Dexamethasone Alters Arachidonate Release from Human Epithelial Cells by Induction of p11 Protein Synthesis and Inhibition of Phospholipase A2 Activity

The effect of the glucocorticosteroid, dexamethasone, on arachidonic acid (AA) release and on protein levels of p11 and cytosolic phospholipase A₂ (cPLA₂) was studied in two epithelial cell lines, HeLa cells and BEAS-2B cells. Dexamethasone treatment of HeLa cells and BEAS-2B cells increased cellular p11 protein and mRNA levels in a time- and dose-dependent manner. It had little effect on levels of cPLA₂ protein. In order to determine if increased p11 protein expression resulted in increased interaction between p11 and cPLA₂, anti-cPLA₂ antibodies were used to immunoprecipitate p11zcPLA₂ complexes and Western blots of the immunoprecipitate were used to detect p11. In cells treated with dexamethasone, more p11 was detected in the anti-cPLA₂ immunoprecipitate compared with control cells. Dexamethasone treatment of HeLa cells prelabeled with [³H]AA decreased the release of [³H]AA under basal conditions and after stimulation with the calcium ionophore A23187 (10^–6 M). In order to determine if altering the p11 protein levels in HeLa cells independent of glucocorticosteroid treatment could also produce an effect on [³H]AA release, cells were stably transfected with plasmids expressing either p11 antisense mRNA or p11 mRNA. Cloned HeLa cells expressing p11 antisense mRNA exhibited less cellular p11 protein compared with control cells and greater [³H]AA release compared with cells transfected with a control vector. Cloned HeLa cells stably transfected with a p11 expression vector exhibited increased p11 cellular protein and diminished [³H]AA release under basal conditions and in response to A23187. Therefore, dexamethasone alteration of epithelial cell AA release may be due in part to induction of p11 protein expression.