Cloning and functional characterization of PELP1/MNAR promoter

Proline-, glutamic acid- and leucine-rich protein 1 (PELP1)/modulator of nongenomic activity of estrogen receptor (MNAR), a novel coactivator of estrogen receptors (ERs; ERalpha and ERbeta), modulates the genomic and nongenomic functions of the ERs. PELP1 expression is developmentally regulated in mammary glands and overexpressed in breast tumors. However, little is known about the regulation of PELP1. In this study, we examined whether PELP1 expression is modulated by steroid hormone 17beta-estradiol (E2)-ER pathway. We found that in MCF-7 breast cancer cells, E2 upregulated PELP1 expression threefold and that this upregulation was reduced by antiestrogen. We also found that E2 modulated PELP1 levels in an actinomycin-D-sensitive manner, suggesting transcriptional regulation. Cloning and analysis of the 2-kb PELP1 promoter region revealed two estrogen-responsive element (ERE) half sites in the PELP1 promoter region. In transient transfection assays, E2 upregulated PELP1 promoter activity in breast, endometrial and osteosarcoma model cancer cell lines in an ICI 182,780-sensitive manner. We demonstrated the recruitment of ER to the PELP1 promoter in vitro using EMSA assays and in vivo using a chromatin immunoprecipitation assay. The PELP1 promoter was similarly upregulated by both ERalpha and ERbeta and differentially regulated by selective estrogen receptor modulators in a cell line-dependent manner. Our results suggest that PELP1 expression is modulated by the E2-ER pathway and that PELP1 is an ER target gene.