Involvement of a novel zinc finger protein, MIZF, in transcriptional repression by interacting with a methyl-CpG-binding protein, MBD2

MBD2, a methyl-CpG-binding protein, is a component of the MeCP1 histone dea cetylase (HDAC) complex and plays a critical role in DNA methylation-mediat ed transcriptional repression. To understand the molecular basis of the met hylation-associated repression, we attempted to identify MBD2-interacting p roteins by a yeast two-hybrid system. Using MBD2 as bait, we isolated a nov el zinc finger protein, referred to as MIZF. A direct interaction between M BD2 and MIZF was confirmed by in vitro binding assays and immunoprecipitati on experiments. Four of seven zinc fingers present in the C-terminal region of MIZF are required for binding with MBD2. The MIZF mRNA is expressed in all human tissues and cell lines examined. The subcellular localization of MIZF is distinct from that of MBD2, although both proteins co-localize in s ome areas of the nuclei; MIZF localizes diffusely in the nucleoplasmic regi on, whereas MBD2 preferentially localizes in major satellites. A reporter a ssay demonstrated that MIZF significantly abrogates transcriptional activit ies. This repression is attenuated by an HDAC inhibitor, trichostatin A, an d is completely dependent on the interaction with MBD2. These results sugge st that MIZF is abundantly present in cells and functions as a negative reg ulator of transcription by binding to MBD2 and recruiting HDAC-containing c omplexes.