The functional significance of angiocidin expression in breast carcinoma progression.

摘要

Thrombospondin 1 (TSP-1) is a high molecular weight extracellular matrix glycoprotein released from thrombin-stimulated platelets and synthesized by many cell types, including epithelial and tumor cells. This extracellular matrix molecule is involved in angiogenesis, but the exact role is controversial. Previous findings in our laboratory strongly support TSP-1's involvement in promoting tumor progression and angiogenesis. Each of the three polypeptide chains of TSP-1 is composed of domains consisting of homologous amino acid sequences. In 1993, we isolated a protein that bound the CSVTCG residues of the type I repeat domain of TSP-1. Antibody raised against the purified protein was used to screen a prostate tumor cell library. The protein, named angiocidin, was successfully cloned using the polyclonal antibody. In this thesis the role of angiocidin expression in breast carcinoma progression was investigated. MDA-MB-231 breast cancer cells were transfected with the full-length angiocidin cDNA in the sense or antisense orientation in order to either over-express or block its expression. Cell adhesion assays were performed to test the adhesive property of the transfected cells to TSP-1. Angiocidin transfectants adhered to TSP-1 more rapidly and about 25% increased adhesion was observed as compared to the control transfectants, while antisense expressing cells were about 60% less adhesive than the control transfectants. The ability of the cells to invade through a porous membrane towards the chemoattractant TSP-1 was also tested using the Boyden chamber invasion assay. The sense transfected cells showed 50% decreased invasion compared to controls and the antisense transfected cells showed a 50% increased invasion compared to controls. The in vivo function of angiocidin was then tested using athymic mice. Angiocidin over-expressing cells showed significant tumor growth suppression compared with the control cells. These studies suggested that angiocidin functions to inhibit the invasive behavior of breast epithelium and contributes to the regression of tumor growth. Long-term goals of this study will be to develop synthetic peptides that mimic the activity of angiocidin. These results may eventually be used as treatment of breast carcinomas.