title: Identification of distinct inhibin and transforming growth factor beta-binding sites on betaglycan: functional separation of betaglycan co-receptor actions.
abstract: Betaglycan is a co-receptor that mediates signaling by transforming growth factor beta (TGFbeta) superfamily members, including the distinct and often opposed actions of TGFbetas and inhibins. Loss of betaglycan expression, or abrogation of betaglycan function, is implicated in several human and animal diseases, although both betaglycan actions and the ligands involved in these disease states remain unclear. Here we identify a domain spanning amino acids 591-700 of the betaglycan extracellular domain as the only inhibin-binding region in betaglycan. This binding site is within the betaglycan ZP domain, but inhibin binding is not integral to the ZP motif of other proteins. We show that the inhibin and TGFbeta-binding residues of this domain overlap and identify individual amino acids essential for binding of each ligand. Mutation of Val614 to Tyr abolishes both inhibin and TGFbeta binding to this domain. Full-length betaglycan V614Y, and other mutations, retain TGFbeta binding activity via a distinct site, but are unable to bind inhibin-A. These betaglycan mutants fail to mediate inhibin antagonism of activin signaling but can present TGFbeta to TbetaRII. Separating the co-receptor actions of betaglycan toward inhibin and TGFbeta will allow the clarification of the role of betaglycan in disease states such as renal cell carcinoma and endometrial adenocarcinoma.
authors.affiliation: Clayton Foundation Laboratories for Peptide Biology, The Salk Institute for Biological Studies, La Jolla, California 92037.
authors.forename: Ezra
authors.initials: E
authors.lastname: Wiater
authors.affiliation: Clayton Foundation Laboratories for Peptide Biology, The Salk Institute for Biological Studies, La Jolla, California 92037; Prince Henry's Institute of Medical Research, 246 Clayton Road, Clayton, Victoria 3168, Australia.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Harrison
authors.affiliation: Clayton Foundation Laboratories for Peptide Biology, The Salk Institute for Biological Studies, La Jolla, California 92037.
authors.forename: Kathy A
authors.initials: KA
authors.lastname: Lewis
authors.affiliation: Clayton Foundation Laboratories for Peptide Biology, The Salk Institute for Biological Studies, La Jolla, California 92037.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Gray
authors.affiliation: Clayton Foundation Laboratories for Peptide Biology, The Salk Institute for Biological Studies, La Jolla, California 92037. Electronic address: vale@salk.edu.
authors.forename: Wylie W
authors.initials: WW
authors.lastname: Vale
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D045744:Cell Line, Tumor; D006801:Humans; D007265:Inhibins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011509:Proteoglycans / Q000737:chemistry*; D018125:Receptors, Transforming Growth Factor beta / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D016212:Transforming Growth Factor beta / Q000737:chemistry* / Q000235:genetics; D014633:Valine / Q000737:chemistry
chemical_list: D011509:Proteoglycans; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta; C071736:betaglycan; D007265:Inhibins; D014633:Valine