Arachidonic Acid Up‐Regulates and Prostaglandin E2 Down‐Regulates the Expression of Pancreatic‐Type Phospholipase A2 and Prostaglandin‐Endoperoxide Synthase 2 in Uterine Stromal Cells

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Abstract
It is well known that arachidonic acid, as a substrate of prostaglandin G/H synthase (PGHS), is converted into prostaglandins of the two‐series. In this work, we attempted to determine whether arachidonic acid and prostaglandin E2 might regulate the expression of PGHS and the pancreatic‐type phospholipase A2(PLA2 I), which may be involved in the liberation of arachidonic acid from membrane phospholipids. For this purpose, we used the uterine stromal cell line U111 which produces prostaglandin E2 and expresses both the constitutive and inducible PGHS enzymes (PGHS1 and PGHS2) and PLA2 I. The results show that PGHS1 which is expressed at a high level in U111 cells, was not modified by arachidonic acid. The expression of PGHS2 and PLA2 I was up‐regulated by increasing arachidonate concentrations (10–10 μM). The maximal response was obtained at 24 h, reaching a 2.3‐fold and 2.6‐fold increase for PGHS2 and PLA2 I expression, respectively, compared to the control level. To discriminate between the effect of arachidonic acid and that of prostaglandins, which are highly increased in the presence of exogenous arachidonic acid, we treated the cells with two inhibitors of PGHS activity, aspirin and meclofenamic acid. Both inhibitors failed to suppress the arachidonate‐induced increase of PLA2 I and PGHS2 expression and even enhanced it either in the presence or absence of arachidonic acid. In contrast, the addition of prostaglandin E2 to the culture medium decreased the expression of both enzymes in a dose‐dependent manner, the maximal response being reached at 1 μM. We conclude that arachidonic acid up‐regulates the expression of PLA2I and PGHS2 in the uterine stromal cells, independently of prostanoids, and that prostaglandin E2 is capable of down‐regulating enzyme expression.

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