okadaic-acid and erbstatin

We investigated the involvement of diverse protein kinases and phosphatases in the transduction pathways elicited by phenobarbital (PB), a well-known inducer of some hepatic cytochromes P450 (CYP). Different inhibitors or activators of protein kinases or phosphatases were assessed for their ability to modulate PB-induction of CYP2B and CYP3A mRNA expression. Rat hepatocytes in primary culture were treated with the test compounds one hour prior to, and then continuously, in the absence or presence of 1 mmol/L PB for 24 h. By northern blot analysis of CYP2B1/2 and 3A1/2 gene expression, we first confirmed the negative role of the adenosine 3':5' cyclic monophosphate (cAMP)/protein kinase A pathway and the positive role of some serine/threonine protein phosphatases in the mechanism of PB-induction. The present data further suggested that Ca2+/calmodulin-dependent protein kinases II (independently of Ca2+) and extracellular signal-regulated kinases 1/2 (ERK1/2) might function respectively as positive and negative regulator in the PB-induction of CYP2B and CYP3A. In contrast, protein kinases C and phosphatidylinositol-3-kinase did not appear to be involved, while the role of tyrosine kinases remained unclear. We conclude that a complex network of phosphorylation/dephosphorylation events might be crucial for PB-induction of rat CYP2B and CYP3A.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Animals; Aryl Hydrocarbon Hydroxylases; Calcium-Calmodulin-Dependent Protein Kinases; Cells, Cultured; Chromones; Cyclic AMP; Cytochrome P-450 CYP2B6; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Enzyme Induction; Enzyme Inhibitors; Flavonoids; Genistein; Hepatocytes; Hydroquinones; Indoles; Intracellular Fluid; Morpholines; Okadaic Acid; Oxidoreductases, N-Demethylating; Phenobarbital; Phosphoric Monoester Hydrolases; Protein Serine-Threonine Kinases; Protein-Tyrosine Kinases; Rats; RNA, Messenger; Signal Transduction

Several inflammatory effects of tumor necrosis factor (TNF) are known to be mediated through activation of a nuclear transcription factor NF-kappaB, but how TNF activates NF-kappaB is incompletely understood. In the present report, we examined the role of protein tyrosine kinases (PTK) in TNF-mediated NF-kappaB activation by using genistein and erbstatin, two potent inhibitors of PTK. The treatment of human myeloid U-937 cells with either inhibitor completely suppressed the TNF-induced NF-kappaB activation in a dose- and time-dependent manner. Suppression correlated with PTK activity, since among the structural analogues of genistein, only an active inhibitor of PTK, quercetin blocked TNF-induced NF-kappaB activation and not daidzein, an inactive inhibitor. Inhibition of NF-kappaB activation was not limited to myeloid cells, as it was observed with T cells and epithelial cells. Both the PTK inhibitors blocked the degradation of IkappaBalpha, the inhibitory subunit of NF-kappaB, and the consequent translocation of the p65 subunit without any significant effect on p50 or on c-Rel. The PTK inhibitors did not interfere with NF-kappaB binding to DNA. The NF-kappaB-dependent CAT reporter gene expression in transient transfection assays was also suppressed by the PTK inhibitors. Both PTK inhibitors abolished TNF-induced activation of N-terminal c-Jun kinase and mitogen-activated protein kinase kinase. Overall, our results suggest that a genistein- and erbstatin-sensitive PTK is involved in the pathway leading to NF-kappaB activation and gene expression by TNF and thus could be used as a target for development of antiinflammatory drugs.

Topics: Biological Transport, Active; Cell Line; Cell Nucleus; Chloramphenicol O-Acetyltransferase; DNA; DNA-Binding Proteins; Enzyme Inhibitors; Gene Expression; Genes, Reporter; Genistein; Humans; Hydroquinones; I-kappa B Proteins; Interleukin-1; NF-kappa B; NF-KappaB Inhibitor alpha; Okadaic Acid; Protein-Tyrosine Kinases; Tetradecanoylphorbol Acetate; Transcription Factor RelA; Tumor Necrosis Factor-alpha

Tissue factor (TF) is a cell-surface glycoprotein responsible for initiating the extrinsic pathway of coagulation. The overexpression of TF in human malignancy has been correlated with the angiogenic phenotype, poor prognosis, and thromboembolic complications. The mechanisms underlying constitutive expression of TF in cancer cells are poorly defined. We cloned TF cDNA on the basis of its strong expression in metastatic MDA-MB-231 breast carcinoma cells in contrast to its weak expression in non-metastatic MCF-7 cells. Transient transfection analysis showed that TF promoter activity in MCF-7 cells could be stimulated by expression of a membrane-targeted raf kinase (raf-CAAX). raf-induced activity was dependent on the presence of an AP-1/NF-kappaB motif in the TF promoter and was inhibited by dominant-negative mutants of jun and by I-kappaB alpha. MDA-MB-231 cells were found to contain higher levels of ERK1/2 kinase activity than did MCF-7 cells. Electrophoretic mobility shift assays showed that MDA-MB-231 nuclear proteins bound strongly to an oligonucleotide corresponding to the AP-1/NF-kappaB sequence, whereas MCF-7 nuclear extracts showed weak binding to this element. Finally, we showed that TF mRNA levels in MDA-MB-231 cells declined after addition of the mitogen-activated protein kinase kinase inhibitor PD98059. Our data showed that activation of the raf-ERK pathway led to activation of TF expression in breast carcinoma cells and suggested that constitutive activation of this pathway leads to high TF expression in MDA-MB-231 cells.

Topics: Base Sequence; Benzoquinones; Breast Neoplasms; Calcium-Calmodulin-Dependent Protein Kinases; Dactinomycin; DNA, Complementary; Enzyme Activation; Enzyme Induction; Enzyme Inhibitors; Female; Flavonoids; Gene Expression Regulation, Neoplastic; Genistein; Humans; Hydroquinones; Lactams, Macrocyclic; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Molecular Sequence Data; Neoplasm Invasiveness; Neoplasm Metastasis; Neoplasm Proteins; Neovascularization, Pathologic; NF-kappa B; Okadaic Acid; Phenols; Proto-Oncogene Proteins c-raf; Quinones; Rifabutin; Signal Transduction; Tetradecanoylphorbol Acetate; Thromboplastin; Transcription Factor AP-1; Transcription, Genetic; Tretinoin; Tumor Cells, Cultured

Cyclic nucleotide-gated (CNG) channels in vertebrate photoreceptors are crucial for transducing light-induced changes in cGMP concentration into electrical signals. In this study, we show that both native and exogenously expressed CNG channels from rods are modulated by tyrosine phosphorylation. The cGMP sensitivity of CNG channels, composed of rod alpha-subunits expressed in Xenopus oocytes, gradually increases after excision of inside-out patches from the oocyte membrane. This increase in sensitivity is inhibited by a protein tyrosine phosphatase (PTP) inhibitor and is unaffected by three different Ser/Thr phosphatase inhibitors. Moreover, it is suppressed or reversed by application of ATP but not by a nonhydrolyzable ATP analog. Application of protein tyrosine kinase (PTK) inhibitors causes an increase in cGMP sensitivity, but only in the presence of ATP. Taken together, these results suggest that CNG channels expressed in oocytes are associated with active PTK(s) and PTP(s) that regulate their cGMP sensitivity by changing phosphorylation state. The cGMP sensitivity of native CNG channels from salamander rod outer segments also increases and decreases after incubation with inhibitors of PTP(s) and PTK(s), respectively. These results suggest that rod CNG channels are modulated by tyrosine phosphorylation, which may function as a novel mechanism for regulating the sensitivity of rods to light.

Topics: Adenosine Triphosphate; Animals; Cyclic GMP; Enzyme Inhibitors; Eye Proteins; Hydroquinones; Ion Channel Gating; Marine Toxins; Microcystins; Okadaic Acid; Oocytes; Oxazoles; Patch-Clamp Techniques; Peptides, Cyclic; Phenols; Phosphorylation; Protein Processing, Post-Translational; Protein Tyrosine Phosphatases; Rod Cell Outer Segment; Staurosporine; Vanadates; Xenopus laevis

A novel strategy for isolating potential anti-tumor drugs is presented. It is predicated on the idea that future anti-tumor drugs will be specific inhibitors of the signal-transduction pathways responsible for cell proliferation. Briefly, retroviral vectors are used to introduce focus-forming oncogenes into a test population of target cells, which are grown to confluence and treated with signal-transduction inhibitors. The inhibitors are screened for the ability to suppress the development of transformed foci without killing the confluent monolayer of non-transformed quiescent cells. For this work, a panel of inhibitors was first screened against the oncogene ras. The protein kinase C (PKC) inhibitor CGP 41251 and the protein tyrosine kinase (PTK) inhibitor CGP 45047 suppressed ras-induced focus formation and left a viable monolayer of quiescent cells. Focus inhibition was reversible; conversely, drug addition to developing foci retarded further expansion. CGP 41251 generally blocked proliferation of ras or control cells, suggesting that oncogenes cannot substitute for PKC. PTK inhibitors erbstatin and CGP 520 and phosphatase inhibitor okadaic acid failed to inhibit focus formation at concentrations toxic to the monolayer. Lavendustin A and CGP 47778A showed neither focus inhibition nor toxicity. In the complementary screen, a single inhibitor (CGP 41251) was tested against several oncogenes, including src, raf and polyomavirus middle T antigen. Focus formation by all oncogenes was suppressed. The strategy has several advantages over current drug-screening assays, and it can be adapted to large-scale screening with many drugs and many oncogenes.

Topics: 3T3 Cells; Alkaloids; Animals; Antigens, Polyomavirus Transforming; Benzamides; Cell Division; Drug Screening Assays, Antitumor; Enzyme Inhibitors; Ethers, Cyclic; Genes, ras; Genes, src; Genetic Vectors; Hydroquinones; Mice; Okadaic Acid; Oncogenes; Phenols; Protein Kinase C; Protein Serine-Threonine Kinases; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-raf; Retroviridae; Signal Transduction; Staurosporine; Styrenes; Sulfones; Thiazoles

Protein tyrosine phosphorylation plays an important role in cell growth, mitosis, and tumorigenesis. It has also been implicated in meiotic maturation and fertilization. We have used anti-phosphotyrosine immunofluorescence and immunoblotting to identify sperm and egg proteins which are phosphorylated on tyrosine residues prior to and during sea urchin fertilization. On immunoblots of sperm proteins, the monoclonal anti-phosphotyrosine antibody detected three major proteins with molecular weights of 44, 82, and 100 kD, and six minor bands at 46, 48, 70, 76, 95, and 150 kD. These phosphotyrosyl proteins were localized to the sperm acrosomal and centriolar fossae. In contrast, staining was found globally in unfertilized eggs, and the antibody recognized two major egg phosphotyrosyl proteins of molecular weights 42 and 50 kD, and five minor bands at 40, 90, 116, 130, and 150 kD. While immunofluorescent staining remained throughout the fertilized egg cytoplasm, there were dynamic changes in the staining intensity of single bands. The 90 kD immunoreactive band increased in intensity, and the 40 and 42 kD bands disappeared by 15 min after fertilization. Loss of the 40 and 42 kD bands was due to dephosphorylation by okadaic acid-sensitive phosphatase(s). The 50 kD immunoreactive protein was unchanged up to the 8-cell stage and was still present in blastulae, indicating its importance throughout fertilization and early development. Alterations in the pattern of phosphotyrosine-containing proteins during fertilization did not depend on nascent proteins and could not be completely mimicked by increasing intracellular calcium, pH, and protein kinase C activity alone. Since changes in the fertilization pattern of phosphotyrosyl proteins occurred during formation of the sperm aster and mitotic spindle, we analyzed the role of protein tyrosine kinase activity in these processes using the tyrosine kinase specific inhibitor, erbstatin. Both the sperm aster and mitotic spindle were disrupted, indicating an involvement of tyrosine phosphorylation in these processes during interphase and mitosis. We conclude that the changes in phosphotyrosyl proteins play an important role in fertilization and early development of sea urchin eggs. Control of microtubule assembly into the sperm aster and mitotic spindle of the first cell cycle are examples of such roles.

Topics: Animals; Calcium-Calmodulin-Dependent Protein Kinases; Ethers, Cyclic; Female; Fertilization; Fluorescent Antibody Technique; Hydroquinones; Immunoblotting; Male; Okadaic Acid; Ovum; Phosphorylation; Protein Tyrosine Phosphatases; Protein-Tyrosine Kinases; Sea Urchins