Monovalent cation dependence of tissue plasminogen activator synthesis by HeLa cells

HeLa cells synthesize and secrete increased levels of tissue plasminogen activator (tPA) when incubated for 18 h with 10-20 nM phorbol myristate acetate. This response was inhibited by a number of conditions which affect intracellular Na+ and K+ concentrations. Removing extracellular Na+, while maintaining isotonicity with choline+, reduced the secretion of both functional and antigenic tPA in a linear fashion. A series of cardiac glycosides and related compounds strongly inhibited tPA secretion with the following rank order of potency: digitoxin = ouabain greater than digoxin greater than digitoxigenin greater than digoxigenin greater than digitoxose greater than digitonin. These compounds also inhibited cellular Na+/K+-ATPase activity over an identical concentration range. Two compounds which selectively increase cellular permeability to K+, valinomycin, and nigericin, strongly inhibited tPA secretion, with IC50 values of approximately 50 nM. In contrast, monensin, which selectively increases cellular permeability to Na+, was much less active. Valinomycin, but not nigericin, also inhibited cellular Na+/K+-ATPase activity. Phorbol myristate acetate, 5-20 nM, increased Na+/K+-ATPase activity up to 2-fold and tPA secretion up to 15-fold. We conclude that the secretion of tPA by HeLa cells treated with phorbol myristate acetate proceeds via a mechanism which requires extracellular Na+ and a functional Na+/K+-ATPase ("sodium pump") enzyme.     

Endotoxin induction of an inhibitor of plasminogen activator in bovine pulmonary artery endothelial cells

We have examined the effects of bacterial lipopolysaccharide (endotoxin) on the fibrinolytic activity of bovine pulmonary artery endothelial cells. Endotoxin suppressed the net fibrinolytic activity of cell extracts and conditioned media in a dose-dependent manner (threshold dose, 0.1 ng/ml; maximal dose, 10-100 ng/ml). The effects of endotoxin required at least 6 h for expression. Cell extracts and conditioned media contained a 44-kDa urokinase-like plasminogen activator. Media also contained multiple plasminogen activators with molecular masses of 65-75 and 80-100 kDa. Plasminogen activators in extracts and media were unchanged by treatment of cells with endotoxin. Diisopropyl fluorophosphate (DFP) abolished fibrinolytic activity of extracts and conditioned media. DFP-treated samples from endotoxin-treated but not untreated cells inhibited urokinase and tissue plasminogen activator, but not plasmin. Inhibitory activity was lost by incubation at pH 3 or heating to 56 degrees C for 10 min. These treatments did not affect inhibitory activity of fetal bovine serum. Incubation of 125I-urokinase with DFP-treated medium from endotoxin-treated cells produced an inactive complex with an apparent molecular mass of 80-85 kDa. The complex could be detected by chromatography on Sephadex G-100, but not by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These findings suggest that low doses of endotoxin suppress fibrinolytic activity in endothelial cells by stimulating the production or expression of a fast-acting, relatively labile inhibitor of plasminogen activator.     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.      

Kinetic studies on the conversion of prostaglandin endoperoxide PGH2 by thromboxane synthase

We have investigated the time course of formation of thromboxane A₂, thromboxane B₂, and the C-17 hydroxy fatty acid, HHT, from arachidonic acid in a washed human platelet suspension. Our results indicate that HHT is not a breakdown product of thromboxane A₂, but rather thromboxane A₂ decomposes exclusively into thromboxane B₂. The kinetics of formation of thromboxane B₂ from the endoperoxide prostaglandin H₂ in human platelet microsomes was examined. Our data suggest that a bimolecular reaction is involved in the formation of thromboxane A₂ from prostaglandin H₂ and that thromboxane synthase is not an isomerase, but may be acting via a dismutase-type reaction. One possibility is that thromboxane and HHT are produced simultaneously from two molecules of prostaglandin H₂.