Overexpression of Sp1 upregulates Klotho expression. HK-2 cells ( a - b ) or HEK-293 cells ( c - d ) were transfected with increasing amount of pcDNA3-Sp1 plasmid or empty control. 48 h after transfection, total proteins were isolated and the protein levels of Sp1 and Klotho were detected by Western blots ( a / c ). Total cell RNAs were isolated for quantitative RT-PCR to analyze the mRNA level of Klotho ( b / d ). Data were expressed as the mean ± SD in three independent experiments. *** p