cyanoginosin-lr and tautomycin

Topics: Alkenes; Antibiotics, Antineoplastic; Antifungal Agents; Cantharidin; Crystallography, X-Ray; Cyclosporine; Enzyme Inhibitors; Humans; Microcystins; Models, Molecular; Okadaic Acid; Peptides, Cyclic; Phosphoprotein Phosphatases; Polyenes; Pyrans; Pyrones; Spiro Compounds; Structure-Activity Relationship

The protein phosphatase (PP) inhibitors nodularin and microcystin-LR induced apoptosis with unprecedented rapidity, more than 50% of primary hepatocytes showing extensive surface budding and shrinkage of cytoplasm and nucleoplasm within 2 min. The apoptosis was retarded by the general caspase inhibitor Z-VAD.fmk. To circumvent the inefficient uptake of microcystin and nodularin into nonhepatocytes, toxins were microinjected into 293 cells, Swiss 3T3 fibroblasts, promyelocytic IPC-81 cells, and NRK cells. All cells started to undergo budding typical of apoptosis within 0.5 - 3 min after injection. This was accompanied by cytoplasmic and nuclear shrinkage and externalization of phosphatidylserine. Overexpression of Bcl-2 did not delay apoptosis. Apoptosis induction was slower and Z-VAD.fmk independent in caspase-3 deficient MCF-7 cells. MCF-7 cells stably transfected with caspase-3 showed a more rapid and Z-VAD.fmk dependent apoptotic response to nodularin. Rapid apoptosis induction required inhibition of both PP1 and PP2A, and the apoptosis was preceded by increased phosphorylation of several proteins, including myosin light chain. The protein phosphorylation occurred even in the presence of apoptosis-blocking concentrations of Z-VAD.fmk, indicating that it occurred upstream of caspase activation. It is suggested that phosphatase-inhibiting toxins can induce caspase-3 dependent apoptosis in an ultrarapid manner by altering protein phosphorylation.

Topics: 3T3 Cells; Animals; Antifungal Agents; Apoptosis; Caspase 3; Caspase Inhibitors; Caspases; Cell Line; Cell Line, Transformed; Enzyme Inhibitors; Gene Expression; Humans; Intracellular Fluid; Marine Toxins; Mice; Microcystins; Okadaic Acid; Oxazoles; Peptides, Cyclic; Phosphoprotein Phosphatases; Phosphorylation; Proto-Oncogene Proteins c-bcl-2; Pyrans; Rats; Rats, Wistar; Spiro Compounds; Tumor Cells, Cultured

Protein phosphatases play significant roles in signal transduction pathways pertaining to cell proliferation, gene expression, and neurotransmission. Serine/threonine phosphatases PP1 and PP2A, which are closely related in primary structure (approximately 50%), are inhibited by a structurally diverse group of natural toxins. As part of our study toward understanding the mechanism of inhibition displayed by these toxins, we have developed research in two directions: (1) The standardization of an assay to be used in acquisition of the structure--activity relationship of inhibition data is reported. This nonradioactive assay affords detection levels of molecular phosphate released from a phosphorylated hexapeptide in subnanomolar quantities. The comparison of our IC50 values of these inhibitors against corresponding literature data provided validation for our method. (2) Computational analysis provided a global model for binding of these inhibitors to PP1. The natural toxins were shown to possess remarkably similar three-dimensional motifs upon superimposition and van der Waals minimization within the PP1 active site.

Topics: Antifungal Agents; Crystallography, X-Ray; Enzyme Inhibitors; Marine Toxins; Microcystins; Models, Molecular; Okadaic Acid; Oxazoles; Peptides, Cyclic; Phosphoprotein Phosphatases; Protein Binding; Protein Conformation; Pyrans; Signal Transduction; Spiro Compounds; Stereoisomerism; Structure-Activity Relationship; Toxins, Biological

Nucleotide excision repair of DNA in mammalian cells uses more than 20 polypeptides to remove DNA lesions caused by UV light and other mutagens. To investigate whether reversible protein phosphorylation can significantly modulate this repair mechanism we studied the effect of specific inhibitors of Ser/Thr protein phosphatases. The ability of HeLa cell extracts to carry out nucleotide excision repair in vitro was highly sensitive to three toxins (okadaic acid, microcystin-LR and tautomycin), which block PP1- and PP2A-type phosphatases. Repair was more sensitive to okadaic acid than to tautomycin, suggesting the involvement of a PP2A-type enzyme, and was insensitive to inhibitor-2, which exclusively inhibits PP1-type enzymes. In a repair synthesis assay the toxins gave 70% inhibition of activity. Full activity could be restored to toxin-inhibited extracts by addition of purified PP2A, but not PP1. The p34 subunit of replication protein A was hyperphosphorylated in cell extracts in the presence of phosphatase inhibitors, but we found no evidence that this affected repair. In a coupled incision/synthesis repair assay okadaic acid decreased the production of incision intermediates in the repair reaction. The formation of 25-30mer oligonucleotides by dual incision during repair was also inhibited by okadaic acid and inhibition could be reversed with PP2A. Thus Ser/Thr- specific protein phosphorylation plays an important role in the modulation of nucleotide excision repair in vitro.

Topics: Antifungal Agents; Base Sequence; DNA; DNA Damage; DNA Repair; Ethers, Cyclic; HeLa Cells; Humans; Marine Toxins; Microcystins; Molecular Sequence Data; Okadaic Acid; Oligonucleotides; Peptides, Cyclic; Phosphoprotein Phosphatases; Phosphorylation; Proteins; Pyrans; Spiro Compounds

Several groups have reported that okadaic acid (OA) and some other tight-binding protein phosphatase inhibitors including microcystin-LR (MCLR), calyculin-A and tautomycin prevent each other from binding to protein phosphatase 2A (PP2A). In this paper, we have introduced an improved procedure for examining to what extent the affinity of an enzyme for a labelled tight-binding ligand is reduced by binding of an unlabelled tight-binding, ligand to the enzyme. Using this procedure, we have analysed the dose-dependent reduction of PP2A binding of [24-3H]OA by addition of OA, MCLR, calyculin-A and tautomycin. The results indicate that the binding of the unlabelled inhibitors to the PP2A molecule causes a dramatic (10(6)-10(8)-fold) increase in the dissociation constant associated with the interaction of [24-3H]OA and PP2A. This suggests that OA and the other inhibitors bind to PP2A in a mutually exclusive manner. The protein phosphatase inhibitors may share the same binding site on the PP2A molecule. We have also measured values of the dissociation constant (Ki) for the interaction of these toxins with protein phosphatase 1 (PP1). For MCLR and calyculin-A, the ratio of the Ki value obtained for PP1 to that for PP2A was in the range 4-9, whereas it was 0.01-0.02 for tautomycin. The value of tautomycin is considerably smaller than that (0.4) calculated from previously reported Ki values.

Topics: Antifungal Agents; Ethers, Cyclic; Marine Toxins; Microcystins; Okadaic Acid; Peptides, Cyclic; Phosphoprotein Phosphatases; Protein Phosphatase 1; Protein Phosphatase 2; Pyrans; Radioligand Assay; Spiro Compounds

Recent studies suggest that the ability to inhibit the activity of certain serine/threonine protein phosphatases underlies the toxicity of several natural compounds including: okadaic acid, microcystin-LR, nodularin, calyculin A and tautomycin. To characterize further the actions of these toxins, this study compares the inhibitory effects of okadaic acid, chemical derivatives of okadaic acid, microcystin-LR, microcystin-LA, nodularin, calyculin A and tautomycin on the activity of serine/threonine protein phosphatases types 1 (PP1), 2A (PP2A) and a recently identified protein phosphatase purified from bovine brain (PP3). This study shows that, like PP1 and PP2A, the activity of PP3 is potently inhibited by okadaic acid, both microcystins, nodularin, calyculin A and tautomycin. Further characterization of the toxins employing the purified catalytic subunits of PP1, PP2A and PP3 under identical experimental conditions indicates that: (a) okadaic acid, microcystin-LR, and microcystin-LA inhibit PP2A and PP3 more potently than PP1 (order of potency PP2A > PP3 > PP1); (b) nodularin inhibits PP1 and PP3 at a similar concentration that is slightly higher than that which affects PP2A, and (c) both calyculin A and tautomycin show little selectivity among the phosphatases tested. This study also shows that the chemical modification of the (C1) carboxyl group of okadaic acid can have a profound influence on the inhibitory activity of this toxin. Esterification of okadaic acid, producing methyl okadaate, or reduction, producing okadaol, greatly decreases the inhibitory effects against all three enzymes tested. Further reduction, producing 1-nor-okadaone, or acetylation, producing okadaic acid tetraacetate, results in compounds with no inhibitory activity. In contrast, the substitution of alanine (-LA) for arginine (-LR) in microcystin has no apparent effect on the inhibitory activity against PP1, PP2A or PP3.

Topics: Animals; Antifungal Agents; Cattle; Cyclic AMP-Dependent Protein Kinases; Esterification; Ethers, Cyclic; Marine Toxins; Microcystins; Okadaic Acid; Oxazoles; Oxidation-Reduction; Peptides, Cyclic; Phosphoprotein Phosphatases; Phosphorylase b; Phosphorylase Kinase; Pyrans; Rabbits; Spiro Compounds

Phosphatase inhibitors microcystin-LR, tautomycin, and okadaic acid caused contraction and increased 20-kDa myosin light chain (MLC20) phosphorylation in Ca(2+)-free solutions in both phasic and tonic smooth muscle permeabilized with beta-escin, and inhibited the heavy meromyosin (HMM) phosphatase activity of smooth muscle homogenates with the same potency sequence: microcystin-LR greater than tautomycin greater than okadaic acid. The sensitivity to all three inhibitors was significantly higher, the half-times of relaxation and dephosphorylation were 4-6 times longer, and the HMM phosphatase and MLC20 kinase activity/smooth muscle cell wet weight was 2.0- and 1.9-fold lower in the tonic, femoral artery, than in the phasic, ileum or portal vein, smooth muscle. Preincubation with 0.2 microM inhibitor-2 decreased the HMM phosphatase activity by 35% in the ileum and by 60% in the femoral artery. The results suggest that the HMM phosphatases of smooth muscle have properties common to type 1 protein phosphatases, but are inhibited only partially by high concentrations of inhibitor-2, and that the lower HMM phosphatase activity of tonic smooth muscle may contribute to its greater sensitivity to phosphatase inhibitors and its slower rate of relaxation.

Topics: Animals; Antifungal Agents; Calcium; Cations, Divalent; Escin; Ethers, Cyclic; Guinea Pigs; In Vitro Techniques; Marine Toxins; Microcystins; Microscopy, Electron; Muscle Contraction; Muscle, Smooth; Muscle, Smooth, Vascular; Myosin-Light-Chain Phosphatase; Okadaic Acid; Peptides, Cyclic; Phosphoprotein Phosphatases; Phosphorylation; Pyrans; Rabbits; Spiro Compounds

Okadaic acid, a specific inhibitor of protein phosphatase 1 in Paramecium causes sustained backward swimming in response to depolarising stimuli (S. Klumpp et al. (1990) EMBO J. 9, 685). Here, we employ okadaic acid, tautomycin, microcystin LR and inhibitor 1 as phosphatase inhibitors to identify a 42 kDa protein in the excitable ciliary membrane that is dephosphorylated by protein phosphatase 1. Identification of the 42 kDa protein was facilitated by the finding that the protein kinase responsible for its phosphorylation uses Ca-ATP as a substrate just as effectively as Mg-ATP. Notably, dephosphorylation of the 42 kDa protein is specifically inhibited by cyclic AMP; cyclic GMP has no effect.

Topics: Animals; Antifungal Agents; Calcium Channels; Calcium-Transporting ATPases; Cilia; Cyclic AMP; Ethers, Cyclic; Marine Toxins; Microcystins; Okadaic Acid; Paramecium; Peptides, Cyclic; Phosphoprotein Phosphatases; Phosphoproteins; Phosphorylation; Protein Phosphatase 1; Protozoan Proteins; Pyrans; Spiro Compounds

Tautomycin inhibited the catalytic subunits of protein phosphatase-1 (Kiapp = 0.16 nM) more potently than protein phosphatase 2A (Kiapp = 0.4 nM), and the native forms of these enzymes in mammalian, protozoan and plant extracts were inhibited in a similar manner. Protein phosphatase 2B was inhibited 10,000-fold less potently, while two other phosphatases and six protein kinases were unaffected at 10 microM. Okadaic acid prevented the binding of tautomycin to protein phosphatase 2A, indicating a common binding site for both inhibitors. The different relative potencies of tautomycin and okadaic acid for protein phosphatases 1 and 2A suggest that parallel use of both inhibitors may help to identify physiological substrates for each enzyme.

Topics: Antifungal Agents; Ethers, Cyclic; In Vitro Techniques; Kinetics; Marine Toxins; Microcystins; Okadaic Acid; Peptides, Cyclic; Phosphoprotein Phosphatases; Phosphorylases; Protein Phosphatase 1; Protein Phosphatase 2; Pyrans; Spiro Compounds; Streptomyces