Activation of CRH receptors type 1 (CRH-R1) by CRH or urocortin (UCN) leads to stimulation of multiple G proteins with consequent effects on diverse signaling cascades in a tissue-specific manner. In human myometrium and human embryonic kidney (HEK)293 cells, binding of UCN to CRH-R1α receptors activates both the Gs and Gq, leading to activation of the adenylyl cyclase/protein kinase A (PKA) and the phospholipase C/protein kinase C and ERK1/2 signaling pathways, respectively. The overall result of these signals is often unpredictable, as these two signaling pathways can interact in many cellular systems, with either potentiation or inhibition of ERK1/2 activity. In the present studies we investigated potential signaling interactions after stimulation of CRH-R1α receptors in human cultured pregnant myometrial cells or HEK293 cells overexpressing recombinant CRH-R1α receptors. We found that the adenylyl cyclase/PKA pathway has the capacity to markedly decrease UCN-induced ERK1/2 activation, and that these effects were due in part to the ability of PKA to phosphorylate the CRH-R1α at position Ser 301 in the third intracellular loop. Mutant CRH-R1α receptors with substitutions at position Ser301, which is the only potential PKA phosphorylation site, were resistant to PKA-dependent phosphorylation and showed altered signaling characteristics, which were dependent upon the amino acid substitution at this position. We conclude that Ser301, which is located in the third intracellular loop of CRK-R1α, is critical for efficient coupling of the receptor to G proteins and to second messenger generation. Phosphorylation by PKA prevents maximal coupling of the CRH-R1α to Gq-protein, and thereby reduces activation of ERK 1/2. (Molecular Endocrinology 18: 624-639, 2004).
ASJC Scopus subject areas
- Molecular Biology
- Endocrinology, Diabetes and Metabolism