Deciphering the Functions of Ets2, Pten and p53 in Stromal Fibroblasts in Multiple Breast Cancer Models

Breast cancer is the second most common cancer in American women, and is also the second leading cause of cancer death in women. It is estimated that nearly a quarter of a million new cases of invasive breast cancer will be diagnosed in women in the United States this year, and approximately 40,000 of these women will die from breast cancer. Although death rates have been on the decline for the past decade, there is still much we need to learn about this disease to improve prevention, detection and treatment strategies. The majority of early studies have focused on the malignant tumor cells themselves, and much has been learned concerning mutations, amplifications and other genetic and epigenetic alterations of these cells. However more recent work has acknowledged the strong influence of tumor stroma on the initiation, progression and recurrence of cancer. Under normal conditions this stroma has been shown to have protective effects against tumorigenesis, however the transformation of tumor cells manipulates this surrounding environment to actually promote malignancy. Fibroblasts in particular make up a significant portion of this stroma, and have been shown to impact various aspects of tumor cell biology. Although the contributions of these stromal fibroblasts to tumor progression have been well studied, the role of specific signaling pathways important for these tumor associated functions remain elusive. In the current studies, we examine the fibroblast specific roles of the proto-oncogene Ets2 as well as the tumor suppressor genes Pten and p53 in tumorigenesis using conditional knockout mouse models. Importantly, the functions of these genes are assessed in multiple breast cancer models to account for the heterogeneity observed in breast cancer. Additionally, gene expression analysis is used to decipher potential mechanisms by which these genes function in the stroma.Deletion of Ets2 in fibroblasts in both PyMT and ErbB2 driven tumorigenesis slowed the progression of these tumors without significantly effecting the development of the normal mammary gland. Gene expression profiling revealed Ets2 controls a tumor specific transcription program in fibroblasts that promotes angiogenesis in both breast cancer models. Interestingly, Ets2 seems to target a portion of the same genes in both models, thereby implicating it as a “master regulator” in these tumor associated cells. Additionally, loss of fibroblast Ets2 impacts gene expression in surrounding endothelial cells. Both the PyMT and ErbB2 derived Ets2 dependent signatures were represented in the stroma of human breast cancer tissue, and could also predict patient outcome in independent whole tumor data.Using a similar strategy, we also examined the function of Pten in the stromal fibroblast compartment. Interestingly, loss of this tumor suppressor gene promoted ErbB2 driven tumorigenesis. Gene expression profiling determined that loss of Pten promotes inflammation and ECM remodeling, which is manifested by increased macrophage proliferation and deposition of collagen. The transcription factor Ets2 was shown to be a downstream target of Pten signaling in fibroblasts, which was at least in part mediated by regulation of miR-320. To our surprise, Pten loss in stromal fibroblasts did not impact Ras mediated tumorigenesis. To determine if this collaboration was specific to the Pten tumor suppressor, we also conditionally deleted p53 in mammary fibroblasts in the context of ErbB2 and Ras epithelial drivers. Conversely to what we observed upon Pten deletion, loss of p53 did not affect ErbB2 driven tumorigenesis, but significantly impacted Ras mediated transformation. Through gene expression arrays, we determined crosstalk between these epithelial cells and fibroblasts induces changes in a specific collaborative fashion. Loss of Pten or p53 promoted the hyperproliferation of surrounding epithelial cells, however deletion of these genes alone was not sufficient to cause tumor development. In summary, we have shown Ets2 to be an important transcription factor driving angiogenesis from the tumor associated fibroblast compartment in both PyMT and ErbB2 breast cancer models. Alternatively, Pten was shown to have strong tumor suppressor function in the stroma in ErbB2 mediated tumorigenesis, however its function was dispensible during Ras induced tumorigenesis. The opposite was observed in the context of fibroblast p53 function which was important in Ras driven tumorigenesis but had modest effects in the context of ErbB2. Understanding this complex communication between tumor cells and the microenvironment is a critical step as we move forward in the battle against cancer.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Molecular, Cellular and Developmental Biology

Grantor dc:publisher

The Ohio State University

Year dc:date

2013

Author dc:creator

• Wallace, Julie

Contributors dc:contributor

• Ostrowski, Michael

• Molecular Biology

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=osu1365496427

OAI identifier oai:identifier

oai:etd.ohiolink.edu:osu1365496427