Molecular Pathways for Immune Recognition of Preproinsulin Signal Peptide in Type 1 Diabetes

Diabetes. 2018 Apr;67(4):687-696. doi: 10.2337/db17-0021. Epub 2018 Jan 17.


The signal peptide region of preproinsulin (PPI) contains epitopes targeted by HLA-A-restricted (HLA-A0201, A2402) cytotoxic T cells as part of the pathogenesis of β-cell destruction in type 1 diabetes. We extended the discovery of the PPI epitope to disease-associated HLA-B*1801 and HLA-B*3906 (risk) and HLA-A*1101 and HLA-B*3801 (protective) alleles, revealing that four of six alleles present epitopes derived from the signal peptide region. During cotranslational translocation of PPI, its signal peptide is cleaved and retained within the endoplasmic reticulum (ER) membrane, implying it is processed for immune recognition outside of the canonical proteasome-directed pathway. Using in vitro translocation assays with specific inhibitors and gene knockout in PPI-expressing target cells, we show that PPI signal peptide antigen processing requires signal peptide peptidase (SPP). The intramembrane protease SPP generates cytoplasm-proximal epitopes, which are transporter associated with antigen processing (TAP), ER-luminal epitopes, which are TAP independent, each presented by different HLA class I molecules and N-terminal trimmed by ER aminopeptidase 1 for optimal presentation. In vivo, TAP expression is significantly upregulated and correlated with HLA class I hyperexpression in insulin-containing islets of patients with type 1 diabetes. Thus, PPI signal peptide epitopes are processed by SPP and loaded for HLA-guided immune recognition via pathways that are enhanced during disease pathogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aminopeptidases
  • Aspartic Acid Endopeptidases / immunology*
  • Aspartic Acid Endopeptidases / metabolism
  • Cell Line
  • Diabetes Mellitus, Type 1 / immunology*
  • Endoplasmic Reticulum
  • Epitopes / immunology*
  • Gene Knockout Techniques
  • Genetic Predisposition to Disease
  • HLA-A Antigens / immunology*
  • HLA-A11 Antigen / immunology
  • HLA-A2 Antigen / immunology
  • HLA-A24 Antigen / immunology
  • HLA-B Antigens / immunology*
  • Humans
  • In Vitro Techniques
  • Insulin / immunology*
  • Insulin / metabolism
  • Minor Histocompatibility Antigens
  • Protective Factors
  • Protein Precursors / immunology*
  • Protein Precursors / metabolism
  • Protein Sorting Signals
  • Protein Transport
  • Risk Factors
  • T-Lymphocytes, Cytotoxic / immunology*


  • Epitopes
  • HLA-A Antigens
  • HLA-A*02:01 antigen
  • HLA-A*11:01 antigen
  • HLA-A*24:02 antigen
  • HLA-A11 Antigen
  • HLA-A2 Antigen
  • HLA-A24 Antigen
  • HLA-B Antigens
  • Insulin
  • Minor Histocompatibility Antigens
  • Protein Precursors
  • Protein Sorting Signals
  • preproinsulin
  • Aminopeptidases
  • ERAP1 protein, human
  • Aspartic Acid Endopeptidases
  • signal peptide peptidase