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Intertissular variations in osteonectin: A monoclonal antibody directed to bone osteonectin shows reduced affinity for platelet osteonectin
Author(s) -
Malaval Luc,
Darbouret Bruno,
Preaudat Corinne,
Jolu JeanPierre,
Delmas Pierre D.
Publication year - 1991
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.5650060402
Subject(s) - osteonectin , monoclonal antibody , platelet , chemistry , microbiology and biotechnology , immunoprecipitation , osteoblast , biochemistry , antibody , biology , immunology , osteocalcin , in vitro , alkaline phosphatase , gene , enzyme
Osteonectin, a major noncollagenous protein of bone, is also synthesized and secreted by various nonmineralized tissues and by platelets. To establish whether there are structural specificities of osteonectin according to its tissular origin, we raised 12 monoclonal antibodies against bovine bone osteonectin and screened them for their ability to recognize bone and platelet osteonectin. When hybridoma culture media were radio‐immunoassayed all MAbs showed the same titer for [ 125 I]human platelet osteonectin and for [ 125 I]bovine bone osteonectin, except MAb 2, which poorly bound platelet osteonectin. Immunoprecipitation and immunoblotting experiments were performed on human bone protein extracts and on material secreted by human platelets upon thrombin stimulation; in these experiments MAb 2 recognized human bone osteonectin and only faintly human platelet osteonectin. A “sandwich” immunoradiometric assay was devised in which osteonectin bound to a solid phase by a first MAb was recognized by a 125 I‐labeled second MAb. In this assay MAb 2, used as a tracer, showed a 100‐fold lower affinity for purified human platelet osteonectin than for purified human bone osteonectin. These results suggest the existence of structural variations in osteonectin obtained from bone and platelets. Whether these variations result from differences in sequence, post‐translational processing, or postsecretional fate remains to be established.