Functional synergy between the transcription factor Sp1 and the estrogen receptor

Mol Endocrinol. 1997 Oct;11(11):1569-80. doi: 10.1210/mend.11.11.9916.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Binding Sites
  • Breast Neoplasms / genetics
  • Breast Neoplasms / pathology
  • Estrogens
  • Gene Expression Regulation*
  • Glutathione Transferase / metabolism
  • HSP27 Heat-Shock Proteins
  • Heat-Shock Proteins / biosynthesis
  • Heat-Shock Proteins / genetics*
  • Humans
  • Neoplasm Proteins
  • Neoplasms, Hormone-Dependent / genetics
  • Neoplasms, Hormone-Dependent / pathology
  • Promoter Regions, Genetic
  • Rabbits
  • Receptors, Estrogen / biosynthesis
  • Receptors, Estrogen / genetics*
  • Receptors, Estrogen / physiology*
  • Recombinant Fusion Proteins / metabolism
  • Regulatory Sequences, Nucleic Acid
  • Sp1 Transcription Factor / physiology*
  • Transcriptional Activation / physiology*
  • Transfection
  • Tumor Cells, Cultured

Substances

  • Estrogens
  • HSP27 Heat-Shock Proteins
  • HSPB1 protein, human
  • Heat-Shock Proteins
  • Neoplasm Proteins
  • Receptors, Estrogen
  • Recombinant Fusion Proteins
  • Sp1 Transcription Factor
  • Glutathione Transferase