P-glycoprotein plays an insignificant role in the presentation of antigenic peptides to CD8+ T cells.
Most antigenic peptides presented to CD8+ T cells are generated from cytosolic precursors and are translocated by TAP into the endoplasmic reticulum, where they associate with MHC class I molecules. TAP-deficient cells exhibit a limited capacity to deliver peptides from cytosolic proteins to class I molecules. One candidate for an alternative peptide transporter is P-glycoprotein, which transports numerous substances, including peptides, across membranes. Elevation of P-glycoprotein expression is partially responsible for the resistance developed by neoplasias to chemotherapeutic drugs. Overexpression of P-glycoprotein has been reported to enhance the expression of class I molecules. Here, we investigated the role of P-glycoprotein in the generation of peptide-MHC complexes. We were unable to detect P-glycoprotein-mediated transport of synthetic peptides into the endoplasmic reticulum of either T2 cells (TAP-deficient) infected with a recombinant vaccinia virus (rVV) expressing P-glycoprotein or drug-resistant cells in which TAP is inactivated by a peptide from the herpes simplex virus ICP47 protein. Expression of rVV-encoded P-glycoprotein in T2 cells was unable to enhance cell surface expression of any of three MHC class I allomorphs tested. rVV-mediated expression of P-glycoprotein enabled T2 cells to produce limited amounts of class I-peptide complexes from cytosolic antigens, but this was not blocked by a drug that inhibits its transporter function, and a similar degree of presentation was mediated by functionally inactive mutated forms of P-glycoprotein. Thus, this was a nonspecific effect that we attributed to diminished membrane integrity resulting from P-glycoprotein overexpression. Taken together, our findings cast serious doubts that P-glycoprotein is a biologically significant transporter of cytosolic peptides.
Russ
G
G
Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892-0440, USA.
Ramachandra
M
M
Hrycyna
C A
CA
Gottesman
M M
MM
Pastan
I
I
Bennink
J R
JR
Yewdell
J W
JW
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000502:physiology*; D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000032:analysis / Q000235:genetics; D000818:Animals; D017951:Antigen Presentation; D001692:Biological Transport; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D015395:Histocompatibility Antigens Class I / Q000032:analysis; D006801:Humans; D007624:KB Cells; D051379:Mice; D008807:Mice, Inbred BALB C
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D015395:Histocompatibility Antigens Class I; C073119:TAP1 protein, human; C486171:Tap1 protein, mouse; C489516:Tap2 protein, mouse; C071692:TAP2 protein, human