Cloning and characterization of a novel zinc finger protein that modulates the transcriptional activity of nuclear receptors.

The orphan nuclear receptor steroidogenic factor-1 (SF-1) plays pivotal roles in the development and function of steroidogenic organs. It transcriptionally regulates an array of factors required for biosynthesis of steroid hormones and is also necessary for the expression of genes in the pituitary and the male reproductive tract. Here we describe the identification of a novel zinc finger protein that modifies the transcriptional potential of SF-1. This factor, which we call Zip67 (zinc finger protein 67 kDa), was cloned through a two-hybrid screen of a human testis cDNA library using the C-terminal part of SF-1 as the bait. Transient transfection experiments demonstrated that Zip67 represses SF-1-dependent transcription in the context of both multimerized SF-1-binding sites and natural SF-1-inducible promoters. The interaction between Zip67 and SF-1 was dependent on an intact activation function-2 domain of SF-1, and we propose a mechanism whereby Zip67 represses transcription through competition with p160 coactivators for binding to SF-1. Zip67 was detected in SF-1 expressing tissues such as testis, adrenal, ovary and spleen in addition to other tissues. In line with the broader expression pattern, we found that Zip67 also affected transcription mediated by several other nuclear receptors. In conclusion, we have isolated a novel zinc-finger protein that influences gene activation through interaction with the functionally important activation function-2 domain of nuclear receptors.