Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To clarify the intracellular signalling mechanisms of atrial natriuretic factor (ANF), we studied its effect on protein phosphorylation in plasma membranes of bovine adrenal cortical cells. ANF (1 x 10(-7) M) inhibited phosphorylation of the 78-kDa protein kinase C (PKC) and a 240-kDa protein in specific manner. In parallel experiments, cGMP (0.5 mM) inhibited phosphorylation of only the 78-kDa PKC but it did not affect phosphorylation of the 240-kDa protein. Phosphorylation of the 78-kDa PKC was enhanced in a Ca(2+)-/phospholipid-dependent manner. However, after prolonged preincubation of plasma membranes with Ca2+ (0.5 mM), the incorporation of 32P-radioactivity rapidly decreased in the 78-kDa PKC and subsequently increased in the 45- and 48-kDa protein bands due to Ca(2+)-dependent proteolytic degradation of 78-kDa PKC. Polyclonal antibodies against brain PKC were used to immunoblot and immunoprecipitate the 78-kDa PKC. Preincubation of plasma membranes with Ca2+ for varying times, followed by immunoblotting revealed a gradual loss of the immunoreactive 78-kDa PKC band in a time-dependent manner. Immunoprecipitation of phosphorylated 78-kDa PKC in plasma membranes showed that its phosphorylation was significantly inhibited in the presence of ANF as compared to control membranes, phosphorylated in the absence of ANF. The results in this present study document a new signal transduction mechanism of ANF at molecular level which possibly involves dephosphorylation of the 78-kDa PKC and a 240-kDa protein in a cGMP-dependent and -independent manner in bovine adrenal glomerulosa cell membranes.
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PMID:Atrial natriuretic factor inhibits autophosphorylation of protein kinase C and A 240-kDa protein in plasma membranes of bovine adrenal glomerulosa cells: involvement of cGMP-dependent and independent signal transduction mechanisms. 789 67

The peptide hormone atrial natriuretic factor (ANF) exerts its effect in a receptor-mediated fashion and the membrane-bound form of guanylate cyclase represents a biologically active ANF receptor; thus, cGMP has been considered a second messenger of ANF. To understand the mechanisms of ANF action, we have studied its effect on protein phosphorylation in the plasma membrane preparations of murine Leydig tumor (MA-10) cells, which overexpress guanylate cyclase-coupled ANF receptor molecules in high density. After pretreatment of the plasma membranes with ANF (100 nM), a marked decrease in phosphorylation of the 78-kDa protein kinase C (PKC) and the 240-kDa protein was observed. Phosphorylation of the 78-kDa PKC was also inhibited by cGMP (0.1 mM); however, phosphorylation of the 240-kDa protein was not affected by cGMP. The quantitative analyses, as determined by densitometric scanning, revealed that both ANF and cGMP inhibited phosphorylation of the 78-kDa PKC by approximately 75% and 45%, respectively. The inhibitory effect of ANF on phosphorylation of the 240-kDa protein was almost 90%, but cGMP did not show any discernible effect on its phosphorylation in plasma membranes of MA-10 cells. Phosphorylation of the 78-kDa PKC was stimulated by Ca2+ and phospholipids, and it immunologically cross-reacted with antiserum against brain PKC. Furthermore, in these plasma membrane preparations, the 78-kDa PKC was immunoprecipitated and its phosphorylation was inhibited by ANF. These data provide evidence for a new signal transduction mechanism of ANF that negatively regulates phosphorylation of the 78-kDa PKC and the 240-kDa protein in a cGMP-dependent and -independent manner in Leydig cells.
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PMID:Atrial natriuretic factor inhibits the phosphorylation of protein kinase C in plasma membrane preparations of cultured Leydig tumor cells. 805 32

The endothelial cell has a unique intrinsic feature: it produces a most potent vasopressor peptide hormone, endothelin (ET-1), yet it also contains a signaling system of an equally potent hypotensive hormone, atrial natriuretic factor (ANF). This raises two related curious questions: does the endothelial cell also contain an ET-1 signaling system? If yes, how do the two systems interact with each other? The present investigation was undertaken to determine such a possibility. Bovine pulmonary artery endothelial (BPAE) cells were chosen as a model system. Identity of the ANF receptor guanylate cyclase was probed with a specific polyclonal antibody to the 180 kDa membrane guanylate cyclase (mGC) ANF receptor. A Western-blot analysis of GTP-affinity-purified endothelial cell membrane proteins recognized a 180 kDa band; the same antibody inhibited the ANF-stimulated guanylate cyclase activity; the ANF-dependent rise of cyclic GMP in the intact cells was dose-dependent. By affinity cross-linking technique, a predominant 55 kDa membrane protein band was specifically labeled with [125I]ET-1. ET-1 treatment of the cells showed a migration of the protein kinase C (PKC) activity from cytosol to the plasma membrane; ET-1 inhibited the ANF-dependent production of cyclic GMP in a dose-dependent fashion with an EC50 of 100 nM. This inhibitory effect was duplicated by phorbol 12-myristate 13-acetate (PMA), a known PKC-activator. The EC50 of PMA was 5 nM. A PKC inhibitor, 1-(5-isoquinolinyl-sulfonyl)-2-methyl piperazine (H-7), blocked the PMA-dependent attenuation of ANF-dependent cyclic GMP formation. These results demonstrate that the 180 kDa mGC-coupled ANF and ET-1 signaling systems coexist in endothelial cells and that the ET-1 signal negates the ANF-dependent guanylate cyclase activity and cyclic GMP formation. Furthermore, these results support the paracrine and/or autocrine role of ET-1.
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PMID:Interaction of atrial natriuretic factor and endothelin-1 signals through receptor guanylate cyclase in pulmonary artery endothelial cells. 809 23

Atrial natriuretic peptide (ANP) is released from the myocardium after the activation of protein kinase C and/or ischemia, events that are associated with an increase in platelet activating factor (PAF) production in this tissue. In this study we demonstrate that PAF, but not lyso-PAF, induces a concentration-dependent increase in ANP secretion in spontaneously beating neonatal rat cardiomyocytes, a response associated with increases in cellular adenosine 3',5'-cyclic monophosphate (cAMP) formation, calcium influx, and the mobilization of calcium from intracellular stores. cAMP formation and calcium influx appear to play major roles in PAF-induced ANP secretion in this system, insofar as PAF-induced ANP release was substantially reduced in the presence of the (R)-p-diastereoisomer of adenosine 3',5'-cyclic monophosphorothioate (10 microM), whereas both PAF-induced calcium influx and ANP secretion were abolished in the presence of the calcium channel antagonist nifedipine (0.1 microM). Consistent with these results, N6-2'-O-dibutyryl cAMP (DBcAMP, 10 microM) and/or forskolin (0.1 microM) simultaneously increased cAMP production, calcium influx, and ANP release in these cells, with both DBcAMP- and forskolin-induced ANP secretion being fully abolished in the presence of 0.1 microM nifedipine. Taken together, these results suggest that PAF, DBcAMP, and forskolin promote ANP secretion in spontaneously beating cardiomyocytes via the activation of a cAMP-dependent, nifedipine-sensitive myocardial calcium channel and that calcium influx is a major requirement for cAMP-induced ANP secretion in this system.
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PMID:Calcium influx in platelet activating factor-induced atrial natriuretic peptide release in rat cardiomyocytes. 816 60

Endothelin-1 (ET-1) is a potent stimulator of atrial natriuretic factor (ANF) secretion from myocardial cells. In heart tissue there are two ET receptor subtypes (ETA-R and ETB-R), which can be pharmacologically distinguished by the ET isopeptides ET-1 and ET-3. However, the identification of the ET-R subtype responsible for the rapid enhancement of ANF release, which occurs within minutes of exposing cardiac myocytes to ET, has not been investigated. In the present study ET-1 was about 100-fold more potent than ET-3 at stimulating membrane phosphoinositide hydrolysis, protein kinase C activation, and ANF release from purified primary atrial myocytes. These responses were completely abolished by BQ123, an ETA-R antagonist. Radioligand binding analyses showed that competitor peptides displaced 125I-ET-1 binding to atrial myocyte ET-Rs with a rank order of potency of ET-1 >> BQ123 > ET-3, a characteristic ETA-R pharmacological profile. While neither ET-1 or ET-3 altered forskolin-stimulated cAMP levels, suggesting the absence of the ETB-R, basal cAMP levels were also unaffected by the ETs. Northern analysis using ET-R subtype-specific probes demonstrated that the ETA-R transcript was present in the cultures at levels at least 50-fold greater than the ETB-R transcript. These findings demonstrate that the stimulation of the phosphatidylinositol/protein kinase C pathway, which is required for maximal ET-stimulated ANF release from primary atrial myocytes, is associated with the activation of only the ETA-R, thus defining a specific function for an endogenous ET-R in myocardial cells.
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PMID:Identification of the receptor subtype responsible for endothelin-mediated protein kinase C activation and atrial natriuretic factor secretion from atrial myocytes. 822 66

The intracellular pathways for basal atrial natriuretic factor (ANF) secretion from the heart and their correlation with ANF processing to the active form were characterized in cultured neonatal rat atrial and ventricular myocytes. Brefeldin A, a fungal antimetabolite that blocks transport of newly synthesized proteins from the endoplasmic reticulum, was used to inhibit nascent protein trafficking. Thus, release of newly synthesized hormone was blocked, but release of stored hormone was unaffected. Whereas brefeldin A inhibited basal ventricular ANF release to 10% of the control value, basal ANF release from atrial cells was enhanced. Furthermore, basal atrial ANF secretion was inhibited by agents preventing myocyte depolarization, Ca2+ influx, release of Ca2+ from intracellular stores, or activation of protein kinase C, whereas ventricular ANF secretion was unaffected by these agents. Brefeldin A did not alter maturational processing of pro-ANF to ANF-(99-126) in either atrial or ventricular cultures. These findings indicate that (1) basal secretion of ANF from ventricular cells relies largely on newly synthesized hormone and is probably constitutive, (2) basal secretion of ANF from atrial cells is independent of transport of newly synthesized protein and occurs via a regulated pathway controlled at least in part by signaling changes associated with myocyte beating, and (3) processing of pro-ANF occurs either with constitutive or regulated secretion of hormone, which may indicate multiple cellular locations for the processing enzyme.
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PMID:Brefeldin A defines distinct pathways for atrial natriuretic factor secretion in neonatal rat atrial and ventricular myocytes. 826 92

During left ventricular hypertrophy, brain natriuretic peptide (BNP) and atrial natriuretic factor (ANF) mRNA levels increase, possibly due to stretch-induced activation of protein kinase C. Phorbol ester treatment of primary cultures of neonatal rat ventricular cardiocytes represents an in vitro model of hypertrophic cell growth and has previously been shown to stimulate ANF synthesis and secretion. Using this model, we studied the synthesis and secretion of BNP to determine whether its regulation in cardiac cells is similar to ANF. Addition of 10(-7) M phorbol 12-myristate 13-acetate (PMA) resulted in a 3- to 4-fold increase in immunoreactive BNP (irBNP) secretion 24-48 h after treatment. Over a concentration range of 10(-8)-10(-6) M, PMA increased irBNP secretion to equivalent levels. Another phorbol ester agonist, phorbol 12,13-didecanoate, stimulated irBNP secretion, while the inactive analog 4 alpha-phorbol 12,13-didecanoate had no effect. Inhibition of protein kinase C (PKC) with 10(-8) M staurosporine decreased basal secretion of irBNP 60% and prevented PMA induction of irBNP, whereas both stimulated and basal secretion of ANF were minimally affected. BNP mRNA increased 6-fold by 3 h of PMA treatment and remained elevated above control levels for 48 h. Staurosporine prevented the increase in BNP mRNA. To determine whether PKC or a PKC-dependent pathway was involved in persistent stimulation of BNP and ANF in cells chronically treated with PMA, ventricular cardiocytes were treated with PMA for 24 h, followed by PMA plus 10(-8) M staurosporine for 24 h. BNP mRNA was reduced to control levels, while ANF mRNA was reduced by an average of 20%. To test whether mRNA stability was involved in the differential effect of chronic phorbol ester treatment, cardiocytes were treated with the protein synthesis inhibitor cycloheximide (20 micrograms/ml). BNP mRNA levels were stimulated as early as 30 min after treatment, but ANF mRNA remained unaffected. Cycloheximide also potentiated PMA's effect on BNP mRNA after 1.5, 9.5, and 24 h of treatment. To test whether a transcriptional mechanism was involved in the stimulation of BNP mRNA by PMA, cells were treated with the inhibitor actinomycin D (5 micrograms/ml) for 24 h in the presence of PMA. Actinomycin D reduced the stimulatory effect of PMA on BNP mRNA.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Phorbol ester stimulates the synthesis and secretion of brain natriuretic peptide from neonatal rat ventricular cardiocytes: a comparison with the regulation of atrial natriuretic factor. 826 60

In cultured rat glomerular mesangial cells, endothelin-1 (ET-1) activated both pp 44 and pp 42 mitogen-activated protein (MAP) kinases. Atrial natriuretic peptide (ANP) inhibited ET-1-induced activation of both pp 44 and pp 42 MAP kinases. ANP also inhibited ET-1-induced translocation of protein kinase C (PKC) and TPA-induced activation of MAP kinase. These results indicate that ANP modulates the functions of mesangial cells, including proliferation and contraction through the inhibition of ET-1-induced activation of MAP kinase in various steps proximal to MAP kinase.
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PMID:Atrial natriuretic peptide inhibits endothelin-1-induced activation of mitogen-activated protein kinase in cultured rat mesangial cells. 839 37

The protease, alpha-thrombin (alpha Th), affects myocardial cell contractility, a feature common among agents that induce hypertrophy. However, it is not known whether cardiac myocytes possess alpha Th receptors (alpha Th-R), or if long term treatment with alpha Th can enhance growth and gene expression. In the present study primary neonatal rat ventricular myocytes expressed a 3.6-kilobase mRNA species that hybridized with a rat alpha Th-R-specific probe. After 48 h, alpha Th induced hypertrophy, sarcomeric organization, and enhanced atrial natriuretic factor (ANF) expression, all of which were blocked by the alpha Th-selective protease inhibitor, D-Phe-Pro-Arg-chloromethyl ketone. The alpha Th-R agonist peptide, SFLLRNPND, was a potent activator of ANF expression, however, the non-agonist, FLLRNPND, was inactive. Transfection experiments showed the enhancement of ANF expression by alpha Th to be transcriptional. The abilities of alpha Th to induce myocyte hypertrophy and to augment ANF transcription and peptide production were inhibited by the protein kinase C inhibitor, chelerythrine, and by the tyrosine kinase inhibitor, tyrphostin. Thus, myocardial cell alpha Th-Rs are stimulated by the specific proteolytic actions of alpha Th, and pathways involving both protein kinase C and protein tyrosine kinases are required for subsequent hypertrophy and ANF expression. Further, these findings suggest a new role for extracellular proteases as regulators of myocardial cell gene expression and growth.
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PMID:Myocardial alpha-thrombin receptor activation induces hypertrophy and increases atrial natriuretic factor gene expression. 839 12

Phenylephrine and noradrenaline (alpha-adrenergic agonism) or isoprenaline (beta-adrenergic agonism) stimulated protein synthesis rates, increased the activity of the atrial natriuretic factor gene promoter and activated mitogen-activated protein kinase (MAPK). The EC50 for MAPK activation by noradrenaline was 2-4 microM and that for isoprenaline was 0.2-0.3 microM. Maximal activation of MAPK by isoprenaline was inhibited by the beta-adrenergic antagonist, propranolol, whereas the activation by noradrenaline was inhibited by the alpha1-adrenergic antagonist, prazosin. FPLC on a Mono-Q column separated two peaks of MAPK (p42MAPK and p44MAPK) and two peaks of MAPK-activating activity (MEK) activated by isoprenaline or noradrenaline. Prolonged phorbol ester exposure partially down-regulated the activation of MAPK by noradrenaline but not by isoprenaline. This implies a role for protein kinase C in MAPK activation by noradrenaline but not isoprenaline. A role for cyclic AMP in activation of the MAPK pathway was eliminated when other agonists that elevate cyclic AMP in the cardiac myocyte did not activate MAPK. In contrast, MAPK was activated by exposure to ionomycin, Bay K8644 or thapsigargin that elevate intracellular Ca2+. Furthermore, depletion of extracellular Ca2+ concentrations with bis-(o-aminophenoxy)ethane-NNN'N'-tetra-acetic acid (BAPTA) or blocking of the L-type Ca2+ channel with nifepidine or verapamil inhibited the response to isoprenaline without inhibiting the responses to noradrenaline. We conclude that alpha- and beta-adrenergic agonists can activate the MEK/MAPK pathway in the heart by different signalling pathways. Elevation of intracellular Ca2+ rather than cyclic AMP appears important in the activation of MAPK by isoprenaline in the cardiac myocyte.
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PMID:Adrenergic receptor stimulation of the mitogen-activated protein kinase cascade and cardiac hypertrophy. 866 Feb 71


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