Isolation and characterization of a novel zinc finger protein MIZF in DNA methylation and transcriptional regulation

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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 DNA sequence CGGACGTT 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. Database search indicated that a variety of human genes including Rb contain this sequence in their promoter region. MIZE actually bound to its recognition sequence within the Rb promoter and repressed the 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 genesilencing.