title: Truncated activin type II receptors inhibit bioactivity by the formation of heteromeric complexes with activin type I. receptors.
abstract: Truncated activin type II receptors have been reported to inhibit activin receptor signaling in Xenopus embryos, although the mechanism of action for this effect has not been fully understood. In the present study we demonstrate that in P19 embryonal carcinoma cells both the induction of the activin responsive 3TP-lux reporter construct and the inhibition of retinoic acid-induced neuronal differentiation by activin are blocked by expression of a truncated activin receptor. To reveal the mechanism of action of truncated activin receptors, the interaction between different activin receptors has been investigated upon coexpression in COS cells followed by cross-linking of 125I-activin A and subsequent immunoprecipitation. Complexes between a truncated activin type IIA receptor and activin type IA and type IB receptors can be formed, as demonstrated by coimmunoprecipitation of these type I receptors with the truncated activin type IIA receptor. Other type I receptors known as ALK-1 and ALK-6 also coimmunoprecipitate with the truncated type IIA receptor, whereas ALK-3 and ALK-5 do not. Furthermore, the activin type IIB2 receptor does not coimmunoprecipitate with the truncated type IIA receptor, but decreases activin binding to the truncated type IIA receptor. In double immunoprecipitation experiments with cell lysates from COS cells, in which full-length activin type IIA and type IIB2 receptors were cotransfected, no interaction between these receptors was found. In contrast, homomeric complexes of full-length activin type IIA receptors were detected. These results implicate that truncated activin receptors can interfere with activin signaling by interacting with activin type I receptors. Additionally, truncated activin type IIB2 receptors might also interfere with type IIA receptor signaling by decreasing activin binding to the type IIA receptor and therefore might be more potent in inhibiting activin signal transduction. Furthermore, our data indicate that truncated type IIA receptors can interact with other type I receptors and as such might inhibit signal transduction by type I receptors other than activin type IA and type IB receptors.
authors.affiliation: Hubrecht Laboratory, Netherlands Institute for Development Biology, Utrecht.
authors.forename: J P
authors.initials: JP
authors.lastname: De Winter
authors.forename: C J
authors.initials: CJ
authors.lastname: De Vries
authors.forename: T A
authors.initials: TA
authors.lastname: Van Achterberg
authors.forename: R F
authors.initials: RF
authors.lastname: Ameerun
authors.forename: A
authors.initials: A
authors.lastname: Feijen
authors.forename: H
authors.initials: H
authors.lastname: Sugino
authors.forename: P
authors.initials: P
authors.lastname: De Waele
authors.forename: D
authors.initials: D
authors.lastname: Huylebroeck
authors.forename: K
authors.initials: K
authors.lastname: Verschueren
authors.forename: A J
authors.initials: AJ
authors.lastname: Van Den Eijden-Van Raaij
mesh_terms: D029404:Activin Receptors; D028341:Activins; D000818:Animals; D002417:Cattle; D054278:Embryonal Carcinoma Stem Cells; D006131:Growth Inhibitors / Q000494:pharmacology; D006133:Growth Substances / Q000378:metabolism / Q000494:pharmacology*; D007265:Inhibins / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000494:pharmacology; D051379:Mice; D015394:Molecular Structure; D016296:Mutagenesis / Q000502:physiology; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017978:Receptors, Growth Factor / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D014162:Transfection
chemical_list: D006131:Growth Inhibitors; D006133:Growth Substances; D017978:Receptors, Growth Factor; D028341:Activins; D007265:Inhibins; D017346:Protein Serine-Threonine Kinases; D029404:Activin Receptors