Identification of novel beta1 integrin binding sites in the type 1 and type 2 repeats of thrombospondin-1.
In addition to the three known beta(1) integrin recognition sites in the N-module of thrombospondin-1 (TSP1), we found that beta(1) integrins mediate cell adhesion to the type 1 and type 2 repeats. The type 1 repeats of TSP1 differ from typical integrin ligands in that recognition is pan-beta(1)-specific. Adhesion of cells that express one dominant beta(1) integrin on immobilized type 1 repeats is specifically inhibited by antagonists of that integrin, whereas adhesion of cells that express several beta(1) integrins is partially inhibited by each alpha-subunit-specific antagonist and completely inhibited by combining the antagonists. beta(1) integrins recognize both the second and third type 1 repeats, and each type 1 repeat shows pan-beta(1) specificity and divalent cation dependence for promoting cell adhesion. Adhesion to the type 2 repeats is less sensitive to alpha-subunit antagonists, but a beta(1) blocking antibody and two disintegrins inhibit adhesion to immobilized type 2 repeats. beta(1) integrin expression is necessary for cell adhesion to the type 1 or type 2 repeats, and beta(1) integrins bind in a divalent cation-dependent manner to a type 1 repeat affinity column. The widely used TSP1 function blocking antibody A4.1 binds to a site in the third type 2 repeat. A4.1 proximally inhibits beta(1) integrin-dependent adhesion to the type 2 repeats and indirectly inhibits integrin-dependent adhesion mediated by the TSP1 type 1 repeats. Although antibody A4.1 is also an antagonist of CD36 binding to TSP1, these data suggest that some biological activities of A4.1 result from antagonism of these novel beta(1) integrin binding sites.
Laboratory of Pathology, NCI, National Institutes of Health, Bethesda, Maryland 20892-1500, USA.
Maria J
MJ
Calzada
Douglas S
DS
Annis
Bixi
B
Zeng
Cezary
C
Marcinkiewicz
Bernhard
B
Banas
Jack
J
Lawler
Deane F
DF
Mosher
David D
DD
Roberts
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001665:Binding Sites; D002448:Cell Adhesion; D004730:Endothelium, Vascular / Q000166:cytology; D006801:Humans; D039201:Integrin alpha3beta1 / Q000378:metabolism; D039041:Integrin alpha4beta1 / Q000378:metabolism; D019012:Integrin beta1 / Q000737:chemistry / Q000378:metabolism*; D019169:Jurkat Cells; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012091:Repetitive Sequences, Nucleic Acid; D013379:Substrate Specificity; D013601:T-Lymphocytes / Q000166:cytology; D019700:Thrombospondin 1 / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology
D000911:Antibodies, Monoclonal; D039201:Integrin alpha3beta1; D039041:Integrin alpha4beta1; D019012:Integrin beta1; D019700:Thrombospondin 1