title: Inhibition of estrogen receptor activity by the tumor promoter 12-O-tetradeconylphorbol-13-acetate: a molecular analysis.
abstract: Cell proliferation and phenotype of cells from female reproductive tissues are regulated by estrogens. It is therefore important to understand how estrogen action can be modulated. It recently has been reported that certain nuclear receptors can antagonize the tumor promoter 12-O-tetradeconylphorbol-13-acetate (TPA) by direct interaction with the transcription factor AP-1, and that the AP-1 constituents cJun and cFos can inhibit receptor activity. This mutual antagonism appears to be based on direct protein-protein interaction. In the human breast cancer cell line MCF-7, TPA leads to growth arrest and altered cell morphology. We have investigated here whether in MCF-7 cells and other cell lines AP-1 and estrogen receptors (ERs) can inhibit each other's activity. We find that TPA or the AP-1 components cJun and cFos can inhibit estradiol-dependent estrogen receptor activity in most cell lines investigated. In addition, ER mRNA is rapidly down-regulated in MCF-7 cells. Gel retardation experiments show that ER DNA binding is inhibited in vitro by cJun protein, while ER also can inhibit cJun DNA binding. However, in vivo we do not observe inhibition of AP-1 activity by ER in the cell lines investigated here. On the contrary, we observed an enhancing effect at low ER concentrations on AP-1. Together our data suggest a new regulatory pathway by which ER activity can be modulated by AP-1. Several mechanisms including ER-AP-1 protein interaction appear to be involved.
authors.affiliation: La Jolla Cancer Research Foundation, California 92037.
authors.forename: M
authors.initials: M
authors.lastname: Tzukerman
authors.forename: X K
authors.initials: XK
authors.lastname: Zhang
authors.forename: M
authors.initials: M
authors.lastname: Pfahl
mesh_terms: D001483:Base Sequence; D015152:Blotting, Northern; D001943:Breast Neoplasms / Q000235:genetics / Q000473:pathology / Q000648:ultrastructure; D002455:Cell Division / Q000187:drug effects; D004273:DNA, Neoplasm / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016760:Proto-Oncogene Proteins c-fos / Q000494:pharmacology; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D011960:Receptors, Estrogen / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000378:metabolism / Q000494:pharmacology*; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000473:pathology / Q000648:ultrastructure
chemical_list: D004273:DNA, Neoplasm; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011960:Receptors, Estrogen; D014157:Transcription Factors; D004958:Estradiol; D013755:Tetradecanoylphorbol Acetate