Abstract 2118: Differential efficiency in the deletion of estrogen receptor β DNA binding domain generates distinct phenotypes in the mouse ventral prostate and ovary
Authors: Maneix Laure , Antonson Per , Rochel-Maia Sabrina S. , Kim Hyun-Jin , Warner Margaret , Gustafsson Jan-Ake 
Published: May 2015

The anti-proliferative properties of estrogen receptor β (ERβ) and its ability to regulate growth and differentiation of the prostate epithelium make it interesting as a therapeutic target in prostate cancer. In 1998, the first ERβ knockout (ERβ-/-) mouse was created by inserting a neocassette into the ERβ gene to interrupt the gene at the DNA binding domain (DBD). In this original knockout, aging ERβ-/- mice develop prostate hyperplasia and upon estradiol treatment, they also develop prostatic intraepithelial neoplasia lesions, which are believed to be premalignant. These mice were also characterized by a reduction in the ability to ovulate and disruption of neuronal migration during fetal development. In 2008, another ERβ mutant mouse was generated by inserting LoxP sites around the third exon of the gene. Upon deletion of exon 3, the female mice were infertile, due to the inability of the female mice to ovulate but there were no other defects in either males or females. Thus it was concluded that, ERβ has very limited physiological function and the phenotype of the original ERβ-/- mouse deemed to be due to the presence of the neocassette which remained in the gene. In the present study, a new ERβ knockout mouse was generated by inserting Lox P sites around the third exon and this exon was deleted by crossing this mouse with either a CMV-Cre or a Rosa-Cre deleter mouse.

The only abnormality found in the new mutant ERβ mouse was the inability of the female mice to ovulate. Sequencing of the ovary mRNA showed that the knockout strategy worked i.e., exon 3 was deleted and a shift in the reading frame was generated, resulting in the creation of two in frame stop codons. Nevertheless, in this new mutant mouse, there were no detectable defects in the prostate, the lungs or the brain. We demonstrated that although two stop codons should have prevented translation of the protein, ventral prostates, lungs and skeletal muscle of these mice produce a full length ERβ protein. This protein was detected in the nuclei of prostate epithelial cells by immunohistochemistry and western blot assays, using a set of four anti-ERβ antibodies directed against different epitopes. In contrast to the original knockout mouse, the expression of Ki67 and androgen receptor in the prostate epithelium was unchanged in the new ERβ-/- mouse. Moreover, DNA binding of prostate nuclear extracts from these mice to Estrogen Responsive Elements and AP-1 responsive elements was inhibited by ERβ-specific antibodies.

We conclude that differential efficiency in the deletion of ERβ DBD generates divergent phenotypes in the mouse ventral prostate and ovary and this discrepancy may be mediated by tissue variations in the efficiency of the Cre recombinase system.

Citation Format: Laure Maneix, Per Antonson, Sabrina S. Rochel-Maia, Hyun-Jin Kim, Margaret Warner, Jan-Ake Gustafsson. Differential efficiency in the deletion of estrogen receptor β DNA binding domain generates distinct phenotypes in the mouse ventral prostate and ovary. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2118. doi:10.1158/1538-7445.AM2014-2118