title: G(12/13) signaling pathways substitute for integrin αIIbβ3-signaling for thromboxane generation in platelets.
abstract: BACKGROUND
  We have previously shown that ADP-induced TXA(2) generation requires signaling from αIIbβ3 integrin in platelets. Here we observed that, unlike ADP, protease-activated receptor (PAR)-mediated TXA(2) generation occurs independently of αIIbβ3. PAR agonists, but not ADP, activate G(12/13) signaling pathways. Hence, we evaluated the role of these pathways in TXA(2) generation.
  
  
  RESULTS
  Inhibition of ADP-induced thromboxane generation by fibrinogen receptor antagonist SC57101 was rescued by co-stimulation of G(12/13) pathways with YFLLRNP. This observation suggested an existence of a common signaling effector downstream of integrins and G(12/13) pathways. Hence, we evaluated role of three potential tyrosine kinases; c-Src, Syk and FAK (Focal Adhesion Kinase) that are known to be activated by integrins. c-Src and Syk kinase did not play a role in ADP-induced functional responses in platelets. Selective activation of G(12/13) pathways resulted in the activation of FAK, in the absence of integrin signaling. Interestingly, αIIbβ3-mediated FAK activation occurred in a Src family kinase (SFK)-independent manner whereas G(12/13) pathway caused FAK activation in a SFK and RhoA-dependent manner. A FAK selective inhibitor TAE-226, blocked TXA(2) generation. However, in comparison to WT mice, Pf4-Cre/Fak-Floxed mice did not show any difference in platelet TXA(2) generation.
  
  
  CONCLUSIONS
  Therefore, we conclude that differential activation of FAK occurs downstream of Integrins and G(12/13) pathways. However, the common effector molecule, possibly a tyrosine kinase downstream of integrins and G(12/13) pathways contributing to TXA(2) generation in platelets remains elusive.
authors.affiliation: Department of Physiology, Temple University School of Medicine, Philadelphia, Pennsylvania, United States of America.
authors.forename: Kamala
authors.initials: K
authors.lastname: Bhavaraju
authors.forename: Parth R
authors.initials: PR
authors.lastname: Lakhani
authors.forename: Robert T
authors.initials: RT
authors.lastname: Dorsam
authors.forename: Jianguo
authors.initials: J
authors.lastname: Jin
authors.forename: Ian S
authors.initials: IS
authors.lastname: Hitchcock
authors.forename: Archana
authors.initials: A
authors.lastname: Sanjay
authors.forename: Satya P
authors.initials: SP
authors.lastname: Kunapuli
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D004789:Enzyme Activation; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D015398:Signal Transduction; D000072377:Syk Kinase; D013928:Thromboxane A2 / Q000096:biosynthesis*; D054460:rho-Associated Kinases / Q000378:metabolism
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D013928:Thromboxane A2; D000244:Adenosine Diphosphate; D011505:Protein-Tyrosine Kinases; D051416:Focal Adhesion Protein-Tyrosine Kinases; D016392:Proto-Oncogene Proteins pp60(c-src); C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D054460:rho-Associated Kinases; D044365:GTP-Binding Protein alpha Subunits, G12-G13