Induction of prostaglandin I(2) receptor by tumor necrosis factor alpha in osteoblastic MC3T3-E1 cells

Mouse osteoblastic cells MC3T3-E1 produced prostaglandin E(2) via the reaction of cyclooxygenase-2 enzyme induced by tumor necrosis factor alpha (TNFalpha). Originally, the mRNA level for prostaglandin I(2) receptor (IP) was low in the cells. However, the addition of TNFalpha brought about a marked increase in the IP mRNA with a lag of about 3 h up to an about 8-fold higher level for 24 h. In addition, the induction of IP was supported by a binding experiment of [(3)H]iloprost (a stable analogue of prostaglandin I(2)). The amount of iloprost bound to the TNFalpha-stimulated cell membranes increased to a saturation level around 30 nM. Dexamethasone, cycloheximide and cyclooxygenase inhibitor suppressed the IP mRNA induction. The finding with the latter two compounds suggested a TNFalpha-dependent de novo synthesis of a protein, which is involved in the IP mRNA induction and may be attributed partially to the induced cyclooxygenase-2.