Figure 4. Promoter deletion assay of platelet-derived growth factor receptor (PDGFR)-β. Four lengths of the PDGFR-β promoter (A) were individually constructed in a luciferase-based reporter vector to produce four pGL4.10[Luc2]-rPDGFR-β vectors (B). Individual promoter activities were measured in normal cells at 24 hr after transfection with the different pGL4.10[Luc2]-rPDGFR-β plasmids (C). Differences in promoter activities between normal and senescent cells with the PDGFR-β segment (0.5 kb) were measured (D). The transcription start site was defined as +1. ** p < 0.01 compared to the group transfected with the reporter vector with the proximal promoter (0.5 kb) of PDGFR-β. ‡p < 0.01 compared to the normal cell group.