Thrombospondin interaction with plasminogen. Evidence for binding to a specific region of the kringle structure of plasminogen

Platelet thrombospondin interacts with plasminogen in a specific and saturable manner. Thrombospondin was found to specifically bind to plasminogen and the nonenzyme chain of plasmin. Preincubation of 125I- labeled thrombospondin with 30 mmol/L lysine was without effect in the binding of thrombospondin to immobilized plasminogen; preincubation of 125I-labeled plasminogen with 30 mmol/L lysine, on the other hand, significantly reduced the binding of plasminogen to immobilized thrombospondin, suggesting that the interaction of thrombospondin with plasminogen is not the direct result of the lysine binding sites of plasminogen. Arginine and benzamidine, ligands known to specifically bind to the kringle 5 domain of plasminogen, blocked the binding of thrombospondin to plasminogen. Limited elastase proteolysis of plasminogen and plasmin resulted in the generation of two distinct thrombospondin binding domains, one of which was retained on lysine- agarose. The isolation and amino-terminal analysis of these domains following elastase proteolysis of plasminogen identified them, respectively, as a domain containing kringle structures 4 and 5 and plasmin and the other domain consisting of kringle 5-plasmin. A 16- residue synthetic peptide, which represents the amino acids linking kringle 4 to kringle 5 (residues 435-450 of native plasminogen), was without effect in either binding to thrombospondin or blocking the binding of thrombospondin to plasminogen. Plasminogen, therefore, possesses a single thrombospondin interactive site that is independent of, but influenced by, the lysine binding site containing kringle structures and most likely is located within the kringle 5 domain.     

Spectrin Nice (beta 220/216): a shortened beta-chain variant associated with an increase of the alpha I/74 fragment in a case of elliptocytosis

We describe a new spectrin variant with a truncated beta-chain. It was discovered in a 17-year-old white boy presenting with intermittent jaundice and spleen enlargement. He also displayed numerous smooth elliptocytes. On sodium dodecyl sulfate-polyacrylamide gel, the truncated beta-chain (beta'-chain) appeared as an additional band of approximately 216 kilodaltons, migrating between spectrin beta-chain and ankyrin. It represented 30% of total beta-chain. The beta'-chain reacted with an antispectrin beta-chain monoclonal antibody. It failed to become phosphorylated when ghosts were incubated in the presence of [gamma-32P] adenosine triphosphate. Whole spectrin tetramerization was defective since the amount of spectrin dimer was increased in spectrin crude extract and the association constant of the spectrin dimer self- association was decreased. Spectrin whole tetramer isolated from spectrin crude extracts contained small quantities of beta'-chain. Spectrin tryptic peptides showed an increase of the 74,000-dalton fragment at the expense of the 80,000-dalton fragment. So far, the latter abnormality has been used to characterize a number of cases of hereditary elliptocytosis or pyropoikilocytosis with no other apparent change. In the present case, we consider that the abnormality is a consequence of the beta-chain alteration. The parents seemed asymptomatic. As a result, we regard this new spectrin variant as deriving from a de novo mutation.     

Collection of peripheral blood hematopoietic progenitors (PBHP) from patients with severe aplastic anemia (SAA) after prolonged administration of granulocyte colony-stimulating factor

The aim of this study was to test whether prolonged administration of granulocyte colony-stimulating factor (G-CSF) would allow the collection by leukapheresis of PBHP in patients with SAA. For this purpose, nine SAA patients, 7 to 46 years old, six of whom were enrolled at diagnosis of their disease and three after previous immunosuppression had failed, were treated with antilymphocyte globulin (ALG) (day 1 to 5), cyclosporin A (5 mg/kg/d orally) (day 6 to 90) and G-CSF 5 micrograms/kg/d (day 6 to 90). A total of 40 leukaphereses were performed, (range 2 to 7 per patient), between days +10 and +168 from G- CSF treatment. White blood cell count at the time of harvest ranged from 1.2 to 18.1 x 10(9)/L. Results can be summarized as follows: the median number of cells collected per patient was 5.0 x 10(8)/kg (range 2.6 to 18.7), the median number of CD34+ cells was 1.8 x 10(6)/kg (range 0.27 to 3.8) and the median number of colony-forming units granulocyte-macrophage (CFU-GM) was 3.9 x 10(4)/kg (range 0 to 39). Twenty leukaphereses performed between days +33 and +77 of G-CSF treatment grew granulocyte macrophages and erythroid colonies in vitro. No colony growth was obtained from 20 leukaphereses performed before day +33 or after day +80. In six patients the total number of CFU-GM recovered were in the range described for autologous peripheral blood stem cell grafts. (2.6 to 39 x 10(4)/kg). In conclusion, this study suggests that circulating hematopoietic progenitors can be recovered after ALG priming and after at least 1 month of G-CSF treatment in a proportion of patients with SAA. Whether these cells will be suitable for autologous transplantation remains to be determined.     

Missense mutation of the erythropoietin receptor is a rare event in human erythroid malignancies

Human erythroid malignancies (polycythemia vera [PV] and erythroleukemia) are associated with erythropoietin (Epo)-independent growth and differentiation. Missense or nonsense mutations in the Epo receptor (Epo-R) have been recently described in experimental erythroleukemia in mice and in cases of erythrocytosis in humans. To search for a similar genetic alteration in erythroleukemia and PV, we entirely sequenced the exons of the Epo-R gene as well as the intron- exon junctions in these disorders using polymerase chain reaction. In 1 of 10 cases of erythroleukemia, a single allele mutation was found in the 8th Epo-R gene exon that changed asparagine 487 into a serine. No Epo-r gene mutation was found in 12 PV cases studied, but the same mutation (N487S) was found in 1 patient with polycythemia that did not fulfill the criteria of PV (polycythemia of unknown origin). We did not detect this mutation after sequencing part of the 8th exon of the Epo-R gene from 21 other patients with polycythemia of unknown origin and 51 normal controls. The Epo-R mutation was also found in Epstein-Barr virus-derived cell lines from both cases, suggesting that it is not related to the malignant clone. Therefore, this mutation does not appear to be somatic, although no familial cases were found. The biologic effect of this mutation was subsequently studied. Erythroid progenitors from the polycythemic patient normally responded to Epo, whereas those from the erythroleukemic patient were Epo-independent due to autocrine stimulation by Epo. The normal and the mutated Epo-R were transfected into the murine Ba/F3 cell line. Both types of cells displayed the same response to Epo for proliferation, differentiation, and inhibition of apoptosis. Although this mutation may destroy a consensus binding site for Grb2, no obvious differences either in the pattern of Epo-induced tyrosine phosphorylated proteins or in the binding of Grb2 to the Epo-R were observed. In conclusion, a somatic Epo-R missense mutation does not appear to be a molecular mechanism involved in the abnormal growth of human erythroleukemia and PV. However, the Epo-R mutation (N487S) that we describe is located in the same tyrosine sequence beginning at AA 485 as the one previously observed (P488S) in as case of polycythemia (Sokol et al, Exp Hematol 22:447, 1994). These results suggest that this phosphopeptide sequence may play an important role in Epo signalling.     

Targeted disruption of the surfactant protein B gene disrupts surfactant homeostasis, causing respiratory failure in newborn mice.

Surfactant protein B (SP-B) is an 8.7-kDa, hydrophobic protein that enhances the spreading and stability of surfactant phospholipids in the alveolus. To further assess the role of SP-B in lung function, the SP-B gene was disrupted by homologous recombination in murine mouse embryonic stem cells. Mice with a single mutated SP-B allele (+/-) were unaffected, whereas homozygous SP-B -/- offspring died of respiratory failure immediately after birth. Lungs of SP-B -/- mice developed normally but remained atelectatic in spite of postnatal respiratory efforts. SP-B protein and mRNA were undetectable and tubular myelin figures were lacking in SP-B -/- mice. Type II cells of SP-B -/- mice contained no fully formed lamellar bodies. While the abundance of SP-A and SP-C mRNAs was not altered, an aberrant form of pro-SP-C, 8.5 kDa, was detected, and fully processed SP-C peptide was markedly decreased in lung homogenates of SP-B -/- mice. Ablation of the SP-B gene disrupts the routing, storage, and function of surfactant phospholipids and proteins, causing respiratory failure at birth.     

Enhancing trauma education worldwide through telemedicine

Advances in information and communication technologies are changing the delivery of trauma care and education. Telemedicine is a tool that can be used to deliver expert trauma care and education anywhere in the world. Trauma is a rapidly-evolving field requiring access to readily available sources of information. Through videoconferencing, physicians can participate in continuing education activities such as Grand Rounds, seminars, conferences and journal clubs. Exemplary programs have shown promising outcomes of teleconferences such as enhanced learning, professional collaborations, and networking. This review introduces the concept of telemedicine for trauma education, and highlights efforts of programs that are utilizing telemedicine to unite institutions across the world.