Autoimmune Disease-Associated Variants of Extracellular Endoplasmic Reticulum Aminopeptidase 1 Induce Altered Innate Immune Responses by Human Immune Cells

Abstract

Endoplasmic reticulum aminopeptidase 1 (ERAP1) gene polymorphisms have been linked to several autoimmune diseases; however, the molecular mechanisms underlying these associations are not well understood. Recently, we demonstrated that ERAP1 regulates key aspects of the innate immune response. Previous studies show ERAP1 to be endoplasmic reticulum-localized and secreted during inflammation. Herein, we investigate the possible roles that ERAP1 polymorphic variants may have in modulating the innate immune responses of human peripheral blood mononuclear cells (hPBMCs) using two experimental methods: extracellular exposure of hPBMCs to ERAP1 variants and adenovirus (Ad)-based ERAP1 expression. We found that exposure of hPBMCs to ERAP1 variant proteins as well as ERAP1 overexpression by Ad5 vectors increased inflammatory cytokine and chemokine production, and enhanced immune cell activation. Investigating the molecular mechanisms behind these responses revealed that ERAP1 is able to activate innate immunity via multiple pathways, including the NLRP3 (NOD-like receptor, pyrin domain-containing 3) inflammasome. Importantly, these responses varied if autoimmune disease-associated variants of ERAP1 were examined in the assay systems. Unexpectedly, blocking ERAP1 cellular internalization augmented IL-1β production. To our knowledge, this is the first report identifying ERAP1 as being involved in modulating innate responses of human immune cells, a finding that may explain why ERAP1 has been genetically associated with several autoimmune diseases.

Effects of polymorphic variation on the mechanism of Endoplasmic Reticulum Aminopeptidase 1

“…In addition, the destruction of smaller peptides in the ER may regulate ERAP1 activity by allosteric activation or inhibition (Nguyen et al, 2011;Evnouchidou et al, 2011). Altered trimming of small peptides may also be relevant to other functions of ERAP1 in the context of innate immunity or blood pressure regulation through Angiotensin degradation (Goto et al, 2006;Aldhamen et al, 2015;Hisatsune et al, 2015).…”

Structural Basis for Antigenic Peptide Recognition and Processing by Endoplasmic Reticulum (ER) Aminopeptidase 2

“…8) the positions of the two cysteine residues are highly similar, suggesting that a similar disulfide bond may be forming in ERAP1. The configuration of this loop may be a structural template that facilitates interactions between ERAP2 or ERAP1 and other proteins in the ER in order to regulate retention and extracellular functions in the context of blood pressure regulation or innate immune responses (46,47).…”

3,4-Diaminobenzoic Acid Derivatives as Inhibitors of the Oxytocinase Subfamily of M1 Aminopeptidases with Immune-Regulating Properties

“…Compounds were purified by reversed-phase HPLC on a C18 chromolith column (Merck) using a 0−50% (v/v) acetonitrile gradient in water containing 0.05% TFA while following the absorbance at 257 nm. The purity of all final compounds employed in the biological assays was greater than 95%, and the structures of the synthesized compounds were determined by 1 H NMR, 13 C NMR, and high-resolution mass spectroscopy (HRMS).…”

“…■ ASSOCIATED CONTENT * S Supporting Information 1 H and 13 C NMR spectra of biologically active compounds 4a, 4u, 4x, and 10n; titration curve of 4u with recombinant mouse IRAP. This material is available free of charge via the Internet at http://pubs.acs.org.…”

“…ERAP1 polymorphic variation was recently shown to quantitatively affect innate immune responses. 13 Since natural polymorphic variation of ERAP1 and ERAP2 can generate a range of enzymatic activities in the population, it has been hypothesized that the activity of these enzymes is an important regulator of immune responses in humans. 14 Inhibition of APAs is a promising approach for selectively regulating immune responses.…”