Peptides generated by Cathepsin S or IRAP-mediated proteolysis in the endosomes are loaded onto MHC class I molecules, which are internalized and transported to early and late endosomal compartments where antigenic peptides can be loaded. A fraction of the internalized cell surface class I molecules enter MHC class II compartments (MIICs) within endocytic vesicles (Gromme et al. 1999, Kleijmeer et al. 2001). Microscopic analysis has revealed that surface MHC-I molecules are internalized and transported to early and late endosomal compartments (Basha et al. 2008, Lizee et al. 2003). A tyrosine-based endocytic trafficking motif (YXXA) is required for the constitutive internalization of MHC-I molecules from the cell surface into early/late endosomes for peptide loading (Basha et al. 2008, Lizee et al. 2003). Upon entry in to these endosomal compartments the MHC class I complexes exchange their pre-bound peptides with exogenously derived antigenic peptides.
Osterhaus, AD, Griffith, JM, Jakobson, E, Kleijmeer, MJ, Escola, JM, Stoorvogel, W, Rabouille, C, Uytdehaag, FG, Geuze, HJ, Melief, CJ
Basha, G, Seipp, RP, Lizée, G, Omilusik, KD, Jefferies, WA, Reinicke, AT
Neefjes, J, Tulp, A, Calafat, J, Grommé, M, Kenter, MJ, Janssen, H, Verwoerd, D, van Binnendijk, RS, Uytdehaag, FG
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