Regulation of transforming growth factor β- and activin-induced transcription by mammalian Mad proteins

Regulation of transforming growth factor β- and activin-induced transcription by mammalian Mad proteins

Clayton Foundation Laboratories for Peptide Biology, The Salk Institute, La Jolla, CA 92037

Abstract

Members of the transforming growth factor β (TGF-β) superfamily are involved in diverse physiological activities including development, tissue repair, hormone regulation, bone formation, cell growth, and differentiation. At the cellular level, these functions are initiated by the interaction of ligands with specific transmembrane receptors with intrinsic serine/threonine kinase activity. The signaling pathway that links receptor activation to the transcriptional regulation of the target genes is largely unknown. Recent work in Drosophila and Xenopus signaling suggested that Mad (Mothers against dpp) functions downstream of the receptors of the TGF-β family. Mammalian Mad1 has been reported to respond to bone morphogenetic protein (BMP), but not to TGF-β or activin. We report here the cloning and functional studies of a novel mammalian Mad molecule, Mad3, as well as a rat Mad1 homologue. Overexpression of Mad3 in a variety of cells stimulated basal transcriptional activity of the TGF-β/activin-responsive reporter construct, p3TP-Lux. Furthermore, expression of Mad3 could potentiate the TGF-β- and activin-induced transcriptional stimulation of p3TP-Lux. By contrast, overexpression of Mad1 inhibited the basal as well as the TGF-β/activin induced p3TP-Lux activity. These findings, therefore, support the hypothesis that Mad3 may serve as a mediator linking TGF-β/activin receptors to transcriptional regulation.

Footnotes

↵ * To whom reprint requests should be addressed at: Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037.
Wylie Vale
Abbreviations: TGF-β, transforming growth factor β; BMP, bone morphogenetic protein; dpp, decapentaplegic; Mad, Mothers against dpp; TRE, TPA responsive element; PAI, plasminogen activator inhibitor; IPTG, isopropyl β-d-thiogalactoside; RT–PCR, reverse transcription–PCR; β-gal, β-galactosidase; FBS, fetal bovine serum.

Data deposition: The sequences reported in this paper have been deposited in the GenBank data base [accession nos. U66478U66478 (Mad1) and U66479U66479 (Mad3)].