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.