Implication of mRNA binding proteins in the regulation of cyclo-oxygenase in human amnion at term

The onset of labour is associated with an increase in prostaglandin synthesis in amnion which appears to be mediated at least in part by an increase in cyclo-oxygenase (COX) expression. We have tested the hypothesis that COX expression is controlled in amnion by the binding of a protein to the COX mRNA which may inhibits its translation, as has been seen in vascular smooth muscle cells. Using differential RNA extraction protocols which extract either total mRNA or only mRNA which is not protein bound, we have found that, in amnion, the increase in COX-2 expression seen after the onset of labour is entirely in the protein bound fraction. Unlike in vascular smooth muscle, increased expression of COX-2 in amnion cells is therefore associated with increased rather than decreased protein binding to the mRNA. This protein may be involved in translation initiation or elongation or in mRNA stability. There does not appear to be a protein bound COX-1 mRNA fraction.