Costimulation of Gi- and G12/G13-mediated signaling pathways induces integrin alpha IIbbeta 3 activation in platelets.
Platelet activation is a complex process induced by a variety of stimuli, which act in concert to ensure the rapid formation of a platelet plug at places of vascular injury. We show here that fibrillar collagen, which initiates platelet activation at the damaged vessel wall, activates only a small fraction of platelets in suspension directly, whereas the majority of platelets becomes activated by mediators released from collagen-activated platelets. In Galpha(q)-deficient platelets that do not respond with activation of integrin alpha(IIb)beta(3) to a variety of mediators like thromboxane A2 (TXA2), thrombin, or ADP, collagen at high concentrations was able to induce aggregation, an effect that could be blocked by antagonists of the TXA2 or P2Y12 receptors. The activation of TXA2 or P2Y12 receptors alone, which in Galpha(q)-deficient platelets couple to G12/G13 and Gi, respectively, did not induce platelet integrin activation or aggregation. However, concomitant activation of both receptors resulted in irreversible integrin alpha(IIb)beta3-mediated aggregation of Galpha(q)-deficient platelets. Thus, the activation of G12/G13- and Gi-mediated signaling pathways is sufficient to induce integrin alpha(IIb)beta3 activation. Although G(q)-mediated signaling plays an important role in platelet activation, it is not strictly required for the activation of integrin alpha(IIb)beta3. This indicates that the efficient induction of platelet aggregation through G-protein-coupled receptors is an integrated response mediated by various converging G-protein-mediated signaling pathways involving G(q) and G(i) as well as G12/G13.
Rudolf Virchow Center for Experimental Biomedicine, University of Würzburg, 97078 Würzburg, Germany. bernhard.nieswandt@virchow.uni-wuerzburg.de
Bernhard
B
Nieswandt
Valerie
V
Schulte
Alexandra
A
Zywietz
Marie-Pierre
MP
Gratacap
Stefan
S
Offermanns
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D003094:Collagen / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005340:Fibrinogen / Q000378:metabolism; D044365:GTP-Binding Protein alpha Subunits, G12-G13; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008822:Mice, Transgenic; D015539:Platelet Activation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction; D013917:Thrombin / Q000494:pharmacology; D013928:Thromboxane A2 / Q000494:pharmacology; D054460:rho-Associated Kinases
D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D013928:Thromboxane A2; D000244:Adenosine Diphosphate; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000255:Adenosine Triphosphate; D005340:Fibrinogen; D003094:Collagen; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D013917:Thrombin; D044365:GTP-Binding Protein alpha Subunits, G12-G13; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins