Direct repression of E2F1-mediated transcription by C/EBPϵ. NIH 3T3 cells or Soas-2 cells were either transfected with an E2F-responsive reporter vector (pGL3B/3 × E2F, 1 μg) or cotransfected with an E2F-responsive reporter vector (1 μg), along with an E2F1 expression vector (0.05 μg). Where indicated, a C/EBPϵ expression vector was added to the transfections. All transfections included the pRL-SV40 vector (0.2 μg). Results represent the mean of triplicate transfections. The experiments were repeated 3 times.