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

Purpose: Abnormalities in the constitutive and IFN-g–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-g signaling pathway, constitutive HLA class I APM component expression, and IFN-g resistance. Experimental Design: The basal and IFN-g–inducible expression profiles of HLA class I APM and IFN-g 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-g on the cell growth was assessed by XTT [2,3-bis(2-methoxy-4-nitro-S-sulfophenynl)-H-tetrazolium-5carboxanilide inner salt] assay. Results: The analysis of 8 melanoma cell lines linked the IFN-g unresponsiveness of Colo 857 cells determined by lack of inducibility of HLA class I surface expression on IFN-g treatment to a deletion of JAK2 on chromosome 9, whereas other IFN-g 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-g . Transfection of wild-type JAK2 into JAK2 Colo 857 not only increased the basal APM expression but also restored their IFN-g sensitivity. Conclusions: Impaired JAK2 expression in melanoma cells leads to reduced basal expression of MHC class I APM components and impairs their IFN-g inducibility, suggesting thatmalfunctional IFN-g signaling might cause HLA class I abnormalities. Clin Cancer Res; 17(9); 2668–78. 2011 AACR.