Regulation of the MDR1 gene by transcriptional repressors selected using peptide combinatorial libraries

The ability to selectively regulate the expression of genes implicated in cancer or other diseases could have important ramifications for both basic research and for therapy. Using peptide combinatorial libraries expressed in yeast, we have screened for novel zinc finger proteins that selectively bind to an overlapping EGR1/SP1/WT1 regulatory site in the promoter of the MDR1 multidrug resistance gene. The novel proteins were only moderately effective in blocking transcription by simple masking of the target site. However, when coupled to mammalian transactivator or repressor domains, they could selectively modulate the expression of reporter genes having promoters containing the MDR1 target site. Moreover, they could also regulate transcription of the chromosomal MDR1 gene. Thus, in K562 cells, 12-O-tetradecanoylphorbol-13-acetate-inducible expression of P-glycoprotein, the product of MDR1 gene, was strongly and selectively inhibited by the presence of a repressor protein targeted to the MDR1 promoter. These studies potentially provide a novel alternative approach to the control of multidrug resistance. They also provide important insights into strategies for developing selective regulators of gene expression.