Post-endoplasmic reticulum rescue of unstable MHC class I requires proprotein convertase PC7.
The function of the peptide-loading complex (PLC) is to facilitate loading of MHC class I (MHC I) molecules with antigenic peptides in the endoplasmic reticulum and to drive the selection of these ligands toward a set of high-affinity binders. When the PLC fails to perform properly, as frequently observed in virus-infected or tumor cells, structurally unstable MHC I peptide complexes are generated, which are prone to disintegrate instead of presenting Ags to cytotoxic T cells. In this study we show that a second quality control checkpoint dependent on the serine protease proprotein convertase 7 (PC7) can rescue unstable MHC I, whereas the related convertase furin is completely dispensable. Cells with a malfunctioning PLC and silenced for PC7 have substantially reduced MHC I surface levels caused by high instability and significantly delayed surface accumulation of these molecules. Instead of acquiring stability along the secretory route, MHC I appears to get largely routed to lysosomes for degradation in these cells. Moreover, mass spectrometry analysis provides evidence that lack of PLC quality control and/or loss of PC7 expression alters the MHC I-presented peptide profile. Finally, using exogenously applied peptide precursors, we show that liberation of MHC I epitopes may directly require PC7. We demonstrate for the first time an important function for PC7 in MHC I-mediated Ag presentation.
Leonhardt
Ralf M
RM
Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06519, USA.
Fiegl
Dorothee
D
Rufer
Elke
E
Karger
Axel
A
Bettin
Barbara
B
Knittler
Michael R
MR
D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000235:genetics / Q000276:immunology*; D002460:Cell Line; D002461:Cell Line, Transformed; D022162:Cytoplasmic Vesicles / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism*; D004792:Enzyme Precursors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D006056:Golgi Apparatus / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D015789:HLA-A2 Antigen / Q000378:metabolism; D015235:HLA-B Antigens / Q000378:metabolism*; D059949:HLA-B51 Antigen; D056945:Hep G2 Cells; D006801:Humans; D008969:Molecular Sequence Data; D010455:Peptides / Q000276:immunology / Q000378:metabolism*; D011485:Protein Binding / Q000276:immunology; D055550:Protein Stability; D021381:Protein Transport / Q000276:immunology; D034622:RNA Interference / Q000276:immunology; D051381:Rats; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013381:Subtilisins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*
D004792:Enzyme Precursors; D015789:HLA-A2 Antigen; D015235:HLA-B Antigens; D059949:HLA-B51 Antigen; D010455:Peptides; D013381:Subtilisins; C107583:proprotein convertase PC7