Generation of a doxycycline-inducible mammary specific Liver Receptor Homolog-1 knock-in mouse (#70)
Background: Breast cancer is one of the leading causes of cancer-related death in Australian women. Almost 70% of postmenopausal women are diagnosed with breast tumours receptive to estrogen receptor-α (ERα). Treatment for these tumours is successful; however treatments for tumours that are not receptive to ERα are less successful. New therapeutic targets need to be developed for treatment for tumours that don’t respond to current treatments. Liver Receptor Homologue-1 (LRH-1) is an orphan nuclear receptor that plays vital roles in embryogenesis, cholesterol homeostasis, steroidogenesis and certain diseases. LRH-1 is aberrantly expressed in 43% of invasive breast cancers and promotes proliferation, migration and invasion of breast cancer cells. To understand the effects of LRH-1 in the development of breast cancer, we have generated a doxycycline inducible mammary epithelial-specific LRH-1 knock-in mouse model, in which the MMTV promoter drives expression of the reverse tetracycline transactivator (rtTA) allowing for selective induction of the human LRH-1 transgene in mammary epithelium. Methods: Real Time-PCR and immunohistochemistry were employed using whole mouse mammary glands. Results: Doxycycline induced homogenous transgene LRH-1 expression specifically throughout the mammary luminal epithelium on short (3 weeks) and long term (3 months) treatment. In addition, doxycycline increased transcript levels of LRH-1 at both treatment time points. Increased LRH-1 expression was associated with an increase in expression of the proliferation marker Ki-67, and decreased expression of the apoptosis marker Caspase 3 protein in epithelial cells at both treatment times. Furthermore, LRH-1 expression altered mammary gland morphogenesis as evident by a reduction in lateral bud number both stages of treatment (p=0.05 vs. control). These observations suggest a role for LRH-1 in mammary epithelial cell proliferation, ductal morphogenesis and branching. Conclusion: We have developed a mammary-specific doxycycline-inducible mouse model, which will be used to further explore the role LRH-1 plays in mammary development and breast cancer.