Preferential inhibition of the platelet-derived growth factor receptor tyrosine kinase by staurosporine

Recent Advances in the Development of Anticancer Drugs that Act against Signalling Pathways

Cancer can be considered a disease of deranged intracellular signalling. The intracellular signalling pathways that mediate the effects of oncogenes on cell growth and transformation present attractive targets for the development of new classes of drugs for the prevention and treatment of cancer. This is a new approach to developing anticancer drugs and the potential, as well as some of the problems, inherent in the approach are discussed. Anticancer drugs that produce their effects by disrupting signalling pathways are already in clinical trial. Some properties of these drugs, as well as other inhibitors of signalling pathways under development as potential anticancer drugs, are reviewed.

Synthesis of piperazine-based thiazolidinones as VEGFR2 tyrosine kinase inhibitors inducing apoptosis

Aim: VEGFR2 tyrosine kinase is a main target in suppressing cancer growth and metastasis. Materials & methods: Piperazine-based thiazolidinones were synthesized and screened for their anticancer and VEGFR2 tyrosine kinase inhibitory activity. Results: Compounds 11, 13 and 16 displayed potent anticancer activity against HepG-2 with IC50 values 0.03–0.06 μM. They were safe on normal human fibroblasts with selectivity indices 8.09, 11.40 and 4.37, respectively. Also, these compounds showed VEGFR2 tyrosine kinase inhibitory activities more than the reference staurosporine with IC50 values <0.3 μM. Lineweaver–Burk plot revealed that these compounds behaved as uncompetitive VEGFR2 tyrosine kinase inhibitors. They also induced caspase-dependent apoptosis in HepG-2. In addition, these compounds revealed good binding within VEGFR2 tyrosine kinase enzyme in comparison with sorafenib reference. Conclusion: Compounds 11, 13 and 16 comprise a new promising scaffold of selective VEGFR2 tyrosine kinase inhibitors with caspase-dependent apoptotic activities.

Combined effects of protein kinase inhibitors and 5-fluorouracil on CEA expression in human colon cancer cells

Previous studies showed that 5-fluorouracil (5-FU) and Staurosporine (ST), a protein kinase inhibitor (PKI), were able to increase the expression of carcinoembryonic antigen (CEA) in human colon cancer cells. In the present study, we examined the in vitro effects of five PKIs, i.e. ST, 1-5-isoquinolinyl-sulfonyl-2-methylpiperazine (H-7), bisindolylmaleimide-I (BIS), Genistein (GEN), and Herbimycin A (HERB) alone or in combination with 5-FU on CEA expression. C22-20, a clonal subline, derived from colon cancer HT-29 line, selected for low expression of CEA, was used in our experimental model. Among the PKIs tested, only ST, at non-toxic concentrations of 5 nM, was capable of increasing the level of CEA. The other PKIs did not modify CEA expression when used either alone or in combination with 5-FU. Flow cytometric analysis showed that treatment of cells with 5-FU + ST resulted in a synergistic increase of CEA expression, being higher than that obtainable with both agents alone. Moreover, the increase of CEA expression occurred not only in membrane fractions but also in cytosolic compartments, as indicated by Western blot analysis. The present study suggests that ST-mediated induction of CEA expression in cancer cells is PKC independent and could be of potential clinical interest for the development of new diagnostic and/or immunotherapeutic approaches.

Platelet-Derived Growth Factor Receptor Transactivation Mediates the Trophic Effects of Angiotensin II In Vivo

In addition to the modulation of vascular tone, angiotensin II (Ang II) has growth factor–like effects in vascular tissue. The mechanisms whereby Ang II mediates these trophic actions are incompletely understood but are thought to include effects on systemic blood pressure, stimulation of transforming growth factor-β (TGF-β) expression, and transactivation of growth factor receptor kinases. To investigate the role of platelet-derived growth factor receptor (PDGFR) transactivation in mediating the growth factor–like effects of Ang II we administered Ang II (200 ng/kg per minute) or saline to male Sprague-Dawley rats by osmotic minipump for 12 days and treated with imatinib mesylate, an inhibitor of the PDGFR tyrosine kinase. In addition to systolic blood pressure elevation, Ang II infusion led to increased vascular weight, media:lumen ratio, matrix expansion, and overexpression of TGF-β mRNA in mesenteric arteries. Without affecting blood pressure or PDGF ligand expression, imatinib attenuated the changes in vessel morphology but further increased TGF-β mRNA. Western blot analysis of mesenteric arterial tissue demonstrated the presence of the β- but not the α-isoform of PDGFR. Phosphorylation of PDGFR-β was increased by Ang II in vascular smooth muscle cells, and this was inhibited by imatinib. The findings of attenuation of vascular hypertrophy and matrix deposition by imatinib indicate that transactivation of the PDGFR in vivo contributes to the growth factor–like effects of Ang II, independent of its hemodynamic effects or its ability to induce TGF-β gene expression.

Focal adhesion kinase suppresses apoptosis by binding to the death domain of receptor-interacting protein

Tumor cells resist the apoptotic stimuli associated with invasion and metastasis by activating survival signals that suppress apoptosis. Focal adhesion kinase (FAK), a tyrosine kinase that is overexpressed in a variety of human tumors, mediates one of these survival signals. Attenuation of FAK expression in tumor cells results in apoptosis that is mediated by caspase 8- and FADD-dependent pathways, suggesting that death receptor pathways are involved in the process. Here, we report a functional link between FAK and death receptors. We have demonstrated that FAK binds to the death domain kinase receptor-interacting protein (RIP). RIP is a major component of the death receptor complex and has been shown to interact with Fas and tumor necrosis factor receptor 1 through its binding to adapter proteins. We have shown that RIP provides proapoptotic signals that are suppressed by its binding to FAK. We thus propose that FAK overexpression in human tumors provides a survival signal function by binding to RIP and inhibiting its interaction with the death receptor complex.

Staurosporine induces rapid homotypic intercellular adhesion of U937 cells via multiple kinase activation

1. Staurosporine is a broad-specificity kinase inhibitor, which has acted as lead compound for the development of some novel cytotoxic compounds for treatment of cancer. This study investigates the unexpected observation that staurosporine can also induce homotypic cellular aggregation. 2. In this study, staurosporine is shown to activate rapid homotypic aggregation of U937 cells, at concentrations below those required to induce cell death. This activity is a particular feature of staurosporine, and is not shared by a number of other kinase inhibitors. The proaggregating activity of staurosporine is inhibited by deoxyglucose, cytochalasin B and colchicine. Staurosporine-induced aggregation can be distinguished from that induced by the phorbol 12-myristate 13-acetate by faster kinetics and insensitivity to cycloheximide. Staurosporine induces translocation of conventional and novel, but not atypical isoforms of protein kinase C (PKC). Aggregation induced by staurosporine is inhibited by a number of inhibitors of PKC isoforms, and by inhibitors of protein tyrosine kinases. Staurosporine also induces rapid phosphorylation of ERK and p38, and inhibitors of both these enzymes block aggregation. 3. Staurosporine induces dysregulated activation of multiple kinase signaling pathways in U937 cells, and the combined activity of several of these pathways is essential for the induction of aggregation.

Pharmacological modulation of carcinoembryonic antigen in human cancer cells: studies with staurosporine

Preliminary studies, performed in our laboratory, showed that staurosporine (ST), a protein-kinase (PK) inhibitor, increases the expression of the carcinoembryonic antigen (CEA) in a human colon cancer cell line. The present study explores the cellular and molecular effects of ST on the CEA expression in breast cancer MCF-7 line and in a number of colon cancer cell lines characterized by the different basal levels of the antigen, including two cloned sublines (i.e. C22.20 and C6.6, expressing low and high CEA levels, respectively). In all cases, increase of the CEA expression was observed at drug concentrations devoid of marked cytostatic effects (e.g. 5 nM) and was accompanied by the enhanced CEA shedding in the supernatant. Moreover, the increase of the CEA levels both occurred in the cell membranes and in the cytosolic compartments and appeared to be the result of the enhanced CEA gene transcription. Similar results have been previously obtained with interferon-gamma. However, ST treatment, different from interferon-gamma, did not up-regulate the level of the HLA class I molecules. A preliminary investigation also showed that other PKC inhibitors did not substantially modulate the CEA expression. Therefore, the biochemical mechanism underlying the effect of ST should not be correlated with that involved in the PKC inhibition. The present study suggests that ST and, presumably, its analogs used in the cancer treatment could enhance the CEA expression on neoplastic cells in patients affected by the CEA-positive malignancies. This appears to be of potential clinical interest for the development of new immunotherapeutic or diagnostic approaches based on the pharmacological modulation of this antigenic marker.

A novel conditional Akt 'survival switch' reversibly protects cells from apoptosis

The anti-apoptotic Akt kinase is commonly activated by survival factors following plasma membrane relocalization attributable to the interaction of its pleckstrin homology (PH) domain with phosphatidylinositol 3-kinase (PI3K)-generated PI3,4-P(2) and PI3,4,5-P(3). Once activated, Akt can prevent or delay apoptosis by phosphorylation-dependent inhibition or activation of multiple signaling molecules involved in apoptosis, such as BAD, caspase-9, GSK3, and NF-kappaB and forkhead family transcription factors. Here, we describe and characterize a novel, conditional Akt controlled by chemically induced dimerization (CID). In this approach, the Akt PH domain has been replaced with the rapamycin (and FK506)-binding domain, FKBP12, to make F3-DeltaPH.Akt. To effect membrane recruitment, a myristoylated rapamycin-binding domain from FRAP/mTOR, called M-FRB, binds to lipid permeable rapamycin (and non-bioactive synthetic 'rapalogs'), leading to reversible heterodimerization of M-FRB with FKBP-DeltaPH.Akt. Like endogenous c-Akt, we show that the kinase activity of membrane-localized F3-DeltaPH.Akt correlates strongly with phosphorylation at T308 and S473; however, unlike c-Akt, phosphorylation and activation of inducible Akt (iAkt) is largely PI3K independent. CID-mediated activation of iAkt results in phosphorylation of GSK3, and contributes to NF-kappaB activation in vivo in a dose-sensitive manner. Finally, in Jurkat T cells stably expressing iAkt, CID-induced Akt activation rescued cells from apoptosis triggered by multiple apoptotic stimuli, including staurosporine, anti-Fas antibodies, PI3K inhibitors and the DNA damaging agent, etoposide. This novel inducible Akt should be useful for identifying new Akt substrates and for reversibly protecting tissue from apoptosis due to ischemic injury or immunological attack.

Regulation of PDGFR-alpha in rat pulmonary myofibroblasts by staurosporine

Upregulation of the platelet-derived growth factor (PDGF) receptor-alpha (PDGFR-alpha) is a mechanism of myofibroblast hyperplasia during pulmonary fibrosis. We previously identified interleukin (IL)-1beta as a major inducer of the PDGFR-alpha in rat pulmonary myofibroblasts in vitro. In this study, we report that staurosporine, a broad-spectrum kinase inhibitor, upregulates PDGFR-alpha gene expression and protein. A variety of other kinase inhibitors did not induce PDGFR-alpha expression. Staurosporine did not act via an IL-1beta autocrine loop because the IL-1 receptor antagonist protein did not block staurosporine-induced PDGFR-alpha expression. Furthermore, staurosporine did not activate a variety of signaling molecules that were activated by IL-1beta, including nuclear factor-kappaB, extracellular signal-regulated kinase, and c-Jun NH2-terminal kinase. However, both staurosporine- and IL-1beta-induced phosphorylation of p38 mitogen-activated protein kinase and upregulation of PDGFR-alpha by these two agents was inhibited by the p38 inhibitor SB-203580. Finally, staurosporine inhibited basal and PDGF-stimulated mitogenesis over the same concentration range that induced PDGFR-alpha expression. Collectively, these data demonstrate that staurosporine is a useful tool for elucidating the signaling mechanisms that regulate PDGFR expression in lung connective tissue cells and possibly for evaluating the role of the PDGFR-alpha as a growth arrest-specific gene.

Platelet-derived growth factor receptor tyrosine kinase inhibitor AG1295 attenuates rat hepatic stellate cell growth

Enhanced activity of receptor tyrosine kinases such as the platelet-derived growth factor-receptorbeta (PDGF-Rbeta) has been implicated as a contributing factor in the development of hepatic fibrosis. In this study we have used tyrosine kinase inhibitors of the tyrphostin class (AG1295) to specifically block autophosphorylation of PDGF-Rbeta and proliferation of rat hepatic stellate cells. We also examined the effect of AG1295 on the PDGF-BB-induced activation of the 44 kd and 42 kd mitogen-activated protein (MAP) kinase isoforms (p44mapk/p42mapk). Rat hepatic stellate cells were treated with AG1295 (10 micromol/L) for 24 hours and stimulated with PDGF-BB for 5 minutes. AG1295 specifically inhibited autophosphorylation of PDGF-Rbeta and caused a 20% decrease in PDGF-BB-stimulated bromodeoxyuridine incorporation by rat hepatic stellate cells. Treatment of rat hepatic stellate cells with AG1295 resulted in an inhibition of the PDGF-BB-induced activation of MAP kinase isoforms. Quantification of the immunoprecipitated tyrosine-phosphorylated phosphatidylinositol 3-kinase, phospholipase C-gamma, and p21ras guanosine triphosphatase-activating protein by Western blotting revealed that AG1295 treatment effectively inhibits tyrosine phosphorylation of these kinases in hepatic stellate cells. Our findings demonstrate that AG1295 is a selective inhibitor of the tyrosine phosphorylation of PDGF-Rbeta and its downstream signaling pathway, and this compound could offer a strategy for the treatment of fibrotic liver diseases.

Activation of cellular responses to interleukin 6 is blocked by staurosporine

Interleukin 6 (IL-6) acts on a wide spectrum of cells and can regulate differentiation or growth in these different cells. The effects of the microbial alkaloid staurosporine (SS) on IL-6 signaling through gp130, and also on the internalization of the IL-6 receptor complex, were studied using HepG2 cells which are well-characterized in their ability to respond to IL-6 by upregulating acute-phase protein production. SS was found effective in the blockade of the signaling cascade of IL-6: phosphorylation of both gp130 and Stat3 was eliminated by SS treatment and the production of IL-6 stimulated haptoglobin by the cells was abolished. In addition, SS reduced the internalization rate of 125I-IL-6 by 50%, resulting in a retention of 125I-IL-6 on the cell surface and a corresponding decrease in degraded 125I-IL-6 in the extracellular medium. SS is commonly employed as an apoptosis inducing agent but the mechanism of its action is not clear. The ability of SS to void the capacity of IL-6, and IL-6-related cytokines such as Oncostatin M, to deliver growth and differentiation signals may be one process by which this agent could promote apoptosis in a variety of cell types.

Potentiation of carbachol-induced amylase release by propionate in guinea pig and vole pancreatic acini

The action of propionate, one of the major end products of microbial fermentation in herbivores was investigated in isolated, perifused pancreatic acini of guinea pigs, voles, and mice. With the use of guinea pig acini, 100 microM propionate had no effect, whereas 300 and 600 microM increased amylase release by six- and ninefold, respectively. Simultaneous perifusion of carbachol (CCh) 10 microM plus propionate 100 microM in guinea pig acini produced a potentiated secretory response that was 130% higher than the summated value obtained with CCh and propionate alone. The potentiation by propionate (100 microM) of CCh (10 microM)-induced amylase release was also obtained in vole pancreatic acini, but the mouse pancreatic preparation did not exhibit a similar potentiation. In contrast to CCh, propionate (100-600 microM) alone had no significant effect on intracellular Ca2+ concentration ([Ca2+]i) and did not alter [Ca2+]i elicited by CCh. Ca ionophore A23187 (5 microM)-induced amylase release in guinea pig acini was enhanced twofold by the addition of propionate. Cellular cAMP content was increased slightly by propionate, but did not alter dose dependently. The cAMP level with combinations of CCh and propionate was almost same as that with CCh alone and propionate alone. Staurosporine did not modify amylase secretion induced by a combination of CCh and propionate. These results suggest that propionate, in addition to a direct action on amylase release, potentiates CCh-induced amylase release in guinea pig and vole acini via a secretory pathway not associated with an increase in [Ca2+]i and cellular cAMP.

Specific inhibitors of platelet-derived growth factor or epidermal growth factor receptor tyrosine kinase reduce pulmonary fibrosis in rats

The proliferation of myofibroblasts is a central feature of pulmonary fibrosis. In this study we have used tyrosine kinase inhibitors of the tyrphostin class to specifically block autophosphorylation of the platelet-derived growth factor receptor (PDGF-R) or epidermal growth factor receptor (EGF-R). AG1296 specifically inhibited autophosphorylation of PDGF-R and blocked PDGF-stimulated [3H]thymidine uptake by rat lung myofibroblasts in vitro. AG1478 was demonstrated as a selective blocker of EGF-R autophosphorylation and inhibited EGF-stimulated DNA synthesis in vitro. In a rat model of pulmonary fibrosis caused by intratracheal instillation of vanadium pentoxide (V2O5), intraperitoneal delivery of 50 mg/kg AG1296 or AG1478 in dimethylsulfoxide 1 hour before V2O5 instillation and again 2 days after instillation reduced the number of epithelial and mesenchymal cells incorporating bromodeoxyuridine (Brdu) by approximately 50% at 3 and 6 days after instillation. V2O5 instillation increased lung hydroxyproline fivefold 15 days after instillation, and AG1296 was more than 90% effective in preventing the increase in hydroxyproline, whereas AG1478 caused a 50% to 60% decrease in V2O5-stimulated hydroxyproline accumulation. These data provide evidence that PDGF and EGF receptor ligands are potent mitogens for collagen-producing mesenchymal cells during pulmonary fibrogenesis, and targeting tyrosine kinase receptors could offer a strategy for the treatment of fibrotic lung diseases.

Differences in the regulation of fibroblast contraction of floating versus stressed collagen matrices

To learn more about the regulation of contraction of collagen matrices by fibroblasts, we compared the ability of lysophosphatidic acid (LPA) and platelet-derived growth factor (PDGF) to stimulate contraction of floating and stressed collagen matrices. In floating collagen matrices, PDGF and LPA stimulated contraction with similar kinetics, but appeared to utilize complementary signaling pathways since contraction obtained by the combination of growth factors exceeded that observed with saturating concentrations of either alone. The PDGF-simulated pathway was selectively inhibited by the protein kinase inhibitor KT5926. In stressed collagen matrices, PDGF and LPA stimulated contraction with different kinetics, with LPA acting rapidly and PDGF acting only after an approximately 1-h lag period. Pertussis toxin, known to block signaling through the Gi class of heterotrimeric G-proteins, inhibited LPA-stimulated contraction of floating but not stressed matrices, suggesting that LPA-stimulated contraction depends on receptors coupled to different G-proteins in floating and stressed matrices. On the other hand, the Rho inhibitor C3 exotransferase blocked contraction of both floating and stressed collagen matrices. These results suggest the possibility that distinct signaling mechanisms regulate contraction of floating and stressed collagen matrices.

Beneficial effects of a novel inhibitor of platelet-derived growth factor receptor autophosphorylation in the rat with mesangial proliferative glomerulonephritis

1. Our original compound, Ki6896 ((4-t-butylphenyl)(4-[(6,7-dimethoxy-4-quinolyl) oxy]phenyl) methanone) strongly inhibited the autophosphorylation of platelet-derived growth factor (PDGF) beta-receptor (IC50=0.31 microM) and that of basic fibroblast growth factor receptor (IC50=3.1 microM), whereas it did not inhibit some other kinases. 2. The [3H]thymidine incorporation and the growth of mesangial cells under the stimulation of PDGF were inhibited by Ki6896 in a dose-dependent manner. 3. In the mesangial proliferative glomerulonephritis rats induced by anti-Thy-1 monoclonal antibody, glomerulosclerosis was ameliorated and the number of glomerular proliferating cells was decreased by the daily administration of Ki6896. However, the accumulation of type I collagen and fibronectin in the glomeruli was not suppressed by Ki6896.

Analysis of rotavirus nonstructural protein NSP5 phosphorylation

The rotavirus nonstructural phosphoprotein NSP5 is encoded by a gene in RNA segment 11. Immunofluorescence analysis of fixed cells showed that NSP5 polypeptides remained confined to viroplasms even at a late stage when provirions migrated from these structures. When NSP5 was expressed in COS-7 cells in the absence of other viral proteins, it was uniformly distributed in the cytoplasm. Under these conditions, the 26-kDa polypeptide predominated. In the presence of the protein phosphatase inhibitor okadaic acid, the highly phosphorylated 28- and 32- to 35-kDa polypeptides were formed. Also, the fully phosphorylated protein had a homogeneous cytoplasmic distribution in transfected cells. In rotavirus SA11-infected cells, NSP5 synthesis was detectable at 2 h postinfection. However, the newly formed 26-kDa NSP5 was not converted to the 28- to 35-kDa forms until approximately 2 h later. Also, the protein kinase activity of isolated NSP5 was not detectable until the 28- and 30- to 35-kDa NSP5 forms had been formed. NSP5 immunoprecipitated from extracts of transfected COS-7 cells was active in autophosphorylation in vitro, demonstrating that other viral proteins were not required for this function. Treatment of NSP5-expressing cells with staurosporine, a broad-range protein kinase inhibitor, had only a limited negative effect on the phosphorylation of the viral polypeptide. Staurosporine did not inhibit autophosphorylation of NSP5 in vitro. Together, the data support the idea that NSP5 has an autophosphorylation activity that is positively regulated by addition of phosphate residues at some positions.

Release of a leukocyte activation inhibitor by staurosporine-treated pulmonary artery endothelial cells

Bovine pulmonary arterial endothelial cells (BPAE) treated with the protein kinase C (PKC) inhibitor staurosporine inhibited O-2. generation by neutrophils exposed to phorbol myristate acetate (PMA) but did not affect O-2. generated enzymatically by xanthine/xanthine oxidase (X/XO). Similar results were obtained with conditioned medium from staurosporine-pretreated BPAE. The inhibitory effects of staurosporine-treated BPAE on O-2. generation were not altered by the superoxide dismutase inhibitor diethylcarbamazine. This BPAE-derived inhibitor was continuously released from staurosporine-pretreated BPAE for at least 5 h. The exact nature of the inhibitor remains unknown, but it appears to be a positively charged molecule with molecular weight <10,000. Treatment of either BPAE or neutrophils with staurosporine or conditioned medium from staurosporine-treated BPAE prevented the neutrophil-mediated decrease in endothelium-bound angiotensin-converting enzyme activity and cytotoxicity in BPAE. In contrast, staurosporine potentiated the H2O2- and X/XO-mediated endothelial cytotoxicity. These data suggest that staurosporine-treated endothelial cells release a soluble factor that inhibits neutrophil activation and protects endothelial cells from neutrophil-mediated injury.

Staurosporine-induced conformational changes of cAMP-dependent protein kinase catalytic subunit explain inhibitory potential

BACKGROUND

Staurosporine inhibits most protein kinases at low nanomolar concentrations. As most tyrosine kinases, along with many serine/threonine kinases, are either proto oncoproteins or are involved in oncogenic signaling, the development of protein kinase inhibitors is a primary goal of cancer research. Staurosporine and many of its derivatives have significant biological effects, and are being tested as anticancer drugs. To understand in atomic detail the mode of inhibition and the parameters of high-affinity binding of staurosporine to protein kinases, the molecule was cocrystallized with the catalytic subunit of cAMP-dependent protein kinase.

RESULTS

The crystal structure of the protein kinase catalytic subunit with staurosporine bound to the adenosine pocket shows considerable induced-fit rearrangement of the enzyme and a unique open conformation. The inhibitor mimics several aspects of adenosine binding, including both polar and nonpolar interactions with enzyme residues, and induces conformational changes of neighboring enzyme residues.

CONCLUSIONS

The results explain the high inhibitory potency of staurosporine, and also illustrate the flexibility of the protein kinase active site. The structure, therefore, is not only useful for the design of improved anticancer therapeutics and signaling drugs, but also provides a deeper understanding of the conformational flexibility of the protein kinase.

Selective inhibition of platelet-derived growth factor (PDGF) receptor autophosphorylation and PDGF-mediated cellular events by a quinoline derivative

This report describes the biological effects of our original compound, Ki6783 ((3,4-dimethoxy)-4-phenoxy-6,7-dimethoxyquinoline), a potent and selective inhibitor of platelet-derived growth factor (PDGF) receptor autophosphorylation. This compound strongly inhibited autophosphorylation of the PDGF beta-receptor in cultured rat glomerular mesangial cells (MC) bearing this receptor (IC50 0.1 microM), although it did not inhibit autophosphorylation of other growth factor receptors even at 100 microM. In a cell-free kinase experiment, it showed selective inhibition of PDGF beta-receptor tyrosine kinase. A kinetic study of the compound to this tyrosine kinase revealed a competitive mode of action to ATP. [3H]Thymidine incorporation and cell proliferation of MC were inhibited by Ki6783 in a dose-dependent manner after Ki6783 and PDGF-BB were added to the culture medium. Furthermore, this compound normalized the fibrotic cell shape of v-sis-transformed NIH3T3 cells, which grow in an autocrine manner via the PDGF receptor. These effects could be explained by the inhibition of intracellular signal transduction triggered by PDGF receptor autophosphorylation, in which activation of mitogen-activated protein kinase occurs. These results suggest that Ki6783 is one of the more potent and selective inhibitors of PDGF receptor autophosphorylation and that it may be useful in ameliorating cell abnormalities due to excess action of PDGF and its receptor systems in several diseases.

Insulin stimulation of Na/H antiport in L-6 cells: a different mechanism in myoblasts and myotubes

Insulin modulation of the Na/H antiport of L-6 cells, from rat skeletal muscle was studied in both myoblasts and myotubes using the fluorescent, pH sensitive, intracellular probe 2',7' bis (carboxyethyl)-5(6)-carboxyfluorescein. Insulin stimulated the Na/H antiport activity in L-6 cells, showing a bell-shaped dose response typical of other insulin responses: a maximum at 10 nM (delta pH of 0.132 +/- 0.007 and 0.160 +/- 0.040 over basal value, for myoblasts and myotubes, respectively; means +/- SD, n = 6-8) and smaller effects at higher and lower concentrations. Phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C, also stimulated the antiport in myoblasts but not in myotubes. Surprisingly the rapid increase in intracellular pH was not observed when insulin and PMA were added simultaneously to myoblasts; apparently these two activators mutually excluded each other. Downregulation of protein kinase C, obtained by preincubation of cells with PMA for 20 hr, totally abolished both hormone and PMA effects in myoblasts, whereas in myotubes insulin stimulation was not affected. Inhibitors of tyrosine kinase activity, such as erbstatin analog and genistein abolished insulin effect on the Na/H antiport, both in myoblasts and in myotubes. Different sensitivity to pertussis toxin in the two cell types suggests that the differentiation process leads to a change in the signal pathways involved in the physiological response to insulin.

Tyrosine phosphorylation of I kappa B-alpha activates NF-kappa B without proteolytic degradation of I kappa B-alpha

The transcription factor NF-kappa B regulates genes participating in immune and inflammatory responses. In T lymphocytes, NF-kappa B is sequestered in the cytosol by the inhibitor I kappa B-alpha and released after serine phosphorylation of I kappa B-alpha that regulates its ubiquitin-dependent degradation. We report an alternative mechanism of NF-kappa B activation. Stimulation of Jurkat T cells with the protein tyrosine phosphatase inhibitor and T cell activator pervanadate led to NF-kappa B activation through tyrosine phosphorylation but not degradation of I kappa B-alpha. Pervanadate-induced I kappa B-alpha phosphorylation and NF-kappa B activation required expression of the T cell tyrosine kinase p56ick. Reoxygenation of hypoxic cells appeared as a physiological effector of I kappa B-alpha tyrosine phosphorylation. Tyrosine phosphorylation of I kappa B-alpha represents a proteolysis-independent mechanism of NF-kappa B activation that directly couples NF-kappa B to cellular tyrosine kinase.

Signal transduction for proliferation of glioma cells in vitro occurs predominantly through a protein kinase C-mediated pathway

Previous work has demonstrated that glioma cells have very high protein kinase C (PKC) enzyme activity when compared to non-malignant glia, and that their PKC activity correlates with their proliferation rate. The purpose of this study was to determine whether the elevated PKC activity in glioma is secondary to an autonomously active PKC isoform implying oncogenic transformation, or whether this activity is driven by upstream ligand-receptor tyrosine kinase interactions. We treated established human glioma cell lines A172, U563 or U251 with either the highly selective PKC inhibitor CGP 41 251, or with genistein, a tyrosine kinase inhibitor. The proliferation rate and PKC activity of all the glioma lines was reduced by CGP 41 251; the IC50 values for inhibiting cell proliferation corresponded to the IC50v values for inhibition of PKC activity. Genistein also inhibited cell proliferation, with IC50 proliferation values approximating those for inhibition of tyrosine kinase activity in cell free protein extracts. Importantly, in genistein-treated cells, downstream PKC enzyme activity was dose dependently reduced such that the correlation coefficient for effects of genistein on proliferation rate and PKC activity was 0.92. These findings suggest that upstream tyrosine kinase linked events, rather than an autonomously functioning PKC, result in the high PKC activity observed in glioma. Finally, fetal calf serum (FCS) evoked a strong mitogenic effect on glioma cell lines. This mitogenic activity was completely blocked by CGP 41 251, suggesting that although the many mitogens in FCS for glioma cells signal initially through genistein-inhibitable tyrosine kinases, they ultimately channel through a PKC-dependent pathway. We conclude that proliferative signal transduction in glioma cells occurs through a predominantly PKC-dependent pathway and that selectively targeting this enzyme provides an approach to glioma therapy.

Secretory non-pancreatic phospholipase A2 and cyclooxygenase-2 expression by tracheobronchial smooth muscle cells

Lipid mediators of inflammation, contribute to airway hyper-reactivity in asthma. Since production of lipid mediators is largely regulated by phospholipase A2 (PLA2), and since PLA2 expression in mesenchymal cells is induced by cytokines and other signals, we examined PLA2 expression by rat tracheobronchial smooth muscle cells (TBSMC). PLA2 expression in TBSMC cultures was markedly increased by tumour-necrosis factor (TNF) alpha (130-fold) and interleukin-1beta (IL-1beta) (7.4-fold). Lipopolysaccharide (LPS;100 ng/ml) resulted in a 51-fold increase in extracellular PLA2 activity. PLA2 expression by LPS-stimulated or cytokine-stimulated cells was downregulated by dexamethasone. Whereas forskolin or dibutyrl cAMP increased PLA2 activity, inhibition of protein kinase A but not tyrosine kinase reduced PLA2 expression. Northern blot analysis showed that TNF alpha and IL-1beta increased both PLA2 and inducible cyclooxygenase (Cox-2) mRNA transcription. Addition of dexamethasone substantially blunted the increase in PLA2 and Cox-2 mRNA. In contrast, the level of Cox-1 mRNA was very low and did not change with the various treatments. Since proinflammatory lipid mediators have been implicated in the pathogenesis of asthma and PLA2 activity regulates generation of these lipid mediators, cytokine-stimulated synthesis and release of PLA2 by airway smooth cells may contribute to the potentiation of airway inflammation in asthma.

Apoptosis of human glioma cells in response to calphostin C, a specific protein kinase C inhibitor

Calphostin C acts at the regulatory domain as a highly selective inhibitor of protein kinase C (PKC), and staurosporine acts at the catalytic domain as a nonspecific PKC inhibitor. The authors investigated the capacity of calphostin C and staurosporine to promote apoptotic fragmentation of DNA in four human glioma cell lines. The exposure of glioma cell lines to 100 nM calphostin C for 2 to 8 hours induced a decrease in particulate PKC activities and exposure for 16 to 24 hours produced a concentration-dependent increase in internucleosomal DNA cleavage on agarose gel electrophoresis. In addition, the human glioma cells showed the classic morphological features of apoptosis: cell shrinkage, nuclear condensation, and the formation of apoptotic bodies. A 24-hour exposure to staurosporine failed to induce internucleosomal DNA fragmentation at concentrations generally used to achieve maximum inhibition of enzyme activity (50 nM) but promoted fragmentation at considerably higher concentration (more than 200 nM). Deoxyribonucleic acid fragments obtained from cells exposed to 100 nM calphostin C for 16 to 24 hours possessed predominantly 5'-phosphate termini, consistent with the action of a Ca++/Mg(++)-dependent endonuclease. Northern and Western blot analyses revealed that the exposure to 100 nM calphostin C for 4 hours failed to alter bcl-2 transcript and protein, but exposure for more than 8 hours decreased the amount of bcl-2 transcript and protein. Together, these observations suggest that calphostin C is capable of inducing apoptotic DNA fragmentation and cell death in a highly concentration dependent manner in human glioma cells and that the apoptosis is closely associated with the decrease in transcription and translation of bcl-2.

Different susceptibility of protein kinases to staurosporine inhibition. Kinetic studies and molecular bases for the resistance of protein kinase CK2

A systematic analysis reveals that out of 20 protein kinases examined, specific for either Ser/Thr or Tyr, the majority are extremely sensitive to staurosporine, with IC50 values in the low nanomolar range. A few of them however, notably protein kinases CK1 and CK2, mitogen-activated protein (MAP) kinase and protein-tyrosine kinase CSK, are relatively refractory to staurosporine inhibition, exhibiting IC50 values in the micromolar range. With all protein kinases tested, namely PKA, CK1, CK2, MAP kinase (ERK-1), c-Fgr, Lyn, CSK and TPK-IIB/p38Syk, staurosporine inhibition was competitive with respect to ATP, regardless of its inhibitory power. In contrast, either uncompetitive or noncompetitive kinetics of inhibition with respect to the phosphoacceptor substrate were exhibited by Ser/Thr and Tyr-specific protein kinases, respectively, consistent with a different mechanism of catalysis by these two sub-families of kinases. Computer modeling based on PKA crystal structure in conjunction with sequence analysis suggest that the low sensitivity to staurosporine of CK2 may be accounted for by the bulky nature of three residues, Val66, Phe113 and Ile174 which are homologous to PKA Ala70, Met120 and Thr183, respectively. In contrast these PKA residues are either conserved or replaced by smaller ones in protein kinases highly sensitive to staurosporine inhibition. On the other hand, His160 which is homologous to PKA Glu170, appears to be responsible for the unique behaviour of CK2 with respect to a staurosporine derivative (CGP44171A) bearing a negatively charged benzoyl substituent: while CGP44171A is 10- 100-fold less effective than staurosporine against PKA and most of the other protein kinases tested, it is actually more effective than staurosporine for CK2 inhibition, but it looses part of its efficacy if it is tested on a CK2 mutant (H160D) in which His160 has been replaced by Asp. It can be concluded from these data that the catalytic sites of protein kinases are divergent enough as to allow a competitive inhibitor like staurosporine to be fairly selective, a feature that can be enhanced by suitable modifications designed based on the structure of the catalytic site of the kinase.

EGF and TPA stimulate de novo synthesis of PGHS-1 and PGHS-2 through different signal transduction pathways

Epidermal growth factor (EGF) as well as phorbol 12-myristate 13-acetate (TPA) stimulate de novo synthesis of PGHS (prostaglandin H synthase)-1 and PGHS-2 mRNA, resulting in increased production of PGE2 in rat tracheal epithelial cells (RTE, EGV-6 cells). Stimulation of PGE2 production by TPA is more potent than that by EGF. Staurosporine and H-7, protein kinase C (PKC) inhibitors, suppressed the increase of mRNA and PGE2 levels caused by TPA, but not that caused by EGF. On the other hand, methyl 2,5-dihydroxycinnamate, a tyrosine kinase inhibitor (TKI), suppressed the increase of mRNA and PGE2 levels caused by EGF, but not that caused by TPA. These results indicate that EGF stimulates de novo synthesis of PGHS-1 and PGHS-2 mRNA through a signal transduction pathway which is independent from PKC-associated mechanisms but dependent upon the tyrosine kinase activity of the EGF receptor.

Cell spreading in Colo 201 by staurosporin is alpha 3 beta 1 integrin-mediated with tyrosine phosphorylation of Src and tensin

Staurosporin, a broad-spectrum kinase inhibitor, induced cell spreading in a human colon cancer cell line, Colo 201. On collagen and laminin, cell spreading was induced in more than 90% of the cells and was dependent on very late activation antigen-3, as shown by an antibody inhibition assay. Cell spreading required divalent cations and showed the order of preference Mn2+ > Mg2+ > Ca2+. On fibronectin, only about 30% of the cells were observed to spread, and spreading occurred via a non-integrin, RGD-independent pathway. Staurosporin-induced spreading was inhibited by treatment with tyrosine kinase inhibitors herbimycin A and methyl 2,5-dihydroxycinnamate. Despite the presence of staurosporin, seven proteins (220, 175, 150, 98, 62, 58, and 45 kDa) showed increased levels of tyrosine phosphorylation in association with cell adhesion. Two of these (58 and 220 kDa) were identified by immunoprecipitation as Src product and tensin, respectively. Flow cytometric analysis showed that the Colo 201 cells expressed the alpha 2, alpha 3, alpha 6, and beta 1 chains of integrin, but expression of these chains was not influenced by staurosporin. Immunofluorescence microscopy revealed that the alpha 3 chain, diffusely expressed on the cell surface in the absence of staurosporin, was concentrated at focal adhesion plaques after staurosporin treatment. Neither alpha 2 nor alpha 6 was focalized by the treatment.

Staurosporine induces tyrosine phosphorylation of a 145 kDa protein but does not activate gp140trk in PC12 cells

Staurosporine, a protein kinase C inhibitor, induces neurite outgrowth in PC12 cells similarly to nerve growth factor (NGF). Since NGF neurotropic effects are transduced by the 'trk' gene product 140 kDa tyrosine kinase receptor, gp140trk, we investigated the role of gp140trk and tyrosine phosphorylations in staurosporine neurotropic effects. A direct correlation between staurosporine neurotropic effects and a novel stimulation of tyrosine phosphorylation of a 145 kDa protein (p145) with the following characteristics has been discovered: (1) Staurosporine specifically induced, among indolcarbazoles-K252a derivatives, in a dose-dependent manner (5-100 nM), p145 tyrosine phosphorylation and neurite outgrowth. (2) Staurosporine-induced p145 tyrosine phosphorylation was selective compared to other neurotropic compounds such as 8-Br-cAMP, acidic and basic fibroblast growth factors and NGF. (3) Staurosporine stimulation of p145 tyrosine phosphorylation gradually increased during the first 8 h of staurosporine treatment coinciding with the initiation of neurotropic effects. (4) K252a, a selective inhibitor of NGF actions, and several tyrphostins did not block staurosporine-induced p145 tyrosine phosphorylation and neurotropic effects. (5) Staurosporine stimulation of p145 tyrosine phosphorylation and neurotropic effects are independent of PKC. (6) Staurosporine did not activate gp140trk-NGF receptor in PC12 cells. The present study proposes staurosporine as a pharmacological tool to study the role of tyrosine phosphorylation pathway(s), such as p145 phosphorylation, in the action of neurotropic agents.

Involvement of protein kinase C in growth regulation of human meningioma cells

In order to investigate the possible role of protein kinase C (PKC)-mediated signal pathways in growth regulation of meningiomas, we examined the effect of two PKC-activating phorbol esters, 12-O-tetradecanoyl-13-phorbol acetate (TPA) and phorbol 12, 13-dibutyrate (PDBu), and PKC inhibitor, staurosporine, on cell proliferation using low-passage human meningioma cells in culture. TPA (0.1 to 100 ng/ml) caused a dose-dependent stimulation of cell proliferation in six of eight meningioma cultures. At optimal concentrations of TPA, the cell growth ranged from 113% to 251% versus control. In contrast, PDBu (0.1 to 100 ng/ml) caused a significant inhibition of cell proliferation in three of five meningioma cultures. At optimal concentrations of PDBu, the cell growth ranged from 52% to 79% of control. Staurosporine exhibited a stimulation of cell proliferation (135% to 178%) in three of four meningioma cultures studied at a concentration of 10(-10) to 10(-9)M, although a tendency of growth inhibition was observed at a lower concentration. A time course of DNA synthesis in response to TPA, assessed by [3H] thymidine incorporation studies, revealed a time- and dose-dependent stimulation and/or inhibition which further depended on the serum concentration of the growth medium used. The overall results indicate that PKC-mediated signal pathways are closely involved in growth regulation of human meningioma cells. The results further suggest that the signalling processes consist of complex mechanisms which await to be elucidated.

Coupling of pancreatic gastrin/cholecystokinin-B (G/CCKB) receptors to phospholipase C and protein kinase C in AR4-2J tumoral cells

Gastrin and cholecystokinin (CCK) have proven trophic effects on the gut. We have previously demonstrated that these peptides stimulate an early event in cellular proliferation, namely ornithine decarboxylase activity (ODC), in a rat exocrine pancreatic cell line AR4-2J. Furthermore, this effect is mediated through a G/CCKB receptor. Thus, in the present study we sought to examine the signal transduction mechanisms linked to the G/CCKB receptor occupancy. Both gastrin and CCK induced a rapid (maximum at 40 s) increase in inositol triphosphates (InsP3) and diacylglycerol (DAG) formation in a dose-dependent manner (EC50 = 5.6 nM) that quickly returned to baseline. Although InsP3 levels remained at baseline, DAG levels demonstrated a second gradual increase that was maximal at 15 min. CCK/gastrin efficiency to stimulate DAG and InsP3 formation (EC50 = 5.6 nM) could be correlated to the G/CCKB receptor occupancy, suggesting a coupling of this receptor to phospholipase C. To examine the involvement of protein kinase C (PKC) activation in the increase in ODC activity, we stimulated the AR4-2J cells with the phorbol ester TPA and observed an increase in ODC activity with a maximal effect at 100 nM. TPA stimulation of ODC activity was completely abolished by the PKC inhibitor staurosporine (50 nM). However, 50 nM staurosporine inhibited only 65% of the gastrin and CCK induced increase in ODC activity suggesting that a portion of the G/CCKB receptor-mediated increase in ODC activity is PKC independent.

Synthesis of phosphatidylinositol 3,4-bisphosphate is regulated by protein-tyrosine phosphorylation but the p85 alpha subunit of phosphatidylinositol 3-kinase may not be a target for tyrosine kinases in thrombin-stimulated human platelets

To elucidate the mechanism involving synthesis of phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P2), which is the main species of 3-phosphorylated phosphoinositides in activated blood platelets, we observed a correlation among protein-tyrosine phosphorylation, protein kinase C (PKC) activation, and PtdIns(3,4)P2 synthesis in these anucleate cells. Thrombin (1 U/ml) elicited marked protein-tyrosine phosphorylation, PKC activation, and PtdIns(3,4)P2 synthesis. In contrast, 1 microM 12-O-tetrade-canoylphorbol 13-acetate barely induced tyrosine phosphorylation and PtdIns(3,4)P2 synthesis although it strongly activated PKC. A variety of kinase inhibitors were tested for their ability to inhibit the thrombin effects. Both staurosporine and tyrphostin inhibited thrombin-stimulated tyrosine phosphorylation and PtdIns(3,4)P2 synthesis. H-7, which specifically, although weakly, inhibited PKC activation, had no effect on tyrosine phosphorylation and PtdIns(3,4)P2 production. Among the various kinase inhibitors tested, staurosporine was the most potent inhibitor of protein tyrosine phosphorylation and PtdIns(3,4)P2 synthesis, and there was a good correlation of the inhibition between these two parameters, although it also inhibited PKC activation. To examine the involvement of PtdIns 3-kinase, which is believed to play an important role in 3-phosphorylated phosphoinositide synthesis, we studied tyrosine phosphorylation and the association with tyrosine-phosphorylated proteins of the p85 alpha subunit of PtdIns 3-kinase in thrombin-stimulated platelets. We did not detect tyrosine-phosphorylated protein by Western blotting where p85 alpha was located. Similarly, when platelet lysates were precipitated with anti-p85 alpha antibodies and then blotted with anti-phosphotyrosine antibodies, tyrosine-phosphorylated p85 alpha was undetectable. Furthermore, when the cell lysates were precipitated with anti-phosphotyrosine antibodies, no p85 alpha was found in the immunoprecipitates. These results show that PtdIns(3,4)P2 synthesis in stimulated platelets is mediated by tyrosine phosphorylation, as it is in proliferating cells, but the p85 alpha subunit of PtdIns 3-kinase may not be a target for tyrosine kinases and that staurosporine, though non-specific, would be a useful tool for elucidating signal transduction involving D-3-phosphorylated phosphoinositide generation and protein-tyrosine phosphorylation in blood platelets.

Basal and acidic fibroblast growth factor-induced atrial natriuretic peptide gene expression and secretion is inhibited by staurosporine

We examined the mechanisms involved in the activation of atrial natriuretic peptide (ANP) gene expression and secretion in response to acidic fibroblast growth factor (aFGF) by studying the effects of staurosporine, a protein kinase C inhibitor, and 12-O-tetradecanoyl phorbol 13-acetate (TPA), an activator of protein kinase C, on basal and AFGF-induced ANP messenger RNA (mRNA) and immunoreactive ANP (IR-ANP) levels in cultured neonatal rat cardiac myocytes. Acidic FGF caused a dose- and time-dependent increase in IR-ANP and immunoreactive N-terminal fragment of proANP (IR-NT-proANP) release into the culture medium from ventricular but not from atrial myocytes. In ventricular cells, 50 ng/ml aFGF for 24 or 48 h resulted in a 70% or 181% increase, respectively, in the accumulation of IR-ANP into the culture medium. Acidic FGF also stimulated ANP gene expression significantly; after 48 h of incubation, the ANP mRNA levels of aFGF-treated ventricular myocytes were 205% (P < 0.001) higher than those of control cells. Staurosporine alone at concentration of 10 nM significantly decreased the basal IR-ANP and IR-NT-proANP secretion, and inhibited the aFGF-induced increase in ANP mRNA and IR-ANP levels in ventricular myocytes. TPA (100 nM) alone significantly stimulated ANP gene expression and secretion but these effects were not augmented by combining aFGF with TPA. High performance liquid chromatographical analysis showed that atrial and ventricular myocytes maintained in serum-free medium were capable of secreting processed, ANP99-126 sized material, and that aFGF did not alter the processing of ANP in ventricular cultures. These results demonstrate that aFGF is a potent stimulator of ANP gene expression and secretion in cultured neonatal rat ventricular but not in atrial cells. The observations that (a) staurosporine completely abolished the effects of aFGF on ANP gene expression and release and (b) ANP secretory and gene expression inducing effects of phorbol ester were not augmented by aFGF, suggest an important role of protein kinase C in mediating aFGF-induced ANP gene expression and secretion.

Signalling pathways as targets for anticancer drug development

Intracellular signalling pathways mediating the effects of oncogenes on cell growth and transformation offer novel targets for the development of anticancer drugs. With this approach, it may be sufficient to target a component of the signalling pathway activated by the oncogene rather than the oncogene product itself. In this review, the abilities of some antiproliferative drugs to inhibit signalling targets are considered. There are some anticancer drugs already in clinical trial that may act by inhibiting signalling targets, as well as drugs in preclinical development. Some problems that may be encountered in developing this new class of anticancer drugs are discussed.

Immunofluorescent quantification of tyrosine phosphorylation of cellular proteins in whole cells by flow cytometry

Tyrosine phosphorylation of proteins, a major event in the transduction of mitogenic signals, was analysed by flow cytometry with a fluorescent antiphosphotyrosine monoclonal antibody, on formaldehyde-fixed, permeabilized cells. We have used this method (PY-Facs) to study activation of normal human T lymphocytes and cells of a leukemic T-cell line: Jurkat. In contrast to normal T cells, Jurkat cells as well as three other leukemic cell lines display a higher constitutive level of tyrosine phosphorylation. This level of tyrosine phosphorylation results from an equilibrium that can be up-regulated by the tyrosine phosphatase inhibitor, vanadate peroxide, and down-regulated by the tyrosine kinase inhibitors, genistein and staurosporine. We have also observed an increased tyrosine phosphorylation of proteins after mitogenic stimulation of Jurkat cells via T-cell receptor triggering. In addition, the entry of normal purified T cells from G0 phase into the cell cycle after co-stimulation with a phorbol ester and an anti-receptor antibody is correlated with a pronounced increase in tyrosine phosphorylation. We thus confirmed that this biochemical event was tightly associated with the activation status of the cells. The rapidity and sensitivity of the method we describe here make it particularly convenient for routine use and processing of a large number of samples, e.g., during analysis of human tumors. Moreover, because it retains sufficiently the integrity of treated cells and does not alter expression of membrane antigens, this method is suitable for multiparametric analysis, particularly for simultaneous studies associating the measure of tyrosine phosphorylation levels with possible modifications of membrane or intracellular structures as well as with cell cycle status.(ABSTRACT TRUNCATED AT 250 WORDS)

Phospholipases and protein kinases during phagocyte activation

Phospholipases and protein kinases are critical for the intracellular transmission and amplification of signals induced by extracellular ligands. Chemotactic activation of phagocytes through G protein coupled receptors leads to inflammatory responses of the immune cells. Downstream of G proteins, phospholipases generate precursors for eicosanoid synthesis and are involved in the functional responses. Recently, the molecular characterization of specific enzymes of the signalling cascades has gained much attention in research.

Inhibition of epidermal growth factor receptor tyrosine kinase activity by hypericin

The naphthodianthrone hypericin produces a potent and irreversible inhibition of the epidermal growth factor (EGF) receptor tyrosine kinase activity. The inhibition was time and temperature dependent but did not depend on EGF activation. The IC50 values obtained were 0.37-8.7 microM with membranes incubated for 30 min at 30 degrees or 10 min at 0 degree, respectively. Kinetic analyses with poly(Glu,Ala,Tyr) 6:3:1 [poly(GAT)] as an exogenous substrate were in agreement with the irreversible nature of the inhibition. Irradiation for 30 min with fluorescent light caused a dramatic photosensitizing effect and resulted in an IC50 value of 44 nM. This effect was due to a type I mechanism, since the exclusion of oxygen did not alter the inhibition curve. The inhibition was inversely proportional to the amounts of membranes used, which probably reflects the non-specific sequestration of hypericin into the lipid bilayer. Ser/Thr protein kinases such as protein kinase A, casein kinase 1 and 2 and the enzyme 5'-nucleotidase, were not inhibited by hypericin not even at high concentrations (> 100 microM).

HLA class II molecule-mediated signal transduction mechanism responsible for the expression of interleukin-1 beta and tumor necrosis factor-alpha genes induced by a staphylococcal superantigen

Superantigens including staphylococcal enterotoxins (SE) bind to major histocompatibility complex class II molecules and interact with T cells bearing particular V beta chains. SEB was shown to induce the expression of interleukin (IL)-1 beta and tumor necrosis factor (TNF)-alpha genes in human peripheral blood monocytes bearing HLA class II molecules. Monoclonal antibodies directed against HLA-DR and -DQ abolished the SEB-induced expression of both the IL-1 beta and TNF-alpha genes, suggesting that the HLA class II molecules mediated the gene expression. Therefore, we investigated the signal transduction mechanism responsible for the expression of IL-1 beta and TNF-alpha genes induced by binding of SEB to the HLA class II molecules. Three protein tyrosine kinase (PTK) inhibitors, genistein, herbimycin A, and tyrphostin, each of which has a different mechanism of action, strongly inhibited the expression of the monokine mRNA induced by SEB. Analyses of PTK activity revealed that SEB induced a rapid increase of membrane-associated PTK activity and this was blocked by tyrphostin. Furthermore, H-7 inhibited the expression of the monokine mRNA induced by SEB, suggesting the involvement of protein kinase C (PKC) in the signaling pathway. The involvement of PKC was confirmed by the observations that phorbol 12-myristate 13-acetate (PMA), a direct activator of PKC, induced the expression of the monokine mRNA and that SEB evoked the activation of membrane-associated PKC. Both activation of PKC and expression of the monokine mRNA induced by SEB appeared to be inhibited by tyrphostin, but those induced by PMA were not. Taken together, these findings indicate that both PTK and PKC play essential roles in HLA class II molecule-mediated signal transduction elicited by SEB and that PTK activation may precede PKC activation in the signaling pathway.

Distinct mechanisms of phospholipase D activation and attenuation utilized by different mitogens in NIH-3T3 fibroblasts

The activation of phospholipase D (PLD) by platelet-derived growth factor (PDGF), prostaglandin F2 alpha and 12-O-tetradecanoylphorbol 13-acetate (TPA) was studied in NIH-3T3 fibroblasts. PLD activation was determined by measuring the production of both [3H]phosphatidic acid and [3H]phosphatidylpropanol (products of the PLD-catalyzed hydrolysis and transphosphatidylation reactions, respectively), in cells that were metabolically pre-labeled with [3H]oleic acid. All mitogens caused a rapid (within 2 min) activation of PLD. Activation of PLD by prostaglandin F2 alpha and PDGF was transient and declined to near basal levels by 15 min and 55 min, respectively. In contrast, TPA-induced activation of PLD was sustained for at least 60 min of incubation. A combination of maximally effective concentrations of PDGF and TPA stimulated PLD activity in a non-additive manner, while the effect of prostaglandin F2 alpha was additional to that of either PDGF or TPA. The protein kinase inhibitor staurosporine inhibited PLD activation by PDGF or TPA with almost identical dose/response curves. In contrast, staurosporine potentiated prostaglandin-F2 alpha-induced PLD activation. The specific protein kinase C inhibitor GF109203X (a bisindolylmaleimide) inhibited PLD activation by prostaglandin F2 alpha and PDGF at concentrations higher than those required for inhibition of PLD activation induced by TPA. Depletion of cellular protein kinase C abolished PLD activation by all three mitogens without affecting in vitro activity of membrane-bound PLD. The distinct kinetics of PLD activation and its differential susceptibility to protein kinase inhibitors suggest the existence of agonist-specific activation and/or inactivation mechanisms. The results indicate also that protein kinase C participates in the mechanism of PLD activation via PDGF, while the effect of prostaglandin F2 alpha involves a pathway independent of protein kinase C.

Anti-CD9 monoclonal antibody elicits staurosporine inhibitable phosphatidylinositol 4,5-bisphosphate hydrolysis, phosphatidylinositol 3,4-bisphosphate synthesis, and protein-tyrosine phosphorylation in human platelets

Phosphoinositide metabolism elicited by anti-CD9 monoclonal antibody, a well-characterized platelet activator, was studied using acetylsalicylic acid-treated human platelets. TP82, which is an anti-CD9 monoclonal antibody, induced classical phosphatidylinositol 4,5-bisphosphate hydrolysis, as monitored by intracellular Ca2+ mobilization and phosphatidic acid production, and synthesis of phosphatidylinositol 3,4-bisphosphate, which is a major component of newly-described 3-phosphorylated inositol phospholipids produced during platelet activation. These changes were severely inhibited by 1 microM staurosporine, a potent, though non-selective, protein kinase inhibitor, which also abolished TP82 induction of tyrosine phosphorylation of multiple platelet proteins. Protein-tyrosine phosphorylation appears necessary to initiate both the classical phosphoinositide turnover and synthesis of the newly-described 3-phosphorylated inositol phospholipids in anti-CD9 monoclonal antibody-induced platelet activation.

Activation of phospholipase D following perturbation of the human T lymphocyte antigen receptor/CD3 complex is dependent upon protein kinase C

Perturbation of the T lymphocyte antigen receptor/CD3 complex or phorbol ester stimulation leads to activation of phospholipase D in the Jurkat T lymphocyte cell line. These observations suggested that phospholipase D activation might result from activation of protein kinase C. In other systems, phospholipase D activity has been shown to be under G-protein or protein kinase C control. Studies detailed here demonstrate that commonly used inhibitors of protein kinase C had unrelated, diverse effects on phospholipase D activity in T lymphocytes. However, protein kinase C down-regulation resulting from prolonged cellular exposure to phorbol esters led to abrogation of anti-CD3-stimulated phospholipase D activation. The results presented underline the complexity of studies employing inhibitors of protein kinase C, suggest interesting approaches to isolation of phospholipase D dependent signalling pathways, confirm that T cell antigen receptor-linked activation of phospholipase D is dependent upon protein kinase C activity and suggest that distant events of T lymphocyte activation are dependent upon the establishment of a positive feedback loop involving protein kinase C and phospholipase D which would result in the prolonged activation of protein kinase C required for certain lymphokine production.

Staurosporine differentially inhibits glioma versus non-glioma cell lines

We have previously demonstrated that the protein kinase C (PKC) activity of human glioma cell lines was significantly elevated (by 3 orders of magnitude) when compared to non-malignant adult human glia, and that the proliferation rate of several established human glioma cell lines correlated with the measured protein kinase C activity. The purpose of this study was to determine whether 1) elevated PKC activity was also a characteristic of fast growing cell lines of non-glial origin, 2) the proliferation rate of non-glioma cell lines correlated with their PKC activity and 3) the proliferation of non-glioma cell lines could be inhibited by staurosporine, a relatively selective PKC inhibitor, which significantly attenuates the growth of glioma cells. Eight established human non-glioma cell lines (bladder, colorectal, rhabdomyosarcoma-oligodendrocyte hybrid, melanoma, cervix, and fibroblast) were compared to the highly proliferative A172 glioma cell line. PKC activity was significantly higher in the glioma cell lines even though 3 of 8 of the non-glioma lines had higher proliferation rates than A172. In non-glioma cell lines, no correlation was found between the PKC activity and proliferation rates. Staurosporine was more effective in decreasing the proliferation of three glioma cell lines compared to the non-glioma cell lines. We conclude that PKC activity is differentially increased in glioma cell lines and that their proliferation rate is more sensitive to inhibition by staurosporine. Targetting the PKC system may prove to be of therapeutic benefit to patients with malignant gliomas.