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Biomedical subjects

V L Rothman

Publications and source records attributed to V L Rothman.

25 records · Page 2Linked to original sources
PubMed1992

Biological activities of peptides and peptide analogues derived from common sequences present in thrombospondin, properdin, and malarial proteins.

Thrombospondin (TSP), a major platelet-secreted protein, has recently been shown to have activity in tumor cell metastasis, cell adhesion, and platelet aggregation. The type 1 repeats of TSP contain two copies of CSVTCG and one copy of CSTSCG, per each of the three polypeptide chains of TSP and show homology with peptide sequences found in a number of other proteins including properdin, malarial circumsporozoite, and a blood-stage antigen of Plasmodium falciparum. To investigate whether these common sequences functioned as a cell adhesive domain in TSP, we assessed the effect of peptides corresponding to these sequences and an antibody raised against one of these sequences, CSTSCG, in three biological assays which depend, in part, on the cell adhesive activity of TSP. These assays were TSP-dependent cell adhesion, platelet aggregation, and tumor cell metastasis. We found that a number of peptides homologous to CSVTCG promoted the adhesion of a variety of cells including mouse B16-F10 melanoma cells, inhibited platelet aggregation and tumor cell metastasis, whereas control peptides had no effect. Anti-CSTSCG, which specifically recognized TSP, inhibited TSP-dependent cell adhesion, platelet aggregation, and tumor cell metastasis, whereas control IgG had no effect. These results suggest that CSVTCG and CSTSCG present in the type I repeats function in the adhesive interactions of TSP that mediate cell adhesion, platelet aggregation, and tumor cell metastasis. Peptides, based on the structure of these repeats, may find wide application in the treatment of thrombosis and in the prevention of cancer spread.

Amino Acid Sequence↗
PubMed1989

The interaction of thrombospondin with platelet glycoprotein GPIIb-IIIa.

The interaction of human platelet thrombospondin (TSP) with human platelet glycoproteins GPIIb-IIIa was studied using a solid-phase binding assay. Polystyrene test tubes were coated with TSP, and 125I-labeled GPIIb-IIIa was added, allowed to bind, and the bound radioactivity was measured. After 90 min, the binding became time independent, and in most experiments, more than 10% of the exogenously added radioactivity was bound to the tube. Analysis of the bound radioactivity by polyacrylamide gel electrophoresis and autoradiography indicated that it was from labeled GPIIb-IIIa. Several lines of evidence indicate that the binding of GPIIb-IIIa to TSP was specific. (a) TSP immobilized on plastic or Sepharose bound 3-10-fold more GPIIb-IIIa than immobilized bovine serum albumin. (b) Addition of unlabeled excess GPIIb-IIIa reversed the binding of 125I-labeled GPIIb-IIIa to immobilized TSP. (c) Addition of EDTA inhibited the binding of GPIIb-IIIa to TSP by more than 90%, whereas addition of 1 mM CaCl2 and 1 mM MgCl2 potentiated the binding by more than 100%. (d) Monoclonal antibodies against TSP and GPIIb-IIIa inhibited the binding by 30-70% as compared with control and polyclonal anti-fibrinogen anti-serum. (e) A plot of GPIIb-IIIa bound versus GPIIb-IIIa added was best described as a rectangular hyperbola by regression analysis with half-saturation at 60 ng/ml GPIIb-IIIa. Similar results were obtained when labeled TSP was added to tubes coated with GPIIb-IIIa. These results show that TSP and GPIIb-IIIa can specifically interact in vitro and suggest that GPIIb-IIIa may function as a platelet TSP receptor during platelet aggregation.

Calcium↗
PubMed1989

The GPIIB-IIIa-like complex may function as a human melanoma cell adhesion receptor for thrombospondin.

The purpose of this study was to determine whether a heterodimeric complex immunologically related to the fibrinogen receptor could function as a thrombospondin (TSP) receptor in TSP-mediated cell-substratum adhesion of human melanoma cells. We found that polyclonal antibodies to the platelet GPIIb-IIIa complex, GPIIIa, and the human vitronectin receptor inhibited TSP-mediated cell adhesion by 63-68%. Immunoprecipitation of detergent extracts of 125I-surface-labeled melanoma cells using either anti-human platelet GPIIb-IIIa or anti-human vitronectin receptor antibody revealed the presence of a single heterodimeric complex, suggesting that both antisera recognize the same integrin receptor, GPIIb-IIIa-like antigen. Adhesion of cells to TSP is likely mediated through a region of the TSP molecule containing the arginine-glycine-aspartic (RGD) peptide sequence, since cell attachment to TSP was inhibited 50-66% in the presence of peptides containing RGD. These results strongly suggest that a GPIIb-IIIa-like/vitronectin receptor can serve as a cell binding site for TSP in mediating cell-substratum adhesion.

Antibodies, Monoclonal↗
PubMed1988

Thrombospondin promotes platelet aggregation.

Thrombospondin (TSP), isolated from human platelets, promotes aggregation of both nonstimulated platelets and platelets stimulated with thrombin or ADP. The TSP-promoted aggregation is specific since a monoclonal antibody against TSP inhibits the effect of exogenously added TSP and inhibits thrombin-induced platelet aggregation in the absence of added TSP. Several lines of evidence suggest that TSP mediates its effect on aggregation of nonstimulated and stimulated platelets through different platelet-surface receptor systems. The TSP-promoted aggregation of nonstimulated platelets was inhibited by a monoclonal antibody to platelet glycoprotein IV (GPIV), but not by a monoclonal antibody to the fibrinogen receptor, GPIIb-IIIa. In contrast, the antibody to GPIIb-IIIa totally inhibited the TSP-potentiated aggregation of thrombin-stimulated platelets, whereas the antibody to GPIV has no effect. Thus, these studies suggest that TSP promotes platelet aggregation by at least two mechanisms--one dependent on and one independent of the platelet fibrinogen receptor system.

Adenosine Diphosphate↗
PubMed1987

Thrombospondin, a potentiator of tumor cell metastasis.

The platelet-secreted protein thrombospondin (TSP) potentiates tumor cell metastasis. Human TSP injected i.v. into mice 5 min prior to i.v. injection of T241 sarcoma cells potentiates lung tumor colony formation. Several lines of evidence suggest that the TSP-enhancing effect involves both TSP-mediated tumor cell adhesion and the host's hemostatic system: TSP potentiates the initial, rapid sequestering of tumor cells in the lung; TSP promotes the adhesion of tumor cells in vitro; the effect of TSP on tumor cell metastasis is dependent on the presence of platelets and a normal plasma clotting system, since TSP does not potentiate lung tumor colony formation in either thrombocytopenic mice or mice anticoagulated with Coumadin. Our results suggest a central role for TSP in the metastatic process.

Animals↗