The activation state of alphavbeta 3 regulates platelet and lymphocyte adhesion to intact and thrombin-cleaved osteopontin.
Cleavage of osteopontin by thrombin has been reported to enhance cell adhesion. We asked whether thrombin could regulate the alpha(v)beta(3)-mediated adhesion of platelets and B lymphocytes to this substrate. Although there was no difference in the extent or the avidity of thrombin- and ADP-stimulated platelet adhesion to intact or thrombin-cleaved human osteopontin, both the extent and avidity of phorbol ester-stimulated B cell adhesion to thrombin-cleaved osteopontin was significantly increased. Thus, these data suggest that the ability of alpha(v)beta(3) to recognize osteopontin can be differentially regulated in a cell-specific manner. To localize the alpha(v)beta(3) binding site on osteopontin, we measured cell adhesion to the two thrombin cleavage products of osteopontin and to a series of nested RGD-containing osteopontin peptides cross-linked to albumin. Whereas ADP-stimulated platelets adhered to the amino-terminal but not the carboxyl-terminal osteopontin fragment and to the osteopontin peptide RGDSVVYGLR, phorbol ester-stimulated B cells did not adhere to this peptide, although they did so in the presence of 1 mm Mn(2+). Thus, our data confirm that thrombin cleavage enhances the accessibility of the binding motif for alpha(v)beta(3) on osteopontin, but this enhancement is also a function of the activation state of alpha(v)beta(3). Moreover, they indicate that the sequence RGDSVVYGLR contains sufficient information to specify activation-dependent alpha(v)beta(3)-mediated platelet and lymphocyte adhesion.
Helluin
O
O
Hematology-Oncology Division, Department of Medicine and the Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Chan
C
C
Vilaire
G
G
Mousa
S
S
DeGrado
W F
WF
Bennett
J S
JS
D000244:Adenosine Diphosphate / Q000494:pharmacology; D001402:B-Lymphocytes / Q000502:physiology*; D001792:Blood Platelets / Q000187:drug effects; D002448:Cell Adhesion; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D004854:Herpesvirus 4, Human; D006801:Humans; D008274:Magnesium / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D053495:Osteopontin; D010973:Platelet Adhesiveness; D011487:Protein Conformation; D019030:Receptors, Vitronectin / Q000502:physiology*; D012795:Sialoglycoproteins / Q000378:metabolism*; D013917:Thrombin / Q000378:metabolism*
D019030:Receptors, Vitronectin; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; D053495:Osteopontin; D000244:Adenosine Diphosphate; D013917:Thrombin; D008274:Magnesium