title: Site-specific phosphorylation of platelet focal adhesion kinase by low-density lipoprotein.
abstract: Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase implicated in signalling pathways mediated by integrins and G-protein-coupled receptors (GPCRs). Upon stimulation FAK is phosphorylated on six tyrosine residues. Here we report the site-specific phosphorylation by low-density lipoprotein (LDL), which is known to induce integrin-independent FAK phosphorylation, and compare this with the effect of thrombin, which phosphorylates FAK via integrin alphaIIbbeta3. Stimulation with LDL reveals (i) a major role for Tyr-925 phosphorylation which surpasses the phosphorylation of the other residues, including Tyr-397, in rate and extent, (ii) alphaIIbbeta3-independent phosphorylation of Tyr-925 and Tyr-397, and (iii) complex formation between FAK and the Src-kinase Fgr but not with c-Src. These patterns differ profoundly from those induced by thrombin. LDL-induced phosphorylation of Tyr-925 and Tyr-397 was inhibited by 60-75% by receptor-associated protein, an inhibitor of members of the LDL receptor family. Thus these findings reveal a novel mechanism of FAK phosphorylation by signalling cascades involving a member of the LDL receptor family.
authors.affiliation: Laboratory for Thrombosis and Haemostasis, Department of Haematology, University Medical Center Utrecht, P.O. Box 85500, 3508 GA Utrecht, The Netherlands. i.relou@azu.nl
authors.forename: Ingrid A M
authors.initials: IA
authors.lastname: Relou
authors.forename: Liane A B
authors.initials: LA
authors.lastname: Bax
authors.forename: Herman J M
authors.initials: HJ
authors.lastname: van Rijn
authors.forename: Jan-Willem N
authors.initials: JW
authors.lastname: Akkerman
mesh_terms: D001792:Blood Platelets / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D026563:LDL-Receptor Related Protein-Associated Protein / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism*; D010766:Phosphorylation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013917:Thrombin / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D026563:LDL-Receptor Related Protein-Associated Protein; D008077:Lipoproteins, LDL; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; D019061:src-Family Kinases; D013917:Thrombin