tokens: Overexpression of p50 in transient cotransfection studies using the proximal CRP promoter ( - 125 / + 9 ) linked to a luciferase reporter caused a 3 - fold increase of luciferase activity , while C / EBPbeta overexpression caused an 18 - fold increase ; simultaneous overexpression of both transcription factors increased luciferase activity approximately 600 - fold .