Effect of cAMP on the association of small GTP-binding proteins with the cytoskeleton of human platelets.
Following activation of human platelets changes in cytoskeletal organization occur: some proteins, which are present in the cytosol or membrane-associated in resting platelets, are recovered in the Triton-insoluble residue in activated cells. Assembly and disassembly of complex effector units on the membrane and inside cells is under the control of low molecular weight GTP-binding proteins, particularly those in the ras family. We investigated the interaction of small GTP-binding proteins with the platelet cytoskeleton and the effect of high cAMP levels on these interactions. At least two GTP-binding proteins of 24 and 28 kDa were detected in the Triton-insoluble residue of resting platelets. Stimulation of platelets with thrombin or concanavalin A (Con A), under non-aggregating conditions, resulted in increased 24 kDa protein-bound GTP, which also contained a significant amount of rap1B. High cAMP levels differently affected this interaction depending on the type of agonist used. cAMP increased association of G-proteins with the cytoskeleton following Con A-activation, while it decreased G-proteins interaction after thrombin stimulation. The activation did not influence the cAMP-dependent phosphorylation of rap1B. No phosphoprotein corresponding to rap1B could be detected in the Triton-insoluble residues, however. These findings could be related to the different mechanisms of cytoskeletal protein recruitment in platelets activated with either thrombin or Con A.
Ramaschi
G
G
Department of Biochemistry, University of Pavia, Italy.
Balduini
C
C
Torti
M
M
Sinigaglia
F
F
D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002458:Cell Fractionation; D003208:Concanavalin A / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000032:analysis / Q000378:metabolism*; D006801:Humans; D015539:Platelet Activation / Q000187:drug effects; D011092:Polyethylene Glycols; D013917:Thrombin / Q000494:pharmacology; D020668:rap GTP-Binding Proteins
D003598:Cytoskeletal Proteins; D003208:Concanavalin A; D011092:Polyethylene Glycols; D000242:Cyclic AMP; D013917:Thrombin; D019204:GTP-Binding Proteins; D020668:rap GTP-Binding Proteins