Mutational analysis of progesterone receptor delineates different sets of regulated genes

Steroid hormone receptors act directly in the nucleus over the chromatin organization and transcriptional activity of several cellular promoters. On the other hand, they have an indirect effect on cytoplasmic signal transduction pathways, including MAPK, impacting ultimately on gene expression. We are interested on distinguishing between direct effects of progesterone receptor (PR) and those mediated by signal transduction pathways on transcription of hormone-responsive genes and cell proliferation. For this, we have stably expressed in a PR-negative breast cancer cell line, tagged forms of the PR isoform B mutated at regions involved either in DNA binding (DBD), or in its ability to interact with estrogen receptor and activate the c-Src/MAPK/Erk/Msk cascade (ERID). Both mutants impair PR-mediated activation of a well-understood model promoter in response to progestin, as well as hormone-induced cell proliferation. Additional mutants affecting transactivation activity of PR (AF2) or a Zn-finger implicated in dimerization (D-box) have also been tested. Microarrays and gene expression experiments in these cell lines define the subsets of hormone-responsive genes regulated by the different modes of action of PRB, as well as genes where the nuclear and nongenomic pathways of PRB cooperate. Correlation between CCND1 expression in the different PR mutants expressing cell lines and their ability to support hormone-induced cell proliferation, confirms CCND1 as a key controller gene. A customized human cDNA microarray containing 826 genes of interest in breast cancer or steroid hormone regulation was used to identify subsets of genes that retain response to progestin in cells expressing defective PRB variants. Previous kinetic experiments performed with T47D cells on this array platform have shown that at 6 h of R5020 treatment, an extensive number of genes change its expression, being a compromise between rapid and long-term effects of this hormone on gene expression (unpublished results). TYML cells containing the empty vector, WT PRB, AF2, DBD and ERID, and T47D parental cells were serum-starved for 24 h and hormone (10 nM R5020) or vehicle-treated for 6 h. Cells were collected and RNA was extracted for microarray hybridization.