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

Abstract

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 Galpha(q), 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 Galpha(i)-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 Gbetagamma scavenger carboxyl terminus of the beta-adrenergic receptor kinase implicated a Gbetagamma-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 Gbetagamma-mediated pathway as a consequence of Galpha(q) 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.

Oxytocin Promotes Long-Term Potentiation by Enhancing Epidermal Growth Factor Receptor-Mediated Local Translation of Protein Kinase Mζ

“…This study provides, to our knowledge, the first evidence for the transactivation of EGFR by OXTR in brain. This regulation has been demonstrated in myometrial and epithelial cells (Zhong et al, 2003;Krishnaswamy et al, 2010), where the EGFR tyrosine kinase may serve as an important effector in a signaling pathway connecting OXTR to PI3K and ERK1/2 to regulate gene expression. Interestingly, it was noted that the inhibition of PLC with U73122 completely prevented OXT-induced increases in PI3K and ERK1/2 activation, suggesting that OXTinduced PLC activation mediates the transactivation of EGFR and its downstream PI3K and ERK1/2 signaling.…”

“…Because OXT has been shown to transactivate EGFR tyrosine kinase in both PHM1 immortalized human myometrial cells (Zhong et al, 2003) and bovine endometrial epithelial cells (Krishnaswamy et al, 2010), we therefore examined whether activation of OXTR could transactivate EGFR and subsequently stimulate PKM protein synthesis. As expected, we found that pretreatment of the synaptoneurosomes with a tyrophostin AG1478 (1 M), a selective inhibitor of EGFR (Levitzki and Gazit, 1995), completely blocked OXT (1 M)-induced increases in PKM protein synthesis (Fig.…”

Interaction of Extracellular Signal-Regulated Protein Kinase 1/2 with Actin Cytoskeleton in Supraoptic Oxytocin Neurons and Astrocytes: Role in Burst Firing

“…This may explain the spontaneous bursts at early stages of actindisrupting agent application and how OT could quickly increase the paranuclear cytosolic F-actin, but not membrane subcortical F-actin, in OT neurons in the presence of cytochalasin B. (Zhong et al, 2003;Wang and Hatton, 2007) and ERK kinase, MEK. pERK1/2 can facilitate F-actin formation through at least two pathways: by increasing production of prostaglandins (PGs) (Wang and Hatton, 2006) and by phosphorylating cofilin (P-cofilin) (phosphorylation of cofilin inhibits its ability to depolymerize F-actin) (Nebl et al, 2004;Pritchard et al, 2004).…”

“…In the signaling pathway for OT actions, pERK1/2 has been identified (Hoare et al, 1999;Zlatnik et al, 2000;Burns et al, 2001). OTR-associated G-protein ␤␥ subunits, a dominant signal in OT-evoked bursts (Wang and Hatton, 2007), can activate ERK1/2 by phosphorylation to form pERK1/2 (Zhong et al, 2003). Another major target of OT actions is actin.…”

“…OT actions on actin are mediated by producing prostaglandins (Wang and Hatton, 2006), a key player in OT-evoked bursts (Hatton and Wang, 2005). The production of prostaglandin also depends on ERK1/2 activation (Zhong et al, 2003;Reversi et al, 2005). Moreover, OTRs are expressed by both SON neurons and astrocytes (Wang and Hatton, 2006), which allows OT to mobilize various cells to actualize the milk-ejection reflex (MER).…”