Differential contribution of TAP and tapasin to HLA class I antigen expression

Abstract

Summary Expression of class I human leucocyte antigens (HLA) on the surface of malignant cells is critical for their recognition and destruction by cytotoxic T lymphocytes. Surface expression requires assembly and folding of HLA class I molecules in the endoplasmic reticulum with the assistance of proteins such as Transporter associated with Antigen Processing (TAP) and tapasin. Interferon‐γ induces both TAP and tapasin so dissection of which protein contributes more to HLA class I expression has not been possible previously. In this study, we take advantage of a human melanoma cell line in which TAP can be induced, but tapasin cannot. Interferon‐γ increases TAP protein levels dramatically but HLA class I expression at the cell surface does not increase substantially, indicating that a large increase in peptide supply is not sufficient to increase HLA class I expression. On the other hand, transfection of either allelic form of tapasin (R240 or T240) enhances HLA‐B*5001 and HLA‐B*5701 antigen expression considerably with only a modest increase in TAP. Together, these data indicate that in the presence of minimal TAP activity, tapasin can promote substantial HLA class I expression at the cell surface.

Multiple Structural and Epigenetic Defects in the Human Leukocyte Antigen Class I Antigen Presentation Pathway in a Recurrent Metastatic Melanoma Following Immunotherapy

“…This result is different from those of previous studies that established the TAP-stabilizing function of tapasin using other cell line systems (12,(45)(46)(47). Several possibilities may explain this discrepancy.…”

“…Later, Yabe et al (35) described a large homozygous deletion of exons 4 -7 in TAPBP in PBMC obtained from a patient with type II bare lymphocyte syndrome. More recently, Belicha-Villanueva et al (12) revealed a tapasin-loss phenotype by the M553 melanoma cell line, although its underlying mechanism remains unclear. We report here the first case of tapasin loss caused by a combination of genetic defects (TAPBP 684delA and LOH) in a malignant cell, although TAPBP 684delA appears to be cancer-unrelated as it is present as a heterozygous germ-line mutation that becomes homozygous after cancer-related LOH.…”

“…Although HLA class I heavy chain and ␤ 2 m subunits are frequently lost because of irreversible mutations, such as loss-of-heterozygosity (LOH), deletion, and missense/frameshift mutations, other antigen-processing machinery components are mostly deregulated; the latter abnormality can often be corrected by IFN-␥. Irreversible antigen-processing machinery defects in tumors caused by mutations are rare and have thus far been described in TAP1 in two tumor cell lines (9,10) and TAP2 in one colorectal tumor lesion (11), whereas IFN-␥-uncorrectable tapasin loss with unknown underlying mechanisms has been identified in one tumor cell line (12). Emerging evidence indicates the presence of multiple defects in HLA class I antigen-processing machinery components within a single tumor cell population (13,14); some of them are acquired sequentially (14).…”

Pseudomonas aeruginosa Cif Protein Enhances the Ubiquitination and Proteasomal Degradation of the Transporter Associated with Antigen Processing (TAP) and Reduces Major Histocompatibility Complex (MHC) Class I Antigen Presentation

“…Cif Inhibits TAP-mediated Peptide Transport into the ER and Cell Surface MHC Class I Antigen Presentation-To determine whether Cif, by decreasing TAP1 abundance, reduced TAPmediated transport of peptides into the ER, studies were conducted to measure peptide translocation into the ER by measuring 125 I-labeled peptide translocation into ER microsomes of airway epithelial cells, as described (11). (ϩCif) OMVs reduced peptide uptake by 61 Ϯ 7%, compared with peptide uptake in cells treated with (ϪCif) OMVs (Fig.…”

“…Peptide Translocation Assays-Peptide translocation was measured as described previously using 125 I-labeled B27#3 glycopeptide-1 and ER microsomes prepared from (ϩCif) OMVor (ϪCif) OMV-treated polarized airway epithelial cells (11).…”