Karen O. Yee

Thrombospondins in cancer

Abstract.The thrombospondins (TSPs) are a family of five proteins that are involved in the tissue remodeling that is associated with embryonic development, wound healing, synaptogenesis, and neoplasia. These proteins mediate the interaction of normal and neoplastic cells with the extracellular matrix and surrounding tissue. In the tumor microenvironment, TSP-1 has been shown to suppress tumor growth by inhibiting angiogenesis and by activating transforming growth factor β. TSP-1 inhibits angiogenesis through direct effects on endothelial cell migration and survival, and through effects on vascular endothelial cell growth factor bioavailability. In addition, TSP-1 may affect tumor cell function through interaction with cell surface receptors and regulation of extracellular proteases. Whereas the role of TSP-1 in the tumor microenvironment is the best characterized, the other TSPs may have similar functions. (Part of a Multi-author Review)

Thrombospondins: from structure to therapeutics

Abstract.The thrombospondins (TSPs) are a family of five proteins that are involved in the tissue remodeling that is associated with embryonic development, wound healing, synaptogenesis, and neoplasia. These proteins mediate the interaction of normal and neoplastic cells with the extracellular matrix and surrounding tissue. In the tumor microenvironment, TSP-1 has been shown to suppress tumor growth by inhibiting angiogenesis and by activating transforming growth factor β. TSP-1 inhibits angiogenesis through direct effects on endothelial cell migration and survival, and through effects on vascular endothelial cell growth factor bioavailability. In addition, TSP-1 may affect tumor cell function through interaction with cell surface receptors and regulation of extracellular proteases. Whereas the role of TSP-1 in the tumor microenvironment is the best characterized, the other TSPs may have similar functions. (Part of a Multi-author Review)

Expression of the Type-1 Repeats of Thrombospondin-1 Inhibits Tumor Growth Through Activation of Transforming Growth Factor-β

In the present study, the type-1 repeats of thrombospondin-1 (TSP-1) were transfected into A431 cells. Expression of all three type-1 repeats (3TSR) and expression of just the second type-1 repeat containing the transforming growth factor (TGF)-beta activating sequence KRFK (TSR2 + KRFK) significantly inhibited in vivo tumor angiogenesis and growth in nude mice. These tumors expressed increased levels of both active and total TGF-beta. A431 cells expressing the second type-1 repeat without the KRFK sequence (TSR2 - KRFK) produced tumors that were slightly larger than the 3TSR and TSR2 + KRFK tumors. These tumors expressed elevated levels of active TGF-beta but levels of total TGF-beta were not different from control tumors. Injection of the peptide, LSKL, which blocks TSP-1 activation of TGF-beta, reversed the growth inhibition observed with cells expressing TSR2 + KRFK to a level comparable to controls. Various residues in the WSHWSPW region and the VTCG sequence of both TSR2+/- KRFK were mutated. Although mutation of the VTCG sequence had no significant effect on tumor growth, mutation of the WSHWSPW sequence reduced inhibition of tumor growth. These findings suggest that the inhibition of tumor angiogenesis and growth by endogenous TSP-1 involves regulation of both active and total TGF-beta and the sequences KRFK and WSHWSPW in the second type-1 repeat.

Characterization of integrin β6 and thrombospondin-1 double-null mice

To identify overlapping and non‐overlapping functions for TSP‐1 and αvβ6, we crossed TSP‐1‐null and β6‐null mice and compared the phenotype of the double‐null mice with those of wild‐type and single‐null mice. The double‐null mice exhibited focal acute and organizing pneumonia that was more severe than the wild‐type and single‐null mice as well as a significantly higher incidence of inflammation in tissues other than the lung. The TSP‐1‐null and β6‐null mice exhibited a five to eight‐fold increase in granulocyte recruitment to the lung three days after exposure to lipopolysaacharide. They also had abnormalities that were infrequently observed in the wild‐type and single‐null mice, including heart degeneration (8.35% in wild‐type and 28.1% in double‐null mice), hyperplasia of the glandular epithelium of the stomach (2.8% in wild‐type and 21.1% in double‐null mice) and endometrial hyperplasia (0% in wild‐type and 38.5% in double‐null females). Furthermore, the β6‐null and double‐null mice displayed a significant elevation in benign and malignant cancers. Stomach papillomas, squamous cell carcinomas of the ear and stomach, and adenocarcinomas of the lungs, vagina/cervix and colon were observed with the highest frequency. These data demonstrate that TSP‐1 and αvβ6 are involved in regulation of the immune system and epithelial homeostasis. They also indicate that αvβ6 functions as a tumor suppressor gene and that activation of TGFβ by TSP‐1 and αvβ6 contributes to normal tissue architecture and function.

Halofuginone inhibits tumor growth in the polyoma middle T antigen mouse via a thrombospondin-1 independent mechanism

Halofuginone inhibits fibrosis by decreasing type I collagen synthesis and tumor growth through an anti-angiogenic mechanism. In vitro data suggested that halofuginone inhibited angiogenesis through upregulating thrombospondin-1(TSP-1) expression and by inhibiting cell proliferation. To determine whether thrombospondin-1 (TSP-1) is necessary for inhibition of tumor growth and angiogenesis by halofuginone, we tested the effect of halofuginone on mammary tumor growth in polyoma middle T antigen, TSP-1 null (TSP-1-/-PyT) transgenic mice. After 30 days of treatment, we found a significant decrease in tumor weight in these mice and the extent of tumor growth inhibition was comparable to that found in TSP-1 expressing PyT mice (TSP-1 +/+PyT). However, no significant difference in tumor weight was observed after 60 days of halofuginone treatment between control and treated mice in both genotypes. Interestingly, type I collagen level was lower in the halofuginone treated TSP-1+/+PyT tumors at 30 days, but this was not observed in the TSP-1-/-PyT mice. Level of type I collagen did not correlate with blood vessel number as a decrease in the number of vessels was observed in the halofuginone treated tumors from both the TSP-1+/+PyT and TSP-1-/-PyT mice as compared to control tumors. Because halofuginone has been shown to inhibit type I collagen synthesis by inhibiting the TGF-? signaling pathway, we measured Smad 2/3 phosphorylation levels and found that halofuginone inhibited Smad 2/3 phosphorylation in cells derived from TSP-1+/+PyT tumors. We also found that it inhibited Smad 2/3 phosphorylation in cells treated with the TGF-? activating sequence of TSP-1, TSR2+RFK. Our data demonstrate that halofuginone inhibits mammary tumor growth in a transgenic mouse model via a TSP-1 independent pathway, by decreasing tumor angiogenesis and by inhibiting TGF-? signaling.

Thrombospondins: from structure to therapeutics: Thrombospondins in cancer

Abstract.The thrombospondins (TSPs) are a family of five proteins that are involved in the tissue remodeling that is associated with embryonic development, wound healing, synaptogenesis, and neoplasia. These proteins mediate the interaction of normal and neoplastic cells with the extracellular matrix and surrounding tissue. In the tumor microenvironment, TSP-1 has been shown to suppress tumor growth by inhibiting angiogenesis and by activating transforming growth factor β. TSP-1 inhibits angiogenesis through direct effects on endothelial cell migration and survival, and through effects on vascular endothelial cell growth factor bioavailability. In addition, TSP-1 may affect tumor cell function through interaction with cell surface receptors and regulation of extracellular proteases. Whereas the role of TSP-1 in the tumor microenvironment is the best characterized, the other TSPs may have similar functions. (Part of a Multi-author Review)

Purification and Analysis of Thrombospondin‐1

Thromboapondin 1 (TSP‐1) is a trimeric matricellular protein that is expressed by many cells. It contains several different domains that allow it to participate in cell adhesion, cell migration, and cell signaling. Recently TSP‐1 has been shown to activate transforming growth factor β (TGF‐β) and to inhibit both angiogenesis and tumor growth. This unit contains protocols for the purification of TSP‐1 from platelet‐rich plasma and the purification of TSP‐1 proteolytic fragments.

Regulation of Angiogenesis and Tumor Growth by Thrombospondin-1

Thrombospondin-1 (TSP-1) is a matricellular protein that has been implicated in playing an important role in inhibiting cancer progression. Many studies have been carried out to characterize the mechanism of its action. While its ability to inhibit tumor angiogenesis through binding of CD36 via the thrombospondin type 1 repeats (TSRs) sequence have been well studied, the long-range effect of TSP-1’s ability to activate transforming growth factor β (TGF-β) is just starting to be characterized. One such effect is shifting the balance of the fibrinolytic system through TSP-1’s ability to inhibit matrix metalloproteinases and plasminogen activator inhibitor-1. A shift in either direction could promote tumor progression, including metastasis, or prevent it by reducing tumor angiogenesis. This delicate balance may be responsible for the conflicting data in the literature on whether TSP-1 is proor antitumorigenic, and the direction of the shift may also be cell-type specific. Lastly, the potential of developing a TSP-based therapy is being realized and clinical trials are now underway.