CD105 antagonizes the inhibitory signaling of transforming growth factor β1 on human vascular endothelial cells

CD105 (endoglin), a receptor for transforming growth factor beta (TGF beta), is highly expressed in tissue-cultured, activated endothelial cells in vitro and in tissues undergoing angiogenesis in vivo. The absence of CD105 in knockout mice leads to their death from defective vascular development, but the role of CD105 in the modulation of angiogenesis has not been elucidated. TGF beta 1 is a well-recognized regulator of angiogenesis. Using an antisense approach, we have shown that inhibition of CD105 protein translation in cultured human endothelial cells enhances the ability of TGF beta 1 to suppress growth and migration in these cells. The ability of endothelial cells to form capillary tubes was evaluated by the use of a 3-dimensional collagen matrix system where TGF beta 1 not only reduced the length of capillary-like structures, but also caused massive mortality in CD105-deficient cells compared to control cultures. These results provide direct evidence that CD105 antagonizes the inhibitory effects of TGF beta 1 on human vascular endothelial cells and that normal cellular levels of CD105 are required for the formation of new blood vessels.