Expression and function of the peptide transporters in escape variants of human renal cell carcinomas.
The transporter associated with antigen processing (TAP) complex is a heterodimeric transmembrane pump consisting of the TAP-1 and TAP-2 subunits; these subunits translocate peptides from the cytoplasm into the lumen of the endoplasmic reticulum, where they bind nascent major histocompatibility complex (MHC) class I molecules. Loss or reduced expression of the TAP genes results in the synthesis of unstable peptide free MHC class I molecules that are only weakly expressed on the cell surface. In a number of human tumor cell lines, downregulation of MHC class I expression has been found to be associated with reduced or absent TAP expression. To investigate whether alterations in MHC class I expression occur during transformation and subsequent progression and whether MHC class I suppression is caused by impaired TAP function, we analyzed the protein expression of MHC class I heavy and light chain and TAP-1 in three renal cell carcinoma (RCC) cell lines and short-term cultures from corresponding normal kidney tissue. In one case a cell line established from a metastatic lesion was also available. Compared with normal epithelial cells, suppression of TAP-1 and MHC class I molecules was detected in all three primary RCC cells and was even more pronounced in the metastatic cell line. In contrast to normal epithelial cells, MHC class I membrane expression of two RCC lines was enhanced by culture in the presence of MHC class I binding peptides or at low temperature (26 degrees C) instead of 37 degrees C. Unstable MHC class I surface expression is caused by dissociation of the MHC class I heavy and light chain molecules as a result of functional defects in the antigen processing machinery, e.g., impaired peptide transport. Attempts to counteract the reduced immunogenicity by transferring the TAP genes into these cells demonstrated that TAP-1-modified RCC cells expressed higher levels of MHC class I molecules. These data indicate that downregulation and instability of MHC class I surface expression in RCC cells is at least partially caused by deficient loading with endogenous peptides and can be restored by TAP gene transfer.
Seliger
B
B
Johannes Gutenberg-Universität, Abteilung für Hämatologie/Onkologie, Mainz, Germany.
Höhne
A
A
Jung
D
D
Kallfelz
M
M
Knuth
A
A
Jaeger
E
E
Bernhard
H
H
Momburg
F
F
Tampé
R
R
Huber
C
C
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D001692:Biological Transport; D002292:Carcinoma, Renal Cell / Q000378:metabolism*; D003080:Cold Temperature; D018014:Gene Transfer Techniques; D015395:Histocompatibility Antigens Class I / Q000378:metabolism; D006801:Humans; D007680:Kidney Neoplasms / Q000378:metabolism*; D009362:Neoplasm Metastasis; D010455:Peptides / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D015395:Histocompatibility Antigens Class I; D010455:Peptides; C073119:TAP1 protein, human