Sequence-specific transcriptional repression by an MBD2-interacting zinc finger protein MIZF

MBD2 is a member of the methyl-CpG-binding protein family that plays an important role in methylated DNA silencing. We have recently identified a novel zinc finger protein, MIZF, as an MBD2-binding partner. To understand the physiological function of MIZF in MBD2-mediated gene silencing, we investigated the DNA-binding properties of MIZF and its potential target genes. Using a cyclic amplification and selection of targets technique, the consensus sequence CGGACGTT, which contains a conserved CGGAC core, was determined as sufficient for MIZF binding. Deletion of individual zinc fingers revealed that five of the seven zinc fingers are required for DNA binding. Reporter assays demonstrated that MIZF represses transcription from the promoter including this DNA sequence. A database search indicated that a variety of human genes, including Rb, contain this sequence in their promoter region. MIZF actually bound to its recognition sequence within the Rb promoter and repressed Rb transcription. These results suggest that MIZF, through its DNA-binding activity, acts as a sequence-specific transcriptional repressor likely involved in MBD2-mediated epigenetic gene silencing.