Interferon γ induces prostaglandin G/H synthase-2 through an autocrine loop via the epidermal growth factor receptor in human bronchial epithelial cells

Abstract

The induction of prostaglandin G/H synthase (PGHS; prostaglandin endoperoxide synthase, cyclooxygenase) by proinflammatory cytokines accounts, at least in part, for the altered eicosanoid biosynthesis in inflammatory diseases. In secondary cultures of normal human bronchial epithelial cells (NHBECs), interferon-γ (IFN-γ, 10 ng/ml for 24 h) increased the amount of prostaglandin E2 (PGE2) released in response to stimulation with exogenous arachidonic acid (5 μM). The enhanced production of PGE2 reflected the upregulation of PGHS-2 as indicated by enhanced expression of PGHS-2 RNA and increased recovery of PGHS-2 protein in NHBECs. IFN-γ did not alter the production of PGE2 in A549 cells (a human lung adenocarcinoma cell line) or 6-keto-PGF(1α) in human umbilical vein endothelial cells (HUVECs), although prostaglandin release and/or the expression of PGHS-2 RNA in these cell lines was upregulated by other proinflammatory cytokines. Induction of PGHS-2 RNA in IFN-γ-treated NHBECs, which peaked at 24 h, suggested the presence of an intermediary substance regulating the expression of PGHS-2. When the binding between the epidermal growth factor (EGF) receptor and its ligands was disrupted by a neutralizing antibody (LA-1), IFN-γ failed to upregulate the release of PGE2 and the expression of PGHS-2 RNA in NHBECs. Furthermore, IFN-γ induced the expression of RNAs for a number of ligands at the EGF receptor TGF-α; heparin-binding EGF-like growth factor (HB-EGF); and amphiregulin in NHBECs, and when administered exogenously, these ligands increased PGF2 release from NHBECs. Heparin at the concentration that neutralized the function of amphiregulin, or antibodies against TGFα or HB- EGF also reduced the release of PGE2 from IFN-γ-stimulated NHBECs. These data are consistent with the presence of an autocrine growth factor/EGF receptor loop regulating PGHS-2 expression and PGE2 synthesis in bronchial epithelial cells.