Thrombospondin-1 suppresses spontaneous tumor growth and inhibits activation of matrix metalloproteinase-9 and mobilization of vascular endothelial growth factor

Abstract

Growth of tumors and metastasis are processes known to require neovascularization. To ascertain the participation of the endogenous angiogenic inhibitor thrombospondin-1 (TSP1) in tumor progression, we generated mammary tumor-prone mice that either lack, or specifically overexpress, TSP1 in the mammary gland. Tumor burden and vasculature were significantly increased in TSP1-deficient animals, and capillaries within the tumor appeared distended and sinusoidal. In contrast, TSP1 overexpressors showed delayed tumor growth or lacked frank tumor development (20% of animals); tumor capillaries showed reduced diameter and were less frequent. Interestingly, absence of TSP1 resulted in increased association of vascular endothelial growth factor (VEGF) with its receptor VEGFR2 and higher levels of active matrix metalloproteinase-9 (MMP9), a molecule previously shown to facilitate both angiogenesis and tumor invasion. In vitro, enzymatic activation of proMMP9 was suppressed by TSP1. Together these results argue for a protective role of endogenous inhibitors of angiogenesis in tumor growth and implicate TSP1 in the in vivo regulation of metalloproteinase-9 activation and VEGF signaling.C ancer is a multistep process that includes deregulation of cell cycle, transformation, invasion of stroma, and metastasis (1). In addition, successful establishment of solid tumors depends on neovascularization (2, 3). More recently, the contribution of angiogenesis has been further supported by the demonstration that angiogenic inhibitors suppress tumor growth. Our present understanding of the mechanism of action of most angiogenic inhibitors is limited, and further efforts are required to evaluate their effects in vivo.Thrombospondin-1 (TSP1) was the first protein to be recognized as a potential endogenous suppressor of capillary morphogenesis in vivo (4). Most likely, modulation of vasculature is not its only function; this was well illustrated by the fact that mice lacking TSP1 developed epithelial lung hyperplasia and pneumonia with multifocal inflammatory sites, but no significant vascular phenotype was observed (5). Inflammation and several pathological conditions have been shown to induce rapid and robust TSP1 expression (6, 7). Its role in these situations remains elusive; however, it has been shown that wound healing is aberrant in TSP1-null mice (8). With respect to antiangiogenic capabilities, TSP1 inhibits endothelial cell proliferation (9) and migration (10) and can induce endothelial apoptosis (11,12). In addition, xenograft implants of tumor cells transfected with TSP1 developed smaller tumors than the parental cell lines in a variety of assays (13-16), and fusion proteins and peptides from specific domains of TSP1 have been shown to inhibit proliferation of melanoma cells and reduce tumor growth in immunosuppressed animals (17). In clinical studies, expression of TSP1 has been inversely correlated with malignant progression of breast cancer, melanoma, and lung carcinomas (18,19). A hypothesis consistent with these data is t...

The effect of thrombospondin-1 on breast cancer metastasis

“…Therefore, even though the TSP-1-null/Pyt tumors had fewer blood vessels, these blood vessels were much larger compared to the wild-type Pyt tumors. Our findings at the 90 day time-point and results that we have published previously with this model [42] are in agreement with those of Iruela-Arispe's group who found that the vessel density did not change between the TSP-1-null/c-neu tumors and the c-neu wild-type tumors; however, the vessels were significantly larger in the TSP-1-null/c-neu mice [10].…”

“…In summary, the TSP-1-null tumors were in general more advanced in malignancy than the wild type tumors. These results are similar to those obtained with the c-neu mouse, another murine transgenic model of breast cancer [10]. At 168 days, tumors from the TSP-1-null/c-neu mice were more than twice as big as the wildtype/c-neu tumors.…”

“…By contrast, TSP-1 is highly expressed by stromal fibroblasts, macrophages and endothelial cells in breast cancer [7]. In the tumor microenvironment, TSP-1 interacts with a wide range of other proteins to affect (1) the level of active transforming growth factor β (TGFβ) [8,9], (2) the level of vascular endothelial cell growth factor (VEGF) [10,11], (3) the composition of the extracellular matrix and the activity of extracellular proteases [10,12], and (4) the survival and migration of endothelial cells [13][14][15]. In addition, TSP-1 may inhibit tumor angiogenesis by down-regulating circulating endothelial cell progenitors [16,17].…”

HER2 signaling modulates the equilibrium between pro- and antiangiogenic factors via distinct pathways: implications for HER2-targeted antibody therapy

“…TSP-1 also inhibits the activity of matrix metalloproteinase-9 (MMP-9) (Ribatti et al, 1998;Rodriguez-Manzaneque et al, 2001). TSP-1 inhibits angiogenesis by binding to the CD36 receptor protein, which is present on the endothelial cell surface (Dawson et al, 1997).…”

In vivo upregulation of CD95 and CD95L causes synergistic inhibition of angiogenesis by TSP1 peptide and metronomic doxorubicin treatment

“…Thrombospondin-1 (TSP1) is an angiogenesis inhibitor, 3 a multidomain protein that binds a variety of receptors, including integrins, CD36, integrin-associated protein, heparan sulfate proteoglycans and more. 4 TSP1 blocks angiogenesis via CD36, a receptor constitutively expressed in a subset of endothelial cells.…”