title: Peptide LSARLAF induces integrin β3 dependent outside-in signaling in platelets.
abstract: BACKGROUND
  Peptide LSARLAF (LSA) can bind and activate integrin αIIbβ3 in the absence of 'inside-out' signal. The active αIIbβ3 mediates 'outside-in' signaling that elicits platelet aggregation, granule secretion and TxA2 production. Here we identify the membrane glycoproteins which mediate LSA-induced platelet activation other than αIIbβ3, and determine the roles of Src, PLCγ2, FcRγ-chain, and SLP-76 in LSA-induced platelet activation.
  
  
  METHODS
  Ligand-receptor binding assay was performed to study the effect of peptide LSA or its control peptide FRALASL (FRA) on integrins binding to their ligands. Spreading of CHO cells expressing αIIbβ3 or αVβ3 on immobilized fibrinogen was measured in the presence of LSA or FRA. Washed β3, Src, FcRγ-chain, LAT and SLP-76 deficient platelets aggregation and secretion were tested in response to LSA.
  
  
  RESULTS
  Ligand-receptor binding assay indicated that LSA promoted the binding of multiple ligands to αIIbβ3 or αVβ3. LSA also enhanced CHO cells with αIIbβ3 or αVβ3 expression spreading on immobilized fibrinogen. β3 deficient platelets failed to aggregate and secrete in response to LSA. The phosphorylation of PLCγ2 and Syk was also β3 dependent. Src, FcRγ-chain, LAT and SLP-76 deficient platelets did not aggregate, secrete ATP or produce TxA2 in response to LSA.
  
  
  CONCLUSIONS
  LSA-induced platelet activation is β3 dependent, and signaling molecules Src, FcRγ-chain, SLP-76 and LAT play crucial roles in LSA-induced β3 mediated signaling.
authors.affiliation: Department of Biochemistry and Molecular Cell Biology, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Haixia
authors.initials: H
authors.lastname: Niu
authors.forename: Zhenlu
authors.initials: Z
authors.lastname: Xu
authors.forename: Ding
authors.initials: D
authors.lastname: Li
authors.forename: Lin
authors.initials: L
authors.lastname: Zhang
authors.forename: Kemin
authors.initials: K
authors.lastname: Wang
authors.forename: Donald B
authors.initials: DB
authors.lastname: Taylor
authors.forename: Junling
authors.initials: J
authors.lastname: Liu
authors.forename: T Kent
authors.initials: TK
authors.lastname: Gartner
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000276:immunology; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D016466:CHO Cells; D002448:Cell Adhesion; D006224:Cricetinae; D017353:Gene Deletion; D039302:Integrin alphaVbeta3 / Q000276:immunology; D039661:Integrin beta3 / Q000235:genetics / Q000276:immunology*; D047908:Intracellular Signaling Peptides and Proteins / Q000276:immunology; D051379:Mice; D009842:Oligopeptides / Q000276:immunology / Q000494:pharmacology*; D051966:Phospholipase C gamma / Q000276:immunology; D010750:Phosphoproteins / Q000235:genetics / Q000276:immunology; D010766:Phosphorylation / Q000187:drug effects; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000276:immunology; D011505:Protein-Tyrosine Kinases / Q000276:immunology; D017452:Receptors, IgG / Q000235:genetics / Q000276:immunology; D015398:Signal Transduction / Q000187:drug effects*; D000072377:Syk Kinase
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D039302:Integrin alphaVbeta3; D039661:Integrin beta3; D047908:Intracellular Signaling Peptides and Proteins; D009842:Oligopeptides; D010750:Phosphoproteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D017452:Receptors, IgG; C092947:SLP-76 signal Transducing adaptor proteins; C113734:leucyl-seryl-alanyl-arginyl-leucyl-alanyl-phenylalanine; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D051966:Phospholipase C gamma