title: Downregulation of the proteasome subunits, transporter, and antigen presentation in hepatocellular carcinoma, and their restoration by interferon-gamma.
abstract: BACKGROUND
  In our previous study, expressions of human histocompatibility leukocyte antigens class I molecules (HLA-I) and the transporter associated with antigen processing (TAP) 1/2 genes were investigated in seven hepatocellular carcinoma (HCC) cell lines. Two cell lines, Hep-3B and HuH-7, showed a reduced level of TAP, which might cause the low surface expression of HLA-I. In order to understand the downregulation mechanism of antigen presentation in tumors, the two cell lines were further investigated.
  
  
  METHODS
  Expressions of HLA-I and antigen presentation-related genes were analyzed by flow cytometry and polymerase chain reaction, respectively. Antigen presentation was tested in 51Cr-release assays.
  
  
  RESULTS
  Flow cytometric analyses revealed low surface expression of HLA-I on Hep-3B and HuH-7 cells. Introduction of HLA-A2 gene did not result in a high surface expression of HLA-A2. This suggested the downregulation of HLA-I expression might be related to defects in the antigen presentation machinery. We then examined expression levels of various antigen presentation-related genes. Hep-3B and HuH-7 demonstrated low expression of the low-molecular-weight protein (LMP) 2, LMP7, TAP1, and HLA-I heavy-chain transcripts. The downregulation of these genes was dissolved by treatment with gamma-interferon. Furthermore, allo-specific cytotoxic T lymphocyte (CTL) lines failed to recognize Hep-3B and HuH-7 cells, while they killed IFN-gamma-treated Hep-3B and HuH-7 cells.
  
  
  CONCLUSIONS
  Our results suggest that defects in the antigen presentation-related molecules might cause downregulation of HLA-I expression, antigen presentation, and subsequently, escape from specific CTL killing. The downregulation could be restored by IFN-gamma treatment, suggesting the potential use of IFN-gamma for therapeutic purposes.
authors.affiliation: Department of Microbiology, Saitama Medical School, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Matsui
authors.forename: Sanae
authors.initials: S
authors.lastname: Machida
authors.forename: Teru
authors.initials: T
authors.lastname: Itani-Yohda
authors.forename: Toshitaka
authors.initials: T
authors.lastname: Akatsuka
mesh_terms: D017951:Antigen Presentation / Q000235:genetics; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000235:genetics*; D003546:Cysteine Endopeptidases / Q000235:genetics*; D015536:Down-Regulation / Q000235:genetics*; D015789:HLA-A2 Antigen / Q000235:genetics*; D015395:Histocompatibility Antigens Class I / Q000235:genetics*; D006801:Humans; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000235:genetics* / Q000627:therapeutic use; D008113:Liver Neoplasms / Q000188:drug therapy / Q000235:genetics*; D026901:Membrane Transport Proteins / Q000235:genetics*; D009097:Multienzyme Complexes / Q000235:genetics*; D046988:Proteasome Endopeptidase Complex; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D015789:HLA-A2 Antigen; D015395:Histocompatibility Antigens Class I; D026901:Membrane Transport Proteins; D009097:Multienzyme Complexes; D007371:Interferon-gamma; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex