Molecular cloning and characterization of a zinc finger protein involved in Id-1-stimulated mammary epithelial cell growth

Id proteins are dominant negative regulators of basic helix-loop-helix tran scription factors. Previous work in our laboratory has shown that constitut ive expression of Id-1 in SCp2 mouse mammary epithelial cells inhibits thei r differentiation and induces proliferation, invasion, and migration, Id-1 expression also correlates with the invasive and aggressive potential of hu man breast cancer cells. However, little is known about Id-1 target genes t hat are important for regulating normal and transformed breast epithelial c ell phenotypes. Now we report the cloning of a novel zinc finger protein, Z fp289, using degenerate primers to specifically amplify cDNAs from Id-1-tra nsfected SCp2 cells. Zfp289 has homology with a yeast zinc finger protein, the GTPase-activating protein Gcs-1, which was initially identified as a ge ne required for the re-entry of cells into the cell cycle after stationary phase growth. Zfp289 mRNA expression pattern correlates with Id-1 expressio n in SCp2 mammary epithelial cells under various experimental conditions as well as in the mouse mammary gland at different stages of development. It is predominantly present in the cytoplasm of the cells as evident from gree n fluorescent protein fusion protein localization. SCp2 mammary epithelial cells with constitutive expression of Zfp289 have a higher S-phase index, c ompared with control cells, when cultured in a serum-free medium. We conclu de that the novel zinc finger protein Zfp289, which may represent the mamma lian homologue of Gcs-1, is potentially an important mediator of the Id-1-i nduced proliferation pathway in mammary epithelial cells.