Estrogen Receptor Regulation in Breast Cancer

Institution: Stanford University
Investigator(s): Lisa McPherson, Ph.D. -
Award Cycle: 1995 (Cycle I) Grant #: 1FB-0377 Award: $75,238
Award Type: Postdoctoral Fellowship
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease

Initial Award Abstract (1995)
In breast cancer, the majority of tumors found in postmenopausal women contain estrogen receptor while tumors in younger women often lack this protein. Estrogen receptor is a protein normally found in various reproduction-related tissues such as the breast and uterus. When estrogen receptor binds estrogen, it becomes activated and can interact with the genes of the cell, resulting in the activation of selected sets of responsive genes. This results in changes in the synthesis of specific RNA's and proteins involved in the regulation of cell proliferation, differentiation and physiologic function. Although normal breast tissue also makes estrogen receptor, the amount of this protein produced in positive breast carcinomas is significantly higher. This may account for some of the differences seen in the abnormal growth of various tumors and tumor cell lines when compared to normal breast tissue development. Breast carcinomas that do not make estrogen receptor tend to recur earlier than estrogen receptor-positive tumors and are also more aggressive, independent of any effect of hormonal therapy. Elucidating the mechanism by which the production of estrogen receptor is controlled in these tumors will lead to strategies by which the growth of aggressive estrogen receptor-negative tumors could be controlled.

Recent experiments have indicated the existence of a protein, Estrogen Receptor Factor-1 (ERF-1), which is involved in the regulation of estrogen receptor production and which is only made in estrogen receptor-positive breast and endometrial carcinomas. In addition to regulating estrogen receptor, it is possible that ERF-1 also regulates other cellular genes critical to breast cancer. We hypothesize that ERF-1 is involved in maintaining the characteristics associated with estrogen receptor production in breast carcinoma. This study seeks to determine the protein sequence of ERF-1 and to study the mechanism by which it regulates estrogen receptor production in breast cancer cell lines. The identification of ERF-1 could aid in the development of gene therapy protocols to stop the progression of tumors lacking both ERF-1 and estrogen receptor.

Final Report (1997)
Breast cancer in older women commonly contains a growth factor receptor called the estrogen receptor, ER. The ER plays a role in the growth of breast tumors, but is also a target for effective drug (e.g., tamoxifen) treatment. We are studying a regulatory protein (ERF-1) that controls the ER gene. The ERF-1 (a transcription factor) protein is known to be involved in ER production in hormonally responsive breast and endometrial carcinomas. ERF-I ‘activates’ the ER gene by binding to a target DNA sequence (CCCTGCGGGG) adjacent to the start of the protein coding sequence of the gene. Our objective was to purify the ERF-1 protein, clone its gene, and further investigate its role in controlling the ER gene and the hormonally responsive breast cancer phenotype.

First, we purified the ERF-1 protein from an ER-positive breast carcinoma cell line, MCF7, using ion exchange and DNA affinity chromatography. Two amino acid sequences from the purified ERF-1 were used to isolate a full-length cDNA clone from an MCF7 cDNA library. The 2.7-kb ERF-1 clone contained the complete protein coding sequence of ERF-1, and adjacent DNA (non-coding) sequences. This ERF-1 clone encodes a protein of 48 kDa that we had previously identified as the AP2? transcription factor. A technique known as ‘gelshift analysis’ was used to show that the ERF-1 DNA clone produced a protein that binds DNA in an identical fashion as the normal ERF-1 from MCF7 cells. In addition, an antibody that recognizes AP2 interacts identically with the cloned ERF-1 protein and the normal ERF-1 protein. Taken together, these results show that ERF-1 is a member of the AP2 family of developmentally regulated transcription factors.

Currently, we are pursuing additional studies to directly demonstrate that ERF-1 regulates the ER gene. First, we are reconstituting ERF-1 in breast carcinoma cell lines lacking this protein. Second, we are inhibiting ERF-l activity in cell lines containing this protein. We will examine the effect that adding or removing ERF-1 activity has on ER gene activation in these modified cells. Given the critical role of ER expression in breast carcinoma biology, ERF-1 is likely to regulate the hormonally responsive breast cancer phenotype. In the future, it is possible that ERF-1 could be used in gene therapy to convert an aggressive hormone-independent tumor into a hormone-responsive tumor that could be treated with currently available drug therapy.

Identification of ERF-1 as a member of the AP2 transcription factor family
Periodical:Proceedings of the National Academy of Sciences of the United States of America
Index Medicus: Proc Nat Acad Sci, U S A
Authors: McPherson LA, Baichwal VR, and Weigel RJ
Yr: 1997 Vol: 94 Nbr: Abs: Pg:4342-4347

Genomic structure of the promoters of the human estrogen receptor-alpha gene demonstrate changes in chromatin structure induced by AP2gamma.
Periodical:Journal of Biological Chemistry
Index Medicus: J Biol Chem
Authors: Schuur ER, McPherson LA, Yang GP, Weigel RJ
Yr: 2001 Vol: 276 Nbr: 18 Abs: Pg:15519-26

AP2a and AP2g: a comparison of binding site specificity and trans-activation of the estrogen receptor promoter and single site promoter constructs
Periodical:Nucleic Acids Research
Index Medicus: Nucleic Acids Res
Authors: Mcpherson, L.A. & Weigel, R.J.
Yr: 1999 Vol: 27 Nbr: 20 Abs: Pg:4040-4049