Urocortin, but Not Corticotropin-Releasing Hormone (CRH), Activates the Mitogen-Activated Protein Kinase Signal Transduction Pathway in Human Pregnant Myometrium: An Effect Mediated via R1α and R2β CRH Receptor Subtypes and Stimulation of Gq-Proteins

• Published in: Molecular endocrinology (Baltimore, Md.) Vol. 14; no. 12; pp. 2076 - 2091
• Main Authors: Grammatopoulos, Dimitris K, Randeva, Harpal S, Levine, Michael A, Katsanou, Efrosini S, Hillhouse, Edward W
• Format: Journal Article
• Language: English
• Published: Endocrine Society 01-12-2000; Oxford University Press
• ISSN: 0888-8809; 1944-9917
• DOI: 10.1210/mend.14.12.0574

CRH and CRH-related peptides such as urocortin
mediate their actions in the human myometrium via activation of two
distinct classes of CRH receptors, R1 and R2. These heptahelical
receptors are able to stimulate a number of different intracellular
signals; one key mediator of G protein-activated intracellular
signaling is the cascade of p42/p44, mitogen-activated protein kinase
(MAPK). We therefore hypothesized that activation of MAPK might mediate
CRH and or/urocortin actions in the myometrium.
In cultured human pregnant myometrial cells, urocortin but not CRH was
able to induce MAPK phosphorylation and activation, suggesting that in
the human myometrium these two peptides have distinct actions and
biological roles. To identify the particular receptor subtypes
mediating this phenomenon, all known CRH receptors present in the human
myometrial cells were stably expressed individually in HEK293 and CHO
cells, and their ability to activate MAPK was tested. The R1α and
R2β, but not the R1β, R1c, or R1d, receptor subtypes were able to
mediate urocortin-induced MAPK activation. The signaling components
were further investigated; activation of Gs, Go, or Gi proteins did not
appear to be involved, but activation of Gq with subsequent production
of inositol triphosphates (IP3) and protein
kinase C (PKC) activation correlated with MAPK phosphorylation. Studies
on Gq protein activation using[α
-32P]-GTP-γ-azidoanilide and
IP3 production in cells expressing the R1α or
R2β CRH receptors demonstrated that urocortin was 10 times more
potent than CRH. Moreover, urocortin (UCN) generated peak responses
that were 50–70% greater than CRH in activating the Gq protein and
stimulating IP3 production.
In conclusion, UCN acting thought multiple receptor subtypes can
stimulate myometrial MAPK via induction of the Gq/phospholipase
C/IP3/PKC pathway, whereas CRH-induced
activation of this pathway appears to be insufficient to achieve MAPK
activation.