PGE2 induces IL-1beta gene expression in mouse osteoblasts through a cAMP-PKA signaling pathway

Prostaglandin E2 (PGE2), an abundant eicosanoid in bone, has been implicated in a number of pathological states associated with bone loss and is also known to stimulate matrix metalloproteinase-1 synthesis and secretion in rat and human osteoblast cells, although the intracellular reactions responsible for this remain unclear. Interleukin-1beta (IL-1beta) is a cytokine that plays a critical role in bone remodeling and appears to act as a downstream effector of most bone-resorbing agents. However, the issue of whether PGE2 regulates the expression of IL-1beta in mouse osteoblasts has not been resolved. In this work, we demonstrate that PGE2 is a potent inducer of IL-1beta production by fetal osteoblasts and show that PGE2 stimulates the activity of the IL-1beta promoter in osteoblasts, suggesting that PGE2 controls IL-1beta gene expression at least at the transcriptional level. PGE2 was found to induce IL-1beta mRNA expression in the cells within 4 h and the level of expression was maintained for 36 h. A dose-related increase in IL-1beta production was found with 0.1-2.0 microM PGE2. The induction of IL-1beta protein in the medium paralleled the induction of IL-1beta mRNA levels. The role of cAMP activation in PGE2-mediated IL-1beta production was examined by the effects of forskolin, an adenylyl cyclase (AC) activator and dideoxyadenosine (DDA), an AC inhibitor. Forskolin enhanced and DDA blocked the production of IL-1beta by PGE2. In addition, PGE2-mediated IL-1beta induction was completely inhibited by the cAMP antagonist, Rp-cAMP, and protein kinase A (PKA) inhibitors of KT5720 and H89. The PGE2-induced production of IL-1beta was also blocked by the PKA inhibitor PKI14-22. However, a specific inhibitor of protein kinase C, calphostin C, had no affect on PGE2-induced IL-1beta gene expression. Among the potential agonists, forskolin was a potent inducer of IL-1beta expression, while phorbol myristate acetate and serum had little effect. These findings indicate that PGE2 involves the cAMP-PKA signaling pathway in regulating IL-1beta gene expression in osteoblasts.