title: An activin-A/C chimera exhibits activin and myostatin antagonistic properties.
abstract: Activins are involved in many physiological and pathological processes and, like other members of the transforming growth factor-beta superfamily, signal via type II and I receptor serine kinases. Ligand residues involved in type II receptor binding are located in the two anti-parallel beta strands of the TGF-beta proteins, also known as the fingers. Activin-A mutants able to bind ActRII but unable to bind the activin type I receptor ALK4 define ligand residues involved in ALK4 binding and could potentially act as antagonists. Therefore, a series of FLAG-tagged activin-A/C chimeras were constructed, in each of which eight residues in the wrist loop and helix region (A/C 46-53, 54-61, 62-69, and 70-78) were replaced. Additionally, a chimera was generated in which the entire wrist region (A/C 46-78) was changed from activin-A to activin-C. The chimeras were assessed for ActRII binding, activin bioactivity, as well as antagonistic properties. All five chimeras retained high affinity for mouse ActRII. Of these, only A/C 46-78 was devoid of significant activin bioactivity in an A3 Lux reporter assay in 293T cells at concentrations up to 40 nM. A/C 46-53, 54-61, 62-69, and 70-78 showed activity comparable with wild type activin-A. When tested for the ability to antagonize ligands that signal via activin type II receptors, such as activin-A and myostatin, only the A/C 46-78 chimera showed antagonism (IC(50), 1-10 nM). Additionally, A/C 46-78 decreased follicle-stimulating hormone release from the LbetaT2 cell line and rat anterior pituitary cells in primary culture in a concentration-dependent manner. These data indicate that activin residues in the wrist are involved in ALK4-mediated signaling. The activin antagonist A/C 46-78 may be useful for the study and modulation of activin-dependent processes.
authors.affiliation: Clayton Foundation Laboratories for Peptide Biology, The Salk Institute, La Jolla, California 92037, USA.
authors.forename: Uwe
authors.initials: U
authors.lastname: Muenster
authors.forename: Craig A
authors.initials: CA
authors.lastname: Harrison
authors.forename: Cynthia
authors.initials: C
authors.lastname: Donaldson
authors.forename: Wylie
authors.initials: W
authors.lastname: Vale
authors.forename: Wolfgang H
authors.initials: WH
authors.lastname: Fischer
mesh_terms: D030201:Activin Receptors, Type I / Q000378:metabolism*; D030301:Activin Receptors, Type II / Q000378:metabolism; D028341:Activins / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000737:chemistry; D002478:Cells, Cultured; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D038681:Follistatin / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008024:Ligands; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D055435:Myostatin; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D016212:Transforming Growth Factor beta / Q000737:chemistry / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: C525718:BMP2 protein, human; C525719:Bmp2 protein, mouse; C525720:Bmp2 protein, rat; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D038681:Follistatin; D008024:Ligands; C525911:MSTN protein, human; C525912:Mstn protein, mouse; C525913:Mstn protein, rat; D055435:Myostatin; D011993:Recombinant Fusion Proteins; D016212:Transforming Growth Factor beta; D028341:Activins; D005640:Follicle Stimulating Hormone; C498932:ACVR1B protein, human; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; C425585:activin receptor type II-A; D001616:beta-Galactosidase