Activation of G12/G13 results in shape change and Rho/Rho-kinase-mediated myosin light chain phosphorylation in mouse platelets

• Published in: The Journal of cell biology 1999-02, Vol.144 (4), p.745-754
• Main Authors: Klages, B, Brandt, U, Simon, M I, Schultz, G, Offermanns, S
• Format: Article
• Language: English
• Subjects: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid - pharmacology; Animals; Blood Platelets - cytology; Blood Platelets - drug effects; Blood Platelets - metabolism; Cell Size - physiology; Cellular biology; Enzymes; GTP-Binding Protein alpha Subunits, G12-G13; GTP-Binding Protein alpha Subunits, Gq-G11; GTP-Binding Proteins - blood; GTP-Binding Proteins - deficiency; GTP-Binding Proteins - genetics; GTPase-Activating Proteins; Intracellular Signaling Peptides and Proteins; Mice; Microscopy, Electron, Scanning; Myosin Light Chains - blood; Phosphorylation; Platelet Aggregation - physiology; Protein Serine-Threonine Kinases - blood; Proteins; Receptors, Thromboxane - metabolism; Regular; rho-Associated Kinases; Thrombin - pharmacology
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.144.4.745

Platelets respond to various stimuli with rapid changes in shape followed by aggregation and secretion of their granule contents. Platelets lacking the alpha-subunit of the heterotrimeric G protein Gq do not aggregate and degranulate but still undergo shape change after activation through thromboxane-A2 (TXA2) or thrombin receptors. In contrast to thrombin, the TXA2 mimetic U46619 led to the selective activation of G12 and G13 in Galphaq-deficient platelets indicating that these G proteins mediate TXA2 receptor-induced shape change. TXA2 receptor-mediated activation of G12/G13 resulted in tyrosine phosphorylation of pp72(syk) and stimulation of pp60(c-src) as well as in phosphorylation of myosin light chain (MLC) in Galphaq-deficient platelets. Both MLC phosphorylation and shape change induced through G12/G13 in the absence of Galphaq were inhibited by the C3 exoenzyme from Clostridium botulinum, by the Rho-kinase inhibitor Y-27632 and by cAMP-analogue Sp-5,6-DCl-cBIMPS. These data indicate that G12/G13 couple receptors to tyrosine kinases as well as to the Rho/Rho-kinase-mediated regulation of MLC phosphorylation. We provide evidence that G12/G13-mediated Rho/Rho-kinase-dependent regulation of MLC phosphorylation participates in receptor-induced platelet shape change.