Previous studies demonstrated high specificity for knockdown of Sp1, Sp3 and Sp4 by RNAi in RD rhabdomyosarcoma and KU7 bladder cancer cells [20, 24], whereas in other cell lines, knockdown of an individual Sp protein also decreased expression of one or both of the other gene products [18–24]. This evidence concerns the gene SP4 and urinary bladder carcinoma.