P4-03-05: Development of an Inducible Estrogen Receptor Co-Activator PELP1 Mammary Tumor Model.

Abstract

Abstract Despite treatment advances, breast cancer remains the second most lethal malignant disease for women worldwide. Given the importance of estrogen receptor (ER) and hormone-dependent nature of breast cancer, pharmacologic agents were developed to either modulate ER functions or reduce circulating estrogens levels. Although targeted endocrine therapies significantly reduce mortality in patients with estrogen sensitive (ER+) tumors, both de novo and acquired resistance limits efficacy. A critical need for identifying more precise diagnostic/prognostic biomarkers and novel therapeutic targets prompted deeper investigation into ER-coregulatory protein function and regulation. ER-coactivator PELP1, mediates both nuclear and extra-nuclear estrogen signaling and crosstalk with growth factors. PELP1 is deregulated in hormone-driven cancers, associates with undifferentiated invasive breast adenocarcinomas and an independent prognostic biomarker in assessing clinical outcome of luminal-like breast cancer patients. Collectively, several studies suggest PELP1 is an ERα coregulator with tumorigenic potential. However, the in vivo significance of PELP1 deregulation during initiation and progression of breast cancer is unknown. To determine the role of PELP1 overexpression in mammary tumorigenesis, we generated an inducible transgenic murine model. Transgene construct (pTetOPELP1) consists of a full-length human PELP1 cDNA linked to luciferase gene reporter through an internal ribosomal entry site (IRES). PELP1 transgene was purified and microinjected into mouse zygotes to generate pTetOPELP1 mice. Founder mice were identified by Southern blot analysis, of genomic DNA extracted from tail biopsies, for transgene integration through germline transmission. pTetOPELP1 mice were breed with mammary gland-specific rtTA mice (MMTVrtTA) to produce MMTVrtTA-TetOPELP1 bitransgenic mice. Potential founder mice were identified by polymerase chain reaction and breed to establish two independent transgenic lines. Transgene expression was induced in adult female bitransgenic animals with 200mg/mL of doxycycline administered in drinking water. Concurrent expression and activity of the luciferase gene reporter was detected specifically in the mammary gland by in vivo bioluminescence imaging, luciferase assay and RT-PCR. Mammary epithelial-specific expression of PELP1 was validated by immunohistochemistry and Western blot analysis. PELP1-mediated morphological and histological changes were analyzed by examining carmine-stained whole mounts and H&E-stained mammary glands sections. Our early findings with MMTVrtTA-TetOPELP1 bitransgenic mice (n=30) early preneoplastic changes and hyperplasia were evident as early as 12 weeks and the formation of mammary tumors by 8 months of age following PELP1 induction by doxycycline treatment. By utilizing the tetracycline-regulatory system, we created a novel, inducible and mammary gland-specific PELP1-expressing transgenic model for future in vivo studies into molecular mechanisms of PELP1-mediated mammary tumorigenesis. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-03-05.