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TGF-β signalling is mediated by two autonomously functioning TβRI:TβRII pairs
Tao Huang1, Laurent David, Valentín Mendoza
1Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229-3900, USA.
The EMBO Journal
|March 23, 2011
Summary
Transforming growth factor-beta (TGF-β) signaling involves two receptor heterodimers. This study shows these TGF-β receptor heterodimers function autonomously in binding and signaling, impacting cell growth and differentiation.
Area of Science:
- Cellular biology
- Molecular signaling
- Biochemistry
Background:
- Transforming growth factor-beta (TGF-β) ligands are crucial for cell growth and differentiation.
- TGF-β signaling relies on a heterotetrameric receptor complex comprising two TβRI:TβRII heterodimers.
- The autonomous function of these heterodimers in TGF-β signaling remains incompletely understood.
Purpose of the Study:
- To investigate whether the two TβRI:TβRII heterodimers in the TGF-β receptor complex bind and signal independently.
- To elucidate the stoichiometry and functional consequences of autonomous heterodimer binding.
Main Methods:
- Utilized a modified TGF-β3 dimer (TGF-β3 WD) with blocked receptor binding on one protomer.
- Assessed receptor binding affinities and stoichiometry using biochemical assays.
- Quantified signaling activity via three established TGF-β functional assays.
- Employed single-molecule fluorescence imaging with GFP-tagged receptors to observe receptor dimerization dynamics.
Main Results:
- TGF-β3 WD exhibited binding affinities for TβRII and TβRI comparable to native TGF-β3, but at half the stoichiometry.
- TGF-β3 WD retained one-quarter to one-half of the signaling activity of TGF-β3.
- Single-molecule imaging revealed increased TβRI and TβRII dimerization with TGF-β3, but not with TGF-β3 WD.
Conclusions:
- The findings provide evidence that the two TβRI:TβRII heterodimers function autonomously in TGF-β receptor assembly and signaling.
- This autonomous action highlights the divergence of TGF-βs from bone morphogenetic proteins, which utilize a RI:RII:RII heterotrimer.
- Understanding autonomous heterodimer function offers insights into TGF-β superfamily signaling mechanisms.
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