In vivo Sp1 binding to the promoters of hTERT, c-Myc, and C17, as determined by ChIP assay. (A, left) Nuclear extracts from the same samples used in ChIP were immunoblotted with c-Myc and Sp1 antibodies. Coomassie blue staining served as loading control. (Right) SYBR green real-time PCR shows diminished Sp1 and c-Myc binding on the hTERT promoter after arsenic (0.75 μM for 12 days) exposure. Mock indicates no nuclear extract in the reaction; No Ab, omission of antibody in the immunoprecipitation procedures. HGF antibody was used as a control IgG. PCR products obtained at 35 cycles and resolved on agarose gel are shown below the graph. (B-C) SYBR green real-time PCR quantification of ChIP using anti-Sp1 antibody shows a significant decrease in Sp1 binding in the promoters of MYC (B) and C17 (C) after arsenic treatment. Error bars represent standard deviations from triplicate experiments.