title: Tec regulates platelet activation by GPVI in the absence of Btk.
abstract: The Tec family kinase Btk plays an important role in the regulation of phospholipase C gamma 2 (PLC gamma 2) downstream of the collagen receptor glycoprotein VI (GPVI) in human platelets. Platelets also express a second member of this family, Tec; however, its function has not been analyzed. To address the role of Tec, we analyzed Btk-/-, Tec-/-, and Btk/Tec double-deficient (Btk-/-/Tec-/-) platelets. Tec-/- platelets exhibit a minor reduction in aggregation to threshold concentrations of collagen or the GPVI-specific agonist collagen-related peptide (CRP), whereas responses to higher concentrations are normal. Tyrosine phosphorylation of PLC gamma 2 by collagen and CRP is not altered in Tec-/- platelets. However, Btk-/-/Tec-/- platelets exhibit a greater reduction in PLC gamma 2 phosphorylation than is seen in the absence of Btk, thus revealing an important role for Tec in this situation. Furthermore, Btk-/-/Tec-/- platelets fail to undergo an increase in Ca2+, aggregation, secretion, and spreading in response to collagen or CRP, whereas they aggregate normally to adenosine diphosphate (ADP) and spread on fibrinogen. A residual GPVI signal exists in the Btk-/-/Tec-/- platelets as CRP synergizes with ADP to mediate aggregation. These results demonstrate an essential requirement for Tec and Btk in platelet activation by GPVI and reveal a functional role for Tec in the regulation of PLC gamma 2 in the absence of Btk.
authors.affiliation: Department of Pharmacology, University of Oxford, Mansfield Rd, Oxford, OX1 3QT, United Kingdom. ben.atkinson@pharm.ox.ac.uk
authors.forename: Ben T
authors.initials: BT
authors.lastname: Atkinson
authors.forename: Wilfried
authors.initials: W
authors.lastname: Ellmeier
authors.forename: Steve P
authors.initials: SP
authors.lastname: Watson
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000502:physiology; D048429:Cell Size; D005340:Fibrinogen / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D015539:Platelet Activation; D010973:Platelet Adhesiveness; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000172:deficiency* / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction
chemical_list: D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D005340:Fibrinogen; C089848:Tec protein-tyrosine kinase; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human