title: Pathological shear stress directly regulates platelet alphaIIbbeta3 signaling.
abstract: Integrin mechanotransduction is a ubiquitous biological process. Mechanical forces are transduced transmembranously by an integrin's ligand-bound extracellular domain through its beta-subunit's cytoplasmic domain connected to the cytoskeleton. This often culminates in the activation of tyrosine kinases directing cell responses. The delicate balance between hemostasis and thrombosis requires exquisitely fine-tuned integrin function, and balance is maintained in vivo despite that the major platelet integrin alpha(IIb)beta(3) is continuously subjected to frictional or shearing forces generated by laminar blood flow. To test the hypothesis that platelet function is regulated by the direct effects of mechanical forces on alpha(IIb)beta(3), we examined alpha(IIb)beta(3)/cytoskeletal interactions in human platelets exposed to shear stress in a cone-plate viscometer. We observed that alpha-actinin, myosin heavy chain, and Syk coimmunoprecipitate with alpha(IIb)beta(3) in resting platelets and that 120 dyn/cm(2) shear stress leads to their disassociation from alpha(IIb)beta(3). Shear-induced disassociation of alpha-actinin and myosin heavy chain from the beta(3) tail is unaffected by blocking von Willebrand factor (VWF) binding to glycoprotein (Gp) Ib-IX-V but abolished by blocking VWF binding to alpha(IIb)beta(3). Syk's disassociation from beta(3) is inhibited when VWF binding to either GpIb-IX-V or alpha(IIb)beta(3) is blocked. Shear stress-induced phosphorylation of SLP-76 and its association with tyrosine-phosphorylated adhesion and degranulation-promoting adapter protein are inhibited by blocking ligand binding to alpha(IIb)beta(3) but not by blocking ligand binding to GpIb-IX-V. Chinese hamster ovary cells expressing alpha(IIb)beta(3) with beta(3) truncated of its cytoskeletal binding domains demonstrate diminished shear-dependent adhesion and cohesion. These results support the hypothesis that shear stress directly modulates alpha(IIb)beta(3) function and suggest that shear-induced alpha(IIb)beta(3)-mediated signaling contributes to the regulation of platelet aggregation by directing the release of constraining cytoskeletal elements from the beta(3)-tail.
authors.affiliation: Michael E. DeBakey Veterans Affairs Medical Center, Baylor College of Medicine and Rice University, Houston, Texas 77030 , USA.
authors.forename: Shuju
authors.initials: S
authors.lastname: Feng
authors.forename: Xin
authors.initials: X
authors.lastname: Lu
authors.forename: Julio C
authors.initials: JC
authors.lastname: Reséndiz
authors.forename: Michael H
authors.initials: MH
authors.lastname: Kroll
mesh_terms: D000185:Actinin / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D003599:Cytoskeleton / Q000378:metabolism*; D051417:Focal Adhesion Kinase 1 / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D033081:Shear Strength; D015398:Signal Transduction / Q000502:physiology*; D013314:Stress, Mechanical; D000072377:Syk Kinase; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C092947:SLP-76 signal Transducing adaptor proteins; D014841:von Willebrand Factor; D000185:Actinin; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; C496050:PTK2 protein, human; C000606896:SYK protein, human; D000072377:Syk Kinase