Activin-A binds to a heterotrimeric receptor complex on the vascular endothelial cell surface. Evidence for a type 3 activin receptor.
The effect of transfection of the type 2 activin receptor, ACTR2, on binding of 125I-activin-A to the surface of bovine aortic endothelial cells (BAEC) was investigated. BAEC transfected either with full-length ACTR2 or with a truncated form of ACTR2 lacking the intracellular kinase domain (ACTR2T) displayed two classes of 125I-activin-A binding sites, one of high affinity (Kd = 250-254 pM) and one of low affinity (Kd = 6.5-16 nM). Affinity labeling of ACTR2-transfected BAEC with 125I-activin-A revealed labeled species of 55, 95, 100, and 160 kDa, all four of which were immunoprecipitated by an anti-ACTR2 monoclonal antibody. Only the 95- and 100-kDa species, however, were immunoprecipitated following denaturation of the affinity-labeled cell lysate with SDS. BAEC transfected with an epitope-tagged form of ACTR2T (ACTR2TMyc) displayed intense 55- and 70-kDa affinity-labeled forms of the truncated receptor, together with a 160-kDa species. As with the full-length receptor, the 160-kDa species associated non-covalently with ACTR2TMyc. These data indicate that, in vascular endothelial cells, ACTR2 forms a high affinity heterotrimeric receptor complex with activin-binding proteins characteristic of type 1 and type 3 activin receptors, and that formation of the complex does not require the kinase domain of ACTR2.
McCarthy
S A
SA
Imperial Cancer Research Fund Laboratories, University of Oxford, John Radcliffe Hospital, United Kingdom.
Bicknell
R
R
D029404:Activin Receptors; D028341:Activins; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002417:Cattle; D002478:Cells, Cultured; D017931:DNA Primers / Q000737:chemistry; D004730:Endothelium, Vascular / Q000378:metabolism*; D066298:In Vitro Techniques; D007265:Inhibins / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D017978:Receptors, Growth Factor / Q000145:classification / Q000378:metabolism*; D014162:Transfection
D017931:DNA Primers; D017978:Receptors, Growth Factor; D028341:Activins; D007265:Inhibins; D029404:Activin Receptors