Cloning and characterization of angiocidin, a tumor cell binding protein for thrombospondin-1.

Thrombospondin-1 (TSP-1) is a matrix protein that has been implicated in mechanisms of tumor progression. Our laboratory previously showed that the CSVTCG (cys-ser-val-thr-cys-gly) sequence of TSP-1 functioned as a tumor cell adhesion domain and CSVTCG peptides as well as an anti-peptide antibody possessed anti-metastatic activity in a murine model of lung metastasis. In a subsequent study, a putative TSP-1 binding protein from lung carcinoma was isolated by CSVTCG-peptide affinity chromatography. In this study, we present the full-length cDNA of this binding protein isolated from a prostate cancer cell (PC3-NI) cDNA library. The purified recombinant protein, termed angiocidin, is a potent inhibitor of tumor growth of Lewis Lung carcinoma in vivo and tumor invasion and angiogenesis in vitro. In addition, the recombinant protein inhibits tumor and endothelial cell proliferation and induces apoptosis. The activity of angiocidin both in vivo and in vitro is partially dependent on its TSP-1 binding activity, since an angiocidin deletion mutant missing a high affinity-binding site for TSP-1 failed to inhibit tumor growth in vivo and was less active in its anti-tumor and anti-angiogenic activities in vitro. These results suggest that the anti-tumor activity of TSP-1 reported in many studies may be mediated in part by binding proteins such as angiocidin. Such proteins may function as tumor-suppressor proteins, which limit the growth of tumors by inhibiting angiogenesis and cell matrix interaction.