Interferon γ-Induced Gene Expression of the Novel Secretory Phospholipase A2 Type IID in Human Monocyte-Derived Macrophages is Inhibited by Lipopolysaccharide

Phospholipase A2 (PLA2) is a superfamily of enzymes that may play a major role in airways inflammation. We investigated the effect of interferon-γ (IFN-γ) on the gene expression of 19 different PLA2 types in human monocyte-derived macrophages and nasal epithelial cells (RPMI 2650). The cells were stimulated with IFN-γ for different lengths of time (up to 48 h), and the mRNA levels of the different PLA2 types were determined by reverse transcriptase–PCR (RT-PCR) and normalized to those of the house-keeping gene, GAPDH. It appeared that IFN-γ clearly increased the expression of secretory PLA2 IID (but not IIA) in macrophages, while both PLA2 IID and IIA were upregulated in RPMI 2650 cells. Moreover, after 18 h, the mRNA levels of cytosolic PLA2 IVA were 2–3 times higher in IFN-γ-stimulated macrophages than controls, while there was no such effect of IFN-γ in RPMI 2650 cells. Lipopolysaccharide (LPS) augmented the increased gene expression of PLA2 IVA but decreased both the basal and the IFN-γ-induced PLA2 IID mRNA expression in macrophages (but not in RPMI 2650 cells). The NF-κB inhibitor Pyrrolidine dithiocarbamate (PDTC) and the phoshatidylinositol 3-kinase (PI3K) inhibitor wortmannin were employed to get an insight into the mechanism behind these observations. Incubation of macrophages with PDTC had no effect on the LPS impairment of PLA2 IID gene expression, but inhibited the LPS mediated activation of PLA2 IVA. No significant effect was noted of PDTC on IFN-γ stimulation, while PI3K had no effect at all on any of the stimuli used. Furthermore, LPS (but not IFN-γ) increased the mRNA levels of the nuclear factor (NF)-κB inhibitors α and ξ in macrophages, but not in RPMI 2650 cells. These findings indicate that (a) the gene expression of secretory types PLA2 IID and IIA in response to IFN-γ is much dependent on cell type, and (b) the regulation of PLA2 type IID in human macrophages is clearly different from that of PLA2 type IVA. (c) PLA2 IVA is probably under control of both NF-κB and IFN-γ-responsive elements (GRE) or IFN-γ-activating sites (GAS). The possibility that PLA2 IID is involved in cytokine-mediated inflammation in the nasal mucosa is inferred, as is the potential role of PLA2 IID in the host defense against LPS-containing bacteria.