Extracellular Signal-Regulated Kinase 1/2 Activation by Myometrial Oxytocin Receptor Involves GαqGβγ and Epidermal Growth Factor Receptor Tyrosine Kinase Activation

• Published in: Endocrinology (Philadelphia) 2003-07, Vol.144 (7), p.2947-2956
• Main Authors: Zhong, Miao, Yang, Ming, Sanborn, Barbara M
• Format: Article
• Language: English
• Subjects: Adrenergic receptors; Biological and medical sciences; Calcium; Calcium (intracellular); Cell activation; Cyclic AMP; Epidermal growth factor; Epidermal growth factor receptors; Extracellular signal-regulated kinase; Fundamental and applied biological sciences. Psychology; Growth factors; Hormones; Inositol trisphosphate; Inositols; Ionomycin; Kinases; Myometrium; Oxytocin; Pertussis; Pertussis toxin; Phospholipase C; Phosphorylation; Platelet-derived growth factor; Platelet-derived growth factor receptors; Pretreatment; Protein kinase A; Protein kinase A inhibitors; Protein kinase C; Protein-tyrosine kinase receptors; Proteins; Receptors (physiology); Thapsigargin; Toxins; Tyrosine; Tyrosine kinase inhibitors; Whooping cough
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2002-221039

The mechanisms by which oxytocin (OT) stimulates extracellular signal-regulated kinase 1/2 (ERK1/2) are only partially understood. OT receptor (OTR) signals predominantly through Gαq, but ERK1/2 phosphorylation (ERK1/2-P) in PHM1 myometrial cells was not eliminated by inhibition of downstream effectors such as phospholipase C or protein kinase C. Inconsistent with a Gαi-coupled response, pertussis toxin inhibition of OT-induced ERK1/2-P was reversed by the protein kinase A inhibitors Rp-cAMPS and KT5720. Consistent with an inhibitory role for protein kinase A, pertussis toxin pretreatment raised cellular cAMP and 8-(4-chlorophenylthio)-cAMP inhibited OT-induced ERK1/2-P. Attenuation of the OT response by the Gβγ scavenger carboxyl terminus of the β-adrenergic receptor kinase implicated a Gβγ-mediated pathway. In both COSM6 cells overexpressing OTR (OTR-COSM6) and in PHM1 cells, the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor AG1478 markedly reduced OT-induced ERK1/2-P, whereas the platelet-derived growth factor receptor tyrosine kinase inhibitor AG1296 had no effect. Furthermore, OT increased EGFR tyrosine phosphorylation in OTR-COSM6 cells, which was inhibited by AG1478 or EGTA plus thapsigargin pretreatment. AG1478 did not affect inositol 1,4,5-triphosphate production by OT or protein kinase C-stimulated ERK1/2-P but completely blocked ionomycin-induced ERK1/2-P and EGFR tyrosine phosphorylation. In both OTR-COSM6 and PHM1 cells, EGTA reduced OT-stimulated ERK1/2-P; no ERK1/2-P was observed when intracellular calcium increases were blocked by pretreatment with thapsigargin plus EGTA. These data are consistent with activation of a Gβγ-mediated pathway as a consequence of Gαq activation in myometrium and OTR-COSM6 cells that results in increased ERK1/2-P. This pathway involves both EGFR activation and an influence of calcium.