Abstract 1402: A reporter mouse model reveals that human CYP19A1 (aromatase) gene expression is induced in breast cancer xenograft stroma and surrounding mammary gland by the cancer cells in vivo.

Abstract

Aromatase enzyme coded by the CYP19A1 gene catalyzes the final step of estrogen biosynthesis and is of major significance in endocrine regulation of breast cancer (BCa). Human CYP19A1 gene expression is regulated through the utilization of various non-translated tissue selective first exons, each controlled by unique sets of e.g. hormones and cytokines. Extragonadal expression pattern and regulation of human CYP19A1 gene is significantly different from that of rodents, which has been a major obstacle in studies focusing on regulation of aromatase gene expression in vivo. To study the tissue-selective regulation of human CYP19A1 gene in vivo, we have generated a transgenic reporter mouse model, hARO-Luc mouse, with a construct composing of a 100-kbp-long 5’-regulatory region of the human CYP19A1 gene attached to a luciferase (Luc) reporter gene. The aim of this study was to investigate human CYP19A1 gene expression in human BCa xenografts, to determine how the BCa cells regulate CYP19A1 gene expression in tumor associated stroma in vivo. In vitro, BCa cells have been shown to induce CYP19A1 gene expression in human breast derived fibroblasts. Furthermore, in order to study the regulation of the human CYP19A1 gene expression in hARO-Luc derived undifferentiated fibroblasts, mesenchymal stromal cells were isolated from bone marrow of female reporter mice. In these cells, human CYP19A1 gene expression was induced by dexamethasone ± TNFα, and PGE2 that are among factors known to drive aromatase gene expression in human mammary fibroblasts through promoters I.4 and I.3/PII. In order to investigate human CYP19A1 expression in BCa xenografts and tumor surrounding mammary gland, the hARO-Luc reporter mice were cross-bred with athymic nude mice. Estrogen-responsive MCF-7 or T47D cells or non-estrogen-responsive MDA-MB-231 cells were injected into inguino-abdominal mammary fat pads of athymic female hARO-Luc mice, and mice that received MCF-7 or T47D cells were also implanted s.c. with estradiol releasing pellet to induce the estrogen-dependent tumor growth. The reporter gene activity was measured from tissue homogenates. MCF-7 and T47D tumors had 5-10 -fold higher Luc activity as compared with the intact mammary gland, indicating a strong up-regulation of the reporter gene in host derived tumor stroma. In contrast, in MDA-MB-231 tumor bearing mice the reporter activity in tumors was only slightly higher as compared with the intact mammary gland. Furthermore, reporter gene activity in mammary gland surrounding MDA-MB-231 tumors was 2-fold higher than in the tumor itself. In conclusion, the data indicate that human BCa cells up-regulate expression of human aromatase gene in the tumor associated stroma in vivo. Citation Format: Päivi Järvensivu, Leena Strauss, Sari Mäkelä, Matti Poutanen, Niina Saarinen. A reporter mouse model reveals that human CYP19A1 (aromatase) gene expression is induced in breast cancer xenograft stroma and surrounding mammary gland by the cancer cells in vivo. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1402. doi:10.1158/1538-7445.AM2013-1402