The molecular adapter SLP-76 relays signals from platelet integrin alphaIIbbeta3 to the actin cytoskeleton.
Platelet adhesion to fibrinogen through integrin alpha(IIb)beta(3) triggers actin rearrangements and cell spreading. Mice deficient in the SLP-76 adapter molecule bleed excessively, and their platelets spread poorly on fibrinogen. Here we used human platelets and a Chinese hamster ovary (CHO) cell expression system to better define the role of SLP-76 in alpha(IIb)beta(3) signaling. CHO cell adhesion to fibrinogen required alpha(IIb)beta(3) and stimulated tyrosine phosphorylation of SLP-76. SLP-76 phosphorylation required coexpression of Syk tyrosine kinase and stimulated association of SLP-76 with the adapter, Nck, and with the Rac exchange factor, Vav1. SLP-76 expression increased lamellipodia formation induced by Syk and Vav1 in adherent CHO cells (p < 0.001). Although lamellipodia formation requires Rac, SLP-76 functioned downstream of Rac by potentiating adhesion-dependent activation of PAK kinase (p < 0.001), a Rac effector that associates with Nck. In platelets, adhesion to fibrinogen stimulated the association of SLP-76 with the SLAP-130 adapter and with VASP, a SLAP-130 binding partner implicated in actin reorganization. Furthermore, SLAP-130 colocalized with VASP at the periphery of spread platelets. Thus, SLP-76 functions to relay signals from alpha(IIb)beta(3) to effectors of cytoskeletal reorganization. Therefore, deficient recruitment of specific adapters and effectors to sites of adhesion may explain the integrin phenotype of SLP-76(-/-) platelets.
Obergfell
A
A
Department of Vascular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Judd
B A
BA
del Pozo
M A
MA
Schwartz
M A
MA
Koretzky
G A
GA
Shattil
S J
SJ
D000199:Actins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001792:Blood Platelets / Q000502:physiology*; D016466:CHO Cells; D002448:Cell Adhesion; D018797:Cell Cycle Proteins; D006224:Cricetinae; D003599:Cytoskeleton / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism; D005340:Fibrinogen; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051567:Proto-Oncogene Proteins c-vav; D011554:Pseudopodia; D015398:Signal Transduction; D000072377:Syk Kinase; D020744:rac GTP-Binding Proteins / Q000378:metabolism
D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; C092947:SLP-76 signal Transducing adaptor proteins; C496618:VAV1 protein, human; D005340:Fibrinogen; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D020744:rac GTP-Binding Proteins