Distinct functional domains of TGF-beta bind receptors on endothelial cells

Transforming growth factor-beta (TGF-beta) is a multi-functional regulator of cell growth and differentiation. Three distinct isoforms of TGF-beta exi st having similar, but not identical actions. TGF-beta 1, but not TGF-beta 2, binds to T beta RII and also to endoglin, a cell surface protein abundan t on endothelial cells, In contrast, the affinity constant of TGF-beta 2 fo r alpha(2)-macro-globulin is 10-fold greater than that of TGF-beta 1. TGF-b eta 2 also binds better than TGF-beta 1 to a glycosyl phosphatidylinositol (GPI)-linked binding protein expressed on vascular endothelial cells, Using chimeric TGF-beta molecules, in which selected regions of TGF-beta 1 have been exchanged for the corresponding region of TGF-beta 2, we demonstrate h ere that amino acids 92-95 or 94-98 of TGF-beta determine isoform specific binding to endoglin, In contrast, exchange of only amino acids 95 and 98 di d not alter TGF-beta specificity. Isoform specific binding to a GPI-linked protein on EJG endothelial cells was modulated by a region containing amino acids 40-68, although exchange of only amino acids 40-47 did not confer is oform specific binding. Significantly, the 92-98 region also modulates bind ing of TGF-beta to the type II receptor whereas isoform specific binding to alpha(2)-macroglobulin requires concerted exchange of amino acids 45 and 4 7, Taken together, these results show that at least three different functio nal domains are important modulators of TGF-beta interaction with binding p roteins and receptors.