ENDOGLIN FORMS A HETEROMERIC COMPLEX WITH THE SIGNALING RECEPTORS FORTRANSFORMING GROWTH-FACTOR-BETA

Human endoglin is a dimeric protein that binds transforming growth fac tor-beta (TGF-beta). A porcine cDNA clone for endoglin was obtained fr om a porcine uterus cDNA library. The deduced sequence of the primary translated product of endoglin consists of 643 amino acids with a high sequence identity (96%) to human endoglin in the transmembrane and in tracellular domains, but with a lower sequence similarity (66%) in the extracellular domain. In contrast to human endoglin, porcine endoglin has no Arg-Gly-Asp tripeptide in its sequence. Antibodies, raised aga inst a peptide corresponding to the intracellular domain of porcine en doglin, immunoprecipitated an 84-kDa protein under reducing condition and a 130-kDa protein under nonreducing condition in porcine aortic en dothelial cells. Porcine endoglin bound TGF-beta1 and -beta3 efficient ly, but TGF-beta2 less efficiently. Endoglin was found to be coimmunop recipitated with TGF-beta receptors type I and/or II by the endoglin a ntibodies or by TGF-beta receptor II antibodies in the presence of lig and. Thus, endoglin and TGF-beta receptors I and/or II most likely for med a heteromeric receptor complex. Endoglin was phosphorylated on ser ine residue(s), which did not change after stimulation by TGF-beta1. T hese results revealed that endoglin is a phosphorylated protein which forms a heteromeric complex with signaling receptors for TGF-beta.