Sarcoma de Ewing con afectación pulmonar: descripción de un caso / No disponible

El sarcoma de Ewing es una neoplasia maligna poco frecuente que suele afectar a niños y adultos jóvenes. Presentamos l caso de un varón de 18 años de edad que consulta por dolor en hombro derecho. La radiografía de tórax reveló una masa en lóbulo superior derecho con afectación costal. Se realizó una biopsia la cual confirmó el diagnóstico (AU)

Ewing’s sarcoma is a rare malignancy neoplasm that usually affects Children and young Adults. We report the case of 18 years-old man who consulted for pain in his right shoulder. The chest radiograph revealed an upper lobe lesion with costal affectation. A biopsy was taken and its histopathological analysis revealed a Ewing’s sarcoma (AU)

Interaction of platelet-derived growth factor with thrombospondin 1.

Key factors that mediate vascular smooth muscle cell proliferation and migration are platelet-derived growth factor (PDGF) and thrombospondin 1 (TSP1). We now report that PDGFBB bound tightly and specifically to TSP1, that this interaction was markedly dependent on the disulphide bond arrangement in TSP1, and that binding of PDGFBB to TSP1 did not preclude PDGFBB from binding to its receptor on rat aortic vascular smooth-muscle cells. At physiologic ionic strength and pH, PDGFBB bound to Ca2+-depleted TSP1 with a dissociation constant of 11 +/- 2 nM and to Ca2+-replete TSP1 with a dissociation constant of 32 +/- 5 nM. Binding was specific, as both soluble TSP1 and unlabelled PDGFBB competed for binding of iodinated PDGFBB to immobilized TSP1, whereas other platelet alpha-granule proteins did not compete. The tertiary structure of TSP1 is regulated by intramolecular disulphide interchange; we found that catalysis of disulphide interchange in TSP1 by protein disulphide isomerase ablated the binding of PDGFBB. The interaction of PDGFBB with TSP1 was weakened by increasing salt concentration and essentially ablated at 0.65 ionic strength; it was inhibited by heparin with a half-maximal effect at 20 i.u./ml, implying that the binding was mediated largely by ionic interactions. An anti TSP1 monoclonal antibody decreased the binding of iodinated PDGFBB to PDGF receptor on rat aortic vascular smooth-muscle cells by 37 +/- 2%, whereas platelet TSP1 non-competitively inhibited binding of iodinated PDGFBB. Uncomplexed PDGFBB bound to PDGF receptor with an affinity 5 +/- 2 times that of PDGFBB-TSP1 complexes. These results suggest that TSP1 might assist in the targeting of PDGF to its receptor on vascular smooth-muscle cells.

Salvage synthesis of purine nucleotides by Helicobacter pylori.

The incorporation of purine nucleotide precursors into Helicobacter pylori and the activities of enzymes involved in nucleotide salvage biosynthetic pathways were investigated by radioactive tracer analysis and nuclear magnetic resonance spectroscopy. The organism took up the nucleobases adenine, guanine and hypoxanthine, and the nucleosides adenosine, guanosine and deoxyadenosine. Any incorporation of deoxyguanosine by the cells was below the detection limits of the methods employed. The activities of adenine-, guanine- and hypoxanthine-phosphoribosyl transferases were established. The bacterium showed high levels of adenosine and guanosine nucleosidase activities and lesser activity for deoxyadenosine; no hydrolysis of deoxyguanosine was detected. Phosphorylase activities were not observed with any of the nucleosides. Phosphotransferase activities with similar rates were demonstrated for adenosine, guanosine and deoxyadenosine; and a weaker activity was detected for deoxyguanosine. No nucleoside kinase activities were observed with any of the nucleosides. The presence of adenylate kinase was established, but no guanylate kinase activity was observed. The study provided evidence for the presence in H. pylori of salvage pathways for the biosynthesis of purine nucleotides.

CTP synthetase and enzymes of pyrimidine ribonucleotide metabolism in Giardia intestinalis.

The presence of the enzyme, CTP synthetase was detected in G. intestinalis and appears to be the major route by which the parasite obtains its cytidine nucleotides, though a low phosphoribosyltransferase activity which directly converted cytosine to CMP, was also detected. The giardial CTP synthetase was substantially purified and appeared to be a dimer of molecular weight of approximately 260,000. The enzyme was activated by the purine ribonucleotide, GTP, as was uracil phosphoribosyltransferase (UPRTase), an earlier enzyme in the pyrimidine ribonucleotide pathway. Detection of other enzyme activities in the present study together with results from previous studies has allowed the delineation of the pathway by which G. intestinalis synthesizes its major pyrimidine ribonucleotides.

De novo synthesis of pyrimidine nucleotides by Helicobacter pylori.

The incorporation of pyrimidine nucleotide precursors into Helicobacter pylori and the activities of enzymes involved in their synthetic pathways were investigated by radioactive tracer analysis and 31P nuclear magnetic resonance spectroscopy. The bacterium was found to take up aspartate and bicarbonate and to incorporate carbon atoms from these precursors into its genomic DNA. Orotate, an intermediate of de novo pyrimidine biosynthesis, and uracil and uridine, precursors for pyrimidine pathways, were also incorporated by the micro-organism. Radiolabelled substrates were used to assess the activities of aspartate transcarbamoylase, orotate phosphoribosyltransferase, orotidylate decarboxylase, CTP synthetase, uracil phosphoribosyltransferase, thymidine kinase and deoxycytidine kinase in bacterial lysates. The study provided evidence for the presence in H. pylori of an operational de novo pathway, and a less active salvage pathway for the biosynthesis of pyrimidine nucleotides.

Identification of possible inhibitory reactive centers in thrombospondin 1 that may bind cathepsin G and neutrophil elastase.

Thrombospondin 1 is a multidomain trimeric glycoprotein from platelets and a variety of normal and transformed cells of both mesenchymal and epithelial origin, which functions in cell adhesion and cell-cell interactions. We have recently shown that human thrombospondin 1 binds and inhibits the neutrophil enzymes, neutrophil elastase [Hogg, P.J., Owensby, D.A., Mosher, D.F., Misenheimer, T.M., & Chesterman, C.N. (1993a) J. Biol. Chem. 268, 7139-7146] and cathepsin G [Hogg, P.J., Owensby, D.A., & Chesterman, C.N. (1993b) J. Biol. Chem. 268, 21811-21818]. One mole of thrombospondin 1 trimer binds 3 mol of neutrophil elastase or up to 6 mol of cathepsin G, with site-binding dissociation constants around the nanomolar range, and the enzymes have been shown to interact with thrombospondin 1 in the vicinity of the calcium-binding type 3 repeats. None of the protein modules in this region, or within the whole thrombospondin 1 molecule, have previously been implicated in the inhibition of proteinases. We noted that there are two stretches of eight amino acids each in the human thrombospondin 1 type 3 repeats, residues 735-742 and 794-801, that have striking similarity to a reactive-site consensus sequence derived from selected members of the Kazal and Streptomyces subtilisin inhibitor families. Synthetic peptides corresponding to the putative P5 through P4' residues of both proposed reactive centers interacted efficiently with the active site of cathepsin G and were competitive inhibitors of the fibronectin-degrading and platelet-activating activities of this enzyme, while only the peptide corresponding to residues 793-801 efficiently interacted with the active site of neutrophil elastase and competitively inhibited its fibronectin-degrading activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of uridine phosphorylase from Giardia lamblia by pyrimidine analogs.

Fifty-six pyrimidine analogs were tested as possible inhibitors of uridine phosphorylase from Giardia lamblia. Values of Ki were determined for eight of these which demonstrated an inhibition greater than 60% under the standard conditions of uridine at 1 mM (approximately 1.5 times the Km) and inhibitor at 1 mM. All were competitive with respect to uridine. The most effective inhibitors were uracil analogs substituted at the C-5 position with electron withdrawing groups (nitro groups or halogens). The inhibitory effect at the 5-position appeared to be further enhanced by substitution at the C-6 position with electron releasing groups. The order of effectiveness as inhibitors was 6-methyl-5-nitrouracil greater than 6-amino-5-nitrouracil greater than 5-benzylacyclouridine greater than 5-nitrouracil greater than 5-fluorouracil greater than 5-bromouracil greater than 6-benzyl-2-thiouracil greater than 1,3-dimethyluracil with Ki values of 10, 12, 44, 56, 119, 230, 190 and greater than 1000 microM, respectively. The compounds were also effective inhibitors of the thymidine phosphorylase activity of the enzyme. The effect of the more potent compounds on G. lamblia in in vitro culture are currently under investigation.

Alanine is a major end product of metabolism by Giardia lamblia: a proton nuclear magnetic resonance study.

1H-NMR spectroscopy was used to monitor the major metabolic end products released by Giardia lamblia when maintained anaerobically in culture in Diamond's TYI-S-33 medium. Spectra were acquired for the cell-free medium and the resonances of metabolites utilised and produced during cell growth identified by the addition of pure compounds and by difference spectroscopy. The major metabolites produced by the parasite were alanine, ethanol and acetate, with increases in concentrations in the media after 4 days' growth (end of log phase) of 18, 15 and 4 mM, respectively. The production of both alanine and ethanol approximated to cell growth, with ethanol formation lagging behind alanine during log growth but predominating after the parasites entered stationary phase. Acetate was formed at a more constant rate during growth. Glucose utilisation was sufficient to account for only 50% of the total carbon appearing in alanine, ethanol and acetate. The aminotransferase inhibitors L-cycloserine and carboxymethoxylamine inhibited growth and selectively inhibited the production of alanine. Analysis of the amino acid composition of the medium by HPLC showed that the only amino acid produced, apart from alanine, was proline, which increased in concentration in the medium by 4 mM after 4 days. There was also a 7 mM increase in ammonia over the same period. The only amino acids that were utilised were arginine and the components of an unresolved peak comprising serine, asparagine and glutamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of uridine (thymidine) phosphorylase from Giardia lamblia.

Giardia lamblia is totally dependent on salvage synthesis for its pyrimidine requirements. The salvage pathway enzyme, uridine phosphorylase (pyrimidine nucleoside phosphorylase) was purified to apparent homogeneity from G. lamblia crude extracts by fast protein liquid chromatography and gel filtration on a Superose 12 column, resulting in an overall 3500 fold purification and a recovery of 7.5%. Mono P chromatofocusing gave rise to a major activity peak eluting from the column at pH 5.9, indicating that the enzyme has an isoelectric point (pI) at approximately this value. The molecular weight was found to be 43,000 +/- 2000 from the Superose 12 column, while sodium dodecyl sulphate-polyacrylamide gel electrophoresis of the purified enzyme gave a single protein band with a subunit molecular weight of 38,000 +/- 2000, indicating that it is a monomer. The activities of uridine, deoxyuridine and thymidine phosphorylases from G. lamblia remained associated throughout the purification procedure, suggesting that one enzyme is responsible for the three enzyme activities. The ratio of activities was consistent throughout the purification procedure. In the reverse (anabolic) direction, the enzyme could use both uracil and thymine as substrates. The properties of the phosphorylase differ significantly from those of the mammalian host.