title: Cripto forms a complex with activin and type II activin receptors and can block activin signaling.
abstract: Activin, nodal, Vg1, and growth and differentiation factor 1 are members of the transforming growth factor beta superfamily and signal via the activin type II (ActRII/IIB) and type I (ALK4) serine/threonine kinase receptors. Unlike activins, however, signaling by nodal, Vg1, and growth and differentiation factor 1 requires a coreceptor from the epidermal growth factor-Cripto-FRL1-Cryptic protein family such as Cripto. Cripto has important roles during development and oncogenesis and binds nodal or related ligands and ALK4 to facilitate assembly of type I and type II receptor signaling complexes. Because Cripto mediates signaling via activin receptors and binds directly to ALK4, we tested whether transfection with Cripto would affect the ability of activin to signal and/or interact with its receptors. Here we show that Cripto can form a complex with activin and ActRII/IIB. We were unable to detect activin binding to Cripto in the absence of ActRII/IIB, indicating that unlike nodal, activin requires type II receptors to bind Cripto. If cotransfected with ActRII/IIB and ALK4, Cripto inhibited crosslinking of activin to ALK4 and the association of ALK4 with ActRII/IIB. In addition, Cripto blocked activin signaling when transfected into either HepG2 cells or 293T cells. We have also shown that under conditions in which Cripto facilitates nodal signaling, it antagonizes activin. Inhibition of activin signaling provides an additional example of a Cripto effect on the regulation of signaling by transforming growth factor-beta superfamily members. Because activin is a potent inhibitor of cell growth in multiple cell types, these results provide a mechanism that may partially explain the oncogenic action of Cripto.
authors.affiliation: Clayton Foundation Laboratories for Peptide Biology, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Gray
authors.forename: Craig A
authors.initials: CA
authors.lastname: Harrison
authors.forename: Wylie
authors.initials: W
authors.lastname: Vale
mesh_terms: D030201:Activin Receptors, Type I / Q000378:metabolism; D030301:Activin Receptors, Type II / Q000378:metabolism*; D028341:Activins / Q000378:metabolism*; D002460:Cell Line; D004815:Epidermal Growth Factor; D058851:GPI-Linked Proteins; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins / Q000378:metabolism*; D011485:Protein Binding; D011506:Proteins; D015398:Signal Transduction
chemical_list: D058851:GPI-Linked Proteins; D036341:Intercellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins; D011506:Proteins; C070636:TDGF1 protein, human; D028341:Activins; D004815:Epidermal Growth Factor; C425423:ACVR1 protein, human; C498932:ACVR1B protein, human; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II