Characterization of a zinc finger protein ZAN75: nuclear localization signal, transcriptional activator activity, and expression during neuronal differentiation of P19 cells.

The ZAN75 cDNA was first identified in NIH 3T3 cells and codes for a DNA-binding protein with two zinc finger motifs. In this study, we characterized the nuclear localization signal of ZAN75, tested if ZAN75 regulates transcription, and examined its expression during embryonic development and neuronal differentiation of P19 mouse embryonal carcinoma cells. By examining the cellular localization of deletion mutants of ZAN75 fused to green fluorescence protein, ZAN75 was revealed to have a bipartite nuclear localization signal sequence upstream of the zinc finger domains. The N-terminal region of ZAN75, when fused to the GAL4 DNA-binding domain, strongly activated transcription. The expression of ZAN75 mRNA was found to be developmentally regulated, showing the highest expression in E11.5 embryos. In situ hybridization experiments using E11.5 embryos showed a high expression of the transcripts in neuronal tissues such as brain and neural tube. The expression of ZAN75 was transiently increased at both the mRNA and the protein levels when P19 cells were treated with retinoic acid to induce neuronal differentiation. Taken together, these results indicate that ZAN75 is a transcriptional activator with a bipartite nuclear localization signal and may play a role in neuronal differentiation.