Establishment of M1Egr1-myc cell lines. M1Egr-1 cells were transduced with an MSCV-puro retroviral vector, encoding for a c-myc transgene. Following selection in puromycin (3.5 mg/mL) surviving clones were expanded, as described in “Materials and methods.” Indicated M1 clones were cultured without or with IL-6 (50 ng/mL) for 48 hours and were assessed for c-Myc (A) and Egr-1 (B) protein expression by Western blotting, using appropriate antibodies, as described in “Materials and methods.”