Endoglin structure and function: Determinants of endoglin phosphorylation by transforming growth factor-beta receptors.

Determination of the functional relationship between the transforming growth factor-beta (TGFbeta) receptor proteins endoglin and ALK1 is essential to the understanding of the human vascular disease, hereditary hemorrhagic telangiectasia. TGFbeta1 caused recruitment of ALK1 into a complex with endoglin in human umbilical vein endothelial cells (HUVECs). Therefore, we examined TGFbeta receptor-dependent phosphorylation of endoglin by the constitutively active forms of the TGFbeta type I receptors ALK1, ALK5, and the TGFbeta type II receptor, TbetaRII.