Biomedical subjects

G P Tuszynski

Publications and source records attributed to G P Tuszynski.

At least 37 records · Page 2Linked to original sources

PubMed1998

Transforming growth factor-beta 1 inhibits generation of angiostatin by human pancreatic cancer cells.

BACKGROUND: Angiostatin, a proteolytic fragment of plasminogen, is a potent inhibitor of angiogenesis. We have previously shown that the human pancreatic cancer cell line ASPC-1 produces enzymatic activity capable of generating angiostatin. In this study we sought to determine whether angiostatin production by ASPC-1 cells was regulated by the growth factor transforming growth factor-beta 1 (TGF-beta 1), a key mediator of tumor angiogenesis. METHODS: ASPC-1 cells were grown to 70% to 80% confluence in 20% fetal calf serum-RPMI. Medium was changed to serum free. TGF-beta 1 was added at concentrations of 0, 1, 5, and 10 ng/mL with or without plasminogen activator inhibitor type-1 (PAI-1) at concentrations of 0, 5, 10, 50, and 100 micrograms/mL. Cells were then cultured for an additional 24 hours. The serum-free conditioned medium was obtained. Angiostatin generation was determined by incubating 20 micrograms of plasminogen with 100 microL of serum-free conditioned medium for 0, 1, 2, 3, 6, 12, and 24 hours. Samples were run on 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred. The membrane was probed with a monoclonal antibody to the kringle 1-3 fragment of plasminogen and developed using enhanced chemiluminescence. RESULTS: TGF-beta 1 and PAI-1 inhibited the conversion of plasminogen into angiostatin in a time- and dose-dependent manner. Antibody to PAI-1 completely blocks TGF-beta 1 mediated angiostatin inhibition. CONCLUSIONS: TGF-beta 1 inhibits the generation of the antiangiogenic molecule angiostatin by human pancreatic cancer cells in a time- and dose-dependent manner. This effect is mediated through modulation of the plasminogen/plasmin system.

Adenocarcinoma↗

PubMed1997

Thrombospondin-1 modulates angiogenesis in vitro by up-regulation of matrix metalloproteinase-9 in endothelial cells.

Evidence suggests that thrombospondin-1 (TSP-1), a 450-kDa glycoprotein in platelets and extracellular matrix, is involved in angiogenesis. However, the mechanisms by which TSP-1 regulates angiogenesis are unknown, and the exact role of TSP-1 in angiogenesis has been controversial: both stimulatory and inhibitory effects of TSP-1 have been reported. In this study, we evaluated the effect of TSP-1 on the capacity of bovine aortic endothelial (BAE) cells to both invade and form microvessel-like tubes in collagen gels. BAE cell tube formation was enhanced by exogenous TSP-1 at relatively low concentrations (1-10 microg/ml) but inhibited at higher concentrations of TSP-1 (>15 microg/ml). In addition, we correlated this biphasic effect on tube formation with the capacity of TSP-1 to stimulate the activity of a matrix metalloproteinase-9 (MMP-9) in BAE cell collagen gel cultures. The TSP-1-mediated stimulation of MMP-9 activity was specific and dose- and time-dependent. Furthermore, TSP-1-stimulated BAE cell invasion and tube formation were reversed by antibodies against both TSP-1 and MMP-9, suggesting that TSP-1 modulates endothelial cell invasion and morphogenesis in vitro by a mechanism involving the regulation of MMP-9 activity. These findings support the conclusion that TSP-1 is a multifunctional modulator of angiogenesis and are consistent with the dynamic presence of TSP-1 in remodeling tissues in which matrix degradation is required.

Animals↗

PubMed1997

The syndecan family of proteoglycans. Novel receptors mediating internalization of atherogenic lipoproteins in vitro.

Cell-surface heparan sulfate proteoglycans have been shown to participate in lipoprotein catabolism, but the roles of specific proteoglycan classes have not been examined previously. Here, we studied the involvement of the syndecan proteoglycan family. First, transfection of CHO cells with expression vectors for several syndecan core proteins produced parallel increases in the cell association and degradation of lipoproteins enriched in lipoprotein lipase, a heparan-binding protein. Second, a chimeric construct, FcR-Synd1, that consists of the ectodomain of the IgG Fc receptor Ia linked to the highly conserved transmembrane and cytoplasmic domains of syndecan-1 directly mediated efficient internalization, in a process triggered by ligand clustering. Third, internalization of lipase-enriched lipoproteins via syndecan-1 and of clustered IgGs via the chimera showed identical kinetics (t1/2 = 1 h) and identical dose-response sensitivities to cytochalasin B, which disrupts microfilaments, and to genistein, which inhibits tyrosine kinases. In contrast, internalization of the receptor-associated protein, which proceeds via coated pits, showed a t1/2 < 15 min, limited sensitivity to cytochalasin B, and complete insensitivity to genistein. Thus, syndecan proteoglycans can directly mediate ligand catabolism through a pathway with characteristics distinct from coated pits, and might act as receptors for atherogenic lipoproteins and other ligands in vivo.

Animals↗

PubMed1997

Thrombospondin-1 and transforming growth factor-beta l promote breast tumor cell invasion through up-regulation of the plasminogen/plasmin system.

BACKGROUND: Pericellular proteolysis is crucial in tumor cell invasion. The plasminogen/plasmin system is one of the main protease systems involved in cancer progression. Thrombospondin-1 (TSP-1), through activation of transforming growth factor-beta 1 (TGF-beta 1), up-regulates the main plasminogen activator, the urokinase-type plasminogen activator (uPA). The objectives of this study were to determine the role of TSP-1 and TGF-beta 1 in the localization of the plasminogen/plasmin system to the tumor cell surface by the uPA receptor (uPAR) and to determine its effect in breast tumor cell invasion. METHODS: The effect of TSP-1 and TGF-beta 1 in uPAR expression was determined in MDA-MB-231 human breast cancer cells by enzyme-linked immunosorbent assay and Western blot analysis. Their effect and the role of the plasminogen/plasmin system in breast tumor cell invasion were studied with a Boyden Chamber assay. RESULTS: uPAR expression was up-regulated more than twofold by both TSP-1 and TGF-beta 1. The effect of TSP-1 involved its receptor and the activation of TGF-beta 1 by TSP-1. Breast tumor cell invasion was up-regulated sevenfold to eightfold by both TSP-1 and TGF-beta 1 compared with the control group. Antibodies against uPA or uPAR neutralized the TSP-1- and TGF-beta 1-promoted breast tumor cell invasion. CONCLUSIONS: TSP-1, through the activation of endogenous TGF-beta 1, up-regulates the plasminogen/plasmin system and promotes tumor cell invasion in breast cancer cells.

Breast Neoplasms↗

PubMed1997

Adhesive proteins and the hematogenous spread of cancer.

The metastatic spread of cancer is a complex and multistep process characterized by a number of biological steps which include the hematogenous and lymphatic arrest and adhesion of circulating tumor cells in the vascular bed, invasion of tumor cells through the basement membrane, and growth of new tumor colonies in the organ parenchyma. In this brief review we describe the role of platelets, the hemostatic system, adhesive proteins and their putative receptors in the hematogenous dissemination of cancer. The major adhesive proteins postulated to play a role in tumor arrest in the vascular bed are thrombospondin-1 (TSP-1), laminin, fibronectin and hyaluronan-proteoglycans. The major tumor and vascular receptors mediating these adhesive interactions are the CSVTCG-specific TSP-1 receptor, the 67-kD laminin receptor, the alpha v beta 3 vitronectin/TSP-1/fibronectin receptor, and CD44 hyaluronan receptor. The discovery of the involvement of these adhesive proteins and receptors in the metastatic spread of cancer as well as components of the hemostatic system offers unique opportunities for the development of antimetastasis therapies for the treatment of cancer.

Animals↗

PubMed1997

Histopathology and clinical assessment correlate with the cysteine-serine-valine-threonine-cysteine-glycine (CSVTCG) receptor of thrombospondin-1 in breast tumors.

Thrombospondin-1 (TSP-1) is a matrix protein implicated in mechanisms of tumor metastasis. TSP-1 has a characteristic Cysteine-Serine-Valine-Threonine-Cysteine-Glycine (CSVTCG) sequence that functions as a tumor cell adhesion domain. Our laboratory has isolated a novel CSVTCG specific tumor cell receptor. Immunohistochemical staining techniques and computerized image analysis were used to identify and quantitate the CSVTCG receptor of TSP-1 in a wide spectrum of human archival breast tumors. Histopathologic and quantitative examination was correlated with clinical findings two years post operation. Increasing amounts of CSVTCG receptor correlated positively with worsening histopathologic and clinical findings. These findings suggest a role for the TSP-1 CSVTCG receptor in breast tumor progression. This receptor may have utility for the diagnosis, staging, and treatment of this common and deadly disease.

Breast Neoplasms↗

PubMed1996

The role of thrombospondin-1 in tumor progression and angiogenesis.

Thrombospondin (TSP-1) is a large glycoprotein secreted by platelets and synthesized by many cell types, including endothelial and tumor cells. Although controversy exists about the biological function of TSP-1, the following observations suggest that TSP-1 may potentiate tumor progression. (1) Tumor metastases in mice are promoted by TSP-1 and inhibited by anti-TSP-1 antibodies. (2) TSP-1 promotes tumor cell adhesion, migration and invasion. (3) TSP-1 promotes angiogenesis in the rat aorta model. (4) TSP-1 up-regulates the plasminogen activator system through a mechanism involving the activation of TGF-beta 1. (5) Human tumors express increased levels of the CSVTCG-specific TSP-1 receptor. (6) Tumor stroma is enriched in TSP-1. (7) Cancer patients have high blood levels of TSP-1. (8) Poor patient survival correlates with a higher expression of the CSVTCG-specific TSP-1 receptor on tumor cells. In this paper we discuss the evidence that TSP-1 promotes tumor progression and present a hypothetical scheme for its mechanism of action.

Amino Acid Sequence↗

PubMed1996

Thrombospondin-1 (TSP-1) promotes the invasive properties of human breast cancer.

TSP-1 is a matrix-bound adhesive glycoprotein, which plays a role in tumor cell proliferation and tumor angiogenesis. The purpose of this study was to investigate the effect of TSP-1 on breast tumor cell invasion. Tumor cell invasion assays were performed using a modified Boyden chamber apparatus with collagen-coated membranes. Four breast cell lines were studied in serum-free media: the malignant MDA-MB-231, SKBR-3, and MCF-7 cell lines, and the benign MCF-10A cell line. Invasion was measured as the summation of the number of cells in five representative high power fields (400x) traversing the collagen barrier after a 3-hr incubation period. The effect of an anti-TSP-1 antibody (100 microgram/ml) was also evaluated in the malignant cell lines. Statistical analysis was performed by ANOVA and Student's unpaired t test. TSP-1 promoted a dose-dependent increase in invasion as compared to buffer controls in all three malignant cell lines. TSP-1 (100 nM) promoted a greater than five-fold increase over controls in tumor cell invasion for MDA-MB-231, SKBR-3, and MCF-7 cell lines (P < 0.005). TSP-1 had no effect on the invasiveness of the benign cell type MCF-10A. Anti-TSP-1 antibody inhibited TSP-1 promoted invasion in the MDA-MB-231, SKBR-3, and MCF-7 cell lines by 45, 48, and 39%, respectively (P = 0.003, 0.044, 0.047). TSP-1 promotes tumor cell invasion of collagen by breast cancer cells. Therapy designed to inhibit TSP-1 may prevent invasion and metastasis in breast cancer.

Analysis of Variance↗

PubMed1996

Inhibition of breast cancer progression by an antibody to a thrombospondin-1 receptor.

BACKGROUND: Thrombospondin-1 (TSP-1) is a matrix-bound adhesive glycoprotein. Breast carcinoma cells exhibit increased expression of a novel TSP-1 receptor. We evaluated the role of this receptor in breast cancer adhesion and progression. METHODS: Adhesion assays were performed to evaluate MDA-MB-231 breast cancer cell adhesion to TSP-1 in vitro in the presence of either nonimmune immunoglobulin G(IgG) or anti-TSP-1 receptor IgG. Receptor-mediated tumor cell progression was evaluated in athymic nude mice. Mice were inoculated with MDA-MB-231 breast cancer cells and randomized to treatment with intraperitoneal injections of saline solution, nonspecific IgG antibody, or an anti-TSP-1 receptor antibody every other day for 20 days. Mice were killed at 21 days. The peritoneal cavity was examined grossly for primary tumor implantation. The liver and lungs were examined histologically for micrometastases. RESULTS: MDA-MB-231 breast cancer cells adhered to TSP-1 in vitro. This adhesion was inhibited to 10% of control by anti-TSP-1 receptor antibody (p < 0.005). Anti-TSP-1 receptor antibody inhibited in vivo breast cancer progression. Mice treated with control IgG antibody or saline solution alone exhibited extensive intraperitoneal seeding. Only one mouse treated with the anti-TSP-1 receptor antibody exhibited any intraperitoneal tumor seeding (p < 0.01). CONCLUSIONS: These data suggest that TSP-1 and its receptor play an important role in breast cancer progression.

Animals↗

PubMed1996

Expression of thrombospondin-1 in cancer: a role in tumor progression.

Thrombospondin-1 (TSP-1), a trimeric high molecular weight glycoprotein, is one of the major secreted proteins of human platelets and an extracellular matrix component of a variety of cells including vascular endothelial cells and tumor cells. TSP-1 has been shown to be highly expressed in human malignant tissues and present in higher than normal levels in the plasma of cancer patients. TSP-1 has also been shown to promote hematogenous tumor spread, tumor cell adhesion and invasion, and angiogenesis. Overall these studies provide compelling evidence for the conclusion that TSP-1 plays an important role in tumor progression.

Blood Platelets↗

PubMed1995

Thrombospondin and transforming growth factor-beta 1 increase expression of urokinase-type plasminogen activator and plasminogen activator inhibitor-1 in human MDA-MB-231 breast cancer cells.

BACKGROUND: Thrombospondin is a high molecular weight adhesive glycoprotein that has been shown to function in mechanisms of tumor progression. The authors' previous studies have shown that thrombospondin promotes human lung carcinoma invasion by up-regulation of the plasminogen activator system through a mechanism involving the activation of transforming growth factor-beta 1 (TGF-beta 1). In this study, a similar thrombospondin-mediated mechanism operative in breast carcinoma cells is described. METHODS: The effect of thrombospondin and TGF-beta 1 on the capacity of a line of breast carcinoma cells to activate plasminogen was measured as well as the physiologic consequences of these activities on cell adhesion and proliferation. Plasminogen activation was assessed by measuring the plasmin activity and plasminogen activator inhibitor-1 (PAI-1) levels in cell-conditioned media and the cell-associated urokinase-type plasminogen activator (uPA) levels. RESULTS: Treatment of MDA-MB-231 breast carcinoma cells with either thrombospondin or TGF-beta 1 caused increased secretion of PAI-1 with a concomitant decrease in plasmin activity, whereas cell-associated uPA expression was increased with respect to controls. Thrombospondin (40 micrograms/ml) or TGF-beta 1 (5 ng/ml) stimulated the cells to secrete 5.5- and 6.7-fold more PAI-1 than controls, respectively, and caused decreased plasmin activity in the cell culture medium. Conversely, either thrombospondin (40 micrograms/ml) or TGF-beta 1 (5 ng/ml) caused the cells to express 4.55- and 5.38-fold more uPA than controls, respectively. Thrombospondin and TGF-beta 1 induced a more flattened and spread appearance in the cells with no effect on proliferation. These effects could be reversed with antibodies to either thrombospondin or TGF-beta 1 and were not due to contamination of thrombospondin with active TGF-beta 1. CONCLUSIONS: Thrombospondin and TGF-beta 1 function similarly to increase cell-associated uPA and cell-secreted PAI-1. These data suggest that thrombospondin may not only function as an adhesive molecule, but through a mechanism involving the activation of TGF-beta 1, may modulate cell surface protease expression. In addition, these observations suggest that thrombospondin and TGF-beta 1 could promote metastasis by increasing uPA-mediated cell invasion, whereas through the action of PAI-1, also protect blood-born tumor emboli from destruction by host fibrinolytic enzymes.

Breast Neoplasms↗

PubMed1995

The effect of thrombospondin on oral squamous carcinoma cell invasion of collagen.

BACKGROUND: Thrombospondin (TSP), a cell matrix protein, and transforming growth factor beta (TGF-beta), a growth regulatory protein, play roles in tumor progression. The purpose of this study was to investigate the effects of TSP and TGF-beta on tumor cell invasion. MATERIALS AND METHODS: Tumor cell invasion assays were performed using a modified Boyden chamber apparatus with collagen-coated membranes. The KB oral carcinoma cell line was studied in serum-free media. Invasion was measured as the summation of the number of cells in five representative low-power fields (x 100) traversing the collagen barrier after a 3-hour incubation period. The effects of antibodies against TSP, TGF-beta and the cysteine-serine-valine-threonine-cysteine-glycine (CSVTCG)-specific TSP receptor were also evaluated. RESULTS: TSP caused a dose-dependent stimulation of tumor cell invasion. Antibodies against TSP, its CSVTCG-specific receptor, and TGF-beta inhibited TSP-promoted invasion by 50% to 71%. CONCLUSIONS: TSP and its CSVTCG-specific receptor promote KB cell invasion of collagen through the production and/or activation of TGF-beta.

Amino Acid Sequence↗

PubMed1994

Thrombospondin (TSP) and transforming growth factor beta 1 (TGF-beta) promote human A549 lung carcinoma cell plasminogen activator inhibitor type 1 (PAI-1) production and stimulate tumor cell attachment in vitro.

A growing body of evidence has recently implicated TSP and TGF-beta in the process of malignancy, such as tumor cell proliferation, tumor angiogenesis, and metastasis. The purpose of the present study was to evaluate potential mechanisms of TSP and TGF-beta in tumor cell attachment and invasion. Our results indicate that both TSP and TGF-beta promoted tumor cell attachment and spreading in the presence of plasminogen. The mechanism for these effects appeared to be due, in part, to the capacity of TSP and TGF-beta to induce tumor cell production of (PAI-1). PAI-1, which is a natural inhibitor of tumor-cell associated urokinase-type plasminogen activator (uPA) activity, inhibited activation of plasminogen to plasmin in the growth media, thereby preventing plasmin-induced detachment of cells. The TSP-promoted production of PAI-1 could be inhibited not only by anti-TSP antibodies but also by a neutralizing antibody against TGF-beta. These results suggest that TSP by a mechanism involving TGF-beta can promote cell adhesion through stimulation of tumor cell secretion of PAI-1. These data provide evidence that TSP not only has the capacity of functioning as a matrix protein to directly promote cell-substratum adhesion but that TSP can also stimulate cell adhesion and spreading by modulating cell surface protease expression through stimulation of tumor-associated production of PAI-1.

Adenocarcinoma↗

PubMed1994

Plasma thrombospondin levels in patients with gynecologic malignancies.

BACKGROUND: Thrombospondin is a high molecular weight glycoprotein, originally described as a secretion product of platelets, that functions as an adhesive protein in cell-cell and cell-substratum interactions. It promotes metastases in the murine model. Plasma thrombospondin has been shown to be elevated in patients with disseminated breast, lung, and gastrointestinal malignancies. METHODS: Blood samples were collected by venipuncture into cubes containing ethylenediamine tetraacetic acid as anticoagulant. They were placed on ice immediately and centrifuged under refrigerated conditions. Plasma was removed and frozen until thrombospondin was quantitated by a competitive enzyme-linked immunosorbent assay. Wilcoxon's two-sample rank-sum test was used to evaluate differences between the patient and control groups. RESULTS: The median plasma thrombospondin level was significantly higher in the patient group compared with the control group, and it was directly correlated with stage of disease. There was no correlation between platelet count and thrombospondin level. CONCLUSIONS: Tumor-synthesized thrombospondin could explain the elevated levels in the patent group and also the observation of the correlation between the thrombospondin level and tumor burden. Its function as an adhesive protein may allow it to act as the mediator of metastases. thrombospondin may promote or mediate the metastatic process through its function in cell adhesion.

Adult↗

PubMed1994

Computer-assisted image analysis of tumor sections for a new thrombospondin receptor.

BACKGROUND: A cell surface receptor (50 kd) has been recently identified in malignant cells that recognizes the tumor cell adhesive domain (ie, cysteine-serine-valine-threonine-cysteine-glycine [CSVTCG]) of thrombospondin (TSP). This CSVTCG-specific TSP receptor can be considered as a new tumor marker, and its concentration on the cell surface may correlate directly with the capacity of tumor cells to invade and metastasize. MATERIALS AND METHODS: Six patients with primary, stages III and IV squamous cell carcinomas of the head and neck were studied. Tumor sections were specifically stained for this receptor with immunohistochemical techniques. The stained specimens were then subjected to computer-assisted image analysis. The area of positive staining and the heterogeneity of the pattern of staining were compared to peritumoral angiogenesis and clinical outcome of the patients. RESULTS: The results indicate that those patients with a high and homogenous positive stain score (mean +/- standard error [SE] 78 +/- 5%) for the CSVTCG-specific TSP receptor had high microvessel density and died from metastatic disease within 12 months of initial treatment (correlation coefficients = 0.95 and 1, respectively). Patients with a low and heterogenous positive stain score for receptor (mean +/- SE 8 +/- 2%; P < 0.001) had low microvessel counts and remained disease-free for at least 2 years. There was no relationship between receptor density and histologic classification of the primary tumors. CONCLUSION: The CSVTCG-specific TSP receptor, quantified through image analysis of immunohistochemical stained tissue sections, is highly predictive of clinical outcome in patients with squamous cell carcinomas of the head and neck.

Adult↗

PubMed1994

Matrix-bound thrombospondin promotes angiogenesis in vitro.

Thrombospondin (TSP) is a multidomain adhesive protein postulated to play an important role in the biological activity of the extracellular matrix. To test this hypothesis, TSP-containing fibrin and collagen matrices were evaluated for their capacity to support angiogenesis and cell growth from explants of rat aorta. This serum-free model allowed us to study the angiogenic effect of TSP without the interference of attachment and growth factors present in serum. TSP promoted dose-dependent growth of microvessels and fibroblast-like cells. The number of microvessels in TSP-containing collagen and fibrin gels increased by 136 and 94%, respectively. The TSP effect was due in part to cell proliferation since a 97% increase in [3H]thymidine incorporation by the aortic culture was observed. The effect was TSP-specific because TSP preparations adsorbed with anti-TSP antibody showed no activity. TSP did not promote angiogenesis directly since no TSP-dependent growth of isolated endothelial cells could be demonstrated. Rather TSP directly stimulated the growth of aortic culture-derived myofibroblasts which in turn promoted microvessel formation when cocultured with the aortic explants. Angiogenesis was also stimulated by myofibroblast-conditioned medium. Partial characterization of the conditioned medium suggests that the angiogenic activity is due to heparin-binding protein(s) with molecular weight > 30 kD. These results indicate that matrix-bound TSP can indirectly promote microvessel formation through growth-promoting effects on myofibroblasts and that TSP may be an important stimulator of angiogenesis and wound healing in vivo.

Animals↗

PubMed1994

Localization of thrombospondin and its cysteine-serine-valine-threonine-cysteine-glycine-specific receptor in human breast carcinoma.

BACKGROUND: Thrombospondin (TSP), a cell-matrix adhesion protein, and cysteine-serine-valine-threonine-cysteine-glycine (CSVTCG), a major TSP cell adhesive domain, have recently been shown to play a role in tumor cell metastasis. In this study we immunohistochemically localized TSP and its newly discovered CSVTCG-specific receptor in normal, benign, and neoplastic breast tissues. EXPERIMENTAL DESIGN: Paraffin sections of normal, benign, and neoplastic breast tissue were examined immunohistochemically for the presence of TSP and its CSVTCG-specific receptor using the avidin-biotin complex immunoperoxidase staining procedure. RESULTS: Positive staining using polyclonal antibodies for TSP and its tumor cell adhesion receptor, isolated from a human adenocarcinoma of the lung, was observed in all primary breast ductal carcinomas examined (N = 11). In contrast, all benign lesions and normal breast tissue stained negative for TSP and its receptor with the exception of two fibrocystic breast samples with hyperplasia. One of the samples showed strong TSP staining of ductal apocrine cells, whereas the other showed apical receptor staining of hyperplastic ductal cells. The negatively staining normal and benign tissues consisted of 1 normal breast, 1 gynecomastia, 5 fibroadenomas, and 6 fibrocystic samples. Positive staining for TSP in ductal carcinoma was only localized in the dense stromal collagen adjacent to tumor, whereas the TSP receptor localized to the tumor cells. Consistent with these immunohistochemical staining results was the observation that protein extracts of breast carcinoma cells contained receptor with no detectable TSP as revealed by Western blotting. Capillary endothelium was focally positive for receptor in regions proximal to ductal epithelium in 8 of 11 neoplastic tissues and in 6 of 14 benign samples. CONCLUSIONS: Our results indicate that increasing expression of stromal TSP and the CSVTCG-specific TSP receptor in ductal epithelium correlates with neoplastic transformation. In addition, our results indicate that both malignant and benign breast tissue can stimulate surrounding capillaries to express the TSP receptor, whereas only carcinoma has the capacity to stimulate surrounding nonendothelial stromal cells, such as myofibroblasts, to secrete a TSP-rich matrix that may contribute to the desmoplastic stromal reaction characteristic of ductal carcinoma tumor. The TSP-rich matrix may then promote tumor cell attachment, migration, and angiogenesis, factors important in tumor growth. The receptor-rich capillary endothelium may promote the cell adhesive interactions important in tumor intravasation. Taken together the results of this study provide a rational basis for a role of TSP in tumor angiogenesis and metastasis.

Amino Acid Sequence↗

PubMed1993

Interaction of thrombospondin with platelet glycoproteins GPIa-IIa and GPIIb-IIIa.

The interaction of human thrombospondin (TSP) with GPIa-IIa and GPIIb-IIIa was studied. The binding for both proteins became time-independent after 60 min. A 7-fold excess concentration of unlabelled GPIa-IIa added either initially, or after time-dependent binding, resulted in a 50% inhibition of GPIa-IIa bound to TSP. GPIa-IIa and GPIIb-IIIa specifically bound TSP since: (a) the binding of GPIIb-IIIa to TSP was dependent on the presence of 1 mM MgCl2 and 1 mM CaCl2, whereas binding of GPIa-IIa was ion-independent. (b) The binding was saturable, with dissociation constants of 0.69 +/- 0.17 microM and 3.77 +/- 1.02 microM for GPIa-IIa and GPIIb-IIIa respectively. (c) GPIIb-IIIa and GPIa-IIa did not significantly bind to BSA. (d) GPIIb-IIIa bound fibrinogen ion-specifically, whereas little or no binding of GPIa-IIa was detectable. (e) Both GPIIb-IIIa and GPIa-IIa bound collagen in an ion-independent manner. (f) GPIIb-IIIa did not compete with GPIa-IIa for binding to TSP. (g) Binding of GPIa-IIa to TSP was inhibited with anti-(GPIa-IIa) (6F1), whereas mouse IgG and anti-(GPIIb-IIIa) (AP-2) had no effect. (h) The interaction of GPIa-IIa with TSP is 5.5-fold more favourable than that of GPIIb-IIIa suggesting that GPIa-IIa may be a preferred binding protein for TSP-mediated platelet adhesion.

Antibodies, Monoclonal↗