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Regulation of transforming growth factor beta- and activin-induced transcription by mammalian Mad proteins
1Clayton Foundation Laboratories for Peptide Biology, Salk Institute, La Jolla, CA 92037, USA.
Abstract:
Members of the transforming growth factor beta (TGF-beta) 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-beta family. Mammalian Mad1 has been reported to respond to bone morphogenetic protein (BMP), but not to TGF-beta 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-beta/activin-responsive reporter construct, p3TP-Lux. Furthermore, expression of Mad3 could potentiate the TGF-beta- and activin-induced transcriptional stimulation of p3TP-Lux. By contrast, overexpression of Mad1 inhibited the basal as well as the TGF-beta/activin induced p3TP-Lux activity. These findings, therefore, support the hypothesis that Mad3 may serve as a mediator linking TGF-beta/activin receptors to transcriptional regulation.
Insights
Researchers identified Mad3, a novel molecule that acts as a mediator in the transforming growth factor beta (TGF-beta) signaling pathway. Mad3 enhances TGF-beta/activin-induced gene transcription, unlike Mad1 which inhibits it.
Area of Science:
- Molecular Biology
- Cell Signaling
- Genetics
Background:
- Transforming growth factor beta (TGF-beta) superfamily ligands regulate diverse physiological processes via transmembrane receptors with serine/threonine kinase activity.
- The downstream signaling pathway connecting receptor activation to target gene transcriptional regulation remains largely uncharacterized.
- Previous studies in model organisms suggested Mad (Mothers against dpp) proteins function downstream of TGF-beta family receptors.
Purpose of the Study:
- To clone and functionally characterize a novel mammalian Mad molecule, Mad3.
- To investigate the role of Mad3 in the TGF-beta/activin signaling pathway.
- To compare the function of Mad3 with a rat Mad1 homologue.
Main Methods:
- Cloning of a novel mammalian Mad3 and a rat Mad1 homologue.
- Overexpression of Mad3 and Mad1 in various cell types.
- Assay of transcriptional activity using a TGF-beta/activin-responsive reporter construct (p3TP-Lux).
Main Results:
- Overexpression of Mad3 stimulated basal and potentiated TGF-beta/activin-induced transcriptional activity of p3TP-Lux.
- Overexpression of Mad1 inhibited both basal and TGF-beta/activin-induced p3TP-Lux activity.
- Mad3 demonstrated a distinct functional role compared to Mad1 in TGF-beta/activin signaling.
Conclusions:
- Mad3 functions as a mediator in the TGF-beta/activin signaling pathway.
- Mad3 links TGF-beta/activin receptors to the transcriptional regulation of target genes.
- Mad3 plays a crucial role in mediating cellular responses to TGF-beta and activin signaling.