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Biomedical subjects

E Haber

Publications and source records attributed to E Haber.

At least 55 records · Page 3Linked to original sources
PubMed1995

Cloning and functional analysis of the promoter for KDR/flk-1, a receptor for vascular endothelial growth factor.

KDR/flk-1 is one of two receptors for vascular endothelial growth factor, a potent angiogenic peptide. KDR/flk-1 is an early marker for endothelial cell progenitors, and its expression is restricted to endothelial cells in vivo. To investigate the molecular mechanisms regulating expression of KDR/flk-1, we cloned and characterized the promoter of the human KDR/flk-1 gene. The transcription start site was localized by primer extension and ribonuclease protection to a nucleotide 303 base pairs (bp) 5' of the initiation methionine codon. The 5'-flanking sequence is rich in G and C residues and contains five Sp1 elements but no TATA consensus sequence. By reporter gene transfection experiments, we found that approximately 4 kilobases of KDR/flk-1 5'-flanking sequence directed high level luciferase activity in bovine aortic endothelial cells; further deletion analysis revealed positive regulatory elements between bp -225 to -164, -95 to -77, -77 to -60, and +105 to +127. Mutation of an atypical GATA sequence between bp +105 and +127 did not affect promoter activity, suggesting that GATA elements are not essential for the high level promoter activity of this gene. Consistent with endothelial cell-restricted expression of KDR/flk-1 mRNA, we found that the 4-kilobase flanking sequence directed high level promoter activity in endothelial cells but not in other cell types. To our knowledge this is the first report characterizing the KDR/flk-1 promoter. Understanding the KDR/flk-1 promoter will allow us to investigate endothelial cell-specific gene regulation and to uncover methods for targeting gene delivery specifically to endothelial cells.

Animals↗
PubMed1994

Promotion of vascular smooth muscle cell growth by homocysteine: a link to atherosclerosis.

Plasma homocysteine levels are elevated in 20-30% of all patients with premature atherosclerosis. Although elevated homocysteine levels have been recognized as an independent risk factor for myocardial infarction and stroke, the mechanism by which these elevated levels cause atherosclerosis is unknown. To understand the role of homocysteine in the pathogenesis of atherosclerosis, we examined the effect of homocysteine on the growth of both vascular smooth muscle cells and endothelial cells at concentrations similar to those observed in clinical studies. As little as 0.1 mM homocysteine caused a 25% increase in DNA synthesis, and homocysteine at 1 mM increased DNA synthesis by 4.5-fold in rat aortic smooth muscle cells (RASMC). In contrast, homocysteine caused a dose-dependent decrease in DNA synthesis in human umbilical vein endothelial cells. Homocysteine increased mRNA levels of cyclin D1 and cyclin A in RASMC by 3- and 15-fold, respectively, indicating that homocysteine induced the mRNA of cyclins important for the reentry of quiescent RASMC into the cell cycle. Furthermore, homocysteine promoted proliferation of quiescent RASMC, an effect markedly amplified by 2% serum. The growth-promoting effect of homocysteine on vascular smooth muscle cells, together with its inhibitory effect on endothelial cell growth, represents an important mechanism to explain homocysteine-induced atherosclerosis.

Animals↗
PubMed1994

Contribution of a single heavy chain residue to specificity of an anti-digoxin monoclonal antibody.

Two distinct spontaneous variants of the murine anti-digoxin hybridoma 26-10 were isolated by fluorescence-activated cell sorting for reduced affinity of surface antibody for antigen. Nucleotide and partial amino acid sequencing of the variant antibody variable regions revealed that 1 variant had a single amino acid substitution: Lys for Asn at heavy chain position 35. The second variant antibody had 2 heavy chain substitutions: Tyr for Asn at position 35, and Met for Arg at position 38. Mutagenesis experiments confirmed that the position 35 substitutions were solely responsible for the markedly reduced affinity of both variant antibodies. Several mutants with more conservative position 35 substitutions were engineered to ascertain the contribution of Asn 35 to the binding of digoxin to antibody 26-10. Replacement of Asn with Gln reduced affinity for digoxin 10-fold relative to the wild-type antibody, but maintained wild-type fine specificity for cardiac glycoside analogues. All other substitutions (Val, Thr, Leu, Ala, and Asp) reduced affinity by at least 90-fold and caused distinct shifts in fine specificity. The Ala mutant demonstrated greatly increased relative affinities for 16-acetylated haptens and haptens with a saturated lactone. The X-ray crystal structure of the 26-10 Fab in complex with digoxin (Jeffrey PD et al., 1993, Proc Natl Acad Sci USA 90:10310-10314) reveals that the position 35 Asn contacts hapten and forms hydrogen bonds with 2 other contact residues. The reductions in affinity of the position 35 mutants for digoxin are greater than expected based upon the small hapten contact area provided by the wild-type Asn. We therefore performed molecular modeling experiments which suggested that substitution of Gln or Asp can maintain these hydrogen bonds whereas the other substituted side chains cannot. The altered binding of the Asp mutant may be due to the introduction of a negative charge. The similarities in binding of the wild-type and Gln-mutant antibodies, however, suggest that these hydrogen bonds are important for maintaining the architecture of the binding site and therefore the affinity and specificity of this antibody. The Ala mutant eliminates the wild-type hydrogen bonding, and molecular modeling suggests that the reduced side-chain volume also provides space that can accommodate a congener with a 16-acetyl group or saturated lactone, accounting for the altered fine specificity of this antibody.

Amino Acid Sequence↗
PubMed1994

R-PEP-27, a potent renin inhibitor, decreases plasma angiotensin II and blood pressure in normal volunteers.

The hemodynamic and humoral effects of the specific human renin inhibitor R-PEP-27 were studied in six normal human subjects on low and high sodium intake diets. An intravenous infusion of R-PEP-27 (0.5 to 16 micrograms/min/kg body wt) reduced blood pressure in a dose-dependent fashion; the mean arterial blood pressure at the end of the infusion fell from 128 +/- 4/83 +/- 4 to 119 +/- 3/71 +/- 3 mm Hg (mean +/- SEM) (P < .01) during the low sodium intake diet. R-PEP-27 had no effect on blood pressure during the high sodium intake diet. R-PEP-27 significantly reduced plasma angiotensin II and aldosterone concentrations. The temporal response to R-PEP-27 suggests that it is a short-lived although highly potent competitive inhibitor of renin; this peptide is a valuable and specific physiologic probe of the renin-angiotensin system.

Adult↗
PubMed1994

Fibrin-targeted recombinant hirudin inhibits fibrin deposition on experimental clots more efficiently than recombinant hirudin.

BACKGROUND: Although the indirect thrombin inhibitor heparin and the more potent direct inhibitor hirudin are useful in preventing thrombosis, a substantial opportunity remains for improving the thrombus selectivity of thrombin inhibitors. METHODS AND RESULTS: To explore the effect of targeting an antithrombin to the surface of a clot, we covalently linked recombinant hirudin to the Fab' (or IgG) of a monoclonal antibody (59D8) that selectively binds to an epitope on fibrin that becomes exposed only after thrombin cleaves fibrinopeptide B. Antibody-coupled hirudin bound to an immobilized peptide of the fibrin beta-chain amino-terminal sequence and inhibited the peptidolytic activity of thrombin more efficiently than free hirudin. Thrombin inhibition dependent on binding to immobilized fibrin monomer was enhanced 1100-fold (P < .0001). Hirudin-59D8 Fab' was 10 times more effective than hirudin in inhibiting fibrin deposition on experimental clot surfaces in fibrinogen solution (P < .0001) and human plasma (P < .0001). The more effective inhibition of thrombin by the conjugate was supported by significantly diminished concentrations of fibrinopeptide A in the plasma supernatant of the clot (P = .0001). Inhibition of clotting by an uncoupled mixture of hirudin and 59D8 Fab' was indistinguishable from that by hirudin alone, indicating that the conjugate's greater inhibitory activity was due to the covalent linkage between antibody and hirudin. CONCLUSIONS: Fibrin-targeted hirudin (in comparison with unmodified hirudin) significantly reduces fibrin deposition on the surface of experimental clots.

Antibodies, Monoclonal↗
PubMed1994

Murine model of accelerated transplant arteriosclerosis.

To define the role of specific gene deletions and mutations in the development of transplant arteriosclerosis, we generated an accelerated model of the disease in mice. Carotid arteries were transplanted between B.10A(2R) (H-2h2) donor mice and C57BL/6J (H-2b) recipients and compared with arteries isografted between H-2b mice. Immunosuppressive drugs were not used. Within 7 days, the allografted carotid artery formed a neointima composed of mononuclear leukocytes (CD45+) that were predominantly monocytes or macrophages (ie, CD11b+ cells with single-lobed nuclei). CD4+ and CD8+ cells were present as well. By 30 days, the neointima became exuberant, and mononuclear leukocytes were largely replaced by smooth muscle cells. Cells staining for proliferating-cell nuclear antigen were abundantly present in the intima at both early and late time points, indicating the proliferation of mononuclear leukocytes and smooth muscle cells. The area of the intima increased from day 7 to day 30 (P < .0005), as did the number of nuclei (P = .0005), but the density of the nuclei decreased (P = .02), suggesting the formation of extracellular matrix. Six of the eight isografts formed no neointima, and in samples from the remaining two, a single layer of smooth muscle neointimal cells covered just a portion of the vessel circumference. This model, which reproduces many of the features of human transplant arteriosclerosis but at an accelerated pace, should prove useful for determining the roles in transplant arteriosclerosis of genes that code for components of immunologic and inflammatory responses.

Animals↗
PubMed1993

26-10 Fab-digoxin complex: affinity and specificity due to surface complementarity.

We have determined the three-dimensional structures of the antigen-binding fragment of the anti-digoxin monoclonal antibody 26-10 in the uncomplexed state at 2.7 A resolution and as a complex with digoxin at 2.5 A resolution. Neither the antibody nor digoxin undergoes any significant conformational changes upon forming the complex. Digoxin interacts primarily with the antibody heavy chain and is oriented such that the carbohydrate groups are exposed to solvent and the lactone ring is buried in a deep pocket at the bottom of the combining site. Despite extensive interactions between antibody and antigen, no hydrogen bonds or salt links are formed between 26-10 and digoxin. Thus the 26-10-digoxin complex is unique among the known three-dimensional structures of antibody-antigen complexes in that specificity and high affinity arise primarily from shape complementarity.

Amino Acid Sequence↗
PubMed1993

Heavy chain position 50 is a determinant of affinity and specificity for the anti-digoxin antibody 26-10.

Antibody produced by a variant of the murine antidigoxin hybridoma 26-10 has reduced affinity for digoxin but enhanced recognition of the digoxin 12-hydroxyl due to a Tyr to His substitution at heavy chain position 50 (Schildbach, J. F., Panka, D. J., Parks, D. R., Jager, G. C., Novotny, J., Herzenberg, L. A., Mudgett-Hunter, M., Bruccoleri, R. E., Haber, E., and Margolies, M. N. (1991) J. Biol. Chem. 266, 4640-4647). Consistent with these data, the 26-10 Fab-digoxin x-ray crystal structure (Jeffrey, P. D., Strong, R. K., Sieker, L. C., Chang, C. Y., Campbell, R. L., Petsko, G. A., Haber, E., Margolies, M. N., and Sheriff, S. (1993) Proc. Natl. Acad. Sci. U. S. A., in press) reveals that Tyr-50 contacts a region of digoxin that includes the hapten-12 carbon. To determine the effects of other heavy chain position 50 substitutions, mutant antibodies were engineered, and their affinities for digoxin and digoxin analogues were measured. The affinity of the mutant antibodies for digoxin roughly correlates with the size of the position 50 side chain. Substitutions of Trp or Phe have no effect on affinity, whereas substitutions of Asn, His, Leu, Ala, Gly, and Asp confer progressively lower affinities. Although Trp and Phe mutants exhibit wild-type specificity, Asn and Asp mutants have improved affinity for digoxin relative to digitoxin (12-deshydroxydigoxin). Leu, Ala, and Gly mutants have improved affinity for 12-acetyldigoxin relative to digoxin as compared with 26-10. These results indicate that position 50 is a determinant of both antibody affinity and fine specificity for antibody 26-10 and that single-amino acid substitutions can alter antibody fine specificity. Models of the mutants were computationally constructed, and haptens were docked into the modeled binding sites. The results suggest that 12-acetyldigoxigenin occupies different orientations in the 26-10 and in the Ala mutant binding sites, resulting in altered binding.

Amino Acids↗
PubMed1993

Physicochemical characterization of a ouabain isomer isolated from bovine hypothalamus.

Recent reports have shown the presence of a ouabain-like inhibitor of Na+/K(+)-ATPase in humans. We have purified a bovine hypothalamic Na+/K(+)-ATPase inhibitory factor (HIF) by using affinity chromatography combined with HPLC. This inhibitor has a molecular weight of 584 as determined by ion-spray mass spectrometry, making it isobaric with ouabain. Glycosidase treatment or acid hydrolysis of HIF released only L-rhamnose, the hexose isomer found in ouabain, as detected by chiral GC/MS. Additionally, enzymatically generated desrhamnosyl HIF was found to have a molecular weight of 438, as does ouabagenin, the aglycone of ouabain. HIF and its aglycone were indistinguishable from ouabain and ouabagenin, respectively, by reversed-phase HPLC retention times. However, derivatization with naphthoylimidazole followed by HPLC revealed different retention times for naphthoylation products of HIF and ouabain. Subsequent CD spectroscopy on isolated naphthoylation products of HIF and ouabain confirmed that they were different. This study provides chromatographic and spectroscopic evidence that ouabain and HIF are isomeric cardenolides. The structural difference is presumed to account for the significant differences in biological properties observed for HIF and ouabain.

Animals↗
PubMed1993

Modulation of antibody affinity by a non-contact residue.

Antibody LB4, produced by a spontaneous variant of the murine anti-digoxin monoclonal antibody 26-10, has an affinity for digoxin two orders of magnitude lower than that of the parent antibody due to replacement of serine with phenylalanine at position 52 of the heavy chain variable region (Schildbach, J.F., Panka, D.J., Parks, D.R., et al., 1991, J. Biol. Chem. 266, 4640-4647). To examine the basis for the decreased affinity, a panel of engineered antibodies with substitutions at position 52 was created, and their affinities for digoxin were measured. The antibody affinities decreased concomitantly with increasing size of the substituted side chains, although the shape of the side chains also influenced affinity. The crystal structure of the 26-10 Fab complexed with digoxin (P.D.J., R.K. Strong, L.C. Sieker, C. Chang, R.L. Campbell, G.A. Petsko, E.H., M.N.M., & S.S., submitted for publication) shows that the serine at heavy chain position 52 is not in contact with hapten, but is adjacent to a tyrosine at heavy chain position 33 that is a contact residue. The mutant antibodies were modeled by applying a conformational search procedure to position side chains, using the 26-10 Fab crystal structure as a starting point. The results suggest that each of the substituted side chains may be accommodated within the antibody without substantial structural rearrangement, and that none of these substituted side chains are able to contact hapten. These modeling results are consistent with the substituents at position 52 having only an indirect influence upon antibody affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Activated platelets form protected zones of adhesion on fibrinogen and fibronectin-coated surfaces.

Leukocytes form zones of close apposition when they adhere to ligand-coated surfaces. Because plasma proteins are excluded from these contact zones, we have termed them protected zones of adhesion. To determine whether platelets form similar protected zones of adhesion, gel-filtered platelets stimulated with thrombin or ADP were allowed to adhere to fibrinogen- or fibronectin-coated surfaces. The protein-coated surfaces with platelets attached were stained with either fluorochrome-conjugated goat anti-human fibrinogen or anti-human fibronectin antibodies, or with rhodamine-conjugated polyethylene glycol polymers. Fluorescence microscopy revealed that F(ab')2 anti-fibrinogen (100 kD) did not penetrate into the contact zones between stimulated platelets and the underlying fibrinogen-coated surface, while Fab antifibrinogen (50 kD) and 10 kD polyethylene glycol readily penetrated and stained the substrate beneath the platelets. Thrombin- or ADP-stimulated platelets also formed protected zones of adhesion on fibronectin-coated surfaces. F(ab')2 anti-fibronectin and 10 kD polyethylene glycol were excluded from these adhesion zones, indicating that they are much less permeable than those formed by platelets on fibrinogen-coated surfaces. The permeability properties of protected zones of adhesion formed by stimulated platelets on surfaces coated with both fibrinogen and fibronectin were similar to the zones of adhesion formed on fibronectin alone. mAb 7E3, directed against the alpha IIb beta 3 integrin blocked the formation of protected adhesion zones between thrombin-stimulated platelets and fibrinogen or fibronectin coated surfaces. mAb C13 is directed against the alpha 5 beta 1 integrin on platelets. Stimulated platelets treated with this mAb formed protected zones of adhesion on surfaces coated with fibronectin. These protected zones were impermeable to F(ab')2 antifibronectin but were permeable to 10 kD polyethylene glycol. These results show that activated platelets form protected zones of adhesion and that the size of molecules excluded from these zones depends upon the composition of the matrix proteins to which the platelets adhere. They also show that formation of protected zones of adhesion by platelets requires alpha IIb beta 3 integrins while the permeability properties of these zones of adhesion are regulated by both alpha IIb beta 3 and alpha 5 beta 1 integrins.

Blood Platelets↗
PubMed1993

Synthetic peptide immunogens for the development of a cardiac myosin light chain-1 specific radioimmunoassay.

To determine if the presence of cardiac light chains in blood could be used to detect acute myocardial infarction, we developed a specific light chain immunoassay. A synthetic peptide sequence specific for human cardiac ventricular myosin light chain 1 (VLC1) was synthesized and designated P348. This peptide coupled to keyhole limpet hemocyanin was used as an immunogen to obtain murine monoclonal antibodies specific for VLC1. Five monoclonal antibodies were obtained. One of these designated Mab-8E3 reacted equally well with both the synthetic peptide and VLC1. Although the 8E3 antibody is specific for VLC1, the use of HPLC purification of skeletal muscle myosin light chain 1 demonstrated that VLC1 is present in human skeletal muscle. The clinical utility of the assay was tested in 18 patients with creatine kinase (CK) and ECG documented acute myocardial infarction. VLC1 was below the limit of detection (< 1 ng/ml) in sera obtained from healthy volunteers and patients without myocardial infarction or chest pain. In contrast VLC1 was elevated in the serum of all 18 patients with acute myocardial infarction. Combining the two test results at the time of admission resulted in 83% of patients having detectable serum levels of one or both markers.

Animals↗
PubMed1992

Platelet factor XIII increases the fibrinolytic resistance of platelet-rich clots by accelerating the crosslinking of alpha 2-antiplasmin to fibrin.

Platelet clots resist fibrinolysis by plasminogen activators. We hypothesized that platelet factor XIII may enhance the fibrinolytic resistance of platelet-rich clots by catalyzing the crosslinking of alpha 2-antiplasmin (alpha 2AP) to fibrin. Analysis of plasma clot structure by polyacrylamide gel electrophoresis and immunoblotting revealed accelerated alpha 2AP-fibrin crosslinking in platelet-rich compared with platelet-depleted plasma clots. A similar study of clots formed with purified fibrinogen (depleted of factor XIII activity), isolated platelets, and specific factor XIII inhibitors indicated that this accelerated crosslinking was due to the catalytic activity of platelet factor XIII. Moreover, when washed platelets were aggregated by thrombin, there was evidence of platelet factor XIII-mediated crosslinking between platelet alpha 2AP and platelet fibrin(ogen). Specific inhibition (by a monoclonal antibody) of the alpha 2AP associated with washed platelet aggregates accelerated the fibrinolysis of the platelet aggregate. Thus in platelet-rich plasma clots, and in thrombin-induced platelet aggregates, platelet factor XIII actively formed alpha 2AP-fibrin crosslinks, which appeared to enhance the resistance of platelet-rich clots to fibrinolysis.

Blood Coagulation Factors↗