Ets2 dependent microenvironmental regulation of mouse mammary tumor development and Ets2 regulation of Cdx2 promoter activity

Targeted disruption of Ets2 has been used to study its role in mammary tumor formation and placental development in mice. Decreased Ets2 function delays Polyoma virus middle-T antigen (PyMT) or neu/ErbB2 induced mammary tumor development in mice. Data is presented here showing that disruption of an Ets2flox allele in all tissues of the mouse significantly delayed tumor formation in the PyMTY315/322F mammary tumor model. Inactivation of the Ets2flox allele specifically within the tumorigenic mammary epithelium had no effect on tumor development. Together with data showing that stromal derived Ets2 can regulate transplanted mammary tumor growth, these studies demonstrate that Ets2 regulates mammary tumor development solely from a stromal tissue source. To define the stromal source, functions of Ets2 were examined in fibroblasts, endothelial cells and macrophages. No effects of Ets2 mutation in fibroblasts could be detected on the growth of co-cultured tumor cells and no effect of Ets2 mutation in endothelial cells could be detected in angiogenesis or vascular permeability. However, Ets2 had a significant impact on macrophage gene expression, including MMP9, MMP3, Cox2, IL1-beta, VEGF and IL-12p40, in response to CSF-1. To determine the significance of this in vivo, bone marrow transplantation was performed to specifically reconstitute functional Ets2 in hematopoietic cells of Ets2 targeted mice or to specifically target Ets2 within the hematopoietic cells of wild-type mice. In the context of spontaneous PyMTY315/322F induced tumor formation or in tumor transplant recipients, hematopoietic derived Ets2 function yielded only partial regulation of mammary tumor formation, implying Ets2 must function within another cell type(s) alone or in combination to regulate mammary tumor development.;In trophoblast stem cells and colon tissue, Ets2 activity correlates with expression of Cdx2, a mediator of placental development and known colon tumor suppressor. Quantitative PCR of chromatin immunoprecipitated DNA showed Ets2 can bind to a distal region of the Cdx2 promoter. Luciferase reporter studies suggested this region is transcriptionally repressive and can be relieved by Ets2. These studies of Ets2 regulation of the Cdx2 promoter provide a potential molecular mechanism for embryonic lethality seen in Ets2 knockout mice.