Functional interactions between the oxytocin receptor and the β2-adrenergic receptor: Implications for ERK1/2 activation in human myometrial cells

Oct 4, 2011Cellular signalling

How oxytocin and beta2-adrenergic receptors work together to activate ERK1/2 in human uterine muscle cells

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Abstract

Inhibition of specific signaling pathways reduced both OTR- and β(2)AR-mediated ERK1/2 activation in human myometrial cells.

The oxytocin receptor (OTR) and β(2)-adrenergic receptor (β(2)AR) both activate the ERK1/2 signaling pathway, which is involved in uterine contraction and labor onset.
Inhibition of the Gαi and Gαq/PKC pathways decreased ERK1/2 activation mediated by both receptors.
The β(2)AR's ability to activate ERK1/2 through the Gαq/PKC pathway was found to occur only when co-expressed with OTR.
An atypical PKC isoform, specifically PKCζ, was implicated in the β(2)AR-mediated signaling process requiring OTR co-expression.
PKCζ translocation to the cell membrane was confirmed to depend on the presence of OTR in the cells.

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The Gq-coupled oxytocin receptor (OTR) and the Gs-coupled β(2)-adrenergic receptor (β(2)AR) are both expressed in myometrial cells and mediate uterine contraction and relaxation, respectively. The two receptors represent important pharmacological targets as OTR antagonists and β(2)AR agonists are used to control pre-term uterine contractions. Despite their physiologically antagonistic effects, both receptors activate the MAP kinases ERK1/2, which has been implicated in uterine contraction and the onset of labor. To determine the signalling pathways involved in mediating the ERK1/2 response, we assessed the effect of blockers of specific G protein-associated pathways. In human myometrial hTERT-C3 cells, inhibition of Gαi as well as inhibition of the Gαq/PKC pathway led to a reduction of both OTR- and β(2)AR-mediated ERK1/2 activation. The involvement of Gαq/PKC in β(2)AR-mediated ERK1/2 induction was unexpected. To test whether the emergence of this novel signalling mechanism was dependent on OTR expression in the same cell, we conducted experiments in HEK 293 cells that were transfected with the β(2)AR alone or co-transfected with the OTR. Using this approach, we found that β(2)AR-mediated ERK1/2 responses became sensitive to PKC inhibition only in cells co-transfected with the OTR. Inhibitor studies indicated the involvement of an atypical PKC isoform in this process. We confirmed the specific involvement of PKCζ in this pathway by assessing PKCζ translocation to the cell membrane. Consistent with our inhibitor studies, we found that β(2)AR-mediated PKCζ translocation was dependent on co-expression of OTR. The present demonstration of a novel β(2)AR-coupled signalling pathway that is dependent on OTR co-expression is suggestive of a molecular interaction between the two receptors.

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Functional interactions between the oxytocin receptor and the β2-adrenergic receptor: Implications for ERK1/2 activation in human myometrial cells

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