Distinct mechanisms of loss of IFN-gamma mediated HLA class I inducibility in two melanoma cell lines

BMC Cancer. 2007 Feb 23;7:34. doi: 10.1186/1471-2407-7-34.

Abstract

Background: The inability of cancer cells to present antigen on the cell surface via MHC class I molecules is one of the mechanisms by which tumor cells evade anti-tumor immunity. Alterations of Jak-STAT components of interferon (IFN)-mediated signaling can contribute to the mechanism of cell resistance to IFN, leading to lack of MHC class I inducibility. Hence, the identification of IFN-gamma-resistant tumors may have prognostic and/or therapeutic relevance. In the present study, we investigated a mechanism of MHC class I inducibility in response to IFN-gamma treatment in human melanoma cell lines.

Methods: Basal and IFN-induced expression of HLA class I antigens was analyzed by means of indirect immunofluorescence flow cytometry, Western Blot, RT-PCR, and quantitative real-time RT-PCR (TaqMan(R) Gene Expression Assays). In demethylation studies cells were cultured with 5-aza-2'-deoxycytidine. Electrophoretic Mobility Shift Assay (EMSA) was used to assay whether IRF-1 promoter binding activity is induced in IFN-gamma-treated cells.

Results: Altered IFN-gamma mediated HLA-class I induction was observed in two melanoma cells lines (ESTDAB-004 and ESTDAB-159) out of 57 studied, while treatment of these two cell lines with IFN-alpha led to normal induction of HLA class I antigen expression. Examination of STAT-1 in ESTDAB-004 after IFN-gamma treatment demonstrated that the STAT-1 protein was expressed but not phosphorylated. Interestingly, IFN-alpha treatment induced normal STAT-1 phosphorylation and HLA class I expression. In contrast, the absence of response to IFN-gamma in ESTDAB-159 was found to be associated with alterations in downstream components of the IFN-gamma signaling pathway.

Conclusion: We observed two distinct mechanisms of loss of IFN-gamma inducibility of HLA class I antigens in two melanoma cell lines. Our findings suggest that loss of HLA class I induction in ESTDAB-004 cells results from a defect in the earliest steps of the IFN-gamma signaling pathway due to absence of STAT-1 tyrosine-phosphorylation, while absence of IFN-gamma-mediated HLA class I expression in ESTDAB-159 cells is due to epigenetic blocking of IFN-regulatory factor 1 (IRF-1) transactivation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Epigenesis, Genetic
  • Genes, MHC Class I
  • HLA Antigens / biosynthesis*
  • Humans
  • Interferon Regulatory Factor-1 / metabolism
  • Interferon-gamma / pharmacology*
  • Melanoma / immunology
  • Melanoma / metabolism*
  • Phosphorylation
  • STAT1 Transcription Factor / metabolism
  • Signal Transduction
  • Skin Neoplasms / immunology
  • Skin Neoplasms / metabolism*
  • Transcriptional Activation
  • Tumor Cells, Cultured

Substances

  • Antineoplastic Agents
  • HLA Antigens
  • IRF1 protein, human
  • Interferon Regulatory Factor-1
  • STAT1 Transcription Factor
  • STAT1 protein, human
  • Interferon-gamma