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Identification of the sequences within the human complement 3 promoter required for estrogen responsiveness provides insight into the mechanism of tamoxifen mixed agonist activity.

Publication ,  Journal Article
Fan, JD; Wagner, BL; McDonnell, DP
Published in: Mol Endocrinol
December 1996

The promoter of the human C3 gene has been shown to be responsive to stimulation by both estrogen and tamoxifen-activated estrogen receptor (ER) in transcriptional assays reconstituted in mammalian cells. Using a series of deletions and point mutations, we have determined that the agonist activity of these two compounds was dependent upon the direct interaction of ER with each of three estrogen response elements (EREs) contained within this promoter. One of these sequences, ERE1 resembles the canonical vitellogenin A2-ERE whereas the other two, ERE2 and ERE3, do not display significant homology to known EREs. Using gene transfer studies it was shown that these sequences are necessary and sufficient for ER-mediated transcription. Interestingly, using in vitro receptor/DNA-binding assays we demonstrated that neither ERE1, ERE2, or ERE3 alone formed high-affinity complexes with purified ER; however when a promoter fragment containing all three sequences was used, specific, high-affinity ER-DNA interactions were observed. It was not surprising, therefore, that, when assayed individually on a heterologous promoter, these sequences function as weak EREs but together they act in a synergistic manner to create a strong ER-dependent enhancer. It has been suggested that tamoxifen mediates its partial agonist activity through AP-1 at target promoters. However, the fact that purified ER can bind directly to the estrogen-responsive sequences within the C3 promoter, and that tamoxifen activity on this promoter is unaffected by AP-1 coexpression, indicates that at least on some promoters tamoxifen can manifest partial agonist activity through a classical ER/ ERE- mediated mechanism.

Duke Scholars

Published In

Mol Endocrinol

DOI

ISSN

0888-8809

Publication Date

December 1996

Volume

10

Issue

12

Start / End Page

1605 / 1616

Location

United States

Related Subject Headings

  • Transfection
  • Transcription, Genetic
  • Transcription Factor AP-1
  • Tamoxifen
  • Sequence Deletion
  • Sequence Analysis, DNA
  • Recombinant Proteins
  • Receptors, Estrogen
  • Promoter Regions, Genetic
  • Humans
 

Citation

Published In

Mol Endocrinol

DOI

ISSN

0888-8809

Publication Date

December 1996

Volume

10

Issue

12

Start / End Page

1605 / 1616

Location

United States

Related Subject Headings

  • Transfection
  • Transcription, Genetic
  • Transcription Factor AP-1
  • Tamoxifen
  • Sequence Deletion
  • Sequence Analysis, DNA
  • Recombinant Proteins
  • Receptors, Estrogen
  • Promoter Regions, Genetic
  • Humans