Molecular pathways for immune recognition of preproinsulin signal peptide in type 1 diabetes
de Ru, A
van Veelen, PA
American Diabetes Association
Reason for embargo
Currently under an indefinite embargo pending publication by American Diabetes Association. No embargo required on publication
The signal peptide region of preproinsulin (PPI) contains epitopes targeted by human leucocyte antigen-A (HLA-A)-restricted (HLA-A0201, A2402) cytotoxic T-cells as part of the pathogenesis of β-cell destruction in type 1 diabetes. We extended PPI epitope discovery to disease-associated HLA-B*1801 and HLA-B*3906 (risk) and HLA-A*1101 and HLA-B*3801 (protective) alleles revealing that 4/6 alleles present epitopes derived from the signal peptide region. During co-translational 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)-dependent, and ER-luminal (TAP-independent) epitopes, each presented by different HLA class I molecules, and N-terminal trimmed by ER aminopeptidase 1 (ERAP1) for optimal presentation. In vivo, TAP expression is significantly up-regulated and correlated with HLA class I hyper-expression 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.
This study was supported by the NIHR Biomedical Research Centre at Guy’s and St Thomas’ Hospital Trusts and King’s College London, a Centre Grant from the Juvenile Diabetes Research Foundation (JDRF; 1-2007-1803 to MP), a JDRF Career Development Award to SJR (5-CDA-2014-221-A-N), a project grant 15/0005156 from Diabetes UK (to NGM & SJR) and a project grant FOR2290-TP1 from the Deutsche Forschungsgemeinschaft (to MKL).
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