Calcium-dependent increase in tyrosine kinase activity stimulated by angiotensin II

Nitric oxide modulates NMDA receptor through a negative feedback mechanism and regulates the dynamical behavior of neuronal postsynaptic components

Nitric oxide (NO) is known to be an important regulator of neurological processes in the central nervous system which acts directly on the presynaptic neuron and enhances the release of neurotransmitters like glutamate into the synaptic cleft. Calcium influx activates a cascade of biochemical reactions to influence the production of nitric oxide in the postsynaptic neuron. This has been modeled in the present work as a system of ordinary differential equations, to explore the dynamics of the interacting components and predict the dynamical behavior of the postsynaptic neuron. It has been hypothesized that nitric oxide modulates the NMDA receptor via a feedback mechanism and regulates the dynamic behavior of postsynaptic components. Results obtained by numerical analyses indicate that the biochemical system is stimulus-dependent and shows oscillations of calcium and other components within a limited range of concentration. Some of the parameters such as stimulus strength, extracellular calcium concentration, and rate of nitric oxide feedback are crucial for the dynamics of the components in the postsynaptic neuron.

13-cis-Retinoic acid specific down-regulation of angiotensin type 1 receptor in rat liver epithelial and aortic smooth muscle cells

Transcriptional repression through cis- and trans-acting factors enabling an alternate approach to control angiotensin type 1 receptor (AT1 or AGTR1 as listed in the MGI database) expression has not been studied. In previous investigations, treatment with retinoic acid was found to be associated with enhanced insulin sensitivity. In our previous study, expression of AT1 was found to be inversely correlated with intracellular glucose concentrations. Therefore, we hypothesized that 13-cis-retinoic acid (13cRA), an antioxidant, enhances insulin-sensitive glucose-mediated down-regulation of the AT1. In this study, we used continuously passaged rat liver epithelial cells. Our study shows that cells exposed to 13cRA specifically down-regulated the AT1 protein in a dose- and time-dependent manner, independently of any change in receptor affinity. Down-regulation of the AT1 expression leads to reduced AngII-mediated intracellular calcium release, a hallmark of receptor-mediated intracellular signaling. Similarly with receptor down-regulation, we observed a significant reduction in AT1 mRNA; however, the AT1 down-regulation was independent of insulin-sensitive glucose uptake and retinoic acid receptor activation (RAR/RXR). Treatment with 13cRA resulted in phosphorylation of p42/p44 MAP kinases in these cells. Subsequent studies using MEK inhibitor PD98059 prevented 13cRA-mediated AT1 down-regulation and restored AngII-mediated intracellular calcium response. Furthermore, 13cRA-mediated inhibitory effects on AT1 were validated in primary rat aortic smooth muscle cells. In summary, our results demonstrate for the first time that 13cRA has a glucose- and RAR/RXR-independent mechanism for transcriptional inhibition of AT1, suggesting its therapeutic potential in systems in which AT1 expression is deregulated in insulin-sensitive and -insensitive tissues.

Pharmacologic effects of 2-methoxyestradiol on angiotensin type 1 receptor down-regulation in rat liver epithelial and aortic smooth muscle cells

BACKGROUND

Delayed onset of cardiovascular disease (CVD) in female patients is not well understood, but could be due in part to the protective effect of estrogen before menopause. Experimental studies have identified the angiotensin type 1 receptor (AT1R) as a key factor in the progression of CVD.

OBJECTIVE

We examined the effects of the estrogen metabolite 2-methoxyestradiol (2ME2) on AT1R expression.

METHODS

Rat liver cells were exposed to 2ME2 for 24 hours, and angiotensin II (AngII) binding and AT1R mRNA expressions were assessed.

RESULTS

In the presence of 2ME2, cells exhibited significant down-regulation of AngII binding that was both dose and time dependent, independent of estrogen receptors (ERα/ERβ). Down-regulation of AngII binding was AT1R specific, with no change in receptor affinity. Under similar conditions, we observed lower expression of AT1R mRNA, significant inhibition of AngII-mediated increase in intracellular Ca(2+), and increased phosphorylation of ERK1/2. Pretreatment of cells with the MEK inhibitor PD98059 prevented 2ME2-induced ERK1/2 phosphorylation and down-regulation of AT1R expression, which suggests that the observed inhibitory effect is mediated through ERK1/2 signaling intermediates. Similar analyses in stably transfected CHO (Chinese hamster ovary) cell lines with a constitutively active cytomegalovirus promoter showed no change in AT1R expression, which suggests that 2ME2-mediated effects are through transcriptional regulation. The effects of 2ME2 on AT1R down-regulation through ERK1/2 were consistently reproduced in primary rat aortic smooth muscle cells.

CONCLUSIONS

Because AT1R has a critical role in the control of CVD, 2ME2-induced changes in receptor expression may provide beneficial effects to the cardiovascular and other systems.

Rosuvastatin inhibits norepinephrine-induced cardiac hypertrophy via suppression of Gh

Statins have recently been shown to produce anti-cardiac hypertrophic effects via the regulation of small GTPases. However, the effects of statins on G protein-mediated cardiac hypertrophy, which is the main pathway of cardiac hypertrophy, have not yet been studied. We sought to evaluate whether statin treatment directly suppresses cardiac hypertrophy through a large G protein-coupled pathway regardless of the regulation of small GTPases. Using neonatal rat cardiomyocytes, we evaluated norepinephrine-induced cardiac hypertrophy for suppressibility of rosuvastatin and the pathways involved by analyzing total protein/DNA content, cell surface area, immunoblotting and RT-PCR for the signal transduction molecule. In a concentration-dependent manner, rosuvastatin inhibited total protein synthesis and downregulated basal and norepinephrine-induced expressions of myosin light chain2 and the c-fos proto-oncogene in cardiomyocytes. Treatment with norepinephrine induced cardiac hypertrophy accompanied by G(h) expression and membrane translocation. Rosuvastatin inhibited G(h) protein activity in cardiomyocytes by inhibiting basal and norepinephrine-stimulated mRNA transcription, protein expression and membrane translocation; however, norepinephrine-stimulated G(q) protein expression was not inhibited. In addition, the norepinephrine-stimulated protein kinase C (PKC)-mitogen-activated protein kinase (MEK 1,2)-extracellular signal-regulated kinases (ERKs) signaling cascade was inhibited by pretreatment with rosuvastatin. Rosuvastatin treatment also helped maintain expression levels of SERCA2a and intracellular calcium concentration. G(h) protein is a novel target of statins in myocardial hypertrophy, and statin treatment may directly suppress cardiac hypertrophy through a large G(h) protein-coupled pathway regardless of the regulation of small GTPases.

Structural and biological investigation of ferrocene-substituted 3-methylidene-1,3-dihydro-2H-indol-2-ones

The Knoevenagel condensation of 1,3-dihydro-2H-indol-2-one with ferrocene carboxaldehyde afforded an approximate 2:1 mixture of the geometrical isomers (E)- and (Z)-3-ferrocenylmethylidene-1,3-dihydro-2H-indol-2-one respectively in an overall 67% yield; the air and solution-stable isomers were readily separated by preparative thin layer chromatography and their structures were unequivocally elucidated in solution, by (1)H NMR spectroscopy, and in the solid phase, by X-ray crystallography; both isomers of displayed in vitro toxicity against B16 melanoma and Vero cell lines in the micromolar range and inhibited the kinase VEGFR-2 with IC(50) values of ca. 200 nM.

Tyrosine kinase and mitogen-activated protein kinase/extracellularly regulated kinase differentially regulate intracellular calcium concentration responses to angiotensin II/III and bradykinin in rat cortical thick ascending limb

The cortical thick ascending limb (CTAL) coexpresses angiotensin (Ang) II/Ang III receptor type 1A (AT(1A)-R) and bradykinin (BK) receptor type 2 (B2-R). In several cell types, these two receptors share the same signaling pathways, although their physiological functions are often opposite. In CTAL, little is known about the intracellular transduction events leading to the final physiological response induced by these two peptides. We investigated and compared in this segment the action of Ang II/III and BK on intracellular calcium concentration ([Ca2+]i) response and metabolic CO2 production, an index of Na+ transport, by using inhibitors of protein kinase C (bisindolylmaleimide), Src tyrosine kinase (herbimycin A and PP2), and MAPK/ERK (PD98059 and UO126). Ang II/III and BK (10(-7) mol/liter) released Ca2+ from the same intracellular pools but activated different Ca2+ entry pathways. Ang II/III- or BK-induced [Ca2+]i increases were similarly potentiated by bisindolylmaleimide. Herbimycin A and PP2 decreased similarly the [Ca2+]i responses induced by Ang II/III and BK. In contrast, PD98059 and UO126 affected the effects of BK to a larger extent than those of Ang II/III. Especially, the Ca2+ influx induced by BK was more strongly inhibited than that induced by Ang II/III in the presence of both compounds. The Na+ transport was inhibited by BK and stimulated by Ang II/III. The inhibitory action of BK on Na+ transport was blocked by UO126, whereas the stimulatory response of Ang II/III was potentiated by UO126 but blocked by bisindolylmaleimide. These data suggest that the inhibitory effect of BK on Na+ transport seems to be directly mediated by an increase in Ca2+ influx dependent on MAPK/ERK pathway activation. In contrast, the stimulatory effect of Ang II/III on Na+ transport is more complex and involves PKC and MAPK/ERK pathways.

Ca(2+)-sensitive tyrosine kinase Pyk2/CAK beta-dependent signaling is essential for G-protein-coupled receptor agonist-induced hypertrophy

G-protein-coupled receptor agonists including endothelin-1 (ET-1) and phenylephrine (PE) induce hypertrophy in neonatal ventricular cardiomyocytes. Others and we previously reported that Rac1 signaling pathway plays an important role in this agonist-induced cardiomyocyte hypertrophy. In this study reported here, we found that a Ca(2+)-sensitive non-receptor tyrosine kinase, proline-rich tyrosine kinase 2 (Pyk2)/cell adhesion kinase beta (CAKbeta), is involved in ET-1- and PE-induced cardiomyocyte hypertrophy medicated through Rac1 activation. ET-1, PE or the Ca(2+) inophore, ionomycin, stimulated a rapid increase in tyrosine phosphorylation of Pyk2. The tyrosine phosphorylation of Pyk2 was suppressed by the Ca(2+) chelator, BAPTA. ET-1- or PE-induced increases in [(3)H]-leucine incorporation and expression of atrial natriuretic factor and the enhancement of sarcomere organization. Infection of cardiomyocytes with an adenovirus expressing a mutant Pyk2 which lacked its kinase domain or its ability to bind to c-Src, eliminated ET-1- and PE-induced hypertrophic responses. Inhibition of Pyk2 activation also suppressed Rac1 activation and reactive oxygen species (ROS) production. These findings suggest that the signal transduction pathway leading to hypertrophy involves Ca(2+)-induced Pyk2 activation followed by Rac1-dependent ROS production.

Dependence of peroxisome proliferator-activated receptor ligand-induced mitogen-activated protein kinase signaling on epidermal growth factor receptor transactivation

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that function as ligand-activated transcription factors regulating lipid metabolism and homeostasis. In addition to their ability to regulate PPAR-mediated gene transcription, PPARalpha and gamma ligands have recently been shown to induce activation of mitogen-activated protein kinases (MAPKs), which in turn phosphorylate PPARs, thereby affecting transcriptional activity. However, the mechanism for PPAR ligand-dependent MAPK activation is unclear. In the current study, we demonstrate that various PPARalpha (nafenopin) and gamma (ciglitazone and troglitazone) agonists rapidly induced extracellular signal-regulated kinase (Erk) and/or p38 phosphorylation in rat liver epithelial cells (GN4). The selective epidermal growth factor receptor (EGFR) kinase inhibitors, PD153035 and ZD1839 (Iressa), abolished PPARalpha and gamma agonist-dependent Erk activation. Consistent with this, PPAR agonists increased tyrosine autophosphorylation of the EGFR as well as phosphorylation at a putative Src-specific site, Tyr845. Experiments with the Src inhibitor, PP2, and the antioxidant N-acetyl-L-cysteine revealed critical roles for Src and reactive oxygen species as upstream mediators of EGFR transactivation in response to PPAR ligands. Moreover, PPARalpha and gamma ligands increased Src autophosphorylation as well as kinase activity. EGFR phosphorylation, in turn, led to Ras-dependent Erk activation. In contrast, p38 activation by PPARalpha and gamma ligands occurred independently of Src, oxidative stress, the EGFR, and Ras. Interestingly, PPARalpha and gamma agonists caused rapid activation of proline-rich tyrosine kinase or Pyk2; Pyk2 as well as p38 phosphorylation was reduced by intracellular Ca2+ chelation without an observable effect on EGFR and Erk activation, suggesting a possible role for Pyk2 as an upstream activator of p38. In summary, PPARalpha and gamma ligands activate two distinct signaling cascades in GN4 cells leading to MAPK activation.

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.

Phosphospecific site tyrosine phosphorylation of p125FAK and proline-rich kinase 2 is differentially regulated by cholecystokinin receptor type A activation in pancreatic acini

The focal adhesion kinases, p125FAK and proline-rich kinase 2 (PYK2), are involved in numerous processes as adhesion, cytoskeletal changes, and growth. These kinases have 45% homology and share three tyrosine phosphorylation (TyrP) sites. Little information exists on the ability of stimulants to cause TyrP of each kinase site and the cellular mechanism involved. We explored the ability of the neurotransmitter/hormone, CCK, to stimulate TyrP at each site. In rat pancreatic acini, CCK stimulated TyrP at each site in both kinases. TyrP was rapid except for pY397FAK. The magnitude of TyrP differed with the different FAK and PYK2 sites. The CCK dose-response curve for TyrP for sites in each kinase was similar. CCK-JMV, an agonist of the high affinity receptor state and antagonist of the low affinity receptor state, was less efficacious than CCK at each FAK/PYK2 site and inhibited CCK maximal stimulation. Thapsigargin decreased CCK-stimulated TyrP of pY402PYK2 and pY925FAK but not the other sites. GF109203X reduced TyrP of only the PYK2 sites, pY402 and pY580. GF109203X with thapsigargin decreased TyrP of pY402PYK2 and the three FAK sites more than either inhibitor alone. Basal TyrP of pY397FAK was greater than other sites. These results demonstrate that CCK stimulates tyrosine phosphorylation of each of the three homologous phosphorylation sites in FAK and PYK2. However, CCK-stimulated TyrP at these sites differs in kinetics, magnitude, and participation of the high/low affinity receptor states and by protein kinase C and [Ca2+]i. These results show that phosphorylation of these different sites is differentially regulated and involves different intracellular mechanisms in the same cell.

The role of the Ca2+-sensitive tyrosine kinase Pyk2 and Src in thrombin signalling in rat astrocytes

We have recently demonstrated that multiple signalling pathways are involved in thrombin-induced proliferation in rat astrocytes. Thrombin acts by protease-activated receptor-1 (PAR-1) via mitogen-activated protein kinase activity. Signalling includes both Gi/(betagamma subunits)-phosphatidylinositol 3-kinase and a Gq-phospholipase C/Ca2+/protein kinase C (PKC) pathway. In the present study, we investigated the possible protein tyrosine kinases which might be involved in thrombin signalling cascades. We found that, in astrocytes, thrombin can evoke phosphorylation of proline-rich tyrosine kinase (Pyk2) via PAR-1. This process is dependent on the increase in intracellular Ca2+ and PKC activity. Moreover, in response to thrombin stimulation Pyk2 formed a complex with Src tyrosine kinase and adapter protein growth factor receptor-bound protein 2 (Grb2), which could be coprecipitated. Furthermore, both thrombin-induced Pyk2 phosphorylation and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation can be attenuated by Src kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine. From these data we conclude that PAR-1 uses Ca2+- and PKC-dependent Pyk2 to activate Src, thereby leading to ERK1/2 activation, which predominantly recruits Grb2 in rat astrocytes.

The N termini of focal adhesion kinase family members regulate substrate phosphorylation, localization, and cell morphology

The focal adhesion kinase (FAK) and cell adhesion kinase beta (CAKbeta, PYK2, CADTK, RAFTK) are highly homologous FAK family members, yet clearly have unique roles in the cell. Comparative analyses of FAK and CAKbeta have revealed intriguing differences in their activities. These differences were investigated further through the characterization of a set of FAK/CAKbeta chimeric kinases. CAKbeta exhibited greater catalytic activity than FAK in vitro, providing a molecular basis for differential substrate phosphorylation by FAK and CAKbeta in vivo. Furthermore, the N terminus may regulate catalytic activity since chimeras containing the FAK N terminus and CAKbeta catalytic domain exhibited a striking high level of catalytic activity and substrate phosphorylation. Unexpectedly, a modulatory role for the N termini in subcellular localization was also revealed. Chimeras containing the FAK N terminus and CAKbeta C terminus localized to focal adhesions, whereas chimeras containing the N and C termini of CAKbeta did not. Finally, prominent changes in cell morphology were induced upon expression of chimeras containing the CAKbeta N terminus, which were not associated with apoptotic cell death, cell cycle progression delay, or changes in Rho activity. These results demonstrate novel regulatory roles for the N terminus of FAK family kinases.

Angiotensin II-mediated signal transduction pathways

The renin-angiotensin system is one of the major cardiovascular systems that controls blood volume, peripheral vascular tone, and blood pressure. Recent studies indicate important roles for angiotensin II in inflammation, atherosclerosis, and congestive heart failure as well. It is gradually becoming clear that angiotensin II exerts effects on the cardiovascular system through several unique mechanisms, including the availability of two different angiotensin II receptors, recruitment of protein tyrosine kinase activity, and receptor tyrosine kinase transactivation. This review discusses the diverse mechanisms of angiotensin II-mediated signal transduction pathways and the various effects of angiotensin II on the cardiovascular system.

Contractile effects of angiotensin peptides in rat aorta are differentially dependent on tyrosine kinase activity

It has been suggested that tyrosine kinase activity participates in the regulation of signal transduction associated with angiotensin II (Ang II)-induced pharmaco-mechanical coupling in rat aortic smooth muscle. We further tested the effects of genistein, a tyrosine-kinase inhibitor, and its inactive analogue, daidzein, on angiotensin I (Ang I), angiotensin III (Ang III) and angiotensin IV (Ang IV) contractions, as compared with those on Ang II. Genistein partially inhibited Ang II- and Ang I-induced contractions. The genistein-induced inhibition was more evident on Ang III and especially important on Ang IV contractile effects. Thus, Ang IV- and Ang III-induced contractions seem to be more dependent on tyrosine kinase activity than those evoked by Ang II or Ang I. Daidzein did not significantly affect the contractile effects of any of angiotensin peptides tested. These results clearly suggest that the inhibition of the action of angiotensin peptides actions by genistein is mediated by inhibition of endogenous tyrosine kinase activity. Furthermore, our data show that the type and/or intensity of tyrosine kinase activity is differentially associated with the contractile effects of different angiotensin peptides in rat aorta. Nifedipine, a blocker of membrane L-type Ca2+ channels, strongly inhibited Ang IV-induced contractions. At the same time, it significantly inhibited Ang III contractile effects as compared with Ang II and Ang I contractions. Meanwhile, we observed a close relationship between calcium influx and tyrosine kinase phosphorylation activity under the stimulatory effects of angiotensin peptides. Furthermore, genistein did not significantly influence the phasic contractions induced by angiotensin peptides in Ca2+-free Krebs-Henseleit solution. Thus, it appears that Ca2+ influx, rather than the release of Ca2+ from IP3-sensitive stores, may play a major role in the contractile effects of angiotensin peptides in rat aorta via tyrosine kinase activation. One argument against a direct action of genistein on the Ca2+ channel itself is that it did not markedly affect the K+-induced contraction (depolarisation) in rat aorta. At the same time, a potential role for tyrosine kinase activity in the process of calcium entry is suggested. An elevation of intracellular calcium via tyrosine kinase-mediated processes may mediate the actions of G-protein coupled receptor agonists in smooth muscle, including angiotensin peptides.

3-Hydroxy-3-methylglutaryl-CoA reductase inhibitors block calcium-dependent tyrosine kinase Pyk2 activation by angiotensin II in vascular endothelial cells. involvement of geranylgeranylation of small G protein Rap1

We recently reported the calcium-dependent activation of tyrosine kinase Pyk2 by angiotensin II (Ang II) in pulmonary vein endothelial cells (PVEC). Since Pyk2 has no calcium binding domain, and neither Ca(2+) nor Ca(2+)/calmodulin directly activates Pyk2, it is not clear how Ca(2+) transduces the signal to activate Pyk2, a key tyrosine kinase, in the early events of Ang II signaling. In the present study, we investigated the mechanism of the calcium-dependent activation of Pyk2 in response to Ang II by using 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors and isoprenoid intermediates in PVEC. We have obtained substantial evidence indicating that Ang II activates Pyk2 through calcium-mediated activation of the geranylgeranylated small G protein Rap1 and the Rap1 association with Pyk2. Thus, the small G protein Rap1 is an intermediary signaling molecule linking Ang II-induced calcium signal to Pyk2 activation in PVEC. In addition, our results indicate that 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors, a class of cholesterol-lowering drugs, could interrupt Ang II signaling independent of cholesterol lowering in endothelial cells.

Angiotensin II mediated signal transduction. Important role of tyrosine kinases

It has been 100 years since the discovery of renin by Bergman and Tigerstedt. Since then, numerous studies have advanced our understanding of the renin-angiotensin system. A remarkable aspect was the discovery that angiotensin II (AngII) is the central product of the renin-angiotensin system and that this octapeptide induces multiple physiological responses in different cell types. In addition to its well known vasoconstrictive effects, growing evidence supports the notion that AngII may play a central role not only in hypertension, but also in cardiovascular and renal diseases. Binding of AngII to the seven-transmembrane angiotensin II type 1 receptor is responsible for nearly all of the physiological actions of AngII. Recent studies underscore the new concept that activation of intracellular second messengers by AngII requires tyrosine phosphorylation. An increasing number of tyrosine kinases have been shown to be activated by AngII, including the Src kinase family, the focal adhesion kinase family, the Janus kinases and receptor tyrosine kinases. These actions of AngII contribute to the pathophysiology of cardiac hypertrophy and remodeling, vascular thickening, heart failure and atherosclerosis. In this review, we discuss the important role of tyrosine kinases in AngII-mediated signal transduction. Understanding the importance of tyrosine phosphorylation in AngII-stimulated signaling events may contribute to new therapies for cardiovascular and renal diseases.

alpha(v)beta(3) integrin induces tyrosine phosphorylation-dependent Ca(2+) influx in pulmonary endothelial cells

The endothelial alpha(v)beta(3) integrin occurs luminally, where its ligation by soluble agents may induce inflammatory signaling. We tested this hypothesis in bovine pulmonary artery endothelial cell monolayers with the use of vitronectin and cross-linking antibodies to ligate and aggregate the integrin. We quantified the endothelial cytosolic Ca(2+) concentration ([Ca(2+)](i)) according to the Fura 2 ratio imaging method in single cells of confluent monolayers. At baseline, endothelial [Ca(2+)](i) levels remained steady at 86 nmol/L for >20 minutes. Cross-linking of the alpha(v)beta(3) integrin through the sequential exposure of monolayers to anti-alpha(v)beta(3) monoclonal antibody LM609 and secondary IgG resulted in a [Ca(2+)](i) increase of 100% above baseline. This increase commenced in <0.5 minute, peaked in <2 minutes, and decayed to baseline in approximately 5 minutes. Similar responses occurred after the addition of vitronectin (400 microg/mL). In contrast, external Ca(2+) depletion blunted the cross-linking-induced [Ca(2+)](i) increase by 60%, a response that was completely inhibited when the monolayers were also pretreated with thapsigargin. Thus, the [Ca(2+)](i) increase was attributable in part to the release of Ca(2+) from endosomal stores but mostly to Ca(2+) influx across the plasma membrane. Induced aggregation of the alpha(v)beta(3) integrin enhanced tyrosine phosphorylation of phospholipase C-gamma1 and increased the accumulation of inositol-1, 4,5-trisphosphate. Genistein, a broad-spectrum tyrosine kinase inhibitor, abrogated both of these effects, as well as the alpha(v)beta(3)-induced [Ca(2+)](i) increases. We conclude that aggregation of the endothelial alpha(v)beta(3) integrin induces a rapid tyrosine phosphorylation-dependent increase in [Ca(2+)](i). This response may subserve the inflammatory role of alpha(v)beta(3) integrin in blood vessels.

Inhibition of extracellular signal-regulated protein kinase or c-Jun N-terminal protein kinase cascade, differentially activated by cisplatin, sensitizes human ovarian cancer cell line

We have studied the roles of c-Jun N-terminal protein kinase (JNK) and extracellular signal-regulated protein kinase (ERK) cascade in both the cisplatin-resistant Caov-3 and the cisplatin-sensitive A2780 human ovarian cancer cell lines. Treatment of both cells with cisplatin but not transplatin isomer activates JNK and ERK. Activation of JNK by cisplatin occurred at 30 min, reached a plateau at 3 h, and declined thereafter, whereas activation of ERK by cisplatin showed a biphasic pattern, indicating the different time frame. Activation of JNK by cisplatin was maximal at 1000 microM, whereas activation of ERK was maximal at 100 microM and was less at higher concentrations, indicating the different dose dependence. Cisplatin-induced JNK activation was neither extracellular and intracellular Ca(2+)- nor protein kinase C-dependent, whereas cisplatin-induced ERK activation was extracellular and intracellular Ca(2+)- dependent and protein kinase C-dependent. A mitogen-activated protein kinase/extracellular signal-regulated kinase kinase inhibitor, PD98059, had no effect on the cisplatin-induced JNK activity, suggesting an absence of cross-talk between the ERK and JNK cascades. We further examined the effect of each cascade on the viability following cisplatin treatment. Either exogenous expression of dominant negative c-Jun or the treatment by PD98059 induced sensitivity to cisplatin in both cells. Our findings suggest that cisplatin-induced DNA damage differentially activates JNK and ERK cascades and that inhibition of either of these cascades sensitizes ovarian cancer cells to cisplatin.

Interactions between two cytoskeleton-associated tyrosine kinases: calcium-dependent tyrosine kinase and focal adhesion tyrosine kinase

The calcium-dependent tyrosine kinase (CADTK), also known as Pyk2/RAFTK/CAKbeta/FAK2, is a cytoskeleton-associated tyrosine kinase. We compared CADTK regulation with that of the highly homologous focal adhesion tyrosine kinase (FAK). First, we generated site-specific CADTK mutants. Mutation of Tyr402 eliminated autophosphorylation and significantly decreased kinase activity. Mutation of Tyr881, a putative Src kinase phosphorylation site predicted to bind Grb2, had little effect on CADTK regulation. Src family tyrosine kinases resulted in CADTK tyrosine phosphorylation even when co-expressed with the Tyr402/Tyr881 double mutant, suggesting that Src/Fyn etc. phosphorylate additional tyrosine residues. Interestingly, CADTK tyrosine-phosphorylated FAK when both were transiently expressed, but FAK did not phosphorylate CADTK. Biochemical experiments confirmed direct CADTK phosphorylation of FAK. This phosphorylation utilized tyrosine residues other than Tyr397, Tyr925, or Tyr576/Tyr577, suggesting that new SH2-binding sites might be created by CADTK-dependent FAK phosphorylation. Last, expression of the CADTK carboxyl terminus (CRNK) abolished CADTK but not FAK autophosphorylation. In contrast, FAK carboxyl terminus overexpression inhibited both FAK and CADTK autophosphorylation, suggesting that a FAK-dependent cytoskeletal function may be necessary for CADTK activation. Thus, CADTK and FAK, which both bind to some, but not necessarily the same, cytoskeletal elements, may be involved in coordinate regulation of cytoskeletal structure and signaling.

Mitogen-activated protein kinase cascade is involved in endothelin-1-induced rat puerperal uterine contraction

The regulation of mitogen-activated protein (MAP) kinase by endothelin-1 (ET-1) in cultured rat puerperal uterine myometrial cells was investigated. ET-1 caused the rapid stimulation of MAP kinase activity. ET-1-induced MAP kinase activation is neither extracellular Ca2+- nor intracellular Ca2+-dependent. ET-1 stimulation also led to an increase in phosphorylation of son-of-sevenless (SOS), and transfection of dominant negative SOS attenuated the ET-1-induced MAP kinase activity. Phorbol-12-myristate 13-acetate (PMA) also induced the MAP kinase activity, but pretreatment of the cultured cells with PMA, to down-regulate protein kinase C (PKC), did not abolish the activation of MAP kinase by ET-1. In addition, down-regulation of PKC had no effect on ET-1-induced SOS phosphorylation. Pertussis toxin, which inactivates Gi/Go proteins, blocked the ET-1-induced MAP kinase activation but not the PMA-induced MAP kinase activation. The results suggested that MAP kinase is acutely activated by ET-1 through a pertussis toxin-sensitive G protein and SOS, not through the PMA-sensitive PKC. In addition, although reverse-transcriptase PCR assays detected messenger RNA for both ET- 1 receptor subtypes in cultured rat puerperal uterine myometrial cells, ET-1-induced MAP kinase activity and uterine contraction were blocked by treatment with BQ485, an antagonist selective for an ET type A receptor (but not by BQ788, an ET type B receptor antagonist). Ritodrine, which is known to relax uterine muscle contraction, attenuated ET-1-induced MAP kinase activity. We further examined the role of MAP kinase pathway in uterine contraction using an inhibitor of MEK activity, PD098059. This inhibitor completely inhibited the ET-1-induced MAP kinase activation and partially, but significantly, inhibited the ET-1-induced uterine contraction. These results indicate that ET-1-induced MAP kinase signaling cascade may play an important role in the ET-1-induced uterine contraction.

EGF stimulates tyrosine phosphorylation of focal adhesion kinase (p125FAK) and paxillin in rat pancreatic acini by a phospholipase C-independent process that depends on phosphatidylinositol 3-kinase, the small GTP-binding protein, p21rho, and the integrity of the actin cytoskeleton

Epidermal growth factor (EGF) is a potent mitogen in many cell types including pancreatic cells. Recent studies show that the effects of some growth factors on growth and cell migration are mediated by tyrosine phosphorylation of the cytosolic tyrosine kinase p125 focal adhesion kinase (p125FAK) and the cytoskeletal protein, paxillin. The aim of the present study was to determine whether EGF activates this pathway in rat pancreatic acini and causes tyrosine phosphorylation of each of these proteins, and to examine the intracellular pathways involved. Treatment of pancreatic acini with EGF induced a rapid, concentration-dependent increase in p125FAK and paxillin tyrosine phosphorylation. Depletion of the intracellular calcium pool or inhibition of PKC activation had no effect on the response to EGF. However, inhibition of the phosphatidylinositol 3-kinase (PI3-kinase) or inactivation of p21rho inhibited EGF-stimulated phosphorylation of p125FAK and paxillin by more than 70%. Finally, cytochalasin D, a selective disrupter of the actin filament network, completely inhibited EGF-stimulated tyrosine phosphorylation of both proteins. All these treatments did not modify EGF receptor autophosphorylation in response to EGF. These results identify p125FAK and paxillin as components of the intracellular pathways stimulated after EGF receptor occupation in rat pancreatic acini. Activation of this cascade requires activation of PI3-kinase and participation of p21rho, but not PKC activation and calcium mobilization.

Role of tyrosine phosphorylation in excitation-contraction coupling in vascular smooth muscle

Increasingly it is recognized that tyrosine phosphorylation plays an important part in the regulation of function in differentiated contractile vascular smooth muscle. Tyrosine kinases and phosphatases are present in large amounts in vascular smooth muscle and have been reported to influence a number of processes crucial to contraction, including ion channel gating, calcium homeostasis and sensitization of the contractile process to [Ca2+]i. This review summarizes current understanding regarding the role of tyrosine phosphorylation in excitation-contraction coupling in blood vessels.

The role of tyrosine kinase in hypoxic constriction of sheep pulmonary artery rings

Complex and incompletely understood mechanisms underline the vascular responses to hypoxia. Recent studies showed that the tyrosine kinase pathway is involved in vasoconstriction of vascular smooth muscle. Therefore, the aim of this study was to determine the tyrosine kinase pathway for the hypoxic contraction in large-diameter sheep pulmonary artery rings in vitro by studying the effects of selective inhibitors of tyrosine kinase and of a protein tyrosine kinase inhibitor. Lowering the pO2 from 96 to 5 mm Hg caused a contraction in arteries precontracted with 5-hydroxytryptamine (5-HT) but not under resting force. Preincubation of arteries with the tyrosine kinase inhibitors, genistein and tyrphostin, abolished the hypoxic contraction without affecting 5-HT contractions. Inhibition of tyrosine phosphatase activity by sodium orthovanadate increased the hypoxic vasoconstriction in 5-HT-precontracted arteries. These results suggest that the tyrosine kinase pathway is involved in hypoxic pulmonary vasoconstriction in sheep isolated pulmonary artery rings.

Adjacent carboxyterminal tyrosine phosphorylation events identify functionally distinct ErbB2 receptor subsets: implications for molecular diagnostics

Site-directed mutagenesis can define the effects of altering one or more amino acids within a protein, but this technique may lack sensitivity when used to characterize proteins which differ conformationally or posttranslationally at multiple sites. A novel alternative approach involves the direct characterization of wild-type protein isoforms identified by site-specific immunodetection. To this end we have developed antibodies which recognize ErbB2 subsets characterized by adjacent tyrosine phosphorylation events (Y1222 and Y1248) in the C-terminal tail of the oncoprotein. Here we use these phosphoantibodies to demonstrate the existence of tyrosine-phosphorylated ErbB2 subsets which differ in their patterns of heterooligomer formation, in vitro autophosphorylation, and recruitment of SH2-containing substrates. Furthermore, Y1222 and/or Y1248 phosphoantibody immunoreactivity is readily detectable in ErbB2-overexpressing human breast tumors, in which context these phosphorylation events exhibit significant discordance. These data confirm the value of site-specific immunodetection as a strategy for characterizing phosphoprotein function in vitro and in vivo and suggest that multisite phosphotyping of human tumors may contribute novel clinicopathologic insights into the significance of the ErbB2 overexpression phenotype.

Ability of various bombesin receptor agonists and antagonists to alter intracellular signaling of the human orphan receptor BRS-3

Bombesin (Bn) receptor subtype 3 (BRS-3) is an orphan receptor that is a predicted member of the heptahelical G-protein receptor family and so named because it shares a 50% amino acid homology with receptors for the mammalian bombesin-like peptides neuromedin B (NMB) and gastrin-releasing peptide. In a recent targeted disruption study, in which BRS-3-deficient mice were generated, the mice developed obesity, diabetes, and hypertension. To date, BRS-3's natural ligand remains unknown, its pharmacology unclear, and cellular basis of action undetermined. Furthermore, there are few tissues or cell lines found that express sufficient levels of BRS-3 protein for study. To define the intracellular signaling properties of BRS-3, we examined the ability of [D-Phe6,beta-Ala11,Phe13, Nle14]Bn-(6-14), a newly discovered peptide with high affinity for BRS-3, and various Bn receptor agonists and antagonists to alter cellular function in hBRS-3-transfected BALB 3T3 cells and hBRS-3-transfected NCI-H1299 non-small cell lung cancer cells, which natively express very low levels of hBRS-3. This ligand stimulated a 4-9-fold increase in [3H]inositol phosphate formation in both cell lines under conditions where it caused no stimulation in untransfected cells and also stimulated an increase in [3H]IP1, [3H]IP2, and 3H]IP3. The elevation of [3H]IP was concentration-dependent, with an EC50 of 20-35 nM in both cell lines. [D-Phe6,beta-Ala11,Phe13,Nle14]Bn-(6-14) stimulated a 2-3-fold increase in [Ca2+]i, a 3-fold increase in tyrosine phosphorylation of p125(FAK) with an EC50 of 0.2-0.7 nM, but failed to either stimulate increases in cyclic AMP or inhibit forskolin-stimulated increases. None of nine naturally occurring Bn peptides or three synthetic Bn analogues reported to activate hBRS-3 did so with high affinity. No high affinity Bn receptor antagonists had high affinity for the hBRS-3 receptor, although two low affinity antagonists for gastrin-releasing peptide and NMB receptors, [D-Arg1,D-Trp7,9, Leu11]substance P and [D-Pro4,D-Trp7,9,10]substance P-(4-11), inhibited hBRS-3 receptor activation. The NMB receptor-specific antagonist D-Nal,Cys,Tyr,D-Trp,Lys,Val, Cys,Nal-NH2 inhibited hBRS-3 receptor activation in a competitive fashion (Ki = 0.5 microM). Stimulation of p125(FAK) tyrosine phosphorylation by hBRS-3 activation was not inhibited by the protein kinase C inhibitor, GF109203X, or thapsigargin, alone or in combination. These results show that hBRS-3 receptor activation increases phospholipase C activity, which causes generation of inositol phosphates and changes in [Ca2+]i and is also coupled to tyrosine kinase activation, but is not coupled to adenylate cyclase activation or inhibition. hBRS-3 receptor activation results in tyrosine phosphorylation of p125(FAK), and it is not dependent on activation of either limb of the phospholipase C cascade. Although the natural ligand is not a known bombesin-related peptide, the availability of [D-Phe6,beta-Ala11, Phe13,Nle14]Bn-(6-14), which functions as a high affinity agonist in conjunction with hBRS-3-transfected cell lines and the recognition of three classes of receptor antagonists including one with affinity of 0.5 microM, should provide important tools to assist in the identification of its natural ligand, the development of more potent selective receptor antagonists and agonists, and further exploration of the signaling properties of the hBRS-3 receptor.

Protein tyrosine phosphorylation and calcium signaling in thyroid FRTL-5 cells

We examined the importance of tyrosine kinase(s) on the ATP-evoked Ca2+ entry and DNA synthesis of thyroid FRTL-5 cells. ATP rapidly and transiently tyrosine phosphorylated a 72-kDa protein(s). This phosphorylation was abolished by pertussis toxin and by the tyrosine kinase inhibitor genistein, and was dependent on Ca2+ entry. Pretreatment of the cells with genistein did not affect the release of sequestered Ca2+, but the capacitative Ca2+ or Ba2+ entry evoked by ATP or thapsigargin was attenuated. Pretreatment of the cells with orthovanadate enhanced the increase in intracellular free Ca2+ ([Ca2+]i), whereas the Ba2+ entry was not increased. Phorbol 12-myristate 13-acetate (PMA) phosphorylated the same protein(s) as did ATP. Genistein inhibited the ATP-evoked phosphorylation of MAP kinase and attenuated both the ATP- and the PMA-evoked DNA synthesis. However, genistein did not inhibit the ATP-evoked expression of c-fos. Furthermore, genistein enhanced the ATP-evoked release of arachidonic acid. Thus, ATP activates a tyrosine kinase via a Ca2+-dependent mechanism. A genistein-sensitive mechanism participates, in part, in the ATP-evoked activation of DNA synthesis. Genistein inhibits only modestly capacitative Ca2+ entry in FRTL-5 cells.

Angiotensin II stimulates ERK via two pathways in epithelial cells: protein kinase C suppresses a G-protein coupled receptor-EGF receptor transactivation pathway

In GN4 rat liver epithelial cells, angiotensin II (Ang II) produces intracellular calcium and protein kinase C (PKC) signals and stimulates ERK and JNK activity. JNK activation appears to be mediated by a calcium-dependent tyrosine kinase (CADTK). To define the ERK pathway, we established GN4 cells expressing an inhibitory Ras(N17). Induction of Ras(N17) blocked EGF- but not Ang II- or phorbol ester (TPA)-dependent ERK activation. In control cells, Ang II and TPA produced minimal increases in Ras-GTP level and Raf kinase activity. PKC depletion by chronic TPA exposure abolished TPA-dependent ERK activation but failed to diminish the effect of Ang II. In PKC-depleted cells, Ang II increased Ras-GTP level and activated Raf and ERK in a Ras-dependent manner. In PKC depleted cells, Ang II stimulated Shc and Cbl tyrosine phosphorylation, suggesting that without PKC, Ang II activates another tyrosine kinase. PKC-depletion did not alter Ang II-dependent tyrosine phosphorylation or activity of p125(FAK), CADTK, Fyn or Src, but PKC depletion or incubation with GF109203X resulted in Ang II-dependent EGF receptor tyrosine phosphorylation. In PKC-depleted cells, EGF receptor-specific tyrosine kinase inhibitors blocked Ang II-dependent EGF receptor and Cbl tyrosine phosphorylation, and ERK activation. In summary, Ang II can activate ERK via two pathways; the latent EGF receptor, Ras-dependent pathway is equipotent to the Ras-independent pathway, but is masked by PKC action. The prominence of this G-protein coupled receptor to EGF receptor pathway may vary between cell types depending upon modifiers such as PKC.

Cholecystokinin-stimulated tyrosine phosphorylation of p125FAK and paxillin is mediated by phospholipase C-dependent and -independent mechanisms and requires the integrity of the actin cytoskeleton and participation of p21rho

Recent studies show that the effects of some oncogenes, integrins, growth factors and neuropeptides are mediated by tyrosine phosphorylation of the cytosolic kinase p125 focal adhesion kinase (p125(FAK)) and the cytoskeletal protein paxillin. Recently we demonstrated that cholecystokinin (CCK) C-terminal octapeptide (CCK-8) causes tyrosine phosphorylation of p125(FAK) and paxillin in rat pancreatic acini. The present study was aimed at examining whether protein kinase C (PKC) activation, calcium mobilization, cytoskeletal organization and small G-protein p21(rho) activation play a role in mediating the stimulation of tyrosine phosphorylation by CCK-8 in acini. CCK-8-stimulated phosphorylation of p125(FAK) and paxillin reached a maximum within 2.5 min. The CCK-8 dose response for causing changes in the cytosolic calcium concentration ([Ca2+]i) was similar to that for p125(FAK) and paxillin phosphorylation, and both were to the left of that for receptor occupation and inositol phosphate production. PMA increased tyrosine phosphorylation of both proteins. The calcium ionophore A23187 caused only 25% of the maximal stimulation caused by CCK-8. GF109203X, a PKC inhibitor, completely inhibited phosphorylation with PMA but had no effect on the response to CCK-8. Depletion of [Ca2+]i by thapsigargin had no effect on CCK-8-stimulated phosphorylation. Pretreatment with both GF109203X and thapsigargin decreased CCK-8-stimulated phosphorylation of both proteins by 50%. Cytochalasin D, but not colchicine, completely inhibited CCK-8- and PMA-induced p125(FAK) and paxillin phosphorylation. Treatment with Clostridium botulinum C3 transferase, which inactivates p21(rho), caused significant inhibition of CCK-8-stimulated p125(FAK) and paxillin phosphorylation. These results demonstrate that, in pancreatic acini, CCK-8 causes rapid p125(FAK) and paxillin phosphorylation that is mediated by both phospholipase C-dependent and -independent mechanisms. For this tyrosine phosphorylation to occur, the integrity of the actin, but not the microtubule, cytoskeleton is essential as well as the activation of p21(rho).

CCK causes rapid tyrosine phosphorylation of p125FAK focal adhesion kinase and paxillin in rat pancreatic acini

Recent studies show CCK stimulates tyrosine phosphorylation (TYR PHOSP) of a number of proteins and evidence from the pancreas and other cellular systems suggest this could be important in mediating some of CCK's growth and secretory effects. In other tissues various neuropeptides such as bombesin can cause tyrosine phosphorylation of p125 focal adhesion kinase (p125FAK) and paxillin which are important in mediating their growth effects. The purpose of the present study was to determine the effects of CCK in rat pancreatic acini on the TYR PHOSP of these latter proteins. In dispersed rat pancreatic acini, cell lysates were incubated with an anti-phosphotyrosine mAb (PY20) which was immunoprecipitated and then analyzed by Western blotting with anti-phosphotyrosine mAb (4G10), anti-p125FAK mAb or anti-paxillin mAb. CCK-8 at 5 min increased TYR PHOSP of five proteins of molecular weight > 60,000 including a broad M(r) 110-130,000 and M(r) 70-80,000. An increase in TYR PHOSP of both p125FAK and paxillin was detected within 1 min of adding CCK and reached a maximum at 2.5 min with a 9.1 +/- 1.9-fold increase for p125FAK and 3.6 +/- 0.6-fold for paxillin. CCK-8 caused a half-maximal increase in TYR PHOSP of p125FAK at 0.1 nM and paxillin at 0.03 nM. CCK-JMV also stimulated an increase in TYR PHOSP of both proteins, but was only 50% as efficacious as CCK-8. CCK-JMV caused a half-maximal increase at 10 nM and maximal at 1 microM for both proteins. To investigate whether the low affinity CCK receptor state also caused TYR PHOSP of both proteins, increasing concentrations of CCK-JMV were added to a maximally effective CCK-8 concentration (1 nM). Detectable inhibition of CCK-8-stimulated TYR PHOSP occurred with 1 microM CCK-JMV and with 3 microM CCK-JMV the CCK-8-stimulated response was inhibited 50% and was the same as that seen with CCK-JMV alone. These studies demonstrate that in rat pancreatic acini, CCK causes rapid TYR PHOSP of both p125FAK and paxillin. This stimulation is mediated by both the high affinity and low affinity CCK receptor states. This phosphorylation of these proteins could be important in mediating CCK's effect on the cytoskeleton or growth effects as shown for a number of other agents (oncogenes, neuropeptides, integrins).

Protein kinase C and protein kinase A inhibit calcium-dependent but not stress-dependent c-Jun N-terminal kinase activation in rat liver epithelial cells

In rat liver epithelial cells (GN4), angiotensin II (Ang II) and thapsigargin stimulate a novel calcium-dependent tyrosine kinase (CADTK) also known as PYK2, CAKbeta, or RAFTK. Activation of CADTK by a thapsigargin-dependent increase in intracellular calcium failed to stimulate the extracellular signal-regulated protein kinase pathway but was well correlated with a 30-50-fold activation of c-Jun N-terminal kinase (JNK). In contrast, Ang II, which increased both protein kinase C (PKC) activity and intracellular calcium, stimulated extracellular signal-regulated protein kinase but produced a smaller, less sustained, JNK activation than thapsigargin. 12-O-Tetradecanoylphorbol 13-acetate (TPA), which slowly activated CADTK, did not stimulate JNK. These findings suggest either that CADTK is not involved in JNK activation or PKC activation inhibits the CADTK to JNK pathway. A 1-min TPA pretreatment of GN4 cells inhibited thapsigargin-dependent JNK activation by 80-90%. In contrast, TPA did not inhibit the >50-fold JNK activation effected by anisomycin or UV. The consequence of PKC-dependent JNK inhibition was reflected in c-Jun and c-Fos mRNA induction following treatment with thapsigargin and Ang II. Thapsigargin, which only minimally induced c-Fos, produced a much greater and more prolonged c-Jun response than Ang II. Elevation of another intracellular second messenger, cAMP, for 5-15 min also inhibited calcium-dependent JNK activation by approximately 80-90% but likewise had no effect on the stress-dependent JNK pathway. In summary, two pathways stimulate JNK in cells expressing CADTK, a calcium-dependent pathway modifiable by PKC and cAMP-dependent protein kinase and a stress-activated pathway independent of CADTK, PKC, and cAMP-dependent protein kinase; the inhibition by PKC can ultimately alter gene expression initiated by a calcium signal.

Paxillin is tyrosine-phosphorylated by and preferentially associates with the calcium-dependent tyrosine kinase in rat liver epithelial cells

We and others have recently cloned a non-receptor, calcium-dependent tyrosine kinase (CADTK; also known as PYK2, CAKbeta, and RAFTK) that shares both overall domain structure and 45% amino acid identity with p125(FAK). We have studied the signaling, activation, and potential function of these related enzymes in GN4 rat liver epithelial cells that express CADTK and p125(FAK) at roughly similar levels. p125(FAK) is nearly fully tyrosine-phosphorylated in resting GN4 cells. In contrast, while CADTK is not tyrosine-autophosphorylated in untreated cells, angiotensin II increases CADTK Tyr(P) by 5-10-fold. With regard to signaling, CADTK activation is correlated with stimulation of c-Jun N-terminal kinase and p70(S6K) pathways but not with the stimulation of mitogen-activated protein kinase or p90(RSK). In this report we assessed the contribution of CADTK and p125(FAK) to tyrosine phosphorylation of focal contact proteins. In adherent GN4 cells, the constitutive activity of p125(FAK) was correlated with basal paxillin, tensin, and p130(CAS) tyrosine phosphorylation. A rapid increase in the tyrosine phosphorylation of each protein was detected after treatment with angiotensin II or other agonists that stimulate CADTK; the prolonged 3-4-fold increase in paxillin tyrosine phosphorylation was the most substantial change. In the WB cell line that expresses 3-fold less CADTK than GN4 cell line agonist-dependent paxillin tyrosine phosphorylation is similarly reduced. Immunoprecipitation of CADTK from GN4 cells revealed CADTK. paxillin complexes that persisted in 500 mM NaCl but not in 0.1% SDS cell lysis buffer. The complexes were largely independent of the tyrosine phosphorylation state of either protein. Surprisingly, we did not detect p125(FAK).paxillin complexes in immunoprecipitates using either of two p125(FAK) antibodies. When CADTK and p125(FAK) were transiently overexpressed in 293(T) cells, both enzymes associated with paxillin, but the avidity of CADTK appeared to be greater. In addition, in transfected 293(T) cells, complexes between CADTK and another potential substrate, p130(CAS), were detected. In summary, in GN4 rat liver epithelial cells stimulation of CADTK was highly correlated with paxillin tyrosine phosphorylation; in addition, CADTK but not p125(FAK) was complexed to paxillin at detectable levels. This suggests that agonist-dependent cytoskeletal changes in epithelial cells might proceed, in part, by CADTK-dependent mechanisms.

Angiotensin II-induced down-regulation of inositol trisphosphate receptors in WB rat liver epithelial cells. Evidence for involvement of the proteasome pathway

Chronic stimulation of WB rat liver epithelial cells by angiotensin II (Ang II) resulted in the down-regulation of both type I and type III myo-inositol 1,4,5-trisphosphate receptors (IP3Rs). Stimulation with vasopressin, bradykinin, epidermal growth factor, or 12-O-tetradecanoylphorbol-13-acetate was without effect. Ang II-induced down-regulation of IP3Rs could be detected within 2 h and resulted in an inhibition of IP3-induced Ca2+ release from permeabilized cells. IP3R down-regulation was reversible, and both homo- and heterooligomers of IP3Rs were equally susceptible to Ang II-induced degradation. Chloroquine and NH4Cl increased the basal levels of IP3Rs by 2-fold, suggesting that the basal turnover of IP3Rs occurs via a lysosomal pathway. However, Ang II-induced degradation of IP3R was not affected by these inhibitors, suggesting that stimulated degradation of IP3Rs occurs via a non-lysosomal pathway. The cysteine protease and proteasomal inhibitor N-acetyl-Leu-Leu-norleucinal completely prevented Ang II-mediated down-regulation of IP3Rs, whereas the structural analog N-acetyl-Leu-Leu-methioninal was without effect. Lactacystin, a highly specific proteasome inhibitor, also blocked Ang II-mediated IP3R degradation. Stimulation with Ang II increased the amount of IP3R immunoprecipitated by anti-ubiquitin antibodies. We conclude that Ang II-stimulated IP3R degradation involves enhanced ubiquitination of the protein and degradation by the proteasome pathway.

Angiotensin II signal transduction in vascular smooth muscle: role of tyrosine kinases

In this review, the role of tyrosine kinases in angiotensin II-mediated signal transduction pathways in vascular smooth muscle is discussed. Angiotensin II was isolated by virtue of its vasoconstrictor abilities and has long been thought to play a critical role in hypertension. However, recent studies indicate important roles for angiotensin II in inflammation, atherosclerosis, and congestive heart failure. The expanding role of angiotensin II indicates that multiple signal transduction pathways are likely to be activated in a tissue-specific manner. Exciting recent data show that angiotensin II directly stimulates tyrosine kinases, including pp60(c-src) kinase (c-Src), focal adhesion kinase (FAK), and Janus kinases (JAK2 and TYK2). Angiotensin II may activate receptor tyrosine kinases, such as Axl and platelet-derived growth factor, by as-yet-undefined autocrine mechanisms. Finally, unknown tyrosine kinases may mediate tyrosine phosphorylation of Shc, Raf, and phospholipase C-gamma after angiotensin II stimulation. These angiotensin II-regulated tyrosine kinases appear to be required for angiotensin II effects, such as vasoconstriction, proto-oncogene expression, and protein synthesis, on the basis of studies with tyrosine kinase inhibitors. Thus, understanding angiotensin II-stimulated signaling events, especially those related to tyrosine kinase activity, may form the basis for the development of new therapies for cardiovascular diseases.

Protein tyrosine kinase, mitogen-activated protein kinase and protein kinase C are involved in the mitogenic signaling of platelet-activating factor (PAF) in HEC-1A cells

We have recently demonstrated that the phospholipid platelet-activating factor (PAF) mediates an autocrine proliferative loop in the endometrial adenocarcinoma cell line HEC-1A. In the present study we investigated the signaling pathways involved in PAF-mediated increase of proliferation in these cells. In particular, we studied the effect of PAF on protein tyrosine phosphorylation and mitogen-activated protein kinase (MAPK) activity, as well as the effect of protein tyrosine kinase (PTK) and protein kinase C (PKC) inhibition on PAF-induced increase of c-fos gene expression and thymidine incorporation in HEC-1A cells. We found that PAF induced a rapid, time- and dose-dependent increase of tyrosine phosphorylation of a subset of proteins of 42, 44, 78, 99, and 150 kDa molecular weight. We also found that PAF increased tyrosine phosphorylation and activity of p42 MAPK, suggesting the involvement of this important intermediary enzyme in the proliferative effect of PAF. The effect of PAF on c-fos gene expression was not prevented by pre incubation with the PTK inhibitors genistein or methyl-2,5-dihydroxycinnamate, whereas was strongly affected by PKC down regulation after long term incubation with PMA or by PKC inhibition with sangivamycin. We also found that genistein and methyl 2,5-dihydroxycinnamate decreased both basal and PAF-stimulated [3H]thymidine uptake in these cells. Similar results were obtained with PD 098059, a specific inhibitor of MAP kinase cascade. PAF-stimulated [3H]thymidine uptake was also prevented by PKC down regulation after long term exposure to PMA and PKC inhibition with the two inhibitors sangivamycin and bis-indolylmaleimide. In conclusion, our results indicate that PAF-induced mitogenesis in HEC-1A cells is mediated by the activation of multiple signaling pathways, involving PTK, MAPK, and PKC activation.

Involvement of tyrosine phosphorylation in endothelin-1-induced calcium-sensitization in rat small mesenteric arteries

1. We have studied the effect of endothelin-1 stimulation on protein tyrosine phosphorylation levels in intact small mesenteric arteries of the rat and investigated the effects of tyrosine kinase inhibition on the contractile response to this agonist. 2. Endothelin-1 stimulated a rapid (20 s), sustained (up to 20 min) and concentration-dependent (1-100 nM) increase in protein tyrosine phosphorylation levels which coincided temporally with the contractile response in intact and alpha-toxin permeabilized small artery preparations. Tyrosine phosphorylation was increased in four main clusters of proteins of apparent molecular mass 28-33, 56-61, 75-85 and 105-115 kDa. Endothelin-1-induced protein tyrosine phosphorylation was independent of extracellular calcium, antagonized by the tyrosine kinase inhibitor tyrphostin A23 but not by the inactive tyrphostin A1. 3. In intact small arteries tyrphostin A23 inhibited the force developed to endothelin-1 at all concentrations studied; at higher concentrations (10 and 100 nM) the profile of contraction was altered from a sustained to a transient response. Tyrphostin A1 inhibited the contractile response to endothelin-1 at all concentrations except 100 nM; the profile of the response was not altered. Neither tyrphostin affected the transient phasic contraction induced by endothelin-1 (100 nM) in the absence of extracellular calcium. 4. In rat alpha-toxin permeabilized mesenteric arteries endothelin-1 caused a concentration-dependent increase in force in the presence of 10 microM GTP and low (pCa 6.7) constant calcium, demonstrating increased sensitivity of the contractile apparatus to calcium. Tyrphostin A23 inhibited this response by approximately 50%, tyrphostin A1 did not affect endothelin-1-induced calcium sensitization of force. 5. We conclude that increased tyrosine phosphorylation is important in the contractile response induced by endothelin-1 in intact small mesenteric arteries. Furthermore our data implicate activation of this signalling pathway in the tonic phase of contraction possibly through modulation of the sensitivity of the contractile apparatus to calcium.

An intracellular calcium signal activates p70 but not p90 ribosomal S6 kinase in liver epithelial cells

In the rat liver epithelial cell lines GN4 and WB, angiotensin II (Ang II) activates the Gq class of regulatory G-proteins, increasing intracellular calcium, protein kinase C activity, and protein tyrosine phosphorylation. We compared the ability of Ang II and other compounds that increase intracellular calcium (i.e. the calcium ionophore A23187 and thapsigargin) or protein kinase C activity (the phorbol ester 12-O-tetradecanoylphorbol-13-acetate) to activate p70 ribosomal S6 kinase (p70(S6K)) and p90 ribosomal S6 kinase (p90(RSK)). In GN4 cells, increasing intracellular calcium stimulated p70(S6K) activity in a rapamycin- and wortmannin- sensitive manner, but did not affect p90(RSK) activity. In contrast, 12-O-tetradecanoylphorbol-13-acetate strongly activated p90(RSK) but only weakly stimulated p70(S6K). The ability of calcium to activate p70(S6K) was confirmed by blocking the A23187-dependent activation through chelation of extracellular calcium with EGTA; the effect of thapsigargin was inhibited by the cell permeant chelator bis-(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester (BAPTA-AM). Similarly, BAPTA-AM prevented the activation of p70(S6K) by Ang II, suggesting that this signal was largely calcium-dependent. In contrast, the Ang II-dependent activation of mitogen-activated protein kinase and p90(RSK) was not inhibited but was enhanced by BAPTA-AM. These results show that in GN4 cells, Ang II selectively activates p70(S6K) through effects on calcium, p90(RSK) through effects on protein kinase C. The activation of p70(S6K) by calcium stimuli or Ang II was independent of calmodulin but correlated well with the activation of the recently identified, nonreceptor calcium-dependent tyrosine kinase (CADTK)/PYK-2. Both calcium- and Ang II-dependent activation of p70(S6K) were attenuated by the tyrosine kinase inhibitor genistein, and activation of p70(S6K) was higher in GN4 than WB cells, correlating with the increased expression and activation of CADTK/PYK-2 in GN4 cells. In summary, these results demonstrate that intracellular calcium selectively activates p70(S6K) in GN4 cells, consistent with increased CADTK/PYK-2 signaling in these cells.

Elevated intracellular calcium concentration increases secretory processing of the amyloid precursor protein by a tyrosine phosphorylation-dependent mechanism

Secretory cleavage of the amyloid precursor protein (APP), a process that releases soluble APP derivatives (APPs) into the extracellular space, is stimulated by the activation of muscarinic receptors coupled to phosphoinositide hydrolysis. The signalling pathways involved in the release process exhibit both protein kinase C- and protein tyrosine phosphorylation-dependent components [Slack, Breu, Petryniak, Srivastava and Wurtman (1995) J. Biol. Chem. 270, 8337-8344]. The possibility that elevations in intracellular Ca2+ concentration initiate the tyrosine phosphorylation-dependent release of APPs was examined in human embryonic kidney cells expressing muscarinic m3 receptors. Inhibition of protein kinase C with the bisindolylmaleimide GF 109203X decreased the carbachol-evoked release of APPs by approx. 30%, as shown previously. The residual response was further decreased, in an additive manner, by the Ca2+ chelator EGTA, or by the tyrosine kinase inhibitor tyrphostin A25. The Ca2+ ionophore, ionomycin, like carbachol, stimulated both the release of APPs and the tyrosine phosphorylation of several proteins, one of which was identified as paxillin, a component of focal adhesions. The effects of ionomycin on APPs release and on protein tyrosine phosphorylation were concentration-dependent, and occurred over similar concentration ranges; both effects were inhibited only partly by GF 109203X, but were abolished by EGTA or by tyrosine kinase inhibitors. The results demonstrate for the first time that ionophore-induced elevations in intracellular Ca2+ levels elicit APPs release via increased tyrosine phosphorylation. Part of the increase in APPs release evoked by muscarinic receptor activation might be attributable to a similar mechanism.

Stimulated mitogen-activated protein kinase is necessary but not sufficient for the mitogenic response to angiotensin II. A role for phospholipase D

Activation of the mitogen-activated protein kinase (MAPK) cascade has been widely associated with cell proliferation; previous studies have shown that angiotensin II (AII), acting on 7-transmembrane G protein-coupled receptors, stimulates the MAPK pathway. In this report we investigate whether the MAPK pathway is required for the mitogenic response to AII stimulation of vascular smooth muscle cells derived from the hypertensive rat (SHR-VSM). AII stimulates the phosphorylation of MAPK, as determined by Western blot specific for the tyrosine 204 phosphorylated form of the protein. This MAPK phosphorylation was inhibited by the presence of the inhibitor of MAPK kinase activation, PD 098059. Using a peptide kinase assay shown to measure the p42 and p44 isoforms of MAPK, the stimulated response to AII was inhibited by PD 098059 with an IC50 of 15.6 +/- 1.6 microM. The AII stimulation of [3H]thymidine incorporation was inhibited by PD 098059 with an IC50 of 17.8 +/- 3.1 microM. PD 098059 had no effect on AII-stimulated phospholipase C or phospholipase D (PLD) activity. When the SHR-VSM cells were stimulated with phorbol ester, there was an activation of MAPK similar in size and duration to the response to AII, but there was no significant enhancement of [3H]thymidine incorporation. There was also no activation of PLD by phorbol ester, while AII produced a robust PLD response. Diversion of the product of the PLD reaction by 1-butanol caused a partial loss of the [3H]thymidine response; this did not occur with tertiary butanol, which did not interfere with the PLD reaction. These results show that in these cells the MAPK cascade is required but not sufficient for the mitogenic response to AII, and suggest that the full mitogenic response requires both MAPK in conjunction with other signaling components, one of which is PLD.

Activation of a novel calcium-dependent protein-tyrosine kinase. Correlation with c-Jun N-terminal kinase but not mitogen-activated protein kinase activation

Many G protein-coupled receptors (e.g. that of angiotensin II) activate phospholipase Cbeta, initially increasing intracellular calcium and activating protein kinase C. In the WB and GN4 rat liver epithelial cell lines, agonist-induced calcium signals also stimulate tyrosine phosphorylation and subsequently increase the activity of c-Jun N-terminal kinase (JNK). We have now purified the major calcium-dependent tyrosine kinase (CADTK), and by peptide and nucleic acid sequencing identified it as a rat homologue of human PYK2. CADTK/PYK2 is most closely related to p125(FAK) and both enzymes are expressed in WB and GN4 cells. Angiotensin II, which only slightly increases p125(FAK) tyrosine phosphorylation in GN4 cells, substantially increased CADTK tyrosine autophosphorylation and kinase activity. Agonists for other G protein-coupled receptors (e.g. LPA), or those increasing intracellular calcium (thapsigargin), also stimulated CADTK. In comparing the two rat liver cell lines, GN4 cells exhibited approximately 5-fold greater angiotensin II- and thapsigargin-dependent CADTK activation than WB cells. Although maximal JNK activation by stress-dependent pathways (e.g. UV and anisomycin) was equivalent in the two cell lines, calcium-dependent JNK activation was 5-fold greater in GN4, correlating with CADTK activation. In contrast to JNK, the thapsigargin-dependent calcium signal did not activate mitogen-activated protein kinase and Ang II-dependent mitogen-activated protein kinase activation was not correlated with CADTK activation. Finally, while some stress-dependent activators of the JNK pathway (NaCl and sorbitol) stimulated CADTK, others (anisomycin, UV, and TNFalpha) did not. In summary, cells expressing CADTK/PYK2 appear to have two alternative JNK activation pathways: one stress-activated and the other calcium-dependent.

Bombesin, bradykinin, vasopressin, and phorbol esters rapidly and transiently activate Src family tyrosine kinases in Swiss 3T3 cells. Dissociation from tyrosine phosphorylation of p125 focal adhesion kinase

Treatment of quiescent Swiss 3T3 cells with bombesin induces a rapid (</=40 s) and transient increase in the kinase activity of the Src family of tyrosine kinases, as determined by autophosphorylation in immune complex kinase assays (4.6 +/- 0.2-fold stimulation, n = 44) and phosphorylation of exogenous substrates. Phorbol 12, 13-dibutyrate increased the activity of Src family kinases with similar kinetics but was less effective than bombesin. However, Src family kinase activation by bombesin is not dependent either on protein kinase C or Ca2+. Bombesin stimulation of Src family kinase activity could also be dissociated from p125 focal adhesion kinase tyrosine phosphorylation. Neither treatment with cytochalasin D nor placement of the cells in suspension prevented the stimulation of Src family kinase activity induced by bombesin, but both abolished bombesin-induced tyrosine phosphorylation of p125 focal adhesion kinase. The stimulation of the Src family kinase activity by bombesin was completely prevented by treatment with vanadate, a potent inhibitor of protein-tyrosine phosphatases. Bradykinin and vasopressin also stimulated Src family kinase activity transiently, and this stimulation was also inhibited by vanadate. Our results dissect two separate pathways that lead to protein tyrosine phosphorylation in neuropeptide-stimulated Swiss 3T3 cells.

Bradykinin B2 receptor-induced and inositol tetrakisphosphate-evoked Ca2+ entry is sensitive to a protein tyrosine phosphorylation inhibitor in ras-transformed NIH/3T3 fibroblasts

Signal transduction from mouse bradykinin B2 receptors to calcium influx was studied in ras-transformed NIH/3T3 (DT) fibroblasts. DT cells were preloaded with fura-2 and whole-cell voltage-clamped. Activation of B2 receptors resulted in a decrease of cellular fluorescence at the excitation wavelength of 340, or 360 nm after MnCl2 application, in both the presence and absence of external Ca2+ in DT cells, at a holding potential of -40 mV. This Mn2+ entry through the Ca2+ influx pathway increased with membrane hyperpolarization. Internal application of inositol 1,3,4,5-tetrakisphosphate (InsP4), but not of inositol 1,4,5-trisphosphate, mimicked membrane potential-dependent Mn2+ entry. Bradykinin- and InsP4-induced Ca2+ influx was blocked by 10-100 microM genistein, a tyrosine kinase inhibitor. B2 receptor activation induced time-dependent tyrosine phosphorylation of mitogen-activated protein kinase and 120 kDa protein, which was dose-dependently inhibited by genistein. Bradykinin was unable to induce Ca2+ oscillations in genistein-treated DT cells. Our results show that bradykinin-induced Ca2+ influx and oscillations depend upon protein tyrosine phosphorylation. The results suggest that two bradykinin B2 receptor-activated signal pathways, protein tyrosine phosphorylation and formation of InsP4, merge at the Ca2+ influx process in ras-transformed NIH/3T3 fibroblasts.

Tyrosine kinase inhibitors enhance a Ca(2+)-activated K+ current (IAHP) and reduce IAHP suppression by a metabotropic glutamate receptor agonist in rat dentate granule neurones

1. Activation of metabotropic glutamate receptors (mGluRs) inhibits a transient Ca(2+)-activated K+ current (IAHP) responsible for the slow after-hyperpolarization that follows depolarizations of dentate granule neurones in rat hippocampal brain slices. Here we show for the first time that this physiological consequence of mGluR stimulation is selectively attenuated by blockers of protein tyrosine kinases (PTKs). 2. Several distinct types of PTK blockers, including genistein, tyrphostin-B42 and lavendustin-A, reduced the inhibition of IAHP by the selective mGluR agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD). Inhibition of IAHP by 5-HT was unaffected. The PTK blockers by themselves doubled the duration of IAHP suggesting that there exists a tonic inhibitory influence on IAHP that is reduced by PTK antagonists. 3. Inclusion of EGTA (1 mM) in the patch pipette also potentiated the IAHP and reduced the inhibitory action of ACPD on IAHP, consistent with the observation of others that chelation of intracellular Ca2+ prevents protein tyrosine phosphorylation induced by ACPD. 4. we propose that mGluR-initiated inositol 1,4,5-trisphosphate (InsP3) production mobilizes intracellular Ca2+ and leads to increased protein tyrosine phosphorylation which in turn leads to inhibition of IAHP.

Ca(2+)-dependent mitogen-activated protein kinase activation in spontaneously hypertensive rat vascular smooth muscle defines a hypertensive signal transduction phenotype

The mechanisms responsible for altered vascular smooth muscle cell (VSMC) function in hypertension remain unknown. In the spontaneously hypertensive rat (SHR) model of genetic hypertension, there are multiple abnormalities in VSMC function, including increased growth, Na(+)-H+ exchange, and increased signal transduction by protein kinase C. The family of kinases termed mitogen-activated protein (MAP) kinases has recently been shown to be essential mediators of growth factor signal transduction. In the present study, alterations in MAP kinase function in the hypertensive phenotype were investigated using early-passage SHR and Wistar-Kyoto (WKY) VSMCs stimulated with angiotensin II (Ang II, 100 nmol/L) or platelet-derived growth factor-BB (PDGF-BB, 10 ng/mL). MAP kinase activity was measured by in-gel kinase assays and Western blot analysis. Two differences between SHR and WKY rats were observed for Ang II-mediated MAP kinase activation: (1) Inactivation after Ang II stimulation was more rapid in SHR than WKY VSMCs. (2) Activity in SHR VSMCs showed a greater dependence on Ca2+ mobilization, since chelation of intracellular Ca2+ with BAPTA inhibited maximal activity by 95% in SHR VSMCs but by only 50% in WKY VSMCs. In contrast to the results with Ang II, no differences in PDGF-stimulated MAP kinase activity were observed. These findings establish activation of MAP kinase by Ang II as a feature that distinguishes SHR VSMCs from WKY VSMCs and suggest that differences in regulation of MAP kinase signaling may alter cellular events that are increased in the SHR genetic model of hypertension.

Interdependence of calcium signaling and protein tyrosine phosphorylation in human endothelial cells

The signal transduction cascade which initiates transmembraneous influx of Ca2+ into endothelial cells in response to the discharge of intracellular Ca2+ stores is thought to involve a step sensitive to tyrosine kinase inhibition. We investigated the interrelationship between Ca2+ signaling and protein tyrosine phosphorylation following cell stimulation with either the receptor-dependent agonist, bradykinin, or the protein-tyrosine phosphatase inhibitor, phenylarsine oxide. In cultured human endothelial cells phenylarsine oxide instigated a concentration-dependent increase in the intracellular concentration of free Ca2+ ([Ca2+]i). This increase in [Ca2+]i was not associated with the tyrosine phosphorylation of phospholipase C gamma, enhanced formation of inositol 1,4,5-trisphosphate, or the rapid depletion of intracellularly stored Ca2+ but was coincident with the enhanced and prolonged tyrosine phosphorylation of a number of cytoskeletal proteins. In bradykinin-stimulated cells the tyrosine phosphorylation of the same cytoskeletal proteins (most notably 85- and 100-kDa proteins) was transient when cells were stimulated in the presence of extracellular Ca2+, was maintained under Ca2+-free conditions, and was reversed following readdition of extracellular Ca2+. These data suggest that the tyrosine phosphorylation of 2 cytoskeletal proteins is determined by the level of Ca2+ present in intracellular stores thus indicating a critical role for tyrosine phosphorylation in the control of capacitative Ca2+ entry in endothelial cells.

Tyrosine kinase signaling pathways modulate angiotensin II-induced calcium ([Ca2+]i) transients in vascular smooth muscle cells

Tyrosine kinases have been implicated in vascular smooth muscle cell proliferation and contraction. Underlying mechanisms may involve C(a2+) -dependent pathways. This study assesses relationships between angiotensin II (Ang II)-stimulated phospholipase C-mediated Ca2+ transients and tyrosine kinase-dependent pathways in vascular smooth muscle cells. Intracellular free Ca2+ concentration ([Ca2+]i) was measured in primary cultured unpassaged vascular smooth muscle cells derived from mesenteric resistance vessels of Wistar-Kyoto rats with the use of fura 2 methodology. [Ca2+]i effects of Ang II (1 nmol/L) were determined in vascular smooth muscle cells in which tyrosine kinase pathways were stimulated by insulin (70 muU/mL; 0.5 nmol/L), insulin-like growth factor-I (1 ng/mL; 0.13 nmol/L), or platelet-derived growth factor-BB (1 ng/mL; 0.04 nmol/L) and in cells in which tyrosine kinase was inhibited by specific inhibitors (1 mumol/L tyrphostin A-23 and genistein). Ang II elicited a rapid and transient [Ca2+]i response (from 94 +/- 8 to 239 +/- 5.8 nmol/L). Activation of the receptor tyrosine kinase by insulin, platelet-derived growth factor, and insulin-like growth factor-I significantly reduced (P < .01) Ang II-induced [Ca2+]i to 161 +/- 7, 189 +/- 3.7, and 183 +/- 5 nmol/L, respectively. In the presence of tyrphostin A-23 and genistein, Ang II-stimulated [Ca2+]i remained persistently elevated and failed to return to basal levels. Tyrphostin A-1, the inactive tyrphostin analogue, had not significant effect on Ang II-induced [Ca2+]i. This study demonstrates that activation of tyrosine kinase pathways reduces Ang II-elicited [Ca2+]i responses, whereas tyrosine kinase inhibition prevents [Ca2+]i recovery after agonist stimulation. Interaction between tyrosine kinase- and phospholipase C-dependent signaling pathways modulates vascular smooth muscle cell [Ca2+]i responses to Ang II.