A tyrosine kinase signaling pathway, regulated by calcium entry and dissociated from tyrosine phosphorylation of phospholipase Cgamma-1, is involved in inositol phosphate production by activated G protein-coupled receptors in myometrium.
Our experiments were conducted to evaluate, in rat myometrium, the potential contribution of a protein tyrosine kinase (PTK) pathway in the hydrolysis of phosphatidylinositol-4,5-bisphosphate mediated by bombesin, endothelin-1 (ET-1), and carbachol. The production of inositol phosphates (InsP) by agonists and AlF4- was partly inhibited (35-40%) by genistein and tyrphostins, two PTK inhibitors. Genistein attenuated uterine contractions elicited by the stimulation of muscarinic and bombesin receptors, whereas pervanadate, a protein tyrosine phosphatase inhibitor, potentiated receptor-mediated contraction. Tyrosine-phosphorylated proteins were detected in detergent extracts from agonist- and pervanadate-stimulated myometrium. The amount of InsP produced in response to pervanadate was related to the tyrosine phosphorylation status of phospholipase C-gamma1. In contrast, with ET-1 and bombesin, phosphorylated phospholipase C-gamma1 made a minor contribution. Additional findings were rather consistent with a role for Ca2+. In fura-2-loaded cells, genistein partly decreased both the transient and sustained intracellular Ca2+ concentration phases induced by bombesin. The removal of extracellular Ca2+ or the addition of nifedipine inhibited (35%) InsP production due to bombesin and ET-1. The inhibitory effects of genistein and tyrphostins were abolished in Ca2+-depleted medium, were not additive with that of nifedipine, and (as for nifedipine) were counteracted by the Ca2+ channel agonist Bay K 8644. The data are consistent with a PTK-mediated process in the activation of the voltage-gated Ca2+ influx that is involved in the production of InsP by stimulated G protein-coupled receptors.
Palmier
B
B
Signalisation et Régulations Cellulaires, Centre National de la Recherche Scientifique, Université Paris-Sud, Orsay Cedex, France.
Vacher
M
M
Harbon
S
S
Leiber
D
D
D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015151:Immunoblotting; D007295:Inositol Phosphates / Q000096:biosynthesis*; D007527:Isoenzymes / Q000502:physiology*; D009215:Myometrium / Q000378:metabolism*; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000502:physiology*; D010738:Type C Phospholipases / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism*; D014590:Uterine Contraction / Q000502:physiology; D014599:Uterus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
D015220:Calcium Channels; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D007527:Isoenzymes; C049925:fura-2-am; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D019204:GTP-Binding Proteins; D002118:Calcium; D016257:Fura-2