title: Functional synergy between the transcription factor Sp1 and the estrogen receptor.
abstract: A GC-rich oligonucleotide containing an estrogen responsive element (ERE) half-site from the heat shock protein 27 (Hsp 27) gene promoter (-105 to -84) [ie. GGGCGGG(N)10GGTCA; Sp1(N)10ERE] forms a complex with the Sp1 and estrogen receptor (ER) proteins. Moreover, promoter-reporter constructs containing this sequence (-108 to -84 or -108 to +23) are also estrogen-responsive. Mutation of the ERE half-site in the Hsp 27-derived oligonucleotides did not result in loss of estrogen responsiveness in transient transfection studies, suggesting that estrogen inducibility was mediated through the Sp1-DNA motif. Gel mobility shift assays using 32P-labeled wild type and ERE mutant Sp1(N)10ERE and consensus Sp1 oligonucleotides showed that Sp1 protein formed a DNA-protein complex with all three nucleotides, and the intensities of retarded bands were enhanced by coincubation with wild type ER and 11C-ER, which does not contain the DNA-binding domain. ER mutants in which N-terminal (19C-ER) and C-terminal (15C-ER) regions were deleted did not enhance Sp1-DNA binding or hormone-induced transactivation of GC-rich promoter-reporter constructs in ER-negative MDA-MB-231 cells, whereas both wild type and 11C-ER restored inducibility. Immunoprecipitation studies also confirmed that the Sp1 and ER proteins physically interact. The interaction of the Sp1 and ER proteins and the resulting enhanced Sp1-DNA binding is observed in the presence or absence of estrogen (hormone-independent), whereas transactivation of promoter-reporter constructs is estrogen-dependent. Thus, the results illustrate a new estrogen-dependent transactivation pathway that involves ER-protein interactions and is ERE-independent.
authors.affiliation: Department of Veterinary Physiology and Pharmacology, Texas A & M University, College Station 77843-4466, USA.
authors.forename: W
authors.initials: W
authors.lastname: Porter
authors.forename: B
authors.initials: B
authors.lastname: Saville
authors.forename: D
authors.initials: D
authors.lastname: Hoivik
authors.forename: S
authors.initials: S
authors.lastname: Safe
mesh_terms: D000818:Animals; D001665:Binding Sites; D001943:Breast Neoplasms / Q000235:genetics / Q000473:pathology; D004967:Estrogens; D005786:Gene Expression Regulation; D005982:Glutathione Transferase / Q000378:metabolism; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D009376:Neoplasms, Hormone-Dependent / Q000235:genetics / Q000473:pathology; D011401:Promoter Regions, Genetic; D011817:Rabbits; D011960:Receptors, Estrogen / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid; D016329:Sp1 Transcription Factor / Q000502:physiology*; D015533:Transcriptional Activation / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D004967:Estrogens; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D011960:Receptors, Estrogen; D011993:Recombinant Fusion Proteins; D016329:Sp1 Transcription Factor; D005982:Glutathione Transferase