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Mol. Cell. Biol., Mar 1997, 1682-1691, Vol 17, No. 3
JJ Lebrun and WW Vale
Activins and inhibins belong to the transforming growth factor beta
(TGF-beta)-like superfamily and exert their effects on a broad range of
cellular targets by modulating cell differentiation and proliferation.
Members of this family interact with two structurally related classes of
receptors (type I and type II), both containing a serine/threonine kinase
domain. When expressed alone, the type II but not the type I activin
receptor can bind activin. However, the presence of a type I receptor is
required for signaling. For TGF-beta1, ligand binding to the type II
receptor results in the recruitment and transphosphorylation of the type I
receptor. Transient overexpression of the two types of activin receptor
results in ligand-independent receptor heteromerization and activation.
Nevertheless, activin addition to the transfected cells increased complex
formation between the two receptors, suggesting a mechanism of action
similar to that observed for the TGF-beta receptor. In the present study,
we generated a stable cell line, overexpressing the two types of activin
receptor upon induction, in the human erythroleukemia cell line K562. We
demonstrate here that activin specifically induces heteromer formation
between the type I and type II receptors in a time-dependent manner. Using
this stable line, we analyzed the effects of activin and inhibin on human
erythroid differentiation. Our results indicate that activin signal
transduction mediated through its type I and type II receptors results in
an increase in the hemoglobin content of the cells and limits their
proliferation. Finally, using cell lines that can be induced to overexpress
ActRII and ActRIB or ActRIB only, we show that the inhibin antagonistic
effects on activin-induced biological responses are mediated through a
competition for the type II activin receptor but also require the presence
of an inhibin-specific binding component.
Copyright © 1997, American Society for Microbiology
Activin and inhibin have antagonistic effects on ligand-dependent heteromerization of the type I and type II activin receptors and human erythroid differentiation
The Clayton Foundation Laboratories for Peptide Biology, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.
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