| Currently approved therapies for breast cancer (BCa) are improving survival, but further therapeutic targets are needed to adequately tailor treatment to the heterogeneity of disease. To identify novel targets, we generated a BCa cDNA library enriched for BCa genes that encode membrane and secreted proteins. From this library, we identified SUSD2 (Sushi Domain Containing 2), which encodes a transmembrane protein with functional domains inherent to adhesion molecules. Previously the Egland laboratory described Susd2 characteristics using an in vivo syngeneic mouse model and cells lines that expressed the mouse homolog. Accelerated tumor growth and decreased survival of mice were observed with tumors expressing Susd2 compared to the vector control. Alterations in vessel appearance, metastasis and tumor infiltrating lymphocytes were also observed. Using quantitative PCR on cDNA derived from MDA-MB-231-SUSD2 and vector control cells lines to analyze expression of genes involved in angiogenesis and metastasis, SUSD2 was found to up-regulate the epithelial to mesenchymal transition (EMT) genes VIM, N-Cadherin, and Twist1 in BCa cell lines, indicating that SUSD2 promotes EMT in BCa. The pro-angiogenic genes, MCP-1, TGFbeta2 and PDGFRbeta, were up-regulated in SUSD2-expressing cell lines compared to control. Furthermore, human umbilical vein endothelial cells (HUVEC) exhibited greater branching and tubule formation when grown in conditioned media from SUSD2-expressing cells compared to vector control. MCP-1 encodes a secreted protein that recruits tumor-associated macrophages (TAMs) into the tumor microenvironment to increase angiogenesis. Susd2 tumors had two-fold more TAMs than vector control, suggesting that the up-regulation of MCP-1 by Susd2 recruits TAMs, which consequently promotes angiogenesis.;To study the function of SUSD2 without the confounding effects of the immune system, MDA-MB-231-SUSD2 and vector cell lines were injected into immune deficient mice and angiogenesis was characterized. Previous work in the Egland laboratory demonstrated that SUSD2 interacts with Galectin-1 (Gal-1), a secreted protein synthesized by carcinoma cells known to promote tumor immune evasion, angiogenesis and metastasis. Utilizing Anginex, an anti-angiogenic peptide targeted to Gal-1, we determined that the effects of SUSD2 on angiogenesis were dependent on Gal-1. Because of its location on the cell surface, expression in BCa and involvement in tumorigenesis, SUSD2 is an attractive novel therapeutic target. |
