Evidence that the signal-initiating membrane protein CD9 is associated with small GTP-binding proteins.
F(ab')2 fragments of anti-CD9 mAb aggregate platelets by a thromboxane-dependent pathway implicating CD9 as signal initiating molecule. We demonstrate that mAbs directed against CD9, but not against GPIIb/IIIa specifically immunoprecipitate, from detergent lysates of human platelets, proteins of 25 and 26 kDa which bind [alpha 32P]GTP on nitrocellulose transfers. The binding is specific since it is blocked by GTP, but not by ATP. The GTP-binding proteins do not belong to a Mg(2+)-sensitive subset since they are unaffected by the addition of 2 microM-20 mM Mg2+. The observations demonstrate that CD9 is associated with selected small G-proteins.
Seehafer
J G
JG
Department of Medicine, Cross Cancer Institute, Edmonton, Alberta, Canada.
Shaw
A R
AR
D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex / Q000032:analysis; D015703:Antigens, CD / Q000502:physiology*; D000943:Antigens, Differentiation / Q000302:isolation & purification / Q000502:physiology*; D001792:Blood Platelets / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000097:blood* / Q000302:isolation & purification / Q000502:physiology; D006160:Guanosine Triphosphate / Q000097:blood; D066298:In Vitro Techniques; D007700:Kinetics; D015636:Magnesium Chloride / Q000494:pharmacology; D008562:Membrane Glycoproteins; D008970:Molecular Weight; D010980:Platelet Membrane Glycoproteins / Q000502:physiology; D015398:Signal Transduction; D060245:Tetraspanin 29
D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D015703:Antigens, CD; D000943:Antigens, Differentiation; C554869:CD9 protein, human; D008562:Membrane Glycoproteins; D010980:Platelet Membrane Glycoproteins; D060245:Tetraspanin 29; D015636:Magnesium Chloride; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins