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Am J Pathol 1999 Aug;155(2):441-52
Overexpression of thrombospondin-1 decreases angiogenesis and inhibits
the growth of human cutaneous squamous cell carcinomas.
Streit M, Velasco P, Brown LF, Skobe M, Richard L, Riccardi L, Lawler J, Detmar M
Cutaneous Biology Research Center, Department of Dermatology, Massachusetts General Hospital, Boston, USA.
The function of the endogenous angiogenesis inhibitor thrombospondin-1 (TSP-1) in epithelial tumor development has remained
controversial. We studied the in vitro growth characteristics and the in vivo tumor xenograft growth of the human squamous cell
carcinoma cell lines A431 and SCC-13, stably transfected to overexpress human TSP-1. Overexpression of TSP-1 inhibited
tumor growth of A431 xenotransplants, and completely abolished tumor formation by SCC-13 cells. TSP-1 overexpressing
A431 tumors were characterized by extensive areas of necrosis and by decreased tumor vessel number and size. The effects of
TSP-1 on tumor cell growth were indirect since tumor cell proliferation rates in vivo and in vitro, anchorage-dependent and
-independent growth in vitro, and susceptibility to induction of apoptosis by serum withdrawal were unchanged in TSP-1
overexpressing tumor cells. However, TSP-1 overexpression up-regulated the TSP-1 receptor CD36, leading to enhanced
adhesion of A431 cells to TSP-1. These findings establish TSP-1 as a potent inhibitor of angiogenesis and tumor growth in
carcinomas of the skin.
Eur J Cancer 1999 Mar;35(3):502-6
Thrombospondin-2 (TSP2) expression is inversely correlated with
vascularity in glioma.
Kazuno M, Tokunaga T, Oshika Y, Tanaka Y, Tsugane R, Kijima H, Yamazaki H, Ueyama Y, Nakamura M
Department of Neurosurgery, Tokai University, School of Medicine, Kanagawa, Japan.
Thrombospondins (TSPs) are angiostatic factors in various cancers. However, the significance of TSPs has not been well
characterised in glioma. We examined TSP1, TSP2 and vascular endothelial growth factor (VEGF) gene expression by reverse
transcription-polymerase chain reaction (RT-PCR) in 37 gliomas. Thirty of the 37 glioma specimens showed VEGF gene
expression. Eighteen of the 37 gliomas expressed the TSP1 gene. Seven gliomas lacked TSP2 gene expression, while the other
30 expressed TSP2. The lack of TSP2 gene expression was significantly associated with higher histological grade (Fisher's test,
P = 0.0019) and increased vessel counts and density (Student's t-test, P < 0.0001), while there were no correlations between
TSP1 and VEGF gene expression and clinicopathological features. These results indicate that the lack of TSP2 gene expression
is a potent factor for enhancement of angiogenesis in glioma.
Biochemistry 1999 Aug 10;38(32):10398-405
Protein disulfide isomerase catalyzes the formation of disulfide-linked
complexes of vitronectin with thrombin-antithrombin.
Essex DW, Miller A, Swiatkowska M, Feinman RD
Department of Medicine, Division of Hematology/Oncology, Department of Biochemistry, State University of New York
Downstate Medical Center at Brooklyn 11203, USA. essex@hscbklyn.edu
In this study, purified preparations of platelet protein disulfide isomerase (PDI), vitronectin, alpha-thrombin, and antithrombin
(AT) were used to demonstrate that PDI catalyzes formation of vitronectin-thrombin-AT complexes. Complex formation
requires reduced glutathione (GSH) and can be prevented by N-ethymaleimide, and the formed complex is dissociated by
reducing agents such as mercaptoethanol. No vitronectin-thrombin complex formed in the absence of AT, indicating that the
thrombin-AT complex is an obligate intermediate in the reaction. Under optimal conditions, the majority of the thrombin-AT is
incorporated into the complex in 60 min. Thrombospondin-1, known to form disulfide-linked complexes with thrombin-AT
[Milev, Y., and Essex, D. W. (1999) Arch. Biochem. Biophys. 361, 120-126], competes with vitronectin for thrombin-AT in
the low-Ca(2+) environment that favors the active form of thrombospondin. The results presented here may also explain
previous studies showing that vitronectin-thrombin-AT complexes form better in plasma (which contains PDI) than with purified
proteins (where PDI was not used). We were able to purify a PDI from plasma that was immunologically identical to the
platelet enzyme. We used the scrambled RNase assay to show that added purified PDI can function in a plasma environment.
Complex formation in plasma was inhibited by inhibitors of PDI. PDI was released from the platelet surface in a soluble form at
high pH (around the physiologic range), suggesting a source of the plasma PDI. In summary, these studies indicate that PDI
functions to form disulfide-linked complexes of vitronectin with thrombin-AT. |
