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-γ (IFN-γ) and lipopolysaccharide (LPS), but not by anti-inflammatory cytokines (interleukin (IL)-4, IL-10, transforming growth factor β (TGF-β)). IFN-γ increased [(3)H]IVDE77 binding steadily over time, while LPS quickly and transiently recruited IRAP to the cell surface. Combined stimulations with IFN-γ 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-γ, LPS or exogenous particles.