Endoplasmic Reticulum Targeting Alters Regulation of Expression and Antigen Presentation of Proinsulin

Abstract

Peptide ligands presented by MHC class I (MHC-I) molecules are produced by degradation of cytosolic and nuclear, but also endoplasmic reticulum (ER)–resident, proteins by the proteasome. However, Ag processing of ER proteins remains little characterized. Studying processing and presentation of proinsulin, which plays a pivotal role in autoimmune diabetes, we found that targeting to the ER has profound effects not only on how proinsulin is degraded, but also on regulation of its cellular levels. While proteasome inhibition inhibited degradation and presentation of cytosolic proinsulin, as expected, it reduced the abundance of ER-targeted proinsulin. This targeting and protein modifications modifying protein half-life also had profound effects on MHC-I presentation and proteolytic processing of proinsulin. Thus, presentation of stable luminal forms was inefficient but enhanced by proteasome inhibition, whereas that of unstable luminal forms and of a cytosolic form were more efficient and compromised by proteasome inhibitors. Distinct stability of peptide MHC complexes produced from cytosolic and luminal proinsulin suggests that different proteolytic activities process the two Ag forms. Thus, both structural features and subcellular targeting of Ags can have strong effects on the processing pathways engaged by MHC-I–restricted Ags, and on the efficiency and regulation of their presentation.

Heat Shock Protein 90 Facilitates Latent HIV Reactivation through Maintaining the Function of Positive Transcriptional Elongation Factor b (p-TEFb) under Proteasome Inhibition

“…From a therapeutic point of view, PIs did not induce T cell activation and selectively promoted the generation of innate immune cytokines. There is a possibility that a PI will influence antigen presentation (35) and therefore may prevent it from triggering the immune system to clear latent HIV reservoirs. This should be taken into consideration when assessing the feasibility of LRAs.…”

Proteasomal Degradation of Proinsulin Requires Derlin-2, HRD1 and p97

“…It has been widely accepted that degradation products of newly synthesized proteins are the source for epitopes presented to CD8 + T-cells in MHC class I molecules. Decreasing proinsulin degradation in pancreatic β-cells therefore potentially opens new avenues for treatment of type 1 diabetes, as blocking proinsulin degradation may affect the presentation of proinsulin-derived epitopes via MHC class I molecules to CD8 + T-cells [ 45 ]. Prevention of ERAD through small compounds like eeyarestatin may decrease proinsulin degradation [ 46 ].…”

Exploring the induction of preproinsulin-specific Foxp3+ CD4+ Treg cells that inhibit CD8+ T cell-mediated autoimmune diabetes by DNA vaccination

“…Interestingly, the ppins75–99 (C18-A10) domain also contained overlapping (nested) immunodominant HLA-DRB*0401-restricted epitopes (i.e., C13-C32, C19-A3 and C22-A5) 50 , indicating that this domain is efficiently processed for MHC class II epitope presentation. Structural features and/or intrinsic expression of ppins designer antigens could affect processing and MHC class I- and class II- epitope presentation 40 51 . We previously showed that the expression of mutant ppinsΔA 12-21 and ppins differed substantially in transiently transfected HEK-293 cells 38 .…”

“…Vaccines against self-proteins contain a non-predictable risk to induce or stimulate autoreactive T cell responses rather than a protective immunity in individual recipients. Factors like MHC I and II composition or genetic factors, but also antigen expression and processing could influence the priming of immune responses 40 51 . We here showed that the ppinsΔA 12-21 antigen (lacking the dominant K b /A 12-21 epitope) induced Treg cells in PD-L1 −/− and PD-1 −/− mice.…”