Agonist-stimulated ligand binding by the platelet integrin alpha IIb beta 3 in a lymphocyte expression system.
The ligand binding activity of the platelet integrin alpha IIb beta 3 is initiated by agonist-generated intraplatelet signals. We studied this process in vitro by expressing recombinant alpha IIb beta 3 in Epstein-Barr virus-immortalized B lymphocytes. We found that phorbol ester stimulation induced the adhesion of lymphocytes expressing alpha IIb beta 3 to immobilized fibrinogen. Moreover, replacement of the transmembrane and cytoplasmic domains of the alpha and beta subunits of alpha IIb beta 3 with those of alpha L beta 2 significantly increased adherence, whereas replacement of only the cytoplasmic domains significantly decreased adherence. This suggests that transmembrane segments are involved in the agonist-induced modulation of alpha IIb beta 3 activity. Similar results were seen when the alpha IIb beta 3 activation-dependent monoclonal antibody PAC-1 was substituted for immobilized fibrinogen. We also found that the adherence of lymphocytes expressing beta 3 with either of the two alpha IIb/alpha L chimeras was similar to that of cells expressing alpha IIb beta 3, whereas the adherence of cells expressing alpha IIb with either of the two beta 3/beta 2 chimeras was substantially decreased, suggesting that the identity of the cytoplasmic domain of beta 3, but not of alpha IIb, is critical for alpha IIb beta 3 function. This report indicates that B lymphocytes contain signal transduction pathways involving protein kinase C that can increase the ligand binding activity of alpha IIb beta 3 and demonstrates the utility of these cells as an expression system for the study of agonist-stimulated alpha IIb beta 3 function.
Loh
E
E
Hematology-Oncology Division, Hospital of the University of Pennsylvania, Philadelphia, USA.
Beaverson
K
K
Vilaire
G
G
Qi
W
W
Poncz
M
M
Bennett
J S
JS
D000595:Amino Acid Sequence; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D001483:Base Sequence; D001792:Blood Platelets / Q000737:chemistry; D002448:Cell Adhesion / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D016023:Integrins / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011485:Protein Binding; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D016023:Integrins; D016169:Lymphocyte Function-Associated Antigen-1; D009842:Oligopeptides; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011993:Recombinant Fusion Proteins; D005340:Fibrinogen; C046617:arginyl-glycyl-aspartyl-serine; D013755:Tetradecanoylphorbol Acetate