HIF-1α displaces Myc binding from p21cip1 promoter and overrides Myc target gene expression. (A) After Ad-ΔODD infection of HCT116 cells, chromatin immunoprecipitation assays were performed with indicated antibodies at the top. Both the proximal and distal regions of p21cip1 promoter were analyzed. Input, genomic DNA prior to immunoprecipitations. (B) Normoxic (N) and hypoxic (H) HCT116 cells were stained by immunofluorescence with anti-Myc antibody (in red) and antibodies against HIF-1α, p21cip1, or hTERT (in green). Only merged images are presented. The cells in panel iii were treated with doxorubicin (Dox). (C) Myc expression levels from 100 individual cells in (B) were plotted in dots along the x-axis against those of HIF-1α, p21, or hTERT in the y-axis. Cells expressing both proteins are depicted in dots along the diagonal lines.