Sp1 binds to the human Klotho gene ( KL ) promoter. ( a ) HEK-293 cells were co-transfected with Full KL/LUC reporter and pcDNA3 or pcDNA3-Sp1 plasmid. 24 h after transfection, cells were lysed and transcriptional activity was detected by dual-luciferase assays. ( b ) Cells were transfected with full length or truncated reporter, combined with pcDNA3 or pcDNA3-Sp1 plasmid. 24 h after transfection, HEK-293 cells were lysed and transcriptional activity was detected. ( c ) HEK-293 cells were transfected with KL5/LUC or mutated KL5/LUC reporter, and transcriptional activity was detected as before. As an internal control, Rinella (pRL-TK) was used to normalize the transfection efficiency. Mean ± SD of triplicate experiments performed independently. *** p