TLR-Mediated Secretion of Endoplasmic Reticulum Aminopeptidase 1 from Macrophages

Abstract

Macrophages play an important role in host defense under several immunological, inflammatory, and/or infectious conditions. In our previous work, we demonstrated that endoplasmic reticulum aminopeptidase 1 (ERAP1) was secreted from macrophages in response to LPS and IFN-γ, and it enhanced their phagocytic activity. In this study, we analyzed the mechanism of LPS/IFN-γ–induced ERAP1 secretion. LPS/IFN-γ–induced secretion of the enzyme from the murine macrophage cell line RAW264.7 was suppressed by polymyxin B. Several agonists of TLRs, such as Pam3CSK4, FSL-1, and ODN1826, induced its secretion. In contrast, neutralizing Abs to IFN-β and TNF-α receptor type 1 suppressed its secretion. Using murine peritoneal macrophages derived from TNF-α and type 1 IFNR knockout mice, we confirmed the involvement of these two cytokines in ERAP1 secretion. In addition, secretion of ERAP1 from both RAW264.7 cells and murine peritoneal macrophages was induced by A23187 and thapsigargin and inhibited by BAPTA-AM and the calmodulin inhibitor W7. These results suggest that LPS/IFN-γ–induced secretion of ERAP1 is mediated by TLRs via induction of intermediate cytokines such as IFN-β and TNF-α, which in turn lead to enhanced cytosolic Ca2+ levels and calmodulin activation.

A Role for Naturally Occurring Alleles of Endoplasmic Reticulum Aminopeptidases in Tumor Immunity and Cancer Pre-Disposition

“…Namely, ERAP1 has been involved in the shedding of cytokine receptors including the type I TNF receptor (TNFR1), type I IL-6 receptor (IL-6Ra), and type II IL-II decoy receptor ( 31 – 33 ). Additionally, macrophages were found to produce a secreted form of ERAP1 in response to interferon-γ and liposaccharides through a TLR-mediated mechanism that leads to enhanced phagocytosis ( 34 , 35 ). Similarly, human PBMCs exposed to ERAP1 externally are activated and show enhanced production of cytokines and chemokines, through mechanisms involving the NLRP3 inflammasome (Aldhamen et al J Innate Immunity , in press).…”

ERAP1 reduces accumulation of aberrant and disulfide-linked forms of HLA-B27 on the cell surface

“…ERAP1 has also been implicated in cytokine receptor shedding (then known as ARTS1) (Cui et al, 2002), and can be secreted from stimulated macrophages resulting in enhanced phagocytic activity (Goto et al, 2011; Goto et al, 2014). Non-synonymous coding variants of the ERAP1 gene are associated with ankylosing spondylitis and other HLA class I-associated immune-mediated inflammatory diseases including Behçet’s (HLA-B51) and psoriasis (HLA-Cw6) (Burton et al, 2007; Genetic Analysis of Psoriasis et al, 2010; Kirino et al, 2013).…”

Endoplasmic Reticulum Aminopeptidase 1 beyond Antigenic Peptide-Processing Enzyme in the Endoplasmic Reticulum

“…45) While ERAP1 is secreted via the conventional secretion pathway through Golgi apparatus, 40) exosomes are known to be derived from endosomal pathway and formed within multivesicular bodies (MVB). 46) It is most conceivable that on fusion of MVB with plasma membrane, exosomes are secreted into the extracellular milieu and then, bind to ERAP1 (Fig. 4).…”