Molecular interactions that confer latency to transforming growth factor-beta.
A major point of regulation of transforming growth factor-beta (TGF-beta) function is through control of activation of the latent TGF-beta complex, which consists of the latency associated peptide (LAP) secreted in non-covalent association with mature TGF-beta. Activation involves proteolysis, dissociation, or altered binding of LAP. However, the mechanism by which LAP confers latency to TGF-beta is poorly understood. Previously, we identified a conserved sequence near the N terminus of LAP as a site of thrombospondin-1 (TSP1) binding to the latent complex. Now we show that expression of the TGF-beta1-latent complex deleted in the TSP1 binding site ((54)LSKL) of LAP (DeltaLSKL LAP) results in secretion of LAP, but not of mature TGF-beta. DeltaLSKL LAP also fails to bind soluble or immobilized TGF-beta1. Consistent with an inability to bind the mature domain, DeltaLSKL LAP is unable to confer latency to TGF-beta, suggesting that the LSKL sequence is important, not only for TSP1 binding and activation, but also for binding to the mature domain. We identified the sequence (94)RKPK in the receptor-binding region of mature TGF-beta1 as the binding site for LAP. Peptides of the RKPK sequence bind LAP and inhibit LAP/TGF-beta association. RKPK peptides also activate latent TGF-beta, presumably by disrupting LAP-mature TGF-beta interactions. These studies provide a molecular basis for both latency and activation by TSP1 through the LSKL sequence of LAP binding to the RKPK sequence of mature TGF-beta.
Young
Geoffrey D
GD
Medical Scientist Training Program, Cell Adhesion and Matrix Research Center, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
Murphy-Ullrich
Joanne E
JE
D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D017077:Culture Media, Conditioned; D004797:Enzyme-Linked Immunosorbent Assay; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000378:metabolism; D011233:Precipitin Tests; D011498:Protein Precursors / Q000378:metabolism; D019700:Thrombospondin 1 / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000502:physiology*; D053773:Transforming Growth Factor beta1
D017077:Culture Media, Conditioned; D010446:Peptide Fragments; D011498:Protein Precursors; D019700:Thrombospondin 1; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1