OBJECTIVE: To investigate the regulation of receptor activator of nuclear factor kappaB ligand (RANKL) and osteoprotegerin (OPG) mRNA expression by prostaglandin E2 (PGE2) in osteoblastic-like cells and involved signaling pathways. METHODS: Rat UMR106 osteoblast-like cells were cultured and treated with various dose of PGE2 or regulators of different signaling pathways such as protein kinase A, protein kinase C, ERK-MAPK and calcium/calmodulin pathways for different period of time,the cells were then harvested at indicated time points, total RNA were isolated and RANKL/OPG mRNA expression were studied by real-time PCR. RESULTS: PGE2, Forskolin and db-cAMP increased RANKL mRNA by 2.8 times (P = 0.002), 2.2 times (P = 0.006) and 2.1 times (P = 0.005) respectively, and inhibited OPG mRNA expression by 12% (P < 0.01), 85% (P = 0.005) and 70% (P = 0.013) respectively, while RANKL and OPG mRNA expression were down-regulated by A23187 by 58% (P = 0.002) and 53% (P = 0.017) respectively. As for inhibitory experiments, the stimulatory effects of PGE2 on RANKL mRNA expression could be inhibited only by KT-5720 by 53% (P < 0.01), while the other inhibitors did not have any effect at all. The inhibitory effects of PGE2 on OPG mRNA expression were partially blocked by KT-5720 by 47% (P = 0.01), verapamil by 38% (P = 0.029) and W7 by 43% (P < 0.01) respectively, while KN-62, chelerythrine and PD98059 had no effects. CONCLUSION: PGE2 can up-regulate the expression of RANKL but down-regulate the expression of OPG. The up-regulation of RANKL mRNA expression by PGE2 was mediated through the activation of PKA signaling pathway while PGE2 induced down-regulation of OPG mRNA expression was predominantly mediated via PKA as well as the Ca2+ /Calmodulin signaling pathways.