title: Down-regulation of retinoic acid receptor beta in mammary carcinoma cell lines and its up-regulation in senescing normal mammary epithelial cells.
abstract: Retinoids are important cellular, dietary factors that regulate differentiation and cellular growth. They serve as ligands for specific nuclear receptors, the retinoic acid receptors (RARs). Ligand-activated receptors regulate gene transcription through target retinoic acid-responsive elements (RAREs) found in promoter regions. We have investigated the expression of retinoic acid receptor genes (alpha, beta, gamma) and retinoid X receptor beta in normal, senescing, and tumorigenic human mammary epithelial cells. We find that most tumor cells show a loss of RAR-beta expression, but that RAR-alpha and -gamma as well as retinoid X receptor beta are variably expressed in both normal and tumor cells. RAR-beta gene expression is induced both by retinoic acid and by fenretinide in normal cells, but tumor cells fail to respond to either. In contrast, RAR-beta expression increases with serial passage in senescing cells. Paradoxically, both normal and tumor cells can trans-activate an exogenous beta-RARE, as demonstrated by reporter gene assays. Oligonucleotide mobility shift assays with the beta-RARE show a single discrete complex in normal cells, whereas tumor cells exhibit a heterogeneous set of larger complexes, which indicates that tumor cells utilize a different array of factors within the beta-RARE. Reporter gene assays with extended promoter regions indicate the presence of negative regulatory elements and/or factor binding sites that reside between -1500 and the RARE located at -59, and that the promoter is down-regulated in MCF-7 tumor cells. Our findings reveal a dichotomy: RAR-beta transcription is down-regulated in tumor cells compared with normal human mammary epithelial cells, and up-regulated in senescence.
authors.affiliation: Division of Cancer Genetics, Dana-Farber Cancer Institute, Boston, Massachusetts.
authors.forename: K
authors.initials: K
authors.lastname: Swisshelm
authors.forename: K
authors.initials: K
authors.lastname: Ryan
authors.forename: X
authors.initials: X
authors.lastname: Lee
authors.forename: H C
authors.initials: HC
authors.lastname: Tsou
authors.forename: M
authors.initials: M
authors.lastname: Peacocke
authors.forename: R
authors.initials: R
authors.lastname: Sager
mesh_terms: D001483:Base Sequence; D015152:Blotting, Northern; D001940:Breast / Q000166:cytology / Q000378:metabolism*; D001943:Breast Neoplasms / Q000378:metabolism*; D002460:Cell Line; D016922:Cellular Senescence; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis / Q000378:metabolism; D015536:Down-Regulation; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D005260:Female; D017313:Fenretinide / Q000494:pharmacology*; D006801:Humans; D008156:Luciferases / Q000096:biosynthesis / Q000378:metabolism; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009687:Nuclear Proteins / Q000302:isolation & purification / Q000378:metabolism; D009838:Oligodeoxyribonucleotides; D015345:Oligonucleotide Probes; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis*; D018168:Receptors, Retinoic Acid / Q000096:biosynthesis*; D047488:Retinoid X Receptors; D014157:Transcription Factors; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
chemical_list: D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; D017313:Fenretinide; D014212:Tretinoin; D008156:Luciferases; D015500:Chloramphenicol O-Acetyltransferase