Endoplasmic reticulum aminopeptidases: biochemistry, physiology and pathology

The role of endoplasmic reticulum aminopeptidases in type 1 diabetes mellitus

Type-I diabetes mellitus (T1DM) is generally considered as a chronic, T-cell mediated autoimmune disease. This notwithstanding, both the endogenous characteristics of β-cells, and their response to environmental factors and exogenous inflammatory stimuli are key events in disease progression and exacerbation. As such, T1DM is now recognized as a multifactorial condition, with its onset being influenced by both genetic predisposition and environmental factors, among which, viral infections represent major triggers. In this frame, endoplasmic reticulum aminopeptidase 1 (ERAP1) and 2 (ERAP2) hold center stage. ERAPs represent the main hydrolytic enzymes specialized in trimming of N-terminal antigen peptides to be bound by MHC class I molecules and presented to CD8+ T cells. Thus, abnormalities in ERAPs expression alter the peptide-MHC-I repertoire both quantitatively and qualitatively, fostering both autoimmune and infectious diseases. Although only a few studies succeeded in determining direct associations between ERAPs variants and T1DM susceptibility/outbreak, alterations of ERAPs do impinge on a plethora of biological events which might indeed contribute to the disease development/exacerbation. Beyond abnormal self-antigen peptide trimming, these include preproinsulin processing, nitric oxide (NO) production, ER stress, cytokine responsiveness, and immune cell recruitment/activity. The present review brings together direct and indirect evidence focused on the immunobiological role of ERAPs in T1DM onset and progression, covering both genetic and environmental aspects.

A Comparative Review of Pregnancy and Cancer and Their Association with Endoplasmic Reticulum Aminopeptidase 1 and 2

The fundamental basis of pregnancy and cancer is to determine the fate of the survival or the death of humanity. However, the development of fetuses and tumors share many similarities and differences, making them two sides of the same coin. This review presents an overview of the similarities and differences between pregnancy and cancer. In addition, we will also discuss the critical roles that Endoplasmic Reticulum Aminopeptidase (ERAP) 1 and 2 may play in the immune system, cell migration, and angiogenesis, all of which are essential for fetal and tumor development. Even though the comprehensive understanding of ERAP2 lags that of ERAP1 due to the lack of an animal model, recent studies have shown that both enzymes are associated with an increased risk of several diseases, including pregnancy disorder pre-eclampsia (PE), recurrent miscarriages, and cancer. The exact mechanisms in both pregnancy and cancer need to be elucidated. Therefore, a deeper understanding of ERAP's role in diseases can make it a potential therapeutic target for pregnancy complications and cancer and offer greater insight into its impact on the immune system.

ERAP2 supports TCR recognition of three immunotherapy targeted tumor epitopes

The therapy of cancer by adoptive T cell transfer (ACT) requires T cell receptors (TCRs) with optimal affinity for HLA class I-bound peptides (pHLA-I). But not every patient responds to ACT. Therefore, it is critical to understand the individual factors influencing the recognition of HLA class I-bound peptides (pHLA-I) by TCRs. Focusing on three immunotherapy-targeted human HLA-A* 02:01-presented T cell epitopes we investigated the contribution of the ER-resident aminopeptidases ERAP1 and ERAP2 to TCR recognition of cancer cells. We found that ERAP2 on its own, when expressed in ERAP-deficient cells, elicited a strong CTL response towards the Tyrosinase_368-376 epitope. In vitro generated TAP-dependent N-terminally extended epitope precursor peptides were differently customized by ERAP1 and ERAP2 and thus may serve as potential source for the Tyrosinase_368-376 epitope. ERAP2 also influenced recognition of the gp100_209-217 tumor epitope and enhanced T cell recognition of the MART-1_26/27-35 epitope in the absence of ERAP1 expression. Our results underline the relevance of ERAP2 for tumor epitope presentation and TCR recognition and may need to be considered when designing ACT in the future.

Uncovering the genomic toll of the Black Death

The Black Death, a notorious devastating pandemic caused by Yersinia pestis infection during the 14th century, posed a formidable challenge to human immune defenses. A new article by Klunk et al. reports that a variant in an antigen-processing gene may have favored survival during the plague and may have undergone genomic selection in Europeans at unprecedented speed.

ERAP2 as a potential biomarker for predicting gemcitabine response in patients with pancreatic cancer

Objective: Pancreatic cancer is one of the most malignant tumors, with rapid metastasis, high mortality rate, and difficult early screening. Currently, gemcitabine is a first-line drug for pancreatic cancer patients, but its clinical effect is limited due to drug resistance. It is particularly important to further identify biomarkers associated with gemcitabine resistance to improve the sensitivity of gemcitabine treatment.

Methods: Drug sensitivity data and the corresponding transcript data derived from the Genomics of Drug Sensitivity in Cancer (GDSC) database for correlation analysis was adopted to obtain genes related to gemcitabine sensitivity. Moreover, the survival model of pancreatic cancer patients treated with gemcitabine in The Cancer Genome Atlas (TCGA) database was utilized to obtain key genes. Multiple in vitro assays were performed to verify the function of the key biomarker.

Results: Endoplasmic Reticulum Aminopeptidase 2 (ERAP2) was identified as a biomarker promoting gemcitabine resistance, and its high expression resulted in a worse prognosis. Besides, gemcitabine significantly increased the mRNA and protein levels of ERAP2 in pancreatic cancer cells. Additionally, ERAP2 knockdown suppressed tumorigenesis and potentiated gemcitabine-induced growth, migration and invasion inhibition in human pancreatic cancer cells.

Conclusions: ERAP2 may be a novel key biomarker for gemcitabine sensitivity and diagnosis, thus providing an effective therapeutic strategy for pancreatic cancer treatment.

A guide to antigen processing and presentation

Antigen processing and presentation are the cornerstones of adaptive immunity. B cells cannot generate high-affinity antibodies without T cell help. CD4⁺ T cells, which provide such help, use antigen-specific receptors that recognize major histocompatibility complex (MHC) molecules in complex with peptide cargo. Similarly, eradication of virus-infected cells often depends on cytotoxic CD8⁺ T cells, which rely on the recognition of peptide-MHC complexes for their action. The two major classes of glycoproteins entrusted with antigen presentation are the MHC class I and class II molecules, which present antigenic peptides to CD8⁺ T cells and CD4⁺ T cells, respectively. This Review describes the essentials of antigen processing and presentation. These pathways are divided into six discrete steps that allow a comparison of the various means by which antigens destined for presentation are acquired and how the source proteins for these antigens are tagged for degradation, destroyed and ultimately displayed as peptides in complex with MHC molecules for T cell recognition.

Antigen presentation in SARS-CoV-2 infection: the role of class I HLA and ERAP polymorphisms

Given the highly polymorphic nature of Human Leukocyte Antigen (HLA) molecules, it is not surprising that they function as key regulators of the host immune response to almost all invading pathogens, including SARS-CoV-2, the etiological agent responsible for the recent COVID-19 pandemic. Several correlations have already been established between the expression of a specific HLA allele/haplotype and susceptibility/progression of SARS-CoV-2 infection and new ones are continuously emerging. Protective and harmful HLA variants have been described in both mild and severe forms of the disease, but considering the huge amount of existing variants, the data gathered in such a brief span of time are to some extent confusing and contradictory. The aim of this mini-review is to provide a snap-shot of the main findings so far collected on the HLA-SARS-CoV-2 interaction, so as to partially untangle this intricate yarn. As key factors in the generation of antigenic peptides to be presented by HLA molecules, ERAP1 and ERAP2 role in SARS-CoV-2 infection will be revised as well.

Relevance Between COVID-19 and Host Genetics of Immune Response

The outbreak of coronavirus disease 2019 (COVID-19) was caused by the newly emerged corona virus (2019-nCoV alias SARS-CoV-2) that resembles the severe acute respiratory syndrome virus (SARS-CoV). SARS-CoV-2, which was first identified in Wuhan (China) has spread globally, resulting in a high mortality worldwide reaching ~4 million deaths to date. As of first week of July 2021, ~181 million cases of COVID-19 have been reported. SARS-CoV-2 infection is mediated by the binding of virus spike protein to Angiotensin Converting Enzyme 2 (ACE2). ACE2 is expressed on many human tissues; however, the major entry point is probably pneumocytes, which are responsible for synthesis of alveolar surfactant in lungs. Viral infection of pneumocytes impairs immune responses and leads to, apart from severe hypoxia resulting from gas exchange, diseases with serious complications. During viral infection, gene products (e.g. ACE2) that mediate viral entry, antigen presentation, and cellular immunity are of crucial importance. Human leukocyte antigens (HLA) I and II present antigens to the CD8⁺ and CD4⁺ T lymphocytes, which are crucial for immune defence against pathogens including viruses. HLA gene variants affect the recognition and presentation of viral antigenic peptides to T-cells, and cytokine secretion. Additionally, endoplasmic reticulum aminopeptidases (ERAP) trim antigenic precursor peptides to fit into the binding groove of MHC class I molecules. Polymorphisms in ERAP genes leading to aberrations in ERAP’s can alter antigen presentation by HLA class I molecules resulting in aberrant T-cell responses, which may affect susceptibility to infection and/or activation of immune response. Polymorphisms from these genes are associated, in global genetic association studies, with various phenotype traits/disorders many of which are related to the pathogenesis and progression of COVID-19; polymorphisms from various genes are annotated in genotype-tissue expression data as regulating the expression of ACE2, HLA’s and ERAP’s. We review such polymorphisms and illustrate variations in their allele frequencies in global populations. These reported findings highlight the roles of genetic modulators (e.g. genotype changes in ACE2, HLA’s and ERAP’s leading to aberrations in the expressed gene products or genotype changes at other genes regulating the expression levels of these genes) in the pathogenesis of viral infection.

Association of ERAP2 polymorphisms in Colombian HLA-B27+ or HLA-B15+ patients with SpA and its relationship with clinical presentation: axial or peripheral predominance

OBJECTIVE

To determine the association between endoplasmic reticulum aminopeptidase (ERAP)1 and ERAP2 single-nucleotide polymorphisms (SNPs) and human leukocyte antigens (HLA)-B27+ or HLA-B15+ patients with spondyloarthritis (SpA).

METHODS

104 patients with SpA according to Assessment of Spondyloarthritis International Society criteria were included in the study. HLA typing was performed by PCR. The polymorphisms were determined by real-time PCR on genomic DNA using customised probes for SNPs rs27044, rs17482078, rs10050860 and rs30187 in ERAP1, and rs2910686, rs2248374 and rs2549782 in ERAP2.

RESULTS

70 of the104 patients with SpA were HLA-B27+ and 34 were HLA-B15+. The distribution of ERAP1 and ERAP2 SNPs between the HLA-B15+ and HLA-B27+ patients with SpA did not reveal differences. Likewise, no differences in the frequencies of ERAP1 SNP haplotypes and alleles HLA-B15 or HLA-B27 were found. Interestingly, however, the frequencies of three particular haplotypes formed by ERAP2 SNPs rs2549782/rs2248374/rs2910686 varied between HLA-B15+ and HLA-B27+ patients: the ERAP2 SNPs haplotype TGT was more common in HLA-B15+ patients with SpA (OR 2.943, 95% CI 1.264 to 6.585; P=0.009), whereas the ERAP2 SNP haplotypes TGC and CAT were more associated with HLA-B27+ patients with SpA: (OR 4.483, 95% CI 1.524 to 13.187; p=0.003) and (OR 9.014, 95% CI 1.181 to 68.807; p=0.009), respectively.

CONCLUSION

An association was found between HLA-B15+ patients with SpA and haplotype TGT of ERAP2 SNPs. On the other hand, HLA-B27+ patients with SpA were associated with ERAP2 haplotypes TGC and CAT. These associations could be related to the clinical presentation of the disease, specifically with a peripheral or axial predominance, respectively.

Structural Basis of Inhibition of Human Insulin-Regulated Aminopeptidase (IRAP) by Benzopyran-Based Inhibitors

Inhibition of the insulin-regulated aminopeptidase (IRAP) improves memory and cognition in animal models. The enzyme has recently been crystallized and several series of inhibitors reported. We herein focused on one series of benzopyran-based inhibitors of IRAP known as the HFI series, with unresolved binding mode to IRAP, and developed a robust computational model to explain the structure-activity relationship (SAR) and potentially guide their further optimization. The binding model here proposed places the benzopyran ring in the catalytic binding site, coordinating the Zn²⁺ ion through the oxygen in position 3, in contrast to previous hypothesis. The whole series of HFI compounds was then systematically simulated, starting from this binding mode, using molecular dynamics and binding affinity estimated with the linear interaction energy (LIE) method. The agreement with experimental affinities supports the binding mode proposed, which was further challenged by rigorous free energy perturbation (FEP) calculations. Here, we found excellent correlation between experimental and calculated binding affinity differences, both between selected compound pairs and also for recently reported experimental data concerning the site directed mutagenesis of residue Phe544. The computationally derived structure-activity relationship of the HFI series and the understanding of the involvement of Phe544 in the binding of this scaffold provide valuable information for further lead optimization of novel IRAP inhibitors.

Aminopeptidase Expression in Multiple Myeloma Associates with Disease Progression and Sensitivity to Melflufen

Simple Summary

The aims of this study were to investigate aminopeptidase expression in multiple myeloma and to identify the aminopeptidases responsible for the activation of the peptide–drug conjugate melflufen in multiple myeloma. We observed a differential expression of aminopeptidases between relapsed/refractory and newly diagnosed multiple myeloma patients. A higher expression of the aminopeptidase genes XPNPEP1, RNPEP, DPP3, and BLMH in multiple myeloma plasma cells was associated with shorter patient overall survival. The peptide–drug conjugate melflufen was particularly active towards plasma cells from relapsed/refractory multiple myeloma patients. Melflufen could be hydrolyzed to its active form by the aminopeptidases LAP3, LTA4H, RNPEP, and ANPEP, all of which are expressed in multiple myeloma. These results indicate critical roles for aminopeptidases in disease progression and the activity of melflufen in multiple myeloma.

Abstract

Multiple myeloma (MM) is characterized by extensive immunoglobulin production leading to an excessive load on protein homeostasis in tumor cells. Aminopeptidases contribute to proteolysis by catalyzing the hydrolysis of amino acids from proteins or peptides and function downstream of the ubiquitin–proteasome pathway. Notably, aminopeptidases can be utilized in the delivery of antibody and peptide-conjugated drugs, such as melflufen, currently in clinical trials. We analyzed the expression of 39 aminopeptidase genes in MM samples from 122 patients treated at Finnish cancer centers and 892 patients from the CoMMpass database. Based on ranked abundance, LAP3, ERAP2, METAP2, TTP2, and DPP7 were highly expressed in MM. ERAP2, XPNPEP1, DPP3, RNPEP, and CTSV were differentially expressed between relapsed/refractory and newly diagnosed MM samples (p < 0.05). Sensitivity to melflufen was detected ex vivo in 11/15 MM patient samples, and high sensitivity was observed, especially in relapsed/refractory samples. Survival analysis revealed that high expression of XPNPEP1, RNPEP, DPP3, and BLMH (p < 0.05) was associated with shorter overall survival. Hydrolysis analysis demonstrated that melflufen is a substrate for aminopeptidases LAP3, LTA4H, RNPEP, and ANPEP. The sensitivity of MM cell lines to melflufen was reduced by aminopeptidase inhibitors. These results indicate critical roles of aminopeptidases in disease progression and the activity of melflufen in MM.

Potentially functional variants of ERAP1, PSMF1 and NCF2 in the MHC-I-related pathway predict non-small cell lung cancer survival

BACKGROUND

Cellular immunity against tumor cells is highly dependent on antigen presentation by major histocompatibility complex class I (MHC-I) molecules. However, few published studies have investigated associations between functional variants of MHC-I-related genes and clinical outcomes of lung cancer patients.

METHODS

We performed a two-phase Cox proportional hazards regression analysis by using two previously published genome-wide association studies to evaluate associations between genetic variants in the MHC-I-related gene set and the survival of non-small cell lung cancer (NSCLC) patients, followed by expression quantitative trait loci analysis.

RESULTS

Of the 7811 single-nucleotide polymorphisms (SNPs) in 89 genes of 1185 NSCLC patients in the discovery dataset of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial, 24 SNPs remained statistically significant after validation in additional 984 NSCLC patients from the Harvard Lung Cancer Susceptibility Study. In a multivariate stepwise Cox model, three independent functional SNPs (ERAP1 rs469783 T > C, PSMF1 rs13040574 C > A and NCF2 rs36071574 G > A) remained significant with an adjusted hazards ratio (HR) of 0.83 [95% confidence interval (CI) = 0.77-0.89, P = 8.0 × 10^-7], 0.86 (0.80-0.93, P = 9.4 × 10^-5) and 1.31 (1.11-1.54, P = 0.001) for overall survival (OS), respectively. Further combined genotypes revealed a poor survival in a dose-response manner in association with the number of unfavorable genotypes (P_trend < 0.0001 and 0.0002 for OS and disease-specific survival, respectively). Also, ERAP1 rs469783C and PSMF1 rs13040574A alleles were associated with higher mRNA expression levels of their genes.

CONCLUSION

These potentially functional SNPs of the MHC-I-related genes may be biomarkers for NSCLC survival, possibly through modulating the expression of corresponding genes.

Lack of Associations between Endoplasmic Reticulum Aminopeptidase 2 Gene Polymorphisms and Ankylosing Spondylitis: A Meta-analysis with Trial Sequential Analysis

Background: Endoplasmic reticulum aminopeptidase 2 (ERAP2) gene is reported to be associated with inflammation-related diseases. Several studies have investigated the associations of ERAP2 gene polymorphisms and susceptibility to ankylosing spondylitis (AS). However, the findings of those studies were inconsistent. The aim of this study was to elucidate the associations by a meta-analysis with trial sequential analysis (TSA).Methods: Online databases of PubMed, Web of Science, EMBASE, Cochrane Library, Wanfang, and CNKI were searched to identify eligible studies on the associations of ERAP2 gene polymorphisms and AS. Study quality was judged based on the Newcastle-Ottawa scale (NOS). Strengths of associations were presented by P-value, odds ratios (ORs), and 95% confidence intervals (95%CIs). TSA was employed to evaluate the information size and statistical power.Results: A total of six studies encompassing 2774 AS patients and 4119 disease-free controls were eligible for this meta-analysis. Five studies reported rs2248374 polymorphism and three studies reported rs2549782 polymorphism. The pooled data suggested that the two polymorphisms were not significantly associated with AS susceptibility: rs2248374, A vs. G, OR = 0.94, 95%CI 0.86-1.02, P = .14; rs2549782, T vs. G, OR = 1.03, 95%CI 0.95-1.12, P = .45. TSA indicated that the sample sizes appeared to be inadequate to obtain a positive outcome.Conclusion: The present findings of this study do not support any evidence on the associations of rs2248374 and rs2549782 polymorphisms in the ERAP2 gene and susceptibility to AS. Additional well-designed and large-sample studies in diverse ethnicities are encouraged to validate the current findings.

Polymorphisms in ERAP1 and ERAP2 Genes Are Associated With Tuberculosis in the Han Chinese

Single nucleotide polymorphisms (SNPs) in the endoplasmic reticulum aminopeptidase (ERAP1 and ERAP2) genes are associated with the pathogenesis of bacterial and viral infections. To search for the variations in the ERAP1 and ERAP2 genes associated with tuberculosis (TB), 449 TB cases and 435 healthy individuals of the Han population in the Yunnan province of China were included in the present study. Eleven SNPs of ERAPs were genotyped using the SNaPshot SNP assay. Allelic, genotypic, and haplotypic association analyses were performed between the TB and control groups. Furthermore, stratification analyses among pulmonary TB (PTB), extrapulmonary TB (EPTB), and healthy controls; and initial treatment TB (ITTB), retreatment TB (RTB), and healthy controls were also performed. The TT genotype of rs26618 in ERAP1 exhibited a protective factor for TB, compared with the role of the CC/CT genotype (P = 0.003; OR = 1.490, 95% CI: 1.140-1.940). In ERAP2, the frequency of the G allele of rs2549782 was higher in the case group than in the control group (0.491 vs. 0.417, P = 0.002, OR = 1.350, 95% CI: 1.118-1.631), and the TT genotype exhibited a protective factor for TB, compared with the role of the GG/GT genotype (P = 0.001; OR = 1.650, 95% CI: 1.230-2.220). The frequency of the C allele of rs1056893 was higher in the case group than in the control group (0.468 vs. 0.394, P = 0.002, OR = 1.350, 95% CI: 1.118-1.631), and the genotype exhibited a difference in the log-additive model (P = 0.002; OR = 1.350, 95% CI: 1.120-1.630). The frequencies of the haplotype rs27037-rs27044-s30187-rs26618-rs26653-rs3734016-GCCCGC in ERAP1 (0.290 vs. 0.240, P-adj = 0.028, OR = 1.320, 95% CI: 1.063-1.638) and the haplotypes rs2549782-rs2248374-rs2287988-rs1056893-GTAGC in ERAP2 (0.446 vs. 0.348, P-adj = 4.80E-05, OR = 1.510, 95% CI: 1.246-1.829) was higher in the TB groups, while the frequencies of the haplotypes rs2549782-rs2248374-rs2287988-rs1056893-TAGAT (0.478 vs. 0.539, P-adj = 0.020, OR = 0.782, 95% CI: 0.649-0.943) were lower in the TB groups. The allelic and genotypic associations were also investigated in the subsequent stratification between the PTB, EPTB and control groups as well as between the ITTB, RTB, and control groups. In conclusion, variations in ERAP1 and ERAP2 genes were identified to be associated with TB in the Han Chinese population.

Engineering anti-cancer nanovaccine based on antigen cross-presentation

Dendritic cells (DCs) present exogenous antigens on major histocompatibility complex (MHC) class I molecules, thereby activating CD8⁺ T cells, contributing to tumor elimination through a mechanism known as antigen cross-presentation. A variety of factors such as maturation state of DCs, co-stimulatory signals, T-cell microenvironment, antigen internalization routes and adjuvants regulate the process of DC-mediated antigen cross-presentation. Recently, the development of successful cancer immunotherapies may be attributed to the ability of DCs to cross-present tumor antigens. In this review article, we focus on the underlying mechanism of antigen cross-presentation and ways to improve antigen cross-presentation in different DC subsets. We have critically summarized the recent developments in the generation of novel nanovaccines for robust CD8⁺ T-cell response in cancer. In this context, we have reviewed nanocarriers that have been used for cancer immunotherapeutics based on antigen cross-presentation mechanism. Additionally, we have also expressed our views on the future applications of this mechanism in curing cancer.

Genetic contribution of endoplasmic reticulum aminopeptidase 1 polymorphisms to liver fibrosis progression in patients with HCV infection

The endoplasmic reticulum aminopeptidase ERAP1 regulates innate and adaptive immune responses, trimming peptides and loading onto HLA class I molecules. Coding single nucleotide polymorphisms within ERAP1 are associated with autoimmune diseases, viral infections, and cancer development. Our purpose was to analyze the influence of ERAP1 variants on fibrogenesis in hepatitis C virus (HCV)-infected patients. A range of ERAP1 polymorphisms were genotyped in 722 unrelated Caucasian patients diagnosed with chronic HCV from two Spanish cohorts. Patients were classified according to their fibrosis stage. Paraffin-embedded tissue microarrays were constructed to assess ERAP1 expression (HCV = 38; alcoholic = 20) by immunohistochemistry. A statistical algorithm was applied to derive a fibrogenesis prediction model. The ERAP1 variants rs30187/T (K528, p_c < 0.001) and rs27044/G (Q730, p_c < 0.001) were related with severe fibrosis. These results were validated in the two independent cohorts. Furthermore, patients with the rs30187/T allele had stronger ERAP1 protein expression than those with the rs30187/C (p < 0.05). The statistical model showed that patients with rs30187 C/T and T/T genotypes took 15.58 years (median) to develop advanced fibrosis, but this value was 32.08 years in patients carrying C/C genotype (p < 0.005). ERAP1 variants may influence the clinical course of fibrogenesis in HCV-infected patients. These polymorphisms could be exploited as constitutive new markers of fibrosis evolution. The results highlight the possibility of using modulators of ERAP1 to generate a protective immune response against chronic HCV infection. KEY MESSAGES: What is known Several ERAP1 polymorphisms are associated with autoimmune diseases and cancer. ERAP1 trims peptides to HLA class I presentation. What is new here ERAP1 polymorphisms are associated with fibrogenesis. The ERAP1 polymorphisms genotype could help us in clinical management of patients. Potential translational impact The use of modulators of ERAP1 could generate a protective response depending on SNPs.

Identification of Prognostic Immune-Related Genes in Pancreatic Adenocarcinoma and Establishment of a Prognostic Nomogram: A Bioinformatic Study

BACKGROUND

The prognosis of pancreatic adenocarcinoma (PAAD) is extremely poor and has not been improved. Thus, an effective method to assess the prognosis of patients must be established to improve their survival rate.

METHOD

This study investigated immune-related genes that could be used as potential therapeutic targets for PAAD. Level 3 gene expression data from the PAAD cohort and the relevant clinical information were obtained from The Cancer Genome Atlas (TCGA) database. For validation, other PAAD datasets (DSE62452) were downloaded from the Gene Expression Omnibus (GEO) database. The PAAD datasets from TCGA and GEO were used to screen immune-related genes through the Molecular Signatures Database using gene set enrichment analysis. Then, the overlapping immune-related genes of the two datasets were identified. Coexpression networks of the immune-related genes were constructed.

RESULTS

A signature of three immune-related genes (CKLF, ERAP2, and EREG) was identified in patients with PAAD. The signature could be used to divide the patients with PAAD into high- and low-risk groups based on their median risk score. Multivariate Cox regression analysis was performed to determine the independent prognostic factors of PAAD. Time-dependent receiver operating characteristic (ROC) curve analysis was conducted to assess the prediction accuracy of the prognostic signature. Last, a nomogram was established to assess the individualized prognosis prediction model based on the clinical characteristics and risk score of the TCGA PAAD dataset. The accuracy of the prognostic signature was further evaluated through functional evaluation and principal component analysis.

CONCLUSIONS

The results indicated that the signature of three immune-related genes had excellent predictive value for PAAD. These findings might help improve personalized treatment and medical decisions.

Polymorphisms in endoplasmic reticulum aminopeptidase genes are associated with cervical cancer risk in a Chinese Han population

Background

Antigen-processing machinery molecules play crucial roles in infectious diseases and cancers. Studies have shown that polymorphisms in endoplasmic reticulum aminopeptidase (ERAP) genes can influence the enzymatic activity of ERAP proteins and are associated with the risk of diseases. In the current study, we evaluated the influence of ERAP gene (ERAP1 and ERAP2) polymorphisms on susceptibility to cervical intraepithelial neoplasia (CIN) and cervical cancer.

Methods

Six single nucleotide polymorphisms (SNPs) in ERAP1 and 5 SNPs in ERAP2 were selected and genotyped in 556 CIN patients, 1072 cervical cancer patients, and 1262 healthy control individuals. Candidate SNPs were genotyped using SNaPshot assay. And the association of these SNPs with CIN and cervical cancer was analysed.

Results

The results showed that allelic and genotypic frequencies of rs26653 in ERAP1 were significantly different between cervical cancer and control groups (P = 0.001 and 0.004). The allelic frequencies of rs27044 in ERAP1 and rs2287988 in ERAP2 were significantly different between control and cervical cancer groups (P = 0.003 and 0.004). Inheritance model analysis showed that genotypes of rs27044, rs26618, rs26653 and rs2287988 SNPs may be associated with the risk of cervical cancer (P = 0.003, 0.004, 0.001 and 0.002). Additionally, haplotype analysis results showed that the ERAP1 haplotype, rs27044C-rs30187T-rs26618T-rs26653G-rs3734016C, was associated with a lower risk of cervical cancer (P = 0.001). The ERAP2 haplotypes rs2549782G- rs2548538A-rs2248374A-rs2287988G-rs1056893T (P = 0.009 and 0.006) and rs2549782T-rs2548538T-rs2248374G-rs2287988A-rs1056893T (P = 0.003 and 0.009) might be associated with cervical cancer and the development from CIN to cervical cancer.

Conclusion

Our results indicated that rs27044, rs26618 and rs26653 in ERAP1 and rs2287988 in ERAP2 influenced susceptibility to cervical cancer.

The rs75862629 minor allele in the endoplasmic reticulum aminopeptidases intergenic region affects human leucocyte antigen B27 expression and protects from ankylosing spondylitis in Sardinia

OBJECTIVES

HLA-B27 and the endoplasmic reticulum aminopeptidase 1 (ERAP1) and ERAP2 genes are predisposing factors for AS. A single nucleotide polymorphism (SNP) in the ERAP2 promoter (rs75862629) coordinates the transcription of both ERAP genes. We investigated whether this SNP associates with AS and whether it affects the expression of the two major HLA-B27 alleles present in Sardinia, the AS-associated B*2705 and the non-AS-associated B*2709.

METHODS

Four SNPs in the ERAP region were genotyped in HLA-B*2705-positive patients with AS (n = 145), B27-positive healthy subjects (n = 126) and B27-negative controls (n = 250) and the allele and haplotype frequencies were derived. The expression of ERAP1 and ERAP2 mRNAs in 36 HLA-B27-positive B lymphoblastoid cell lines was measured by quantitative PCR. An electrophoretic mobility shift assay was performed to search for a nuclear factor binding the DNA sequence encompassing rs75862629. The expression of HLA-B27 molecules related to the SNP at rs75862629 was determined by flow cytometry.

RESULTS

The minor allele G at rs75862629 was found significantly increased in B27 healthy individuals, both B*2705 and B*2709, compared with B*2705-positive patients with AS and B27-negative controls. The electrophoretic mobility shift assay indicated the lack of binding of a transcription factor as the cause of the observed reduction in the ERAP2 concomitant with a higher ERAP1 expression. Of note, this occurs with a different cell surface expression of the HLA-B*2705 and HLA-B*2709 molecules.

CONCLUSION

SNP rs75862629, by modulating simultaneously the expression of ERAP1 and ERAP2, provides protection from AS in HLA-B27-positive subjects in Sardinia. This has a functional impact on HLA-B27 expression and likely on disease onset.

An Overview on ERAP Roles in Infectious Diseases

Endoplasmic reticulum (ER) aminopeptidases ERAP1 and ERAP2 (ERAPs) are crucial enzymes shaping the major histocompatibility complex I (MHC I) immunopeptidome. In the ER, these enzymes cooperate in trimming the N-terminal residues from precursors peptides, so as to generate optimal-length antigens to fit into the MHC class I groove. Alteration or loss of ERAPs function significantly modify the repertoire of antigens presented by MHC I molecules, severely affecting the activation of both NK and CD8+ T cells. It is, therefore, conceivable that variations affecting the presentation of pathogen-derived antigens might result in an inadequate immune response and onset of disease. After the first evidence showing that ERAP1-deficient mice are not able to control Toxoplasma gondii infection, a number of studies have demonstrated that ERAPs are control factors for several infectious organisms. In this review we describe how susceptibility, development, and progression of some infectious diseases may be affected by different ERAPs variants, whose mechanism of action could be exploited for the setting of specific therapeutic approaches.

The roles of ERAP1 and ERAP2 in autoimmunity and cancer immunity: New insights and perspective

Autoimmunity and cancer affect millions worldwide and both, in principal, result from dysregulated immune responses. There are many well-known molecules involved in immunological process playing as a double-edged sword, by which associating autoimmune diseases and cancer. In this regard, Endoplasmic reticulum aminopeptidases (ERAP) 1, which belongs to the M1 family of aminopeptidases, plays a central role as a "molecular ruler", proteolyzing of N-terminal of the antigenic peptides before their loading onto HLA-I molecules for antigen presentation in the Endoplasmic Reticulum (ER). Several genome-wide association studies (GWAS) highlighted the significance of ERAP1 and ERAP2 in autoimmune diseases, including Ankylosing spondylitis, Psoriasis, Bechet's disease, and Birdshot chorioretinopathy, as well as in cancers. The expression of ERAP1/2 is mostly altered in different cancers compared to normal cells, but how this affects anti-cancer immune responses and cancer growth has been little explored. Recent studies on the immunological outcomes and the catalytic functions of ERAP1 and ERAP2 have provided a better understanding of their potential pathogenetic role in autoimmunity and cancer. In this review, we summarize the role of ERAP1 and ERAP2 in the autoimmune diseases and cancer immunity based on the recent advances in GWAS studies.

Exploration of zinc-binding groups for the design of inhibitors for the oxytocinase subfamily of M1 aminopeptidases

The oxytocinase subfamily of M1 aminopeptidases consists of three members, ERAP1, ERAP2 and IRAP that play several important biological roles, including key functions in the generation of antigenic peptides that drive human immune responses. They represent emerging targets for pharmacological manipulation of the immune system, albeit lack of selective inhibitors is hampering these efforts. Most of the previously explored small-molecule binders target the active site of the enzymes via strong interactions with the catalytic zinc(II) atom and, while achieving increased potency, they suffer in selectivity. Continuing our earlier efforts on weaker zinc(II) binding groups (ZBG), like the 3,4-diaminobenzoic acid derivatives (DABA), we herein synthesized and biochemically evaluated analogues of nine potentially weak ZBGs, based on differential substitutions of functionalized pyridinone- and pyridinethione-scaffolds, nicotinic-, isonicotinic-, aminobenzoic- and hydrazinobenzoic-acids. Crystallographic analysis of two analogues in complex with a metalloprotease (MMP-12) revealed unexpected binding topologies, consistent with the observed affinities. Our results suggest that the potency of the compounds as inhibitors of ERAP1, ERAP2 and IRAP is primarily driven by the occupation of active-site specificity pockets and their proper orientation within the enzymes.

Inhibitors of ER Aminopeptidase 1 and 2: From Design to Clinical Application

Endoplasmic Reticulum aminopeptidase 1 and 2 are two homologous enzymes that help generate peptide ligands for presentation by Major Histocompatibility Class I molecules. Their enzymatic activity influences the antigenic peptide repertoire and indirectly controls adaptive immune responses. Accumulating evidence suggests that these two enzymes are tractable targets for the regulation of immune responses with possible applications ranging from cancer immunotherapy to treating inflammatory autoimmune diseases. Here, we review the state-of-the-art in the development of inhibitors of ERAP1 and ERAP2 as well as their potential and limitations for clinical applications.

Regulation of ERAP1 and ERAP2 genes and their disfunction in human cancer

The endoplasmic reticulum (ER) aminopeptidases ERAP1 and ERAP2 are two multifunctional enzymes playing an important role in the biological processes requiring trimming of substrates, including the generation of major histocompatibility complex (MHC) class I binding peptides. In the absence of ERAP enzymes, the cells exhibit a different pool of peptides on their surface which can promote both NK and CD8⁺ T cell-mediated immune responses. The expression of ERAP1 and ERAP2 is frequently altered in tumors, as compared to their normal counterparts, but how this affects tumor growth and anti-tumor immune responses has been little investigated. This review will provide an overview of current knowledge on transcriptional and post-transcriptional regulations of ERAP enzymes, and will discuss the contribution of recent studies to our understanding of ERAP1 and ERAP2 role in cancer immunity.

Influence of ERAP1 and ERAP2 gene polymorphisms on disease susceptibility in different populations

The endoplasmic reticulum aminopeptidases (ERAPs), ERAP1 and ERAP2, makes a role in shaping the HLA class I peptidome by trimming peptides to the optimal size in MHC-class I-mediated antigen presentation and educating the immune system to differentiate between self-derived and foreign antigens. Association studies have shown that genetic variations in ERAP1 and ERAP2 genes increase susceptibility to autoimmune diseases, infectious diseases, and cancers. Both ERAP1 and ERAP2 genes exhibit diverse polymorphisms in different populations, which may influence their susceptibly to the aforementioned diseases. In this article, we review the distribution of ERAP1 and ERAP2 gene polymorphisms in various populations; discuss the risk or protective influence of these gene polymorphisms in autoimmune diseases, infectious diseases, and cancers; and highlight how ERAP genetic variations can influence disease associations.

An allelic variant in the intergenic region between ERAP1 and ERAP2 correlates with an inverse expression of the two genes

The Endoplasmatic Reticulum Aminopeptidases ERAP1 and ERAP2 are implicated in a variety of immune and non-immune functions. Most studies however have focused on their role in shaping the HLA class I peptidome by trimming peptides to the optimal size. Genome Wide Association Studies highlighted non-synonymous polymorphisms in their coding regions as associated with several immune mediated diseases. The two genes lie contiguous and oppositely oriented on the 5q15 chromosomal region. Very little is known about the transcriptional regulation and the quantitative variations of these enzymes. Here, we correlated the level of transcripts and proteins of the two aminopeptidases in B-lymphoblastoid cell lines from 44 donors harbouring allelic variants in the intergenic region between ERAP1 and ERAP2. We found that the presence of a G instead of an A at SNP rs75862629 in the ERAP2 gene promoter strongly influences the expression of the two ERAPs with a down-modulation of ERAP2 coupled with a significant higher expression of ERAP1. We therefore show here for the first time a coordinated quantitative regulation of the two ERAP genes, which can be relevant for the setting of specific therapeutic approaches.

Molecular pathways for antigenic peptide generation by ER aminopeptidase 1

Endoplasmic Reticulum aminopeptidase 1 (ERAP1) is an intracellular enzyme that can generate or destroy potential peptide ligands for MHC class I molecules. ERAP1 activity influences the cell-surface immunopeptidome and epitope immunodominance patterns but in complex and poorly understood manners. Two main distinct pathways have been proposed to account for ERAP1's effects on the nature and quantity of MHCI-bound peptides: i) ERAP1 trims peptides in solution, generating the correct length for binding to MHCI or overtrimming peptides so that they are too short to bind, and ii) ERAP1 trims peptides while they are partially bound onto MHCI in manner that leaves the peptide amino terminus accessible. For both pathways, once an appropriate length peptide is generated it could bind conventionally to MHCI, competing with further trimming by ERAP1. The two pathways, although not necessarily mutually exclusive, provide distinct vantage points for understanding of the rules behind the generation of the immunopeptidome. Resolution of the mechanistic details of ERAP1-mediated antigenic peptide generation can have important consequences for pharmacological efforts to regulate the immunopeptidome for therapeutic applications, and for understanding association of ERAP1 alleles with susceptibility to autoimmune disease and cancer. We review current evidence in support of these two pathways and discuss their relative importance and potential complementarity.

Contribution of the exosome-associated form of secreted endoplasmic reticulum aminopeptidase 1 to exosome-mediated macrophage activation

Macrophages secrete endoplasmic reticulum aminopeptidase 1 (ERAP1) in response to lipopolysaccharide (LPS) and interferon (IFN)-γ to enhance their phagocytic and nitric oxide (NO) synthetic activities. In this study, we found that a subset of secreted ERAP1 bound to exosomes released from LPS/IFN-γ-treated murine RAW264.7 macrophages compared to untreated cells. ERAP1-bound exosomes enhanced phagocytic and NO synthetic activities of macrophages more efficiently than free ERAP1 and exosomes derived from untreated cells. Deletion of the exon 10 coding sequence in ERAP1 gene resulted in loss of binding to exosomes. By comparing the activities of exosomes derived from wild-type and ERAP1 gene-deficient RAW264.7 cells, we observed that ERAP1 contributed to the exosome-dependent phagocytosis and NO synthesis of the cells. Upon stimulation of RAW264.7 cells with LPS/IFN-γ, TNF-α, IFN-γ, and CCL3 were also associated with the released exosomes. Analyses of cytokine function revealed that while CCL3 in the exosomes was crucial to the phagocytic activity of RAW264.7 cells, TNF-α and IFN-γ primarily contributed to the enhancement of NO synthesis. These results suggest that treatment with LPS/IFN-γ alters the physicochemical properties of exosomes released from macrophages in order to facilitate association with ERAP1 and several cytokines/chemokines. This leads to exosome-mediated enhancement of macrophage functions. It is possible that packaging effector molecules into exosomes upon inflammatory stimuli, facilitates the exertion of effective pathophysiological functions on macrophages. Our data provide the first evidence that ERAP1 associated with exosomes plays important roles in inflammatory processes via activation of macrophages.

The ERAP gene is associated with HCV chronic infection in a Chinese Han population

Endoplasmic reticulum aminopeptidases (ERAPs), ERAP1 and ERAP2, are critical components in the antigen-presentation system and are specialized to produce optimal-sized peptides for HLA I binding. ERAP gene polymorphisms have been correlated with HLA-associated diseases. To investigate the association between ERAP gene polymorphisms and HCV chronic infection, a TaqMan assay was used to genotype 4 SNPs (rs27044, rs30187, rs26618 and rs26653) in ERAP1 and 2 SNPs (rs2248374 and rs2549782) in ERAP2 genes in 376 Chinese Han HCV chronic infections and 324 healthy Chinese Han controls. The allelic distribution of rs26618 in the ERAP1 gene and rs2248374 in ERAP2 gene were both significantly different in case and control groups. The C-allele of rs26618 had an increased HCV chronicity risk compared with the T-allele (P=.025, OR=1.318, 95%CI: 1.035-1.677), and the same effect was found in A-allele of rs2248374 compared with G-allele (P=0.046, OR=1.244, 95%CI: 1.004-1.540). There were notable differences in the genotype distribution in analysis using the dominant genetic model in rs26618 (CC+CT vs. TT; P=0.007, OR=1.473, 95%CI: 1.091-1.989) and recessive genetic model in rs2248374 (AA vs. AG+GG; P=0.003, OR=1.548, 95%CI: 1.026-2.335). In addition, rs26618 and rs2248374-genotype combination played noteable effects on the clinical parameters. These results indicated that the ERAP gene may play a critical role in HCV chronicity in this Chinese Han population.

A haplotypic variant at the IRGM locus and rs11747270 are related to the susceptibility for chronic periodontitis

OBJECTIVE AND DESIGN

Immunity-regulated GTPase M (IRGM) plays a critical role in the defense against intracellular bacteria by regulating autophagy formation. This direct genetic association study aimed to determine whether variants at the IRGM genetic locus are associated with chronic periodontitis.

MATERIALS AND SUBJECTS

Using PCR and melting curve analysis 390 periodontitis patients and 770 healthy controls have been genotyped regarding six polymorphisms in the IRGM gene (rs13361189, rs10065172, rs4958847, rs1000113, rs11747270, rs931058).

RESULTS

Frequency distribution of alleles and genotypes for the six polymorphisms were not significantly different between the periodontitis and the control group. Also following stratification according to gender and smoking no significant linkage was found for any of the IRGM variants with periodontitis. Analysis of a subsample of patients revealed a significant association for rs11747270 with severe periodontitis (p = 0.003). Pairwise linkage analysis revealed one block composed of rs13361189, rs10065172, rs4958847, rs1000113 and 11747270 with strong or even complete linkage disequilibrium (r ² > 0.9). Four haplotypes showed a frequency of > 1%, among which the haplotype C-T-A-T-G was significantly associated with chronic periodontitis (p = 0.0051; OR 4.66, 95% CI 1.41-15.42).

CONCLUSIONS

One rare haplotype of the IRGM locus is significantly associated with chronic periodontitis in a German cohort.

The interplay between HLA-B27 and ERAP1/ERAP2 aminopeptidases: from anti-viral protection to spondyloarthritis

The human leukocyte antigen class I gene HLA-B27 is the strongest risk factor for ankylosing spondylitis (AS), a chronic inflammatory arthritic disorder. More recently, the Endoplasmic Reticulum Aminopeptidase (ERAP) 1 and 2 genes have been identified by genome wide association studies (GWAS) as additional susceptibility factors. In the ER, these aminopeptidases trim the peptides to a length suitable to fit into the groove of the major histocompatibility complex (MHC) class I molecules. It is noteworthy that an epistatic interaction between HLA-B27 and ERAP1, but not between HLA-B27 and ERAP2, has been highlighted. However, these observations suggest a paramount centrality for the HLA-B27 peptide repertoire that determines the natural B27 immunological function, i.e. the T cell antigen presentation and, as a by-product, elicits HLA-B27 aberrant behaviours: (i) the misfolding leading to ER stress responses and autophagy and (ii) the surface expression of homodimers acting as ligands for innate immune receptors. In this context, it has been observed that the HLA-B27 carriers, besides being prone to autoimmunity, display a far better surveillance to some viral infections. This review focuses on the ambivalent role of HLA-B27 in autoimmunity and viral protection correlating its functions to the quantitative and qualitative effects of ERAP1 and ERAP2 polymorphisms on their enzymatic activity.

Ligand-Induced Conformational Change of Insulin-Regulated Aminopeptidase: Insights on Catalytic Mechanism and Active Site Plasticity

Insulin-regulated aminopeptidase (IRAP) is an enzyme with several important biological functions that is known to process a large variety of different peptidic substrates, although the mechanism behind this wide specificity is not clearly understood. We describe a crystal structure of IRAP in complex with a recently developed bioactive and selective inhibitor at 2.53 Å resolution. In the presence of this inhibitor, the enzyme adopts a novel conformation in which domains II and IV are juxtaposed, forming a hollow structure that excludes external solvent access to the catalytic center. A loop adjacent to the enzyme's GAMEN motif undergoes structural reconfiguration, allowing the accommodation of bulky inhibitor side chains. Atomic interactions between the inhibitor and IRAP that are unique to this conformation can explain the strong selectivity compared to homologous aminopeptidases ERAP1 and ERAP2. This conformation provides insight on IRAP's catalytic cycle and reveals significant active-site plasticity that may underlie its substrate permissiveness.

Connecting genetic risk to disease end points through the human blood plasma proteome

Genome-wide association studies (GWAS) with intermediate phenotypes, like changes in metabolite and protein levels, provide functional evidence to map disease associations and translate them into clinical applications. However, although hundreds of genetic variants have been associated with complex disorders, the underlying molecular pathways often remain elusive. Associations with intermediate traits are key in establishing functional links between GWAS-identified risk-variants and disease end points. Here we describe a GWAS using a highly multiplexed aptamer-based affinity proteomics platform. We quantify 539 associations between protein levels and gene variants (pQTLs) in a German cohort and replicate over half of them in an Arab and Asian cohort. Fifty-five of the replicated pQTLs are located in trans. Our associations overlap with 57 genetic risk loci for 42 unique disease end points. We integrate this information into a genome-proteome network and provide an interactive web-tool for interrogations. Our results provide a basis for novel approaches to pharmaceutical and diagnostic applications.

Individual genetic variation can affect the levels of protein in blood, but detailed data sets linking these two types of data are rare. Here, the authors carry out a genome-wide association study of levels of over a thousand different proteins, and describe many new SNP-protein interactions.

Polymorphisms in ERAP1 and ERAP2 are shared by Caninae and segregate within and between random- and pure-breeds of dogs

Specific polymorphisms in the endoplasmic reticulum amino peptidase genes ERAP1 and ERAP2, when present with certain MHC class receptor types, have been associated with increased risk for specific cancers, infectious diseases and autoimmune disorders in humans. This increased risk has been linked to distinct polymorphisms in both ERAPs and MHC class I receptors that affect the way cell-generated peptides are screened for antigenicity. The incidence of cancer, infectious disease and autoimmune disorders differ greatly among pure breeds of dogs as it does in humans and it is possible that this heightened susceptibility is also due to specific polymorphisms in ERAP1 and ERAP2. In order to determine if such polymorphisms exist, the ERAP1 and ERAP2 genes of 10 dogs of nine diverse breeds were sequenced and SNPs causing synonymous or non-synonymous amino acid changes, deletions or insertions were identified. Eight ERAP1 and 10 ERAP2 SNPs were used to create a Sequenom MassARRAY iPLEX based test panel which defined 24 ERAP1, 36 ERAP2 and 128 ERAP1/2 haplotypes. The prevalence of these haplotypes was then measured among dog, wolf, coyote, jackal and red fox populations. Some haplotypes were species specific, while others were shared across species, especially between dog, wolf, coyote and jackal. The prevalence of these haplotypes was then compared among various canid populations, and in particular between various populations of random- and pure-bred dogs. Human-directed positive selection has led to loss of ERAP diversity and segregation of certain haplotypes among various dog breeds. A phylogenetic tree generated from 45 of the most common ERAP1/2 haplotypes demonstrated three distinct clades, all of which were rooted with haplotypes either shared among species or specific to contemporary dogs, coyote and wolf.

Endoplasmic reticulum aminopeptidase 1 and rheumatic disease: functional variation

PURPOSE OF REVIEW

To review the recent developments in our understanding of endoplasmic reticulum (ER) aminopeptidase 1 (ERAP1) function in relation to its role in major histocompatibility complex (MHC) class I peptide presentation and human leukocyte antigen (HLA) class I-associated diseases.

RECENT FINDINGS

ERAP1 polymorphisms exhibiting loss-of-function have been associated with protection from AS. The aminopeptidase function of ERAP1 optimizes peptides for binding and presentation by MHC class I. Most of the studies have revealed reduced MHC class I expression in situations of reduced ERAP1 function. Under these circumstances, the presented peptides are often N-terminally extended, and cell surface complexes are unstable and fall apart more readily. In contrast, peptides presented by HLA-B*27 : 05 when ERAP1 is silenced are frequently extended on the C-terminus. Recent work has emphasized on the importance of assessing the function of allotypes encoded by ERAP1 haplotypes, rather than effects of single amino acid substitutions. The allotypes found in a series of AS patients were poorer at restoring HLA-B27 expression than allotypes found in unaffected controls, which may seem contrary to the genetic data linking loss-of-function to protection.

SUMMARY

More work is needed to understand how ERAP1 variants associated with risk and protection influence the quality and quantity of peptides available for binding to HLA class I molecules in the ER. Moreover, we need to determine allele-specific effects of ERAP1 variants in the context of HLA-B*51 and HLA-Cw*6, which are associated with Behçet's disease and psoriasis, respectively.

Brown but not white adipose cells synthesize omega-3 docosahexaenoic acid in culture

Adipose tissue is a complex endocrine organ which coordinates several crucial biological functions including fatty acid metabolism, glucose metabolism, energy homeostasis, and immune function. Brown adipose tissue (BAT) is most abundant in young infants during the brain growth spurt when demands for omega-3 docosahexaenoic acid (DHA, 22:6n-3) is greatest for brain structure. Our aim was to characterize relative biosynthesis of omega-3 long chain polyunsaturated fatty acids (LCPUFA) from precursors in cultured white (WAT) and brown (BAT) cells and study relevant gene expression. Mouse WAT and BAT cells were grown in regular DMEM media to confluence, and differentiation was induced. At days 0 and 8 cells were treated with albumin bound d5-18:3n-3 (d5-ALA) and analyzed 24h later. d5-ALA increased cellular eicosapentaenoic acid (EPA, 20:5n-3) and docosapentaenoic acid (DPA, 22:5n-3) in undifferentiated BAT cells, whereas differentiated BAT cells accumulated 20:4n-3, EPA and DPA. DHA as a fraction of total omega-3 LCPUFA was greatest in differentiated BAT cells compared to undifferentiated cells. Undifferentiated WAT cells accumulated EPA, whereas differentiated cells accumulated DPA. WAT accumulated trace newly synthesized DHA. Zic1 a classical brown marker and Prdm16 a key driver of brown fat cell fate are expressed only in BAT cells. Ppargc1a is 15 fold higher in differentiated BAT cells. We conclude that in differentiated adipose cells accumulating fat, BAT cells but not WAT cells synthesize DHA, supporting the hypothesis that BAT is a net producer of DHA.

Adipocyte aminopeptidases in obesity and fasting

This study checked the existence of a diverse array of aminopeptidase (AP) enzymes in high (HDM) and low (LDM) density microsomal and plasma membrane (MF) fractions from adipocytes of control, monosodium glutamate obese and food deprived rats. Gene expression was detected for ArgAP, AspAP, MetAP, and two AlaAP (APM and PSA). APM and PSA had the highest catalytic efficiency, whereas AspAP the highest affinity. Subcellular distribution of AP activities depended on metabolic status. Comparing catalytic levels, AspAP in HDM, LDM and MF was absent in obese and control under food deprivation; PSA in LDM was 3.5-times higher in obese than in normally fed control and control and obese under food deprivation; MetAP in MF was 4.5-times higher in obese than in food deprived obese. Data show new AP enzymes genetically expressed in subcellular compartments of adipocytes, three of them with altered catalytic levels that respond to whole-body energetic demands.

Crystal Structure of Insulin-Regulated Aminopeptidase with Bound Substrate Analogue Provides Insight on Antigenic Epitope Precursor Recognition and Processing

Aminopeptidases that generate antigenic peptides influence immunodominance and adaptive cytotoxic immune responses. The mechanisms that allow these enzymes to efficiently process a vast number of different long peptide substrates are poorly understood. In this work, we report the structure of insulin-regulated aminopeptidase, an enzyme that prepares antigenic epitopes for cross-presentation in dendritic cells, in complex with an antigenic peptide precursor analog. Insulin-regulated aminopeptidase is found in a semiclosed conformation with an extended internal cavity with limited access to the solvent. The N-terminal moiety of the peptide is located at the active site, positioned optimally for catalysis, whereas the C-terminal moiety of the peptide is stabilized along the extended internal cavity lodged between domains II and IV. Hydrophobic interactions and shape complementarity enhance peptide affinity beyond the catalytic site and support a limited selectivity model for antigenic peptide selection that may underlie the generation of complex immunopeptidomes.

TLR-mediated secretion of endoplasmic reticulum aminopeptidase 1 from macrophages

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 Ca(2+) levels and calmodulin activation.