Cytosolic phospholipase A (cPLA2α) catalyzes the formation of arachidonic acid in prostaglandin synthesis. In contrast to the well-described down-regulation of cPLA2α, up-regulation of cPLA2α by glucocorticoids has been reported in human amnion fibroblasts, which may play a key role in parturition. The mechanisms underlying this paradoxical induction of cPLA2α by glucocorticoids remain largely unknown. Using cultured human amnion fibroblasts, we found that the induction of cPLA2α by cortisol required ongoing transcription and synthesis of at least one other protein. The induction of cPLA 2α by cortisol was abolished by mutagenesis of a glucocorticoid response element (GRE) in the promoter. The same GRE was found mediating the classical inhibition of cPLA2α expression by cortisol in human fetal lung fibroblasts (HFL-1). Cortisol increased Gαs expression in amnion fibroblasts but not in HFL-1 cells. Inhibition of Gαs with NF449 attenuated the phosphorylation of cAMP response element-binding protein-1 (CREB-1) and the induction of cPLA2α by cortisol in amnion fibroblasts. Both glucocorticoid receptor (GR) and CREB-1 were found bound to the GRE upon cortisol stimulation of amnion fibroblasts. The induction of cPLA2α by cortisol was blocked by GR antagonist RU486 or protein kinase A inhibitor H89 or dominantnegative CREB-1. In conclusion, cortisol activates the cAMP/protein kinase A/CREB-1 pathway via Gαs induction, and the phosphorylated CREB-1 interacts with GR at the GRE to promote cPLA2α expression in amnion fibroblasts.
ASJC Scopus subject areas
- Molecular Biology