C/EBPα directly modulates Id2 transcriptional activity. A. HEK 293T and PLC/PRF/5 cells were transfected with different truncations of Id2 luciferase reporter vectors (-1044/+360, -747/+360, -164/+360 or -102/+360). The corresponding relative luciferase activities were determined by a reporter gene assay. B. HEK 293T and PLC/PRF/5 cells were cotransfected with Id2 luciferase reporter vectors (-1044/+360, -747/+360, -164/+360 or -102/+360) and C/EBPα or pWPXL. The corresponding relative luciferase activities were determined by a reporter gene assay. C. Potential binding site for C/EBPα in the Id2 promoter identified with the JASPAR database. D. C/EBPα or pWPXL and Id2 luciferase reporter vectors (wild-type or mutant C/EBPα-binding sites, -164/+360) were cotransfected into HEK 293T and PLC/PRF/5 cells. The corresponding relative luciferase activities were determined by a reporter gene assay. **P<0.01. E. ChIP analysis of C/EBPα (tagged with FLAG) binding to the Id2 promoter. F. PLC/PRF/5 and Huh7 cells were transfected with C/EBPα or pWPXL, and the expression levels of C/EBPα and Id2 were detected by real-time PCR. G. PLC/PRF/5 and Huh7 cells were transfected with C/EBPα or pWPXL, and the expression levels of C/EBPα and Id2 were detected by western blot analysis.