Interferon-gamma rapidly increases peptide transporter (TAP) subunit expression and peptide transport capacity in endothelial cells

Human cytotoxic T lymphocytes (CTL) recognize specific complexes of HLA class I molecules and peptides, which assemble when nascent class I molecules bind peptides transported from the cytoplasm into the endoplasmic reticulum by the heterodimeric transporter associated with antigen processing (TAP). Increased class I molecule expression on the cell surface increases the efficiency of CTL lysis. The kinetics of interferon (IFN)-gamma induction of TAP, peptide transport capacity, and HLA class I molecule expression was determined in endothelial cells, which are targets of CTL following transplantation or viral infection, TAP mRNAs are induced rapidly, increasing 20-fold (TAP1) or 10-fold (TAP2) by 12 h, whereas HLA class I mRNA is induced more slowly, increasing 10-fold in 24 h. TAP1 and TAP2 proteins are also induced rapidly, increasing 10-fold in 24 h, whereas HLA class I heavy chain proteins and surface expression increase more slowly. Peptide transport capacity in endothelial and HeLa cells increases within 6 h of IFN-gamma treatment, suggesting that the IFN-gamma-induced TAP heterodimers are functional. Therefore, the IFN-gamma-induced increase in TAP proteins is accompanied by an increased peptide transport capacity, which may be important in supporting the subsequent rise in HLA class I protein expression.