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Molecular interactions that confer latency to transforming growth factor-beta
Geoffrey D Young1, Joanne E Murphy-Ullrich
1Medical Scientist Training Program, Cell Adhesion and Matrix Research Center, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
The Journal of Biological Chemistry
|June 23, 2004
Summary
The latency associated peptide (LAP) binds mature transforming growth factor-beta (TGF-beta) via its RKPK sequence, conferring latency. Thrombospondin-1 (TSP1) binding to LAP
Area of Science:
- Molecular Biology
- Cell Signaling
- Protein Interactions
Background:
- Transforming growth factor-beta (TGF-beta) function is tightly regulated by the activation of its latent complex.
- The latent complex comprises mature TGF-beta non-covalently bound to the latency associated peptide (LAP).
- Mechanisms of LAP-mediated latency and activation by factors like thrombospondin-1 (TSP1) remain incompletely understood.
Purpose of the Study:
- To elucidate the molecular mechanism by which LAP confers latency to TGF-beta.
- To identify the specific binding interactions between LAP and mature TGF-beta.
- To understand the role of the LAP LSKL sequence in TGF-beta latency and TSP1-mediated activation.
Main Methods:
- Generated and expressed a TGF-beta1 latent complex with a deleted TSP1 binding site ((54)LSKL) in LAP (DeltaLSKL LAP).
- Assessed secretion of LAP and mature TGF-beta.
- Investigated binding of DeltaLSKL LAP to soluble and immobilized TGF-beta1.
- Identified the LAP binding site on mature TGF-beta1 using peptide-based assays.
- Evaluated the effect of RKPK peptides on LAP/TGF-beta association and latent TGF-beta activation.
Main Results:
- DeltaLSKL LAP was secreted but failed to bind mature TGF-beta1, indicating the LSKL sequence is crucial for this interaction.
- DeltaLSKL LAP could not confer latency to TGF-beta, highlighting the LSKL sequence's role in maintaining latency.
- The RKPK sequence within the receptor-binding region of mature TGF-beta1 was identified as the LAP binding site.
- RKPK peptides disrupted LAP/TGF-beta association and activated latent TGF-beta, suggesting a mechanism for TSP1-mediated activation.
Conclusions:
- The LSKL sequence in LAP directly binds the RKPK sequence in mature TGF-beta, establishing latency.
- This LAP-TGF-beta interaction is essential for TSP1 to bind and activate the latent complex.
- These findings provide a molecular framework for TGF-beta latency and activation.