Two derivatives of green fluorescent protein-labeled 4T1 (CRL-2539; ATCC) cells were kindly provided by Professor Jonas Fuxe (Karolinska Institute, Solna, Sweden). Lentivirus-mediated knockdown of C/EBPβ was described previously in Johansson et al.4 (link) Sh C/EBPβ cell line expressed C/EBPβ shRNA, whereas sh control expressed control shRNA. Both cell lines were cultured in RPMI-1640 (Gibco, Waltham, MA, USA) supplemented with 10% fetal calf serum and 1% penicillin and streptomycin in a humidified incubator at 37 °C in an atmosphere containing 5% CO2 and 95% O2.