9%, P<0.05). Infusion of valsartan (10 mg x kg(-1). d(-1), an angiotensin II type 1 (AT(1)) receptor blocker, for 2 weeks after COL prevented the ventricular remodeling and preserved the response to PC (%I/LV=27.4+/-3.8%), although valsartan alone did not change %I/LV. Diazoxide, a mitoK(ATP) channel opener, protected both sham-operated and remodeled hearts (%I/LV=14.1+/-3.1% and 8.3+/-3.6%).

CONCLUSIONS

The myocardium remodeled after infarction is refractory to PC, which is probably due to interruption of cellular signaling by PC upstream of mitoK(ATP) channels. An AT(1) receptor blocker is beneficial not only for suppression of ventricular remodeling but also for preservation of the PC mechanism.

Activation of mitogen-activated protein kinases is required for alpha1-adrenergic agonist-induced cell scattering in transfected HepG2 cells

Activation of alpha1B-adrenergic receptors ((alpha1B)AR) by phenylephrine (PE) induces scattering of HepG2 cells stably transfected with the (alpha1B)AR (TFG2 cells). Scattering was also observed after stimulation of TFG2 cells with phorbol myristate acetate (PMA) but not with hepatocyte growth factor/scatter factor, epidermal growth factor, or insulin. PMA but not phenylephrine rapidly activated PKCalpha in TFG2 cells, and the highly selective PKC inhibitor bisindolylmaleimide (GFX) completely abolished PMA-induced but not PE-induced scattering. PE rapidly activated p44/42 mitogen-activated protein kinase (MAPK), p38 MAPK, c-Jun N-terminal kinase (JNK), and AP1 (c-fos/c-jun). Selective blockade of p42/44 MAPK activity by PD98059 or by transfection of a MEK1 dominant negative adenovirus significantly inhibited the PE-induced scattering of TFG2 cells. Selective inhibition of p38 MAPK by SB203850 or SB202190 also blocked PE-induced scattering, whereas treatment of TFG2 cells with the PI3 kinase inhibitors LY294002 or wortmannin did not inhibit PE-induced scattering. Blocking JNK activation with a dominant negative mutant of JNK or blocking AP1 activation with a dominant negative mutant of c-jun (TAM67) significantly inhibited PE-induced cell scattering. These data indicate that PE-induced scattering of TFG2 cells is mediated by complex mechanisms, including activation of p42/44 MAPK, p38 MAPK, and JNK. Cell spreading has been reported to play important roles in wound repair, tumor invasion, and metastasis. Therefore, catecholamines acting via the (alpha1)AR may modulate these physiological and pathological processes.

p38 mitogen-activated protein kinase pathway protects adult rat ventricular myocytes against beta -adrenergic receptor-stimulated apoptosis. Evidence for Gi-dependent activation

We have shown that stimulation of beta-adrenergic receptors (beta-AR) by norepinephrine (NE) increases apoptosis in adult rat ventricular myocytes (ARVMs) via a cAMP-dependent mechanism that is antagonized by activation of G(i) protein. The family of mitogen-activated protein kinases (MAPKs) is involved in the regulation of cardiac myocyte growth and apoptosis. Here we show that beta-AR stimulation activates p38 kinase, c-jun N-terminal kinases (JNKs), and extracellular signal-regulated kinase (ERK1/2) in ARVMs. Inhibition of p38 kinase with SB-202190 (10 micrometer) potentiated beta-AR-stimulated apoptosis as measured by flow cytometry and terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) staining. SB-202190 at this concentration specifically blocked beta-AR-stimulated activation of p38 kinase and its downstream substrate MAPK-activated protein kinase-2 (MAPKAPK2). Pertussis toxin, an inhibitor of G(i)/G(o) proteins, blocked the activation of p38 kinase and potentiated beta-AR-stimulated apoptosis. Activation of G(i) protein with the muscarinic receptor agonist carbachol protected against beta-AR-stimulated apoptosis. Carbachol also activated p38 kinase, and the protective effect of carbachol was abolished by SB-202190. PD-98059 (10 micrometer), an inhibitor of ERK1/2 pathway, blocked beta-AR-stimulated activation of ERK1/2 but had no effect on apoptosis. These data suggest that 1) beta-AR stimulation activates p38 kinase, JNKs, and ERK1/2; 2) activation of p38 kinase plays a protective role in beta-AR-stimulated apoptosis in cardiac myocytes; and 3) the protective effects of G(i) are mediated via the activation of p38 kinase.

alpha(1)-adrenoceptor subtypes differentially couple to growth promotion and inhibition in Chinese hamster ovary cells

We have compared the coupling of human alpha(1A)-, alpha(1B)-, and alpha(1D)-adrenoceptors (expressed at approximately 2000 fmol/mg protein in Chinese hamster ovary cells) to cellular growth promotion (as assessed by [(3)H]thymidine incorporation) and related signaling mechanisms. Maximum elevation of intracellular Ca(2+) by the three subtypes occurred with the rank order alpha(1A) (1691 nM) > alpha(1D) (1215 nM) > alpha(1B) (360 nM). In contrast, activation of the ERK, JNK, and p38 forms of mitogen-activated protein kinases occurred with the rank order alpha(1D) > alpha(1A) > alpha(1B). alpha(1A)-Adrenoceptor stimulation inhibited basal and growth factor-stimulated [(3)H]thymidine incorporation by 74%, and this was mitigated by p38 inhibition. In contrast, alpha(1D)-adrenoceptor stimulation enhanced cellular growth by 136%, and this was blocked by two distinct inhibitors of ERK activation. We conclude that within a given cell type alpha(1)-adrenoceptor subtypes can have opposite effects on cellular growth, although their proximal signal transduction displays only quantitative differences.

Requirement of activation of the extracellular signal-regulated kinase cascade in myocardial cell hypertrophy

The signal transduction mechanisms mediating hypertrophic responses in myocardial cells (MCs) remain uncertain. We investigated the role of the extracellular signal-regulated kinase (ERK) cascade in myocardial cell hypertrophy by the strategy of using the adenovirus-mediated overexpression of mitogen-activated protein kinase (MAPK)/ERK kinase (MEK), which is the upstream activator of ERK. We generated recombinant adenoviruses expressing constitutively active MEK1 (MEK1 EE) and dominant negative MEK1 (MEK1 DN). Overexpression of MEK1 EE in MCs activated ERK1/2 and subsequently induced atrial natriuretic peptide (ANP) mRNA expression. In addition, MEK1 EE overexpression resulted in an increase in cell size and sarcomeric reorganization. In contrast, overexpression of MEK1 DN in MCs inhibited endothelin-1 (ET-1)-, phenylephrine (PE)-, leukemia inhibitory factor (LIF)-, isoproterenol (ISP)-, and mechanical stretch-induced ERK activation and ANP mRNA expression. MEK1 DN overexpression inhibited ET-1-, PE-, LIF-, and ISP-induced increases in cell size and sarcomeric reorganization. Consistent with the observed effects on cellular morphology, overexpression of MEK1 EE resulted in an increase in amino acid incorporation, while overexpression of MEK1 DN inhibited ET-1-, PE-, LIF-, ISP-, and mechanical stretch-induced increases in amino acid incorporation. These results indicate that the ERK cascade plays an important role in the signaling pathway leading to the development of myocardial cell hypertrophy.

A farnesyltransferase inhibitor attenuates cardiac myocyte hypertrophy and gene expression

The overexpression of either oncogenic ras or calmodulin in cardiac myocytes can elicit a hypertrophic response, albeit their recruitment by physiologically relevant stimuli remains unresolved. The present study utilized a pharmacological approach to examine the role of ras and calmodulin in norepinephrine- and endothelin-1-stimulated hypertrophy of neonatal rat cardiac myocytes. The pretreatment of cardiac myocytes with the farnesyltransferase inhibitor BMS-191563 (25 microM) increased the level of unfarnesylated ras in the cytosolic fraction, and caused a concomitant 42 +/- 2% decrease in immunodetectable farnesylated ras in the particulate fraction. In parallel, BMS-191563 pretreatment inhibited norepinephrine-mediated 3H-leucine uptake (80 +/- 10% decrease: n = 6; P<0.01), whereas a significant but less pronounced effect on the endothelin-1 response (46 +/- 6% decrease: n = 6; P<0.05) was observed. The calmodulin inhibitor W7 caused a 50 +/- 10% decrease (n = 8; P<0.05) of norepinephrine stimulated protein synthesis, whereas the endothelin-1 response was unaffected. Consistent with the recruitment of ras, BMS-191563 pretreatment attenuated norepinephrine and endothelin-1-stimulated extracellular signal-regulated kinase (ERK) activity. However, PD098059-mediated inhibition of MEK-dependent stimulation of ERK did not alter the hypertrophic response of either agonist. At the molecular level, the pretreatment with either BMS-191563 or W7 attenuated the norepinephrine-mediated increase of prepro-ANP and -BNP mRNA. Likewise, BMS-191563 caused a significant decrease of endothelin-1-mediated expression of the natriuretic peptide mRNAs, but to a lesser extent, as compared to norepinephrine. Thus, the present study has shown the treatment of neonatal rat cardiac myocytes with a farnesyltransferase inhibitor can attenuate the hypertrophic phenotype in response to physiologically relevant stimuli, thereby supporting a role of the small GTP-binding protein ras. Moreover, these data further suggest alternative ras-independent signaling pathways are also implicated in the hypertrophic response, albeit, there appears to exist a stimulus-specific heterogeneity in their recruitment.

Ca2+/calmodulin-dependent kinase II and calcineurin play critical roles in endothelin-1-induced cardiomyocyte hypertrophy

Endothelin-1 (ET-1) induces cardiac hypertrophy. Because Ca(2+) is a major second messenger of ET-1, the role of Ca(2+) in ET-1-induced hypertrophic responses in cultured cardiac myocytes of neonatal rats was examined. ET-1 activated the promoter of the beta-type myosin heavy chain gene (beta-MHC) (-354 to +34 base pairs) by about 4-fold. This activation was inhibited by chelation of Ca(2+) and the blocking of protein kinase C activity. Similarly, the beta-MHC promoter was activated by Ca(2+) ionophores and a protein kinase C activator. beta-MHC promoter activation induced by ET-1 was suppressed by pretreatment with the calmodulin inhibitor, W7, the Ca(2+)/calmodulin-dependent kinase II (CaMKII) inhibitor, KN62, and the calcineurin inhibitor, cyclosporin A. beta-MHC promoter activation by ET-1 was also attenuated by overexpression of dominant-negative mutants of CaMKII and calcineurin. ET-1 increased the activity of CaMKII and calcineurin in cardiac myocytes. Pretreatment with KN62 and cyclosporin A strongly suppressed ET-1-induced increases in [(3)H]phenylalanine uptake and in cell size. These results suggest that Ca(2+) plays a critical role in ET-1-induced cardiomyocyte hypertrophy by activating CaMKII- and calcineurin-dependent pathways.

The Akt-glycogen synthase kinase 3beta pathway regulates transcription of atrial natriuretic factor induced by beta-adrenergic receptor stimulation in cardiac myocytes

We examined the mechanism of atrial natriuretic factor (ANF) transcription by isoproterenol (ISO), an agonist for the beta-adrenergic receptor (betaAR), in cardiac myocytes. ISO only modestly activated members of the mitogen-activated protein kinase family. ISO-induced ANF transcription was not affected by inhibition of mitogen-activated protein kinases, whereas it was significantly inhibited by KN93, an inhibitor of Ca(2+)/calmodulin-dependent kinase (CaM kinase II). Production of 3'-phosphorylated phosphatidylinositides (3 phosphoinositides) was also required for ISO-induced ANF transcription. ISO caused phosphorylation (Ser-473) and activation of Akt through CaM kinase II- and 3 phosphoinositides-dependent mechanisms. Constitutively active Akt increased myocyte surface area, total protein content, and ANF expression, whereas dominant negative Akt blocked ISO-stimulated ANF transcription. ISO caused Ser-9 phosphorylation and decreased activities of GSK3beta. Overexpression of GSK3beta inhibited ANF transcription, which was reversed by ISO. ISO failed to reverse the inhibitory effect of GSK3beta(S9A), an Akt-insensitive mutant. Kinase-inactive GSK3beta increased ANF transcription. Cyclosporin A partially inhibited ISO-stimulated ANF transcription, indicating that calcineurin only partially mediates ANF transcription. These results suggest that both CaM kinase II and 3 phosphoinositides mediate betaAR-induced Akt activation and ANF transcription in cardiac myocytes. Furthermore, betaAR-stimulated ANF transcription is predominantly mediated by activation of Akt and subsequent phosphorylation/inhibition of GSK3beta.

Deactivation of the sympathetic nervous system in patients with chronic congestive heart failure

In this article, we review the basic biology, signal transduction pathways, and clinical pharmacology associated with cardiac beta-adrenergic receptors (beta-ARs) in the context of the use of beta-blocking agents in patients with chronic congestive heart failure. Adrenergic receptors, particularly the beta-AR subtypes (beta(1)-AR and beta(2)-AR), are known to play a critical role in the modulation of cardiac function, providing for both "adaptive" and "maladaptive" compensatory changes. In the context of exercise or self-preservation, the adrenergic nervous system, acting via beta-ARs permits an appropriately rapid, highly-dynamic increase in cardiac function. Conversely, in individuals with chronic congestive heart failure, the sustained, heightened activation of adrenergic nervous system, as manifested by increases in circulating catecholamines, results in down- regulation and desensitization of myocardial beta-ARs, and potentially, significant myocardial damage. A number of recent clinical trials have demonstrated a marked mortality benefit from using beta-blocking agents such as metoprolol and carvedilol in patients with heart failure. The pharmacologic properties of several of these drugs and some of the specifics of their usefulness and limitations are discussed herein.

Epidermal growth factor induces hypertrophic responses and Stat5 activation in rat ventricular cardiomyocytes

Epidermal growth factor (EGF) was tested for its ability to promote hypertrophic responses in neonatal rat ventricular cardiomyocytes. Exposure of these cells to 100 n m EGF for 2-18 h resulted in a time-dependent increase in protein synthesis reaching 174+/-18% of control values at 18 h. After 30 min stimulation, the mRNA levels of c-jun and c-fos were also increased 20- and 36-fold, respectively. We also investigated EGF-induced activation of Stat (signal transducers and activators of transcription) proteins as well as the possible interactions of this signaling pathway with the p38 and p42/44 MAP kinases cascades. EGF did not activate Stat1 and Stat3, but did induce a rapid and transient activation of Stat5, which corresponded mainly to Stat5b DNA-binding. The EGF-promoted Stat5 DNA-binding was decreased in a concentration-dependent manner by the p38 MAPK inhibitor SB 203580 (IC(50)=1.2 microm), whereas it was tripled by 50 micro m PD 98059, an inhibitor of the p42/44 MAPK cascade. This is the first demonstration that EGF increases protein synthesis and early response gene expression in cardiomyocytes, responses considered as markers of hypertrophy in these cells. The results further show that EGF activates Stat5, that this response requires p38 MAPK stimulation, and it is negatively modulated by p42/44 MAPK.

Activation of extracellular signal-regulated protein kinases is associated with a sensitized locomotor response to D(2) dopamine receptor stimulation in unilateral 6-hydroxydopamine-lesioned rats

Evidence indicates that mitogen-activated protein kinase (MAPK) pathways play a crucial role in the neurobiology of the nervous system. In the present study, dopamine receptor-mediated regulation of extracellular signal-regulated kinases (ERKs) was examined in rats in which the nigrostriatal dopaminergic pathway was unilaterally lesioned by 6-hydroxydopamine (6-OHDA). Subcutaneous injections of the D(2) receptor agonist quinpirole significantly increased tyrosine-phosphorylated ERK1/2 in lesioned striatum, whereas the D(1) receptor agonist SKF38393 failed to activate ERKs. Quinpirole-induced phosphorylation of ERK1/2 was seen as early as 3 min and peaked at 15 min after the challenge. In parallel, striatal ERK kinase activity, measured by the in vitro kinase assay, was increased 2.5-fold on the lesioned side after the administration of quinpirole. Immunohistochemical examination of brain sections after quinpirole administration revealed significant increases in ERK1/2 immunostaining in perinuclear and intranuclear areas of striatal neurons. This increase was much more pronounced on the lesioned than the intact side. Furthermore, quinpirole-induced contralateral rotation was decreased by 48.7 and 50.7%, respectively, when the striatal ERK pathway was selectively inhibited by a single intrastriatal injection of the MAPK/ERK kinase inhibitor PD098059 or after a continuous 7 d intrastriatal infusion of ERK1/2 antisense oligodeoxynucleotide. The results demonstrate, for the first time, that the ERK signaling pathway is activated in denervated striatum in response to stimulation of D(2) dopamine receptors and that the resulting imbalance in striatal ERK activity contributes, at least in part, to neuronal plasticity that underlies D(2) dopamine receptor-mediated contralateral rotation in unilateral 6-OHDA denervated rats.

Cardiovascular α1-adrenoceptor subtypes: functions and signaling

α1-Adrenoceptors (α1AR) are G protein-coupled receptors and include α1A, α1B, and α1D subtypes corresponding to cloned α1a, α1b, and α1d, respectively. α1AR mediate several cardiovascular actions of sympathomimetic amines such as vasoconstriction and cardiac inotropy, hypertrophy, metabolism, and remodeling. α1AR subtypes are products of separate genes and differ in structure, G protein-coupling, tissue distribution, signaling, regulation, and functions. Both α1AAR and α1BAR mediate positive inotropic responses. On the other hand, cardiac hypertrophy is primarily mediated by α1AAR. The only demonstrated major function of α1DAR is vasoconstriction. α1AR are coupled to phospholipase C, phospholipase D, and phospholipase A2; they increase intracellular Ca2+ and myofibrillar sensitivity to Ca2+ and cause translocation of specific phosphokinase C isoforms to the particulate fraction. Cardiac hypertrophic responses to α1AR agonists might involve activation of phosphokinase C and mitogen-activated protein kinase via Gq. α1AR subtypes might interact with each other and with other receptors and signaling mechanisms.Key words: cardiac hypertrophy, inotropic responses, central α1-adrenoreceptors, arrythmias.

Activation of extracellular signal-regulated protein kinases is associated with a sensitized locomotor response to D(2) dopamine receptor stimulation in unilateral 6-hydroxydopamine-lesioned rats

Evidence indicates that mitogen-activated protein kinase (MAPK) pathways play a crucial role in the neurobiology of the nervous system. In the present study, dopamine receptor-mediated regulation of extracellular signal-regulated kinases (ERKs) was examined in rats in which the nigrostriatal dopaminergic pathway was unilaterally lesioned by 6-hydroxydopamine (6-OHDA). Subcutaneous injections of the D(2) receptor agonist quinpirole significantly increased tyrosine-phosphorylated ERK1/2 in lesioned striatum, whereas the D(1) receptor agonist SKF38393 failed to activate ERKs. Quinpirole-induced phosphorylation of ERK1/2 was seen as early as 3 min and peaked at 15 min after the challenge. In parallel, striatal ERK kinase activity, measured by the in vitro kinase assay, was increased 2.5-fold on the lesioned side after the administration of quinpirole. Immunohistochemical examination of brain sections after quinpirole administration revealed significant increases in ERK1/2 immunostaining in perinuclear and intranuclear areas of striatal neurons. This increase was much more pronounced on the lesioned than the intact side. Furthermore, quinpirole-induced contralateral rotation was decreased by 48.7 and 50.7%, respectively, when the striatal ERK pathway was selectively inhibited by a single intrastriatal injection of the MAPK/ERK kinase inhibitor PD098059 or after a continuous 7 d intrastriatal infusion of ERK1/2 antisense oligodeoxynucleotide. The results demonstrate, for the first time, that the ERK signaling pathway is activated in denervated striatum in response to stimulation of D(2) dopamine receptors and that the resulting imbalance in striatal ERK activity contributes, at least in part, to neuronal plasticity that underlies D(2) dopamine receptor-mediated contralateral rotation in unilateral 6-OHDA denervated rats.

Hybrid transgenic mice reveal in vivo specificity of G protein-coupled receptor kinases in the heart

G protein-coupled receptor kinases (GRKs) phosphorylate activated G protein-coupled receptors, including alpha(1B)-adrenergic receptors (ARs), resulting in desensitization. In vivo analysis of GRK substrate selectivity has been limited. Therefore, we generated hybrid transgenic mice with myocardium-targeted overexpression of 1 of 3 GRKs expressed in the heart (GRK2 [commonly known as the beta-AR kinase 1], GRK3, or GRK5) with concomitant cardiac expression of a constitutively activated mutant (CAM) or wild-type alpha(1B)AR. Transgenic mice with cardiac CAMalpha(1B)AR overexpression had enhanced myocardial alpha(1)AR signaling and elevated heart-to-body weight ratios with ventricular atrial natriuretic factor expression denoting myocardial hypertrophy. Transgenic mouse hearts overexpressing only GRK2, GRK3, or GRK5 had no hypertrophy. In hybrid transgenic mice, enhanced in vivo signaling through CAMalpha(1B)ARs, as measured by myocardial diacylglycerol content, was attenuated by concomitant overexpression of GRK3 but not GRK2 or GRK5. CAMalpha(1B)AR-induced hypertrophy and ventricular atrial natriuretic factor expression were significantly attenuated with either concurrent GRK3 or GRK5 overexpression. Similar GRK selectivity was seen in hybrid transgenic mice with wild-type alpha(1B)AR overexpression concurrently with a GRK. GRK2 overexpression was without effect on any in vivo CAM or wild-type alpha(1B)AR cardiac phenotype, which is in contrast to previously reported in vitro findings. Furthermore, endogenous myocardial alpha(1)AR mitogen-activated protein kinase signaling in single-GRK transgenic mice also exhibited selectivity, as GRK3 and GRK5 desensitized in vivo alpha(1)AR mitogen-activated protein kinase responses that were unaffected by GRK2 overexpression. Thus, these results demonstrate that GRKs differentially interact with alpha(1B)ARs in vivo such that GRK3 desensitizes all alpha(1B)AR signaling, whereas GRK5 has partial effects and, most interestingly, GRK2 has no effect on in vivo alpha(1B)AR signaling in the heart.

beta(2)-adrenergic receptor overexpression exacerbates development of heart failure after aortic stenosis

BACKGROUND

Beta-adrenergic signaling is downregulated in the failing heart, and the significance of such change remains unclear.

METHODS AND RESULTS

To address the role of beta-adrenergic dysfunction in heart failure (HF), aortic stenosis (AS) was induced in wild-type (WT) and transgenic (TG) mice with cardiac targeted overexpression of beta(2)-adrenergic receptors (ARs), and animals were studied 9 weeks later. The extents of increase in systolic arterial pressure (P<0.01 versus controls), left ventricular (LV) hypertrophy (TG, 94+/-6 to 175+/-7 mg; WT, 110+/-6 to 168+/-10 mg; both P<0.01), and expression of ANP mRNA were similar between TG and WT mice with AS. TG mice had higher incidences of premature death and critical illness due to heart failure (75% versus 23%), pleural effusion (81% versus 45%), and left atrial thrombosis (81% versus 36%, all P<0.05). A more extensive focal fibrosis was found in the hypertrophied LV of TG mice (P<0.05). These findings indicate a more severe LV dysfunction in TG mice. In sham-operated mice, LV dP/dt(max) and heart rate were markedly higher in TG than WT mice (both P<0.01). dP/dt(max) was lower in both AS groups than in sham-operated controls, and this tended to be more pronounced in TG than WT mice (-32+/-5% versus -16+/-6%, P=0.059), although dP/dt(max) remained higher in TG than WT groups (P<0.05).

CONCLUSIONS

Elevated cardiac beta-adrenergic activity by beta(2)-AR overexpression leads to functional deterioration after pressure overload.

Cardiac hypertrophy with preserved contractile function after selective deletion of GLUT4 from the heart

Glucose enters the heart via GLUT1 and GLUT4 glucose transporters. GLUT4-deficient mice develop striking cardiac hypertrophy and die prematurely. Whether their cardiac changes are caused primarily by GLUT4 deficiency in cardiomyocytes or by metabolic changes resulting from the absence of GLUT4 in skeletal muscle and adipose tissue is unclear. To determine the role of GLUT4 in the heart we used cre-loxP recombination to generate G4H(-/-) mice in which GLUT4 expression is abolished in the heart but is present in skeletal muscle and adipose tissue. Life span and serum concentrations of insulin, glucose, FFAs, lactate, and beta-hydroxybutyrate were normal. Basal cardiac glucose transport and GLUT1 expression were both increased approximately 3-fold in G4H(-/-) mice, but insulin-stimulated glucose uptake was abolished. G4H(-/-) mice develop modest cardiac hypertrophy associated with increased myocyte size and induction of atrial natriuretic and brain natriuretic peptide gene expression in the ventricles. Myocardial fibrosis did not occur. Basal and isoproterenol-stimulated isovolumic contractile performance was preserved. Thus, selective ablation of GLUT4 in the heart initiates a series of events that results in compensated cardiac hypertrophy.

Cross-talk between alpha(1B)-adrenergic receptor (alpha(1B)AR) and interleukin-6 (IL-6) signaling pathways. Activation of alpha(1b)AR inhibits il-6-activated STAT3 in hepatic cells by a p42/44 mitogen-activated protein kinase-dependent mechanism

Treatment of primary rat hepatocytes or tranfected HepG2 cells with the alpha(1B)-adrenergic receptor (alpha(1B)AR) agonist phenylephrine (PE) significantly inhibited interleukin 6 (IL-6)-induced STAT3 binding, tyrosine phosphorylation, and IL-6-induced serum amyloid A mRNA expression. Western analyses and in vitro kinase assays indicate that this inhibition is not due to either down-regulation of STAT3 protein expression nor inactivation of upstream-located JAK1 and JAK2. Blocking the new RNA and protein syntheses antagonized the inhibitory effect of PE on IL-6-activated STAT3, suggesting synthesis of an inhibitory factor(s) is involved. The inhibitory effect of PE on IL-6 activation of STAT3 was also abolished by the tyrosine phosphatase inhibitor sodium vanadate, indicating involvement of protein tyrosine phosphatases. Furthermore, preincubation of the cells with the specific MEK1 inhibitor PD98059 or a dominant negative MEK1 reversed the inhibitory effect of PE, and expression of constitutively activated MEK1 alone abolished IL-6-activated STAT3. Taken together, these data indicate that PE inhibits IL-6 activation of STAT3 in hepatic cells by a p42/44 mitogen-activated protein kinase-dependent mechanism, and tyrosine phosphatases are involved. This inhibitory cross-talk between the alpha(1B)AR and IL-6 signaling pathways implicates the alpha(1B)AR involvement in regulating the IL-6-mediated inflammatory responses.

Differential regulation of 46 and 54 kDa jun N-terminal kinases and p38 mitogen-activated protein kinase by human alpha(1A)-adrenoceptors expressed in Rat-1 cells

We have investigated the alpha(1A)-adrenoceptor-mediated activation of 46 and 54 kDa isoforms of c-jun N-terminal kinase (JNK) and of p38 mitogen-activated protein kinase. The alpha(1)-adrenoceptor agonist phenylephrine activated all three kinases but with different time courses and maximal effects. Activation of all three kinases was insensitive to the phosphatidylinositol-3-kinase inhibitor wortmannin but was enhanced by the protein kinase C inhibitor bisindolylmaleimide I; a protein kinase C-activating phorbol ester inhibited JNK but not p38 activation. Activation of 54 kDa JNK, but not of the other two kinases, was inhibited by pertussis toxin and the phospholipase C inhibitor U 73,122. We conclude that alpha(1)-adrenoceptor stimulation activates 46 kDa JNK, 54 kDa JNK and p38 but uses at least partly different pathways to do so.