Efficient and Qualitatively Distinct MHC Class I-Restricted Presentation of Antigen Targeted to the Endoplasmic Reticulum

Abstract

For most nascent glycoprotein Ags, the MHC class I-restricted processing pathway begins in the endoplasmic reticulum (ER). From this location, they are translocated to the cytosol for degradation by the proteasome. A reasonable assumption is that processing of exocytic Ags is less efficient than that of cytosolic Ags, due to the requirement for additional handling, but that the processing pathways for the two types of proteins are otherwise similar. To test this, we compared the presentation of three epitopes within influenza nucleoprotein (NP) when this Ag is targeted to the cytosol or the ER. Surprisingly, under conditions of limited Ag expression, presentation of two proteasome-dependent epitopes is comparable when NP is targeted to the ER while presentation of a third is negatively impacted. Furthermore, presentation of the third epitope is unaffected by the addition of proteasome inhibitor when cytosolic NP is expressed but is significantly enhanced when exocytic NP is expressed. These results indicate that delivery of Ag to the ER need not preclude efficient presentation and that processing of cytosolic and ER-targeted Ag is qualitatively distinct.

Re-evaluating the Generation of a “Proteasome-Independent” MHC Class I-Restricted CD8 T Cell Epitope

“…Processing and presentation of NP 50 -57 to CTL is diminished in the presence of the proteasome inhibitor Lac (Fig. 1A), especially when Ag expression is limited (15). In contrast, generation of NP 147-155 from a full-length Ag is increased under similar conditions (Fig.…”

“…We have observed previously that two MHC I-restricted epitopes of influenza A PR/8/34 NP exhibit opposite sensitivities to protease inhibitors that affect the proteasome (14,15). Processing and presentation of NP 50 -57 to CTL is diminished in the presence of the proteasome inhibitor Lac (Fig.…”

“…1A and Ref. 15). Presentation of NP 50 -57 and NP 147-155 epitopes from minigene constructs that do not require processing is unaffected by proteasome inhibitors (Fig.…”

“…to block, and actually enhance, presentation of the H-2K d -restricted epitope from influenza A PR/8/34 nucleoprotein (NP), NP [147][148][149][150][151][152][153][154][155] (14,15). Furthermore, mutation of an immediately flanking alanine residue to a proline (influenza NP with aa 146 mutated from alanine to proline (A146P)) results in a substrate that can be processed to yield the antigenic peptide only in the presence of these inhibitors (14).…”

Role of T cell help and endoplasmic reticulum targeting in protective CTL response against influenza virus

“…However, ER processing has been reported for the envelope protein of the human immunodeficiency virus 1 [41] and leader sequence-competent synthetic minigenes [42]. A recent study on the influenza virus NP showed that delivery of antigen to the ER yields efficient presentation [43]. Taken together, it is possible that in our case the NP 366-374 is also processed in the lumen of the ER in B lymphocytes and this may provide a selective advantage to the generation of a dominant CTL response.…”