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Science. 2009 Jul 10;325(5937):213-7. doi: 10.1126/science.1172845. Epub 2009 Jun 4.

IRAP identifies an endosomal compartment required for MHC class I cross-presentation.

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INSERM, U580, 75015 Paris, France; Université Paris Descartes, Faculté de Médecine René Descartes, 75015 Paris, France.


Major histocompatibility complex (MHC) class I molecules present peptides, produced through cytosolic proteasomal degradation of cellular proteins, to cytotoxic T lymphocytes. In dendritic cells, the peptides can also be derived from internalized antigens through a process known as cross-presentation. The cellular compartments involved in cross-presentation remain poorly defined. We found a role for peptide trimming by insulin-regulated aminopeptidase (IRAP) in cross-presentation. In human dendritic cells, IRAP was localized to a Rab14+ endosomal storage compartment in which it interacted with MHC class I molecules. IRAP deficiency compromised cross-presentation in vitro and in vivo but did not affect endogenous presentation. We propose the existence of two pathways for proteasome-dependent cross-presentation in which final peptide trimming involves IRAP in endosomes and involves the related aminopeptidases in the endoplasmic reticulum.

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