Functional coupling of rat metabotropic glutamate 1a receptors to phospholipase D in CHO cells: involvement of extracellular Ca2+, protein kinase C, tyrosine kinase and Rho-A.

We report here that metabotropic glutamate 1a (mGlu1a) receptors, stably expressed in CHO cells, stimulate phospholipase D (PLD) activity. Several mGlu receptor agonists were found to exert this effect, with a rank order of potency of: L-quisqualate>L-glutamate>(1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD]=(S)-3,5-dihydroxyphenylglycine [(S)-DHPG]. Both L-glutamate- and (1S,3R)-ACPD-stimulated PLD activity were attenuated by the selective mGlu receptor antagonist (S)-alpha-methyl-4-carboxyphenylglycine. mGlu1a receptor-stimulated PLD was inhibited either by the selective protein kinase C (PKC) inhibitor, GF109203X, or via PKC downregulation. MGlu1a receptor-PLD coupling required extracellular Ca2+ and was sensitive to La3+ and Zn2+, inhibitors of intracellular Ca2+ store-operated Ca2+ influx. mGlu1a receptor-PLD coupling was inhibited by the selective tyrosine kinase inhibitor, genistein. In addition, mGlu1a receptor-PLD coupling was also inhibited by cell transfection with the selective Rho (small GTP-binding protein) inhibitors: C3-exoenzyme and dominant negative mutant RhoA constructs. Brefeldin A, a selective ADP-ribosylation factor (ARF) inhibitor, and a dominant negative ARF6 mutant, failed to significantly influence mGlu1a receptor-stimulated PLD activity. We conclude that mGlu1a receptors activate PLD via a mechanism that is dependent on extracellular Ca2+, PKC, tyrosine kinase and RhoA but independent of ARF.     

Human urotensin II-induced aorta ring contractions are mediated by protein kinase C, tyrosine kinases and Rho-kinase: inhibition by somatostatin receptor antagonists

Human urotensin II-(1-11) and its N-terminally shortened analogues, human urotensin II-(4-11)-OH and human urotensin II-(4-11)-NH2 are potent vasoconstrictor peptides in isolated rat thoracic aorta. Human urotensin II-induced tonic aorta ring contractions are inhibited by the Ca2+ channel antagonists, verapamil, nitrendipine and diltiazem; D609 (Tricyclodecan-9-yl-xanthogenate, K), selective inhibitor of phosphatidylcholine-specific phospholipase C and partially by phospholipase C inhibitor U-73122 [1-[6-((17ss-3 Methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-25-dione] and a selective inhibitor of phosphatidyl-inositol-specific phospholipase C-ET-18-OCH3 (Edelfosine,1-O-octadecyl-2O-methyl-rac-glycero-3-phosphorylcholine); protein kinase C inhibitors, chelerythrine and NPC-15437 [S-2,6-diamino-N-[[1-(1-oxotridecyl)-2-piperidinyl]methyl]-hexanamide dihydrochloride]; tyrosine kinase inhibitors, genistein and tyrphostin B42 and Rho-kinase inhibitor HA-1077 [1-(5-isoquinolinylsulfonyl)-homopiperazine dihydrochloride]. This indicates that human urotensin II-induced tonic contractions of the rat aorta are mediated by phospholipase C, protein kinase C, tyrosine kinases and Rho-kinase related pathways. In the high K+ medium, human urotensin II induces dose-dependent phasic oscillations of aortic rings. These are inhibited by Ca2+ channel antagonists, the phospholipase C inhibitor, U-73122 and protein kinase C inhibitors, chelerythrine and NPC-15437, indicating that human urotensin II-induced phasic oscillations of the rat aorta are mediated by phospholipase C and protein kinase C-dependent pathways. Given their close structural similarity, several somatostatin analogues, importantly containing DCys5 and DTrp7 and expressing different degrees of somatostatin receptor antagonist activity, were tested for possible inhibitory effects on human urotensin II-induced contractions of the rat aorta rings. Pre-incubation of rat aorta rings in the presence of somatostatin analogues, which are preferentially sst2 specific binders: PRL-2882; PRL-2903 and PRL-2915 at micro-molar concentrations significantly blocked the development of human urotensin II-induced tonic contractions. Somatostatin receptor antagonists dose-dependently inhibited human urotensin II-induced Ca2+ transients in rat thoracic aorta rings. These somatostatin receptor antagonists displayed moderate affinities for recombinant rat and human urotensin II receptor binding sites. The data support the suggestion that urotensin II receptor and somatostatin type 2/5 receptors display similar surface topologies and that analogues of somatostatin could provide useful lead compounds for the development of more potent urotensin II receptor antagonists.     

Comparison of the involvement of protein kinase C in agonist-induced contractions in mouse aorta and corpus cavernosum

Protein kinase C (PKC) is involved in the regulation of vascular smooth muscle contraction. However, the role of PKC in erectile function is poorly understood. This study investigated whether PKC mediates agonist-induced contractions in mouse penile tissue (corpora cavernosa). We also compared the effects of PKC activators and inhibitors on contractile responses in mouse corpus cavernosum with those in mouse aorta. Aortic rings and corpus cavernosal strips from C57BL/6J mice were mounted in the organ bath for isometric tension recording. Our data showed that a PKC(alpha/beta) selective inhibitor, G(?)6976 (10 microM), inhibited phenylephrine and 9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F(2alpha) (U46619, a thromboxane mimetic)-induced contractions in mouse aorta, reducing the maximum contraction by 94% and 17%, respectively. A non-selective PKC inhibitor, chelerythrine (30 microM), also significantly reduced phenylephrine- and U46619-induced maximum contractions in mouse aorta. However, G(?)6976 and chelerythrine had no significant effects on phenylephrine- and U46619-induced contractions in corpus cavernosum. Furthermore, a PKC activator, phorbol-12,13-dibutyrate (0.1 microM), significantly increased contractions in aorta (208+/-14% of KCl-induced maximum contraction) but failed to cause contractions in corpus cavernosum at 1 and 10 microM. Western blot analysis data suggested that protein expression of PKC was similar in aorta and corpus cavernosum. Taken together, our data indicate that PKC does not have a significant role in agonist-induced contractions in mouse corpus cavernosum, whereas it mediates the contractile response to agonists in the aorta.     

Atrial peptides inhibit protein kinase C-mediated contraction in rat aorta

The effects of atriopeptin III on phorbol ester-induced contraction were examined in aorta from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Precontracted SHR aorta was less responsive than WKY aorta to atriopeptin III-induced relaxation. Additionally, SHR aorta had significantly greater basal and phorbol ester-stimulated protein kinase C (PKC) activity than WKY aorta. The altered PKC response as well as hyporesponsiveness to atriopeptin III in SHR aorta may contribute to an altered vascular response and to the pathogenesis of hypertension.     

Phorbol 12,13-dibutyrate,an activator of protein kinase C,stimulates both contraction and Ca2+ fluxes in dog saphenous vein

Summary The vascular effects of phorbol 12,13-dibutyrate (PDBu) were studied in the dog saphenous vein. PDBu (1 M) caused contraction (0.58 ± 0.22 g/mg wet wt.) and Ca uptake (74.2 ± 41.2 mol/kg wet wt.) which were unaffected by 10 M phentolamine (N = 6). The PDBu-induced contraction was greatly (60–80%) inhibited in Ca²⁺-free solution. 15 Ca efflux measurements performed in Ca²⁺-free solution showed that PDBu did not cause Ca release from intracellular storage sites. The contractile response to PDBu (1 nM-1 M) was significantly correlated with the magnitude of Ca uptake; contraction and the rise in tissue Ca²⁺ also had a similar time course. Correlation between the two measures persisted when the responses to PDBu were augmented by co-administration with 20 mM KCl. However, no synergism occurred between the two agonists. Both the contraction and Ca uptake responses to PDBu were reduced by nifedipine and verapamil, each at 1 M. In the Triton X-100 skinned saphenous vein, where the voltage-dependent Ca channel is not functional, 10 M PDBu did not cause contractions in the presence of 0.1 M Ca²⁺. Thus, contraction of the intact saphenous vein by PDBu characteristically exhibits great Ca dependence and PDBu seems to activate the voltage-dependent Ca channel, presumably through stimulation of protein kinase C; the ensuing Ca entry is primarily responsible for contraction. However, the mechanism responsible for the PDBu-induced contractions that are resistant to Ca²⁺-free PSS or Ca entry blockers remains to be defined. It appears that the dog saphenous vein differs from dog femoral artery, rabbit aorta and pig carotid artery where PDBu contractions do not display dependence on external Ca²⁺. Send offprint requests to P. J. S. Chin at the above address     

Contribution of RhoA kinase and protein kinase C to weak relaxant effect of pinacidil on carbachol-induced contractions in sensitized guinea-pig trachealis

The exact mechanisms underlying the weak bronchodilator effect of K_ATP channel openers on cholinergic stimulations is unknown. The present study was designed to examine the relaxant efect of pinacidil in guinea-pig trachea stimulated with carbachol by the presence of calcium sensitizer inhibitors; HA 1077, a rhoA kinase inhibitor, and chelerythrine, a protein kinase C inhibitor. Adenosine (10 μM) was used as other contractile agent for comparison. Tracheal tissues were isolated from ovalbumin sensitized guineapigs and changes in tension were recorded isometrically. Pinacidil (1–100 μM, cumulatively) and HA 1077 (0.01–30 μM, cumulatively) produced concentration-dependent relaxations in unstimulated tisues. The relaxant response to pinacidil decreased in carbachol contracted tissues, but increased in adenosine-stimulated tissues. Pretreatment of the tissues with HA 1077 (0.1 μM) and chelerythrine (10 μM) increased the pinacidil-induced relaxations by ∼%100 and %40, respectively. Glibenclamide, a KATP channel blocker, partially antagonized the pinacidil response in contracted tissues. Glibenclamide also inhibited the carbachol and adenosine induced contractions. These results suggest that diminish effect of pinacidil may have related to the enhanced calcium sensitization by cholinergic stimulation. Rho kinase inhibitors appear more effective than PKC inhibitors to achieve of this failure. Two authors made an equal contribution to this study.     

Inhibition of protein kinase C-mediated contraction by Rho kinase inhibitor fasudil in rabbit aorta

Protein kinase C (PKC) activation by a phorbol ester increases myosin light chain (MLC₂₀) phosphorylation through inhibition of MLC phosphatase (MLCP) and enhances contraction of vascular smooth muscle. We investigated whether Rho kinase, which is known to inhibit MLCP, is involved in the MLC₂₀ phosphorylation caused by a phorbol ester, 12-deoxyphorbol 13-isobutyrate (DPB), in rabbit aortas. DPB (1 M) increased MLC₂₀ phosphorylation and tension. The Rho kinase inhibitor fasudil (10 M) inhibited the DPB-induced contraction and decreased the MLC₂₀ phosphorylation at Ser19, a site phosphorylated by MLC kinase, although it did not affect the phosphorylation of total MLC₂₀. Rinsing a 65.4 mM KCl-contracted aorta with Ca²⁺-free, EGTA solution caused rapid dephosphorylation of MLC₂₀ and relaxation. When DPB was present in the rinsing solution, the MLC₂₀ dephosphorylation and the relaxation were inhibited. In this protocol, Ro31-8220 (10 M), a PKC inhibitor, suppressed the phosphorylation of total MLC₂₀ and Ser19 induced by DPB. Fasudil also inhibited the Ser19 phosphorylation to a degree similar to Ro31-8220 and accelerated relaxation, which was less than the relaxation caused by Ro31-8220. The phospholipase A₂ inhibitor ONO-RS-082 (5 M) inhibited the DPB-induced Ser19 phosphorylation but only transiently decreased the tension, suggesting the involvement of arachidonic acid in the phosphorylation and the existence of a MLC₂₀ phosphorylation-independent mechanism. When fasudil was combined with ONO-RS-082, fasudil exerted additional inhibition of the tension without further inhibition of the Ser19 phosphorylation. DPB phosphorylated the 130 kDa myosin binding subunit (MBS) of MLCP and fasudil inhibited the phosphorylation. These data suggest that the inhibition by fasudil of DPB-induced contraction and phosphorylation of MLC₂₀ at the MLC kinase-targeted site is a result of inhibition of Rho kinase. Thus, the PKC-dependent Ca²⁺-sensitization of vascular smooth muscle involves Rho kinase. A MLC₂₀ phosphorylation-independent mechanism is also involved in the Ca²⁺-sensitization.     

Cross-talk between Bcr-Abl tyrosine kinase, protein kinase C and telomerase-a potential reason for resistance to Glivec in chronic myelogenous leukaemia

To prevent the resistance to Glivec in patients with chronic myelogenous leukaemia (CML), it is necessary to get a good understanding of its potential mechanisms. The present hypothesis accents on the mechanisms whereby Bcr-Abl tyrosine kinase remains inhibited by Glivec, but alternative signalling pathways become activated-the potential reason associates with activation of telomerase after long-term treatment with Glivec and recovery of cell proliferation and immortality. The hypothesis is based on the observations about differences in telomere dynamics and telomerase activity between chronic and blast phases of CML patients, as well as about the potential effect of Glivec on the cross-talk between telomerase, Bcr-Abl tyrosine kinase and protein kinase C family-key enzymes in CML. It proceeds from recently published data, demonstrating that protein kinase C activates and c-Abl tyrosine kinase inhibits telomerase. During optimization of chemical structure, Glivec loose its effect on protein kinase C and enhances the effect on Bcr-Abl tyrosine kinase, resulting in a high potential to activate telomerase indirectly through its effect on both kinases. Experimental preclinical data are given in confirmation of this hypothesis.     

Effects of phorbol ester on carbachol-induced contraction in bovine ciliary muscle: possible involvement of protein kinase C

The aim of the research was to characterize muscarinic receptors of bovine ciliary muscle and to investigate the desensitization process. The role of protein kinase C was analyzed. The results show that muscarinic receptors of bovine ciliary muscle have the pharmacological characteristics of the M₃ subtype. Acute exposure to phorbol esters (1 μM phorbol 12,13-dibutyrate, PDB, or 0.1 μM phorbol 12-myristate 13-acetate, PMA, for 15 and 5 min, respectively) resulted in antagonism of muscarinic receptor-mediated contraction. Long-term pretreatment (18 h) with PMA to down-regulate protein kinase C resulted in potentiation of carbachol-induced contraction, reduction of agonist-induced desensitization and loss of phorbol ester-induced desensitization. Staurosporine (3 μM) and H₇ [1-(5-isoquinolinesulfonyl)-2-methyl-piperazine] (1 μM), protein kinase C inhibitors, produced a significant potentiation of the contractile effect of carbachol, reduced the desensitization produced by repeated addition of carbachol and suppressed that induced by phorbol esters. In vitro incubation with carbachol, PDB or PMA did not cause any modification of the binding of labeled [³H]quinuclidinyl benzilate. In vitro incubation with PDB and PMA produced, as expected, a significant translocation of protein kinase C from the cytosol to the membrane. The incubation of the ciliary muscle with carbachol, using the protocol of exposure that induced maximal desensitization of contractile responses, produced a significant redistribution of the enzyme from the cytosol to the membrane. These findings suggest that agonist-induced modulation of functional cholinergic sensitivity in ciliary muscle is correlated, at least partially, to the translocation of protein kinase C from the cytosol to the membrane. The desensitization by phorbol esters is completely due to protein kinase C activation; during the desensitization process, direct modification of the density and affinity of muscarinic receptors is not involved.     

Veratridine causes the Ca2+-dependent increase in diacylglycerol formation and translocation of protein kinase C to membranes in cultured bovine adrenal medullary cells

Summary Our previous studies suggested that protein kinase C is involved in the veratridine (an activator of voltage-dependent Na⁺ channels)-induced phosphorylation and activation of tyrosine hydroxylase as well as the synthesis of catecholamines in adrenal medulla (Uezono et al. 1989). In the present study, we investigated whether treatment of cultured bovine adrenal medullary cells with veratridine causes the accumulation of diacylglycerol, a physiological activator of protein kinase C and the translocation of protein kinase C from cytosol to membrane, a process required for protein kinase C activation. Veratridine (100 mol/l) increased diacylglycerol level about 2.2 fold in a monophasic manner, with peaking at 5 min and declining toward the basal level within 20 min. Veratridine also increased membrane protein kinase C from 15.6% to 26.9% of total protein kinase C in a timecourse similar to that of diacylglycerol accumulation. Both stimulatory effects of veratridine were inhibited by tetrodotoxin and not observed in Ca²⁺-free, EGTA-containing medium. Amiloride, an inhibitor of Na⁺/Ca²⁺ and Na⁺/H⁺ exchange, did not alter veratridine-induced events. These results suggest that veratridine-induced Ca²⁺ influx contributes to the accumulation of diacylglycerol and the activation of protein kinase C in adrenal medullary cells. Send offprint requests to Y. Uezono at the above address     

Sensitivity of rabbit aorta and mesenteric artery to norepinephrine: role of tyrosine kinases

We tested the hypothesis that the differential sensitivity of rabbit aorta and mesenteric artery to norepinephrine is due to tyrosine kinase activity. The EC50 of aorta to norepinephrine was 6.5 times more sensitive than that in mesenteric artery. Basal myosin light chain phosphorylation was significantly greater in aorta as compared to mesenteric artery. Vanadate increased norepinephrine sensitivity significantly more in mesenteric artery than aorta, whereas genistein had the opposite effect. Basal phosphotyrosine levels were significantly higher in aorta than in mesenteric artery, the percentage increase in total tyrosine phosphorylated protein was significantly higher in mesenteric artery. These results suggest that the higher basal phosphotyrosine levels in the aorta may be responsible for the higher basal level of myosin light chain phosphorylation and this may be the basis for the higher sensitivity of the aorta to norepinephrine when compared with the mesenteric artery.     

Phorbol ester,an activator of protein kinase C,enhances calcium-dependent release of sympathetic neurotransmitter

Summary The effect of phorbol ester, phorbol 12,13-dibutyrate, was investigated on the overflow of tritium from ³H-noradrenaline-loaded sympathetic neurons of the isolated perfused salivary gland of the rat. Stimulation (1 Hz for 60 s)-evoked overflow of tritium was enhanced by phorbol ester. A significant enhancement was seen at 1 nmol/l, which increased to a maximum level (over 4-fold) at 30 nmol/l. The spontaneous overflow of radioactivity, however, was not affected by any concentration of phorbol ester. The facilitatory effect of phorbol ester on stimulation-evoked overflow was observed in the presence of inhibitors of neuronal and extraneuronal uptake as well as after removal of negative feedback inhibition of release by presynaptic alpha-adrenoceptors. Tyramine (7 mol/l for 10 min) caused a marked increase in the overflow of tritium in either the presence or absence of calcium. However, tyramine-induced overflow was not enhanced by phorbol ester. It is concluded that protein kinase C of sympathetic neurons is involved in an exocytotic release of the transmitter.     

糖尿病合并症与蛋白激酶C

糖尿病 (DM )可引起体内各系统的合并症。实验研究表明 ,二酰基甘油 (DAG) 蛋白激酶C(PKC)通路的活动增加与DM合并症的产生密切相关 ,可能是DM时多种生化指标引起合并症产生的最后的细胞内共同通路。在已知的 11中PKC亚型中 ,PKC β和 ε与DM合并症的产生最为密切     

Nicotine-induced release of noradrenaline and neuropeptide Y in guinea-pig heart: role of calcium channels and protein kinase C

Summary The role of calcium, calcium influx through calcium channels, and activation of protein kinase C for the nicotine-induced release of noradrenaline and of the sympathetic co-transmitter neuropeptide Y (NPY) was investigated in the guinea-pig isolated perfused heart. In the coronary venous overflow noradrenaline and NPY were determined by high-pressure liquid chromatography and radioimmunoassay, respectively. In the presence of extracellular calcium (1.85 mmol/l) nicotine (1–100 mol/l) evoked a concentration-dependent overflow of both transmitters with a molar ratio of approximately 1500 (noradrenaline):1 (NPY). The nicotine-induced (100 mol/l) overflow of noradrenaline and NPY was in a linear manner related (r = 0.79 and 0.90, respectively; p < 0.05) to the extracellular calcium concentration (0–1.85 mmol/l), and it was prevented by calcium-free perfusion. The L-type calcium channel blocker felodipine (100 nmol/l) did not affect the nicotine-induced (100 mol/l) transmitter overflow. On the other hand, the neuronal (N-type) calcium channel blockers -conotoxin (100 nmol/l) and cadmium chloride (50 mol/l) reduced the nicotine-induced (100 pmol/l) transmitter overflow to 20% of the control value, suggesting a role of N-type calcium channels in mediating the calcium influx for the nicotine-induced transmitter release. The nicotine-induced (30 mol/l) overflow of both transmitters was two- to three-fold increased by activation of protein kinase C (phorbol 12-myristate 13-acetate; 100 nmol/l). The transmitter overflow was unaffected by 4-phorbol 12,13-didecanoate (100 nmol/l), a phorbol ester which does not stimulate protein kinase C. Further supporting a modulatory role of protein kinase C, inhibition of the enzyme by either polymyxin B (100 gmol/I) or by cremophor RH-30 (1mol/l) almost completely suppressed the overflow of noradrenaline and NPY. The results of the present study indicate that nicotine evokes a concentration-dependent exocytotic co-release of noradrenaline and NPY in the guinea-pig isolated perfused heart which is characterized by its dependence on extracellular calcium, calcium influx through N-type calcium channels and activation of protein kinase C.This work was supported by a grant from the Forschungsrat Rauchen und Gesundheit Send of fprint requests to M. Haass at the above address     

On electrophysiological responses to phorbol esters which stimulate protein kinase C in rabbit sino-atrial node cells

Summary Effects of phorbol esters on spontaneously beating rabbit sino-atrial (SA) node cells were investigated by means of voltage clamp technique. In a small SA node specimen, 12-O-tetradecanoylphorbol-13-acetate (TPA) 10^–7 mol/l lengthened the cycle length (CL) and at over 3 × 10^–7 mol/l prolonged the action potential duration (APD). Action potential amplitude (APA), maximum diastolic potential (MDP) and maximum rate of rise (V _max) were unaffected. Amiloride 10^–3 mol/1, an inhibitor of Na⁺-H⁺ exchange, did not reverse the phorbol ester-induced effects. In voltage-clamp experiments, TPA 1-10 × 10^–7 mol/l slightly increased the slow inward current (I _si) and the time-dependent inward current (I _h) which activates during hyperpolarization. The outward current and the tail current were reduced, although the activation curve was not shifted along the voltage axis. In the presence of 10^–7 mol/l isoprenaline, TPA produced dysrhythmia and a transient inward current in voltage-clamp experiments. In the presence of 5 × 10^–5 mol/l phenylephrine or 2 × 10^–6 mol/l acetylcholine, TPA also elicited dysrhythmia. 4-betaphorbol-12,13-dibutyrate (PBD) induced similar electrophysiological effects as TPA, but 4-alpha-phorbol-12,13-didecanoate (PDD) never did so even in the presence of isoprenaline. These results suggest that TPA and PDB might mobilize intracellular Ca²⁺ via protein kinase C activation in the presence of isoprenaline, phenylephrine or acetylcholine, resulting in dysrhythmia due to delayed afterdepolarization.Send offprint requests to Hiroyasu Satoh     

Vanadium adversely affects sperm motility and capacitation status via protein kinase A activity and tyrosine phosphorylation

Vanadium is a chemical element that enters the atmosphere via anthropogenic pollution. Exposure to vanadium affects cancer development and can result in toxic effects. Multiple studies have focused on vanadium’s detrimental effect on male reproduction using conventional sperm analysis techniques. This study focused on vanadium’s effect on spermatozoa following capacitation at the molecular level, in order to provide a more detailed assessment of vanadium’s reproductive toxicity. We observed a decrease in germ cell density and a structural collapse of the testicular organ in seminiferous tubules during vanadium treatment. In addition, various sperm motion parameters were significantly decreased regardless of capacitation status, including sperm motility, rapid sperm motility, and progressive sperm motility. Curvilinear velocity, straight-line velocity, average path velocity, beat cross frequency, and mean amplitude of head lateral displacement were also decreased after capacitation. Capacitation status was altered after capacitation. Vanadium dramatically enhanced protein kinase A (PKA) activity and tyrosine phosphorylation. Taken together, our results suggest that vanadium is detrimental to male fertility by negatively influencing sperm motility, motion kinematics, and capacitation status via abnormal PKA activity and tyrosine phosphorylation before and after capacitation.     

The interaction of aluminium with soluble protein kinase C from mouse brain

The interaction of aluminium ion species with soluble protein kinase C, Ca²⁺/phospholipid-dependent protein kinase, from mouse brain has been examined in vitro. The activity of protein kinase C was increased by addition of Ca²⁺ displaying an EC₅₀ value of 10.3±1.1 × 10^–6 M. The A1 species inhibited the activity with an IC₅₀ values of 8.6±0.5 × 10^–5 M and 2.7±0.3 × 10^–5 M in the presence of 0.5 mM Ca²⁺ and absence of Ca²⁺, respectively. Concerning the EC₅₀ for Ca²⁺ activation, this was increased by the A1 species in a dose-dependent manner. Moreover, the inhibition was of a non-competitive type with respect to H1 histone and of a mixed type with respect to ATP. It is likely that the inhibition was caused by 1) the blocking of Mg²⁺ binding to ATP, 2) the blocking of Ca²⁺ binding to protein kinase C. Our results suggested that protein kinase C was involved in neurotoxicity of A1.     

蛋白激酶C激活剂和抑制剂对肿瘤坏死因子杀瘤活性的影响

以小鼠成纤维细胞瘤L929细胞为靶细胞,研究蛋白激酶C(PKC)的激活剂和抑制剂对人重组肿瘤坏死因子(rHuTNF)杀瘤活性的影响.各种药物与rHuTNF 10 ng·ml~(-1)和放线菌素D 1 μg·ml~(-1)温育18 h,结果表明PKC的激活剂佛波醇-12-肉豆蔻酸盐-13-乙酸盐(PMA)2.5～160ng·ml~(-1)可浓度依赖性地抑制rHuTNF的杀瘤活性.Sc-10(1～16μg·ml~(-1))单独作用很弱,但可浓度依赖地增强PMA 10 ng·ml~(-1)或A23187 0.5μg·ml~(-1)的抑制作用,PKC抑制剂1-(5-异喹啉磺酰基)-2-甲基哌嗪(H-7)单独作用对rHuTNF杀瘤活性无影响,但可减弱PMA 50ng·ml~(-1)的抑制作用.槲皮囊2～16μg·ml~(-1)则可直接抑制rHuTNF的杀瘤活性,钙调蛋白抑制剂N-(6-氨己基)-5-氯-1-萘磺酰胺(W-7)及其同系物也有微弱的抑制作用.结果提示PKC在rHuTNF杀瘤作用中起着重要作用.     

Quercetin inhibits tyrosine phosphorylation by the cyclic nucleotide-independent,transforming protein kinase,pp60src

Summary The bioflavonoid quercetin is a potent inhibitor of a cyclic nucleotide-independent, tumor virus-coded protein kinase which phosphorylates tyrosine residues and acts as a cellular transforming protein. Half-maximal inhibition of the protein kinase occurred at 3–4 M quercetin whereas rutin was much less effective. The finding, that quercetin inhibits a cyclic nucleotide-independent protein kinase activity, may provide clues to the diverse pharmacological effects of the bioflavonoids.