Regulation of plasmin-induced protease-activated receptor 4 activation in platelets.
Plasmin, a major extracellular protease, activates platelets through PAR4 receptors. Plasmin-induced full aggregation is achieved at lower concentrations (0.1 U/mL) in murine platelets as compared to human platelets (1 U/mL). In COS7 cells expressing the murine PAR4 (mPAR4) receptor, 1 U/mL plasmin caused a higher intracellular calcium mobilization than in cells expressing the human PAR4 (hPAR4) receptor. This difference was reversed when the tethered ligand sequences of mPAR4 and hPAR4 were interchanged through site-directed mutagenesis. We further investigated whether PAR3 expressed in murine platelets serves as a co-receptor for PAR4 activation by plasmin. In COS7 cells, co-expressing mPAR3 and mPAR4, plamsin produced a smaller intracellular calcium mobilization compared to cells expressing mPAR4 alone, suggesting that PAR3 might inhibit plasmin-induced PAR4 stimulation. Consistent with these results, PAR3 null murine platelets also showed a greater plasmin-induced calcium mobilization and aggregation compared to wild-type murine platelets. In conclusion, murine platelets are more sensitive to activation by plasmin than human platelets due to differences in the primary sequence of PAR4. In contrast to thrombin-dependent activation of platelets, wherein PAR3 acts as a co-receptor, mPAR3 inhibits plasmin-induced PAR4 activation.
Department of Physiology, Temple University School of Medicine, Philadelphia, PA, USA.
Yingying
Y
Mao
Jianguo
J
Jin
James L
JL
Daniel
Satya P
SP
Kunapuli
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D019556:COS Cells; D002118:Calcium / Q000097:blood; D002522:Chlorocebus aethiops; D005341:Fibrinolysin / Q000494:pharmacology* / Q000502:physiology; D006801:Humans; D051379:Mice; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D018179:Receptors, Thrombin / Q000097:blood* / Q000502:physiology
D018179:Receptors, Thrombin; C105295:protease-activated receptor 3; D005341:Fibrinolysin; C112908:protease-activated receptor 4; D002118:Calcium