Malignant germ cell tumours of the testis express interferon-gamma, but are resistant to endogenous interferon-gamma

Cytokines possess discrepant effects on tumour cells varying from anti- to proapoptotic activities. We recently reported that testicular germ cell tumours (TGCT) express a functional form of the proinflammatory cytokine interferon-gamma (IFNgamma). The present study asked whether TGCT-derived IFNgamma influences survival or death of neoplastic germ cells. Analysis of TGCT cell lines demonstrated that they expressed and secreted IFNgamma, but were resistant to the endogenous IFNgamma since neutralisation of IFNgamma by a specific blocking antibody had no influence on the proliferation and/or the degree of apoptosis of tumour cells. To study mechanisms providing tumour resistance to endogenous IFNgamma, we analysed primary TGCT and two human TGCT cell lines (NTERA and NCCIT) for the expression of IFNgamma receptor and for the level of phosphorylation of the signal transducer and activator of transcription (STAT)-1. In situ hybridisation, immunocytochemistry, Western blot analysis and flow cytometry indicated that primary TGCT as well as NCCIT and NTERA cell lines expressed the heterodimeric cell surface IFNgamma receptor which consists of both 90-kDa alpha- and the 85-kDa beta-chains. However, the downstream transcription factor STAT-1 was not phosphorylated constitutively, indicating that STAT-1 is not activated by the endogenous IFNgamma. Upon application of recombinant human IFNgamma in excess, however, STAT-1 was phosphorylated and the interferon regulatory factor-1 (IRF-1) was induced, suggesting that both IFNgammaR and STAT-1 are functionally intact in TGCT. Altogether our results suggest that despite secreting biologically active IFNgamma, the concentration of the endogenous IFNgamma is too low to stimulate the IFNgammaR/STAT signalling pathway in TGCT in an autocrine and/or paracrine manner.