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

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 (PLA2I), which may be involved in the liberation of arachidonic acid from membrane phospholipids. For this purpose, we used the uterine stromal cell line UIII, 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 UIII cells, was not modified by arachidonic acid. The expression of PGHS2 and PLA2 I was up-regulated by increasing arachidonate concentrations (1-10 microM). 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 microM. We conclude that arachidonic acid up-regulates the expression of PLA2 I and PGHS2 in the uterine stromal cells, independently of prostanoids, and that prostaglandin E2 is capable of down-regulating enzyme expression.

An in vitro investigation of the actions of reproductive hormones on the cervix of the ewe in the follicular stage: The effects of 17β-estradiol, oxytocin, FSH, and arachidonic acid on the cervical pathway for the synthesis of prostaglandin E2

“…Increased production of PG in various tissues after stimulation by polyunsaturated fatty acids has been previously reported in rat uterine stromal cells [49] and in endometrial cells from the late-pregnant ewes [25]. In our study, AA increased levels of COX-2 and cPLA 2 after 48 hours of incubation and these results were in agreement with what previously shown in bovine endometrial cells [50].…”

Prostaglandin E2 Amplifies Cytosolic Phospholipase A2- and Cyclooxygenase-2-dependent Delayed Prostaglandin E2 Generation in Mouse Osteoblastic Cells

“…For instance, the induction of COX-2 expression in cytokine-stimulated mast cells was not affected by several PLA 2 and COX inhibitors, indicating that the regulatory mechanism was PG-independent (41). Arachidonic acid up-regulated, whereas PGE 2 down-regulated, the induction of COX-2 in uterine stromal cells (42). IL-1␤-induced arachidonic acid release and subsequent COX-2-dependent PGE 2 generation were augmented significantly in sPLA 2 -transfected compared with normal CHO-K1 cells, without accompanying changes in cPLA 2 and COX-2 expression (20).…”

Involvement of Phosphatidate Phosphohydrolase in Arachidonic Acid Mobilization in Human Amnionic WISH Cells

“…It seems likely that at short times, the free AA may act as a signaler rather than an intermediary metabolite. As a matter of fact, it has been suggested that exogenous AA up-regulates the expression of COX-2 in uterine stromal cells (38). The induction is not due to conversion of AA to prostaglandin by COX-1 because it occurs even in the presence of aspirin, a well known inhibitor of COX activity.…”