A role for YY1 in repression of dominant negative LEF-1 expression in colon cancer

Lymphoid enhancer factor 1 (LEF-1) mediates Wnt signaling via recruitment of b-catenin to target genes. The LEF1 gene is aberrantly transcribed in colon cancers because promoter 1 (P1) is a Wnt target gene and is activated by TCF–b-catenin complexes. A second promoter in intron 2 (P2) produces dominant negative LEF-1 isoforms (dnLEF-1), but P2 is silent because it is repressed by an upstream distal repressor element. In this study we identify Yin Yang 1 (YY1) transcription factor as the P2-specific factor necessary for re-pression. Site-directed mutagenesis and EMSA were used to identify a YY1-binding site at+25 in P2, and chromatin immunoprecipitation assays detected YY1 binding to endogenous LEF1 P2. Mutation of this site relieves P2 repression in tran-sient transfections, and knockdown of endogenous YY1 relieves repression of integrated P2 reporter constructs and decreases the H3K9me3 epigenetic marks. YY1 is responsible for repressor specificity because introduction of a single YY1-binding site into the P1 promoter makes it sensitive to the distal repressor. We also show that induced expres-sion of dnLEF-1 in colon cancer cells slows their rate of proliferation. We propose that YY1 plays an important role in preventing dnLEF-1 expression and growth inhibition in colon cancer