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N Osman

Publications and source records attributed to N Osman.

At least 37 records · Page 2Linked to original sources
PubMed1994

CD7 is associated with CD3 and CD45 on human T cells.

The CD7 cluster of mAb identifies a 40-kDa glycopolypeptide that is present on a major subset of human T cells. CD7 Ag mediates an accessory pathway of T cell activation in that cross-linked CD7 mAb are mitogenic, and signals delivered via CD7 Ag stimulate integrin-mediated adhesion. We have found that the CD7 molecule is associated with a tyrosine kinase whose major substrate is CD45. In vitro phosphorylation of CD7, CD3, or CD45 immunoprecipitates prepared from lysates of human T cells showed a similar pattern of multiple phosphorylated polypeptides; in addition, these immunoprecipitates phosphorylated a tyrosine kinase-specific peptide. Surface-iodinated T cells were lysed and immunoprecipitated with CD7, CD3, and CD45 mAb. Bands characteristic of CD45 and CD3 were identified in CD7 immunoprecipitates. Confirmation of an association of CD7 with CD3 and CD45 was obtained from Western blotting and fluorescence resonance energy transfer experiments. Furthermore, we provide evidence using immunoprecipitation and Western blotting that CD7 exists as a homodimer. These data support the hypothesis that CD7 exists in an oligomeric complex with CD3/TCR, the protein tyrosine phosphatase CD45, and a tyrosine kinase, thereby providing a physical basis for the accessory role of the CD7 molecule in T cell activation.

Antigen-Antibody Complex↗
PubMed1993

Physical association of CD5 and the T cell receptor/CD3 antigen complex on the surface of human T lymphocytes.

The physical association of CD5 and the T cell antigen receptor (TcR)/CD3 complex on the surface of intact human lymphocytes was investigated using co-capping experiments and fluorescence resonance energy transfer (FRET) analyses. Antibody-induced capping of CD5 or CD3 and double indirect immunofluorescence labeling revealed a specific co-localization of a significant fraction of CD3 and CD5 molecules on the T cell surface. By means of FRET measurements we studied further the physical proximity of CD5 and the TcR/CD3 complex at the surface of normal lymphocytes. Significant fluorescence energy transfer was measured between CD5 and CD3 molecules indicating that the associated molecules were within 10 nm of one another. No energy transfer was observed between the integrin alpha 4 beta 7 and CD3 or CD5. The close physical proximity measured between CD5 and CD3 correlates with our co-capping data and taken together the results show that the association of CD5 and the TcR/CD3 complex first detected by immunoprecipitation occurs on the surface of human T cells under physiologically relevant conditions.

Antigens, CD↗
PubMed1993

Biochemical characterization of murine Fc gamma RI.

The biochemical analysis of murine Fc gamma RI has been difficult because this receptor is co-expressed with other Fc receptors on the cell surface of myeloid cells and all precipitate together with immune complexes. To overcome this problem and to study cells which expressed Fc gamma RI and only this Fc receptor, stable transfection of Chinese hamster ovary (CHO) cells (Fc gamma RI-) with Fc gamma RI cDNA was performed thereby permitting biochemical characterization of Fc gamma RI in isolation from other Fc receptors. Studies of Fc gamma RI+CHO cells showed the mature Fc gamma RI to be a 70,000 MW single-chain receptor on the cell surface. The 70,000 MW molecule was also identified on the Fc gamma RI+ cell lines, J774 (a macrophage-like cell line), and 18.81 (a pre-B-cell line). Fc gamma RI was shown to be N-linked glycosylated and after deglycosylation to have a protein core of 49,000 MW. Fc gamma RI was found to be phosphorylated and after PMA stimulation, the level of phosphorylation was increased; serine residues in the cytoplasmic tail were identified as the phosphate acceptors. Thus, Fc gamma RI can now be definitely characterized as a 70,000 MW phosphoprotein.

Animals↗
PubMed1992

Structure and mapping of the gene encoding mouse high affinity Fc gamma RI and chromosomal location of the human Fc gamma RI gene.

We describe the isolation and characterization of the gene encoding the mouse high affinity Fc receptor Fc gamma RI. Using a mouse cDNA Fc gamma RI probe four unique overlapping genomic clones were isolated and were found to encode the entire 9 kb of the mouse Fc gamma RI gene. Sequence analysis of the gene showed that six exons account for the entire Fc gamma RI cDNA sequences including the 5'- and 3'-untranslated sequences. The first and second exons encode the signal peptide; exons 3, 4, and 5 encode the extracellular Ig binding domains; and exon 6 encodes the transmembrane domain, the cytoplasmic region, and the entire 3'-untranslated sequence. This exon pattern is similar to Fc gamma RIII and Fc epsilon RI but differs from the related Fc gamma RII gene which contains 10 exons and encodes the b1 and b2 Fc gamma RII. Southern blot analysis had shown that the mouse Fc gamma RI gene is a single copy gene with no RFLP in inbred strains of mice, but analysis of an intersubspecies backcross of mice showed that unlike other mouse FcR genes which are on mouse chromosome 1 the locus encoding Fc gamma RI, termed Fcg1, is located on chromosome 3. Interestingly, the Fcg1 locus is located near the end of a region with known linkage homology to human chromosome 1. Analysis of human x rodent somatic cell hybrid cell lines indicates that the human FCG1 locus encoding the human Fc gamma RI maps to chromosome I and therefore possibly linked to other FcR genes on this chromosome. These results suggest that the linkage relationships among these genes in the human genome are not preserved in the mouse.

Amino Acid Sequence↗
PubMed1992

Evidence for an association between the T cell receptor/CD3 antigen complex and the CD5 antigen in human T lymphocytes.

In this work we report that CD5, a T cell accessory activation antigen and receptor for the B cell surface protein CD72, is associated with the T cell antigen receptor (TcR)/CD3 complex in human T lymphocytes. In vitro phosphorylation of either CD3 or CD5 immunoprecipitates prepared from CD3-stimulated Jurkat and peripheral blood T cells in the presence of the detergent polyoxyethelene 10 oleyl ether (Brij96) showed, unexpectedly, an identical pattern of five phosphopolypeptides of 70, 59, 56, 21 and 18 kDa, respectively. Peptide mapping of the five bands demonstrated that the same protein kinase substrates co-precipitated with both CD3 and CD5 and that the majority of the protein phosphorylation occurred on tyrosine residues. These data suggested that the TcR/CD3 complex and and the CD5 antigen might be associated in T cells. Evidence to support this hypothesis was obtained from analysis of immunoprecipitates prepared from surface-iodinated T cells. Bands characteristic of the TcR and CD3 antigens were identified in CD5 immunoprecipitates and conversely, CD5 was identified in CD3 immunoprecipitates. Conformation that CD3 and CD5 co-precipitated in the presence of Brij96 was obtained by Western blotting. Quantitative immunodepletion demonstrated that between 10%-20% of cell surface CD5 was associated with the TcR/CD3 complex in Brij96 detergent lysates of human T cells and, furthermore, that this association was independent of T cell activation. The association of these two receptors provides a possible physical basis for the accessory role of the CD5 antigen in T cell activation.

Antigens, CD↗
PubMed1992

Fc gamma receptors: gene structure and receptor function.

Molecular studies of murine Fc gamma R have revealed much exciting new information about the structure and regulation of Fc gamma RI and Fc gamma RII genes and of the Fc gamma RI protein. The Fc gamma RI gene is composed of six exons, whereas the Fc gamma RII gene is composed of ten. The extracellular domains are encoded by individual exons in both genes (three in Fc gamma RI and two in Fc gamma RII); however, the Fc gamma RII gene shows greatest complexity in the region encoding the cytoplasmic tail and membrane spanning region, which is encoded by four exons compared to only one in the Fc gamma RI gene. Expression of Fc gamma RII is controlled by elements within the first 641 bases upstream of the transcription initiation site. The function of the domains of Fc gamma RI has been defined with the surprising finding that in the absence of the third domain the first two extracellular domains function as a broadly specific low affinity Fc gamma RII-like receptor.

Amino Acid Sequence↗
PubMed1992

Comparative effects of enalapril and nifedipine on renal hemodynamics in hypertensive renal allograft recipients.

The comparative effects of enalapril (E) and nifedipine (N) on renal hemodynamics were assessed in twenty-two moderately hypertensive, cadaveric renal transplant patients who were maintaining stable renal function. Fourteen patients were on cyclosporin (CSA) and eight were receiving azathioprine with prednisolone (AZA). In each patient effective renal plasma flow (ERPF) was determined four times, first baseline, second with E, third as another baseline after a washout period, and fourth with N; and renal vascular resistance (RVR) was derived in each. ERPF and RVR were significantly compromised in the CSA group (202 +/- 55 ml/min and 65 +/- 18 mmHg/ml/min) compared to the AZA group (302 +/- 99 and 43 +/- 15 respectively). During E therapy, RVR further increased in the CSA group to 82 +/- 37 while it decreased in the AZA group to 31 +/- 7 (both changes were significant when compared to their respective baseline values). N, on the other hand, only significantly lowered RVR in the AZA group. Furthermore, two patients, one from each group, developed acute reversible renal failure shortly after E therapy. However, both agents were effective in lowering blood pressure to a comparable degree in both groups. In conclusion, our data showed a somewhat less favourable renal hemodynamic response to short-term enalapril therapy in hypertensive renal transplant patients maintained on CSA. However, the significance of such hemodynamic changes for long-term renal function remains uncertain.

Adult↗
PubMed1991

Chimeric Fc receptors identify functional domains of the murine high affinity receptor for IgG.

Chimeric Fc gamma R have been generated between the mouse high affinity receptor for IgG (Fc gamma RI) and the low affinity receptor for IgG (Fc gamma RII) by exchanging the first two domains of the three-domain extracellular structure of Fc gamma RI with the homologous two-domain extracellular structure of Fc gamma RII. Studies of the affinity and specificity of binding of mouse Ig classes to these receptors defined functional regions of Fc gamma RI and showed some surprising results. After removal of the third extracellular domain of Fc gamma RI, the remaining two domains (domains 1 and 2) retained the capacity to bind Ig in the form of immune complexes, however, they bound monomeric IgG2a with a reduced affinity. Surprisingly, these two domains in the absence of the third domain bound not only IgG2a but also IgG1 and IgG2b, i.e., the third domain of Fc gamma RI suppresses the intrinsic capacity of the first two domains to act as a low affinity Fc gamma RII-like molecule. Linking the third extracellular domain of Fc gamma RI to the two extracellular domains of Fc gamma RII resulted in a receptor that retained the specificity and affinity of Fc gamma RII. Thus, the removal of domain 3 from Fc gamma RI resulted in the conversion of Fc gamma RI to an "Fc gamma RII-like" receptor. These findings indicate that domains 1 and 2 of Fc gamma RI form an Ig-binding motif, and although domain 3 is not essential for Fc binding by Fc gamma RI, it plays a crucial role in determining the specific high affinity interaction of Fc gamma RI with IgG2a.

Animals↗
PubMed1991

Extrauterine pregnancy in Mozambique.

Epidemiologic, clinical and management information was collected from the case histories of 103 women operated on for an extrauterine pregnancy at the Department of Obstetrics and Gynaecology of the Central Hospital in Maputo (Mozambique) from April 1st, 1987 to March 31st, 1988. We observed a decline in extrauterine pregnancies (9.76%), an association of pelvic schistosomiasis (3.9%), and a high percentage of women with ruptured tubes and subsequent hemoperitoneum (75.7%).

Adult↗
PubMed1991

[Schistosomiasis: possible cause of ectopic pregnancy. Four clinical cases].

The Authors describe 4 cases of ectopic pregnancy associated with foci of schistosomiasis and point out the relevance of mass screening on urine, stool and vaginal secretions in those areas where schistosomiasis is endemic and frequent the involvement of female genital tract. Utilization of laparoscopy in all cases where as adnexal mass and/or a history of unexplained infertility is found is finally advocated.

Female↗
PubMed1990

Molecular cloning and expression of the mouse high affinity Fc receptor for IgG.

Full length cDNA clones encoding the mouse Fc gamma RI were isolated by using redundant oligonucleotide probes based on previously determined amino acid sequence of protein bound to an IgG2a antibody column. Sequence analysis of cDNA clones indicates that mouse Fc gamma RI is a transmembrane glycoprotein that is composed of three disulfide bonded extracellular Ig binding domains unlike Fc gamma RII of man and mouse. These extracellular domains contain five potential sites of N-linked glycosylation; three sites in the first domain and one in each of the second and third domains. In addition a transmembrane region is present followed by a cytoplasmic tail of 84 amino acids. Analysis of the amino acid sequence of the first two extracellular domains of Fc gamma RI indicate that these are highly homologous to the extracellular domains of Fc gamma RII; the third domain is different and shows a lower level of homology to other FcR domains but is clearly related to the Ig super-family. Transfected cells expressing Fc gamma RI were shown to bind immune complexes of rabbit IgG; and monomeric IgG2a bound to transiently transfected cells with an affinity of approximately 5 x 10(7) M-1, i.e. the receptor was of high affinity and therefore was by definition Fc gamma RI. Northern analysis demonstrated that Fc gamma RI mRNA could be detected in the Fc gamma RI+ myeloid cell lines WEH1 3B and J774. Finally, Southern analysis indicated that Fc gamma RI is likely to be encoded by a single copy gene of approximately 9 kb.

Amino Acid Sequence↗
PubMed1990

Mouse macrophage beta subunit (CD11b) cDNA for the CR3 complement receptor/Mac-1 antigen.

The cDNA for the common beta Mac-1 subunit (CD11b) of the mouse LFA-1/Mac-1/p150,95 group of leukocyte cell adhesion receptors, formally designated integrin beta 2, has been cloned and sequenced. Clones were isolated from cDNA libraries made from J774 macrophage and WEHI-3B myelomonocytic tumor cells which express this subunit as a component of the macrophage activation antigen 1 (Mac-1), also known as complement receptor type 3 (CR3). This subunit is expressed as a single, abundant mRNA species approximately 2.7 kilobase (kb) in size. The 2422 base pair (bp) cDNA sequence obtained codes for a 771 amino acid protein organized with leader, extracellular, transmembrane, and cytoplamic domains of 23, 680, 23, and 46 amino acids, respectively, yielding an 82,700 mature protein of 747 amino acids. The mouse beta Mac-1 subunit is highly similar to its human counterpart with an overall sequence identity of 81% and identical positioning of 5 out of 6 potential N-linked glycosylation sites, as well as 56 Cys residues that are organized in repeating motifs characteristic of integrin beta subunits. The most highly conserved regions are the transmembrane and cytoplasmic domains where only 4 out of 69 amino acids differ, indicating that the functions associated with this domain in Mac-1-mediated processes, such as iC3b-triggered phagocytosis, have been evolutionarily conserved.

Amino Acid Sequence↗
PubMed1988

Lipid peroxidation in purified plasma membrane fractions of rat liver in relation to the hepatoxicity of carbon tetrachloride.

Preparations of rat liver sinusoidal plasma membrane have been tested for their ability to metabolize the hepatotoxin carbon tetrachloride (CCl4) to reactive free radicals in vitro and compared in this respect with standard preparations of rat liver microsomes. The sinusoidal plasma membranes were relatively free of endoplasmic reticulum-associated activities such as the enzymes of the cytochrome P450 system and glucose-6-phosphatase. CCl4 metabolism was measured as (i) covalent binding of [14C]-CCl4 to membrane protein, (ii) electron spin resonance spin-trapping of CCl3. radicals and (iii) CCl4-induced lipid peroxidation. By all of these tests, purified sinusoidal plasma membranes were found unable to metabolize CCl4. The fatty acid composition of the plasma membranes was almost identical to that of the microsomal preparation and both membrane fractions exhibited similar rates of the lipid peroxidation that was stimulated non-enzymically by gamma-radiation or incubation with ascorbate and iron. The absence of CCl4-induced lipid peroxidation in the plasma membranes seems to be due, therefore, to an absence of CCl4 activation rather than an inherent resistance to lipid peroxidation. We conclude that damage to the hepatocyte plasma membrane during CCl4 intoxication is not due to a significant local activation of CCl4 to CCl3. within that membrane.

Animals↗
PubMed1981

The kinetic mechanism of inhibition of liver pyridoxal kinase with tryptophan metabolites.

The activity of purified liver pyridoxal kinase (ATP:pyridoxal 5-phosphotransferase, EC 2.7.1.35) was determined in the presence of 13 different tryptophan metabolites. Only 3-hydroxykynurenine, 3-hydroxyanthranilic acid, xanthurenic acid and quinolinic acid were found to inhibit the enzyme with I50 values of 0.1, 0.12, 0.36 and 0.42 mM, respectively. The inhibition was not related to the presence of pyridine nucleus in the metabolites molecule as was proved from the patterns of inhibition.

3-Hydroxyanthranilic Acid↗