Association of IFN-γ Signal Transduction Defects with Impaired HLA Class I Antigen Processing in Melanoma Cell Lines

Abstract

Purpose Abnormalities in the constitutive and IFN-γ–inducible HLA class I surface antigen expression of tumor cells is often associated with an impaired expression of components of the antigen processing machinery (APM). Hence, we analyzed whether there exists a link between the IFN-γ signaling pathway, constitutive HLA class I APM component expression, and IFN-γ resistance. Experimental Design The basal and IFN-γ–inducible expression profiles of HLA class I APM and IFN-γ signal transduction cascade components were assessed in melanoma cells by real-time PCR (RT-PCR), Western blot analysis and/or flow cytometry, the integrity of the Janus activated kinase (JAK) 2 locus by comparative genomic hybridization. JAK2 was transiently overexpressed in JAK2− cells. The effect of IFN-γ on the cell growth was assessed by XTT [2,3-bis(2-methoxy-4-nitro-S-sulfophenynl)-H-tetrazolium-5-carboxanilide inner salt] assay. Results The analysis of 8 melanoma cell lines linked the IFN-γ unresponsiveness of Colo 857 cells determined by lack of inducibility of HLA class I surface expression on IFN-γ treatment to a deletion of JAK2 on chromosome 9, whereas other IFN-γ signaling pathway components were not affected. In addition, the constitutive HLA class I APM component expression levels were significantly reduced in JAK2− cells. Furthermore, JAK2-deficient cells were also resistant to the antiproliferative effect of IFN-γ. Transfection of wild-type JAK2 into JAK2− Colo 857 not only increased the basal APM expression but also restored their IFN-γ sensitivity. Conclusions Impaired JAK2 expression in melanoma cells leads to reduced basal expression of MHC class I APM components and impairs their IFN-γ inducibility, suggesting that malfunctional IFN-γ signaling might cause HLA class I abnormalities.

HLA class II antigen-processing pathway in tumors: Molecular defects and clinical relevance

“…They include either gene-inactivating mutations, silencing through promoter methylation, transcriptional downregulation or post-translational alterations, such as an altered phosphorylation pattern. [42][43][44][45] In the following section, we will focus on structural alterations and de-regulation of HLA class II antigen expression since they are the best characterized abnormalities affecting HLA class II antigen expression in tumors.…”

The Role of Immune Escape and Immune Cell Infiltration in Breast Cancer

“…Loss or downregulation of MHC class I surface antigens allows tumor cells to escape immune surveillance [24,25]. Tumor cells of distinct origin are able to silence MHC class I surface expression, which is often caused by diminished expression of components of the MHC class I antigen processing and presentation machinery (APM) and of the interferon (IFN) signal transduction pathway and associated with a worse outcome [26]. Concerning BC, HLA class I expression levels have been shown to be significantly downregulated in BC, which is necessary for the transformation of normal cells into abnormal cells.…”

Immunological and clinical significance of HLA class I antigen processing machinery component defects in malignant cells

“…Loss of LMP2 upregulation after IFNγ treatment has been associated with defects in transcription factors such as interferon response factor 1 (IRF1) and signal transducer and activator of transcription (STAT1) binding to promoter sequences [43]. Furthermore, defects in Janus kinase 2 (JAK2) expression have been linked to lack of interferon-mediated upregulation of LMP2 and LMP10 in melanoma [44]. …”