Mipu1, a novel rat zinc-finger protein, inhibits transcriptional activities of AP-1 and SRE in mitogen-activated protein kinase signaling pathway

Mipu1 is a novel rat gene recently identified in our lab. Mipu1 cDNA contains a 1,824 bp open reading frame (ORF) and encoded a 608 amino acid protein with an N-terminal Krüppel-associated box (KRAB) domain and classical zinc finger C2H2 motifs in the C-terminus. Mipu1 protein is located in the nuclei. Fused to Gal-4 DNA-binding domain and cotransfected with pG5-luc, Mipu1 played a transcriptional suppressive effect. Deletion analysis with a series of truncated fusion proteins indicated that the KRAB motif was a basal repression domain. Overexpression of Mipu1 in H9c2 myogenic cells inhibited the transcriptional activities of SRE and AP-1. RNAi of Mipu1 in H9c2 myogenic cells activated the transcriptional activities of SRE and AP-1. These results suggested that Mipu1 protein might act as a transcriptional repressor in mitogen-activated protein kinase (MAPK) signaling pathway to mediate cellular functions.