Bone sialoprotein coated on glass and plastic surfaces is recognized by different beta 3 integrins.
Integrins have important roles in mediating cell-matrix interactions, essential for cell migration and signaling. In bone, integrins are suggested to play a role through their ability to mediate cell attachment to bone matrix proteins. In the present study, the subunit composition of integrins binding bone sialoprotein and osteopontin coated on either glass or plastic surfaces was analyzed using cells isolated from bone. Thus, integrin antibodies to alpha v beta 3, alpha IIb beta 3, alpha v, alpha IIb, and beta 3 and the peptides GRGDSP and KQAGDV were used to define the integrins involved in the attachment in vitro of a preparation of multinucleated cells expressing the enzyme tartrate-resistant acid phosphatase. Binding to osteopontin coated on either glass or plastic surfaces was mediated via the alpha v beta 3 integrin. Interestingly, the isolated cells bound to bone sialoprotein coated on plastic via the alpha v beta 3 integrin, but used a different integrin, alpha IIb beta 3, when the protein was coated on glass. It appears that bone sialoprotein when coated on glass and plastic, respectively, changes conformation, thereby altering the contact surface and subsequently the binding specificity. Alternatively, the protein contains two different binding sites, selectively exposed on glass or plastic as a result of different protein binding. The results demonstrate that bone sialoprotein contains domains, or can change conformation, such that it can interact with either the alpha IIb beta 3 or the alpha v beta 3 integrin. Whether the integrins were located on the multinucleated cells proper or on platelets bound to these cells could not be unequivocally concluded. The possible presence of platelets should, however, be considered when interpreting data from the isolated osteoclast system.
Flores
M E
ME
Department of Immunology, Microbiology, Pathology, and Infectious Diseases, Karolinska Institutet, Huddinge University Hospital, Sweden.
Heinegård
D
D
Reinholt
F P
FP
Andersson
G
G
D000135:Acid Phosphatase / Q000032:analysis; D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D001667:Binding, Competitive; D001792:Blood Platelets / Q000378:metabolism; D001842:Bone and Bones / Q000166:cytology* / Q000378:metabolism; D002448:Cell Adhesion; D005898:Glass; D039661:Integrin beta3; D058574:Integrin-Binding Sialoprotein; D016023:Integrins / Q000032:analysis / Q000378:metabolism*; D007527:Isoenzymes / Q000032:analysis; D008969:Molecular Sequence Data; D053495:Osteopontin; D010969:Plastics; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D012795:Sialoglycoproteins / Q000378:metabolism*; D000071681:Tartrate-Resistant Acid Phosphatase
D015703:Antigens, CD; C546873:Ibsp protein, rat; D039661:Integrin beta3; D058574:Integrin-Binding Sialoprotein; D016023:Integrins; D007527:Isoenzymes; D010969:Plastics; D010980:Platelet Membrane Glycoproteins; D012795:Sialoglycoproteins; C506897:Spp1 protein, rat; D053495:Osteopontin; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase