Generation of C127-derived cell lines expressing estrogen or progesterone receptors for studying gene regulation on bovine papilloma virus minichromosomes.

To study regulation of transcription by multiple steroid hormones we have stably introduced expression vectors for human estrogen and rabbit progesterone receptors into the genome of the murine fibroblast cell line C127. These cells express functional endogenous glucocorticoid receptor and support bovine papilloma virus minichromosomes, a useful system for studying the role of chromatin structure on gene expression. Three clones containing progesterone receptor integrates and six containing estrogen receptors integrates were selected and characterized. All three progesterone and four of the estrogen receptors containing cell lines expressed functional receptors that were able to transactivate transcription from a mouse mammary tumor virus and Xenopus vitellogenin promoter, respectively, in steroid-specific manner. Levels of steroid binding varied between 38 and 890 fmol/mg protein for progesterone receptor, and between 22 and 94 fmol/mg protein for estrogen receptor. The observed dissociation constants of 1.8-2.5 nM (Organon.2058) and 0.75-2.8 nM (17 beta-Estradiol) are consistent with previously reported values for wild type rabbit progesterone receptor and the estrogen receptor derivative employed. Finally, we demonstrate that transcription of a mouse mammary tumor virus construct in a novel nontransforming bovine papilloma virus vector is regulated by both progestin and glucocorticoid agonists in line C127PR9.