The Translocon Protein Sec61 Mediates Antigen Transport from Endosomes in the Cytosol for Cross-Presentation to CD8+ T Cells

• Published in: Immunity (Cambridge, Mass.) Vol. 42; no. 5; pp. 850 - 863
• Main Authors: Zehner, Matthias, Marschall, Andrea L., Bos, Erik, Schloetel, Jan-Gero, Kreer, Christoph, Fehrenschild, Dagmar, Limmer, Andreas, Ossendorp, Ferry, Lang, Thorsten, Koster, Abraham J., Dübel, Stefan, Burgdorf, Sven
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 19-05-2015; Elsevier Limited
• Subjects: Animals; Antigens; Antigens - immunology; Antigens - metabolism; CD8-Positive T-Lymphocytes; Cell Line; Cross-Priming - immunology; Cytosol - immunology; Cytosol - metabolism; Cytotoxicity; Endosomes - metabolism; Experiments; Flow cytometry; Lymphocytes; Membrane Proteins - chemistry; Membrane Proteins - metabolism; Mice; Microscopy; Models, Biological; Protein Transport; Proteins; SEC Translocation Channels; Software
• ISSN: 1074-7613; 1097-4180
• DOI: 10.1016/j.immuni.2015.04.008

The molecular mechanisms regulating antigen translocation into the cytosol for cross-presentation are under controversial debate, mainly because direct data is lacking. Here, we have provided direct evidence that the activity of the endoplasmic reticulum (ER) translocon protein Sec61 is essential for endosome-to-cytosol translocation. We generated a Sec61-specific intrabody, a crucial tool that trapped Sec61 in the ER and prevented its recruitment into endosomes without influencing Sec61 activity and antigen presentation in the ER. Expression of this ER intrabody inhibited antigen translocation and cross-presentation, demonstrating that endosomal Sec61 indeed mediates antigen transport across endosomal membranes. Moreover, we showed that the recruitment of Sec61 toward endosomes, and hence antigen translocation and cross-presentation, is dependent on dendritic cell activation by Toll-like receptor (TLR) ligands. These data shed light on a long-lasting question regarding antigen cross-presentation and point out a role of the ER-associated degradation machinery in compartments distinct from the ER.
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•Sec61 is recruited toward antigen-containing endosomes•An ER-retained intrabody to prevent Sec61 transport from the ER toward endosomes•Endosomal Sec61 is required for antigen translocation and cross-presentation•Recruitment of Sec61 toward antigen-containing endosomes via TRIF signaling
Presentation of extracellular antigens on MHC I molecules to activate cytotoxic T cells requires antigen translocation into the cytosol for proteasomal degradation. Burgdorf and colleagues demonstrate that such translocation is mediated by Sec61, a protein from the ER, which is translocated toward antigen-containing endosomes after stimulation of the dendritic cell with pro-inflammatory factors.