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EMBO J. 2009 Dec 2;28(23):3730-44. doi: 10.1038/emboj.2009.296. Epub 2009 Oct 22.

Calreticulin-dependent recycling in the early secretory pathway mediates optimal peptide loading of MHC class I molecules.

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Cancer Sciences Division, University of Southampton School of Medicine, Southampton, UK.


Calreticulin is a lectin chaperone of the endoplasmic reticulum (ER). In calreticulin-deficient cells, major histocompatibility complex (MHC) class I molecules travel to the cell surface in association with a sub-optimal peptide load. Here, we show that calreticulin exits the ER to accumulate in the ER-Golgi intermediate compartment (ERGIC) and the cis-Golgi, together with sub-optimally loaded class I molecules. Calreticulin that lacks its C-terminal KDEL retrieval sequence assembles with the peptide-loading complex but neither retrieves sub-optimally loaded class I molecules from the cis-Golgi to the ER, nor supports optimal peptide loading. Our study, to the best of our knowledge, demonstrates for the first time a functional role of intracellular transport in the optimal loading of MHC class I molecules with antigenic peptide.

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