Signaling through GP Ib-IX-V activates alpha IIb beta 3 independently of other receptors.
Platelet adhesion to von Willebrand factor (VWF) activates alpha IIb beta 3, a prerequisite for thrombus formation. However, it is unclear whether the primary VWF receptor, glycoprotein (GP) Ib-IX-V, mediates alpha IIb beta 3 activation directly or through other signaling proteins physically associated with it (eg, FcR gamma-chain), possibly with the contribution of other agonist receptors and of VWF signaling through alpha IIb beta 3. To resolve this question, human and GP Ibalpha transgenic mouse platelets were plated on dimeric VWF A1 domain (dA1VWF), which engages only GP Ib-IX-V, in the presence of inhibitors of other agonist receptors. Platelet adhesion to dA1VWF induced Src kinase-dependent tyrosine phosphorylation of the FcR gamma-chain and the adapter molecule, ADAP, and triggered intracellular Ca(2+) oscillations and alpha IIb beta 3 activation. Inhibition of Ca(2+) oscillations with BAPTA-AM prevented alpha IIb beta 3 activation but not tyrosine phosphorylation. Pharmacologic inhibition of protein kinase C (PKC) or phosphatidylinositol 3-kinase (PI 3-kinase) prevented alpha IIb beta 3 activation but not Ca(2+) oscillations. Inhibition of Src with 2 distinct compounds blocked all responses downstream of GP Ib-IX-V under static or flow conditions. However, dA1VWF-induced responses were reduced only slightly in GP Ibalpha transgenic platelets lacking FcR gamma-chain. These data establish that GP Ib-IX-V itself can signal to activate alpha IIb beta 3, through sequential actions of Src kinases, Ca(2+) oscillations, and PI 3-kinase/PKC.
Kasirer-Friede
Ana
A
Department of Cell Biology, The Scripps Research Institute, 10550 N Torrey Pines Rd, La Jolla, CA 92037, USA.
Cozzi
Maria Rita
MR
Mazzucato
Mario
M
De Marco
Luigi
L
Ruggeri
Zaverio M
ZM
Shattil
Sanford J
SJ
D000818:Animals; D001792:Blood Platelets / Q000378:metabolism / Q000502:physiology; D020013:Calcium Signaling; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010973:Platelet Adhesiveness; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins; D011493:Protein Kinase C / Q000378:metabolism; D017452:Receptors, IgG / Q000378:metabolism; D015398:Signal Transduction; D019061:src-Family Kinases / Q000378:metabolism; D014841:von Willebrand Factor / Q000378:metabolism
D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D017452:Receptors, IgG; C032193:glycoprotein receptor GPIb-IX; D014841:von Willebrand Factor; D019869:Phosphatidylinositol 3-Kinases; D019061:src-Family Kinases; D011493:Protein Kinase C