Identification of zinc finger proteins bound to a silencer region in the rat glutathione transferase P gene

The rat glutathione transferase P (GST-P) gene is strongly induced during chemical hepatocarcinogenesis, whereas mRNA of this gene is rarely expressed in normal rat liver. We previously identified a silencer region in the promoter of this gene. This silencer has several DNA binding sites and at least three proteins (Silencer factor- A, -B, and -C (SF-A, SF-B, and SF-C) bind to these sites. We previously cloned and characterized the Nuclear Factor 1 (NF1) family and the CCAAT/enhancer-binding protein (C/EBP) family as SF-A and SF-B, respectively. However, SF-C which binds to GST-P silencer 2 (GPS2) remains to be cloned. By screening using yeast one-hybrid system, several zinc finger proteins were identified as a candidate of SF-C. The gel-mobility shift analyses showed that BTEB2, EZF, LKLF, TFIIIA, TIEG1, and novel zinc finger protein MZFP bound to GPS2 with different affinities. Several proteins of these are known to be transcriptional activators or repressors, suggesting that zinc finger proteins bind to GPS2 and regulate GST-P expression in the rat liver.