The type 1 repeats of thrombospondin 1 activate latent transforming growth factor-beta.
Thrombospondin (TSP) is complexed with transforming growth factor-beta (TGF-beta) in the alpha-granules of stimulated platelets. TSP stripped of associated TGF-beta activity (sTSP) activates latent TGF-beta secreted by bovine aortic endothelial cells (BAE) in culture. To better understand the interactions of TSP with TGF-beta, we investigated which region of sTSP interacts with TGF-beta. The chymotrypsin-resistant core of TSP, which contains the procollagen-like region and the properdin-like type 1 repeats, activated both latent TGF-beta secreted by BAE and a recombinant form of the small latent TGF-beta complex at levels similar to or better than sTSP. The core fragment bound 125I-TGF-beta in solution and shifted the elution profile of 125I-TGF-beta in gel permeation chromatography. Fusion constructs of the type 1, 2, and 3 repeats and the COOH terminus of TSP1 were tested for their ability to activate latent TGF-beta. Only the type 1 construct, containing the three properdin-like repeats of TSP found in the 50-kDa fragment, activated latent TGF-beta. In addition, a polyclonal antibody against the type 1 construct inhibits activation of latent TGF-beta by intact TSP, suggesting that this region is exposed in the intact molecule. These results show that the type 1 properdin-like repeats of TSP are responsible for activating recombinant and endothelial cell-derived latent TGF-beta and that this site is exposed in intact TSP.
Schultz-Cherry
S
S
Department of Pathology, University of Alabama at Birmingham 35294.
Lawler
J
J
Murphy-Ullrich
J E
JE
D000595:Amino Acid Sequence; D000818:Animals; D001011:Aorta / Q000166:cytology; D002417:Cattle; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D002850:Chromatography, Gel; D002918:Chymotrypsin / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D011347:Procollagen / Q000737:chemistry; D011414:Properdin / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism / Q000494:pharmacology; D012091:Repetitive Sequences, Nucleic Acid; D013329:Structure-Activity Relationship; D019699:Thrombospondins; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D015815:Cell Adhesion Molecules; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D011347:Procollagen; D011993:Recombinant Fusion Proteins; D019699:Thrombospondins; D016212:Transforming Growth Factor beta; D011414:Properdin; D002918:Chymotrypsin