Role of Galphaq and phospholipase C-beta2 in human platelets activation by thrombin receptors PAR1 and PAR4: studies in human platelets deficient in Galphaq and phospholipase C-beta2.
Thrombin responses in human platelets are mediated by the protease-activated receptors (PAR), PAR1 and PAR4. The signalling pathways mediating PAR activation have not been fully delineated for human platelets. We assessed cytoplasmic Ca2+ mobilization in response to activation with thrombin and PAR1 (SFLLRN) and PAR4 (GYPGKF) peptides in two patients whose platelets were deficient in two major signalling proteins, Galphaq or phospholipase (PLC)-beta2. In normal platelets, thrombin induced a biphasic Ca2+ response with a rapid rise to a peak followed by a sustained elevation in Ca2+. The peak Ca2+ rise was impaired in both patients at lower thrombin concentrations. At higher concentrations, it was decreased in PLC-beta2-deficient platelets; the sustained Ca2+ elevation observed in normal and Galphaq-deficient platelets was reduced in PLC-beta2-deficient platelets. The response to SFLLRN was decreased in both patients at lower concentrations. The peak Ca2+ in response to GYPGKF was reduced in both patients; the sustained Ca2+ increase was markedly decreased in PLC-beta2-deficient platelets. These studies provide evidence that, in human platelets, both Galphaq and PLC-beta2 play a major role in responses to PAR1 and PAR4 activation, and that PLC-beta2 is required for the sustained Ca2+ rise upon thrombin activation.
Vaidyula
Vijender R
VR
Sol Sherry Thrombosis Research Center and Department of Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Rao
A Koneti
AK
D001792:Blood Platelets / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005656:Fungal Proteins / Q000494:pharmacology*; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins / Q000172:deficiency / Q000502:physiology*; D006801:Humans; D007527:Isoenzymes / Q000172:deficiency / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology; D054799:Phospholipase C beta; D010749:Phosphoprotein Phosphatases; D015539:Platelet Activation; D018179:Receptors, Thrombin; D029702:Schizosaccharomyces pombe Proteins; D013917:Thrombin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000172:deficiency / Q000502:physiology*
D005656:Fungal Proteins; D007527:Isoenzymes; C410165:PAR1 protein, S pombe; D010446:Peptide Fragments; D018179:Receptors, Thrombin; D029702:Schizosaccharomyces pombe Proteins; C082835:thrombin receptor peptide (42-47); D010749:Phosphoprotein Phosphatases; D010738:Type C Phospholipases; C518036:PLCB2 protein, human; D054799:Phospholipase C beta; D013917:Thrombin; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins; C112908:protease-activated receptor 4; D002118:Calcium