Processing of a multiple membrane spanning Epstein-Barr virus protein for CD8(+) T cell recognition reveals a proteasome-dependent, transporter associated with antigen processing-independent pathway.
Epstein-Barr virus (EBV) latent membrane protein (LMP)2 is a multiple membrane spanning molecule which lacks ectodomains projecting into the lumen of the endoplasmic reticulum (ER). Human CD8(+) cytotoxic T lymphocytes (CTL)s recognize a number of epitopes within LMP2. Assays with epitope-specific CTLs in two different cell backgrounds lacking the transporter associated with antigen processing (TAP) consistently show that some, but not all, LMP2 epitopes are presented in a TAP-independent manner. However, unlike published examples of TAP-independent processing from endogenously expressed antigens, presentation of TAP-independent LMP2 epitopes was abrogated by inhibition of proteasomal activity. We found a clear correlation between hydrophobicity of the LMP2 epitope sequence and TAP independence, and experiments with vaccinia minigene constructs expressing cytosolic epitope peptides confirmed that these more hydrophobic peptides were selectively able to access the HLA class I pathway in TAP-negative cells. Furthermore, the TAP-independent phenotype of particular epitope sequences did not require membrane location of the source antigen since (i) TAP-independent LMP2 epitopes inserted into an EBV nuclear antigen and (ii) hydrophobic epitope sequences native to EBV nuclear antigens were both presented in TAP-negative cells. We infer that there is a proteasome-dependent, TAP-independent pathway of antigen presentation which hydrophobic epitopes can selectively access.
Lautscham
G
G
Cancer Research Campaign Institute for Cancer Studies and Medical Research Council Centre for Immune Regulation, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
Mayrhofer
S
S
Taylor
G
G
Haigh
T
T
Leese
A
A
Rickinson
A
A
Blake
N
N
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000276:immunology*; D017951:Antigen Presentation / Q000276:immunology*; D002461:Cell Line, Transformed; D003546:Cysteine Endopeptidases / Q000276:immunology*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells; D018604:Epitope Mapping; D018984:Epitopes, T-Lymphocyte / Q000276:immunology; D015234:HLA-A Antigens / Q000276:immunology; D059871:HLA-A24 Antigen; D015235:HLA-B Antigens / Q000276:immunology; D015796:HLA-B27 Antigen / Q000276:immunology; D059947:HLA-B40 Antigen; D004854:Herpesvirus 4, Human / Q000276:immunology*; D006801:Humans; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000276:immunology*; D009687:Nuclear Proteins / Q000276:immunology; D046988:Proteasome Endopeptidase Complex; D015398:Signal Transduction / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D014407:Tumor Cells, Cultured; D014763:Viral Matrix Proteins / Q000276:immunology*
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D015853:Cysteine Proteinase Inhibitors; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D018984:Epitopes, T-Lymphocyte; D015234:HLA-A Antigens; D059871:HLA-A24 Antigen; D015235:HLA-B Antigens; D015796:HLA-B27 Antigen; D059947:HLA-B40 Antigen; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; C073119:TAP1 protein, human; D014763:Viral Matrix Proteins; C071692:TAP2 protein, human; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex