Background and aim: The presentation of human leukocyte antigens (HLA) class I requires the coordinated expression of numerous components involved in antigen processing and antigen presentation. Tumor cells may alter the expression of these components to decrease HLA class I expression, allowing them to escape immune surveillance. The aim of this study is to investigate the expressions of these components, including proteasome subunits, and their involvement in the expression of HLA class I in human colon cancer cells.
Methods: Four human colon cancer cell lines, HCT116, SW403, LoVo and DLD-1, were used to examine the expression of HLA class I by flow cytometry. Reverse transcription-polymerase chain reaction was performed to assess the expression of beta2-microglobulin, heavy chains, transporter subunits, immunoproteasomes subunits and proteasome activator 28 (PA28) subunits.
Results: Human leukocyte antigen class I was expressed highly in HCT116 and SW403 cells and weakly in LoVo cells, but was not expressed in DLD-1 cells. The DLD-1 cells were deficient in the expression of proteasome subunits including low molecular weight polypeptide proteasome subunit 2 (LMP2), multicatalytic endopeptidase complex-like-1 (MECL-1), PA28alpha and PA28beta, whereas other HLA class I-expressing cell lines expressed all components tested. gamma-Interferon (IFN-gamma) treatment of DLD-1 cells restored the expression of LMP2, MECL-1 and PA28beta, but not the expression of HLA class I. Enforced expression of PA28alpha induced the expression of HLA class I in IFN-gamma-treated DLD-1 cells, but not in untreated DLD-1 cells.
Conclusion: These results suggest that the impaired expression of proteasome subunits is involved in the loss of HLA class I expression in human colon cancer cells.
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