STAT1 and fibrosarcoma: We then investigated the nuclear translocation of STAT1 upon IFN stimulation in simian virus 40 (SV40)–transformed fibroblasts from a healthy control (C), patients P1, P2, and P3, the STAT1-deficient fibrosarcoma cell line U3C, and its parental cell line 2C4 by immunofluorescence staining with a specific antibody.