Presence and regulation of insulin-regulated aminopeptidase in mouse macrophages

INTRODUCTION: The insulin-regulated aminopeptidase (IRAP) is expressed in several cell types, where it is mainly located in specialized secretory endosomes that are quickly recruited to the cell surface upon cell type-specific activation. Here we describe for the first time the expression and subcellular distribution of IRAP in macrophages. METHODS: IRAP mRNA expression, protein expression and presence at the cell surface was investigated by real-time polymerase chain reaction (PCR), Western blot and [(3)H]IVDE77 binding, respectively. RESULTS: IRAP mRNA expression was increased by interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS), but not by anti-inflammatory cytokines (interleukin (IL)-4, IL-10, transforming growth factor beta (TGF-beta)). IFN-gamma increased [(3)H]IVDE77 binding steadily over time, while LPS quickly and transiently recruited IRAP to the cell surface. Combined stimulations with IFN-gamma and LPS showed the same pattern as LPS alone. Latex particles also induced a transient recruitment of IRAP to the cell surface, but no difference was observed in phagocytic uptake between wild-type and IRAP(-/-) macrophages, suggesting that the enzymatic activity of IRAP is not required for the ingestion of particles. CONCLUSION: IRAP is more highly expressed in pro-inflammatory M1-activated macrophages and its presence at the cell surface is modulated upon exposure to IFN-gamma, LPS or exogenous particles.