A novel interaction between FlnA and Syk regulates platelet ITAM-mediated receptor signaling and function.
Filamin A (FlnA) cross-links actin filaments and connects the Von Willebrand factor receptor GPIb-IX-V to the underlying cytoskeleton in platelets. Because FlnA deficiency is embryonic lethal, mice lacking FlnA in platelets were generated by breeding FlnA(loxP/loxP) females with GATA1-Cre males. FlnA(loxP/y) GATA1-Cre males have a macrothrombocytopenia and increased tail bleeding times. FlnA-null platelets have decreased expression and altered surface distribution of GPIbalpha because they lack the normal cytoskeletal linkage of GPIbalpha to underlying actin filaments. This results in approximately 70% less platelet coverage on collagen-coated surfaces at shear rates of 1,500/s, compared with wild-type platelets. Unexpectedly, however, immunoreceptor tyrosine-based activation motif (ITAM)- and ITAM-like-mediated signals are severely compromised in FlnA-null platelets. FlnA-null platelets fail to spread and have decreased alpha-granule secretion, integrin alphaIIbbeta3 activation, and protein tyrosine phosphorylation, particularly that of the protein tyrosine kinase Syk and phospholipase C-gamma2, in response to stimulation through the collagen receptor GPVI and the C-type lectin-like receptor 2. This signaling defect was traced to the loss of a novel FlnA-Syk interaction, as Syk binds to FlnA at immunoglobulin-like repeat 5. Our findings reveal that the interaction between FlnA and Syk regulates ITAM- and ITAM-like-containing receptor signaling and platelet function.
Falet
Hervé
H
Division of Translational Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. hfalet@rics.bwh.harvard.edu
Pollitt
Alice Y
AY
Begonja
Antonija Jurak
AJ
Weber
Sarah E
SE
Duerschmied
Daniel
D
Wagner
Denisa D
DD
Watson
Steve P
SP
Hartwig
John H
JH
D020816:Amino Acid Motifs; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D002448:Cell Adhesion; D005260:Female; D064448:Filamins; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000172:deficiency / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase; D013922:Thrombocytosis / Q000235:genetics / Q000378:metabolism
D064448:Filamins; C529499:FlnA protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse