The toll-like receptor 2/1 (TLR2/1) complex initiates human platelet activation via the src/Syk/LAT/PLCγ2 signalling cascade.
The specific TLR2/1 complex activator Pam3CSK4 has been shown to provoke prominent activation and aggregation of human non-nucleated platelets. As Pam3CSK4-evoked platelet activation does not employ the major signalling pathway established in nucleated immune cells, we investigated if the TLR2/1 complex on platelets may initiate signalling pathways known to be induced by physiological agonists such as collagen via GPVI or thrombin via PARs. We found that triggering TLR2/1 complex-signalling with Pam3CSK4, in common with that induced via GPVI, and in contrast to that provoked by PARs, involves tyrosine phosphorylation of the adaptor protein LAT as well as of PLCγ2 in a src- and Syk-dependent manner. In this respect, we provide evidence that Pam3CSK4 does not cross-activate GPVI. Further, by the use of platelets from a Glanzmann's thrombasthenia patient lacking β(3), in contrast to findings in nucleated immune cells, we show that the initiation of platelet activation by Pam3CSK4 does not involve integrin β(3) signalling; whereas the latter, subsequent to intermediate TXA2 synthesis and signalling, was found to be indispensable for proper dense granule secretion and full platelet aggregation. Together, our findings reveal that triggering the TLR2/1 complex with Pam3CSK4 initiates human platelet activation by engaging tyrosine kinases of the src family and Syk, the adaptor protein LAT, as well as the key mediator PLCγ2.
Department of Clinical and Experimental Medicine, Linköping University, SE-58185 Linköping, Sweden; Department of Biomedicine, School of Health and Medical Sciences, Örebro University, SE-70182 Örebro, Sweden. Electronic address: knut.falker@oru.se.
Knut
K
Fälker
Department of Biomedicine, School of Health and Medical Sciences, Örebro University, SE-70182 Örebro, Sweden.
Kristin
K
Klarström-Engström
Department of Biomedicine, School of Health and Medical Sciences, Örebro University, SE-70182 Örebro, Sweden.
Torbjörn
T
Bengtsson
Department of Clinical and Experimental Medicine, Linköping University, SE-58185 Linköping, Sweden.
Tomas L
TL
Lindahl
Department of Biomedicine, School of Health and Medical Sciences, Örebro University, SE-70182 Örebro, Sweden.
Magnus
M
Grenegård
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D003435:Crotalid Venoms / Q000494:pharmacology; D006801:Humans; D016023:Integrins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D037181:Lectins, C-Type; D055666:Lipopeptides / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D009536:Niacinamide / Q000031:analogs & derivatives / Q000494:pharmacology; D051966:Phospholipase C gamma / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D015539:Platelet Activation / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D000072377:Syk Kinase; D013915:Thrombasthenia / Q000378:metabolism / Q000473:pathology; D051194:Toll-Like Receptor 1 / Q000737:chemistry / Q000378:metabolism*; D051195:Toll-Like Receptor 2 / Q000737:chemistry / Q000378:metabolism; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
C477642:2-(7-(3,4-dimethoxyphenyl)imidazo(1,2-c)pyrimidin-5-ylamino)nicotinamide; D048868:Adaptor Proteins, Signal Transducing; D003435:Crotalid Venoms; D016023:Integrins; D047908:Intracellular Signaling Peptides and Proteins; C110810:LAT protein, human; D037181:Lectins, C-Type; D055666:Lipopeptides; D008565:Membrane Proteins; C560312:Pam2CSK4 lipopeptide; D010980:Platelet Membrane Glycoproteins; D011743:Pyrimidines; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; C098341:platelet membrane glycoprotein VI; D009536:Niacinamide; C028890:convulxin; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D019061:src-Family Kinases; D051966:Phospholipase C gamma; D002118:Calcium
Human platelets; LAT; PLCγ2; Pam3CSK4; Syk; TLR2