Proteomic and Functional Analysis of Fibroblasts in Breast Cancer

PUBLIC ABSTRACT

Interactions between cancer cells and their surrounding microenvironment, the "stroma," are predicted to be critical in the growth and progression of carcinomas. Several studies have shown that stroma is a key determinant of proliferation, cell death, motility, and differentiation of epithelial cells. Fibroblasts, the predominant cells in the stroma, synthesize and organize the extracellular matrix components; generate biological signals, regulatory molecules including growth and angiogenic factors; and remodel enzymes such as matrix metalloproteases.

As in other solid tumors, research on breast cancer in the past decades has focused on the transformed epithelial cells, with the stromal microenvironment remaining largely unexplored. Recent in vivo and in vitro studies have convincingly demonstrated that growth, differentiation, invasive behavior, and polarity of normal mammary epithelial cells and breast carcinomas are influenced by surrounding stromal cells. In fact, breast tumor development is dependent upon the formation of a supporting tumor stroma that comprises extracellular matrix proteins, newly formed blood vessels, inflammatory cells, and activated fibroblasts myofibroblasts. Nevertheless, the complex interplay between malignant cells themselves, endothelial cells, and stromal fibroblasts remains poorly understood. Cell-to-cell crosstalk may involve angiogenic factors, growth factors, cytokines, chemokines,and proteases. Such secreted proteins may play a key role in triggering signals between these two types of cells. The modifications that occur in the stroma and fibroblast may also be triggered by activation of different signaling pathways in the cells.

We hypothesize that stromal cells from normal and breast cancer tissue have distinct proteomic profiles and that some of the molecules secreted by stromal cells provide the signals for metastasis of epithelial cells. These molecules should be identifiable by comparing the ¿secretome¿ of stromal cells derived from normal breast tissue versus those derived from breast cancer. The innovative aspect of this proposal is the use of state-of-the-art mass spectrometry-based technologies to identify the specific candidate molecules that are likely to play such a role. In addition, the changes in cancer-derived stromal cells should include activation of signaling pathways that are not observed in normal stromal cells. This proposal also seeks to take a discovery-based approach to identify these activated signaling molecules that might distinguish stromal cells that have the potential to induce or support breast cancers. Another innovative aspect is the use of specific biological assays in cell culture systems and animal models to test the role of the most promising candidates, including autotoxin identified in preliminary studies, in breast cancer initiation and metastasis. Our studies are likely to provide a comprehensive list of global changes in the fibroblasts associated with breast cancers and serve as a foundation for systematic exploration of the role of stromal fibroblasts in breast cancer.

The relevance of our studies is that identification of stromal changes during early stages of breast tumorigenesis could help predict tumor progression. If such molecules are identified, interfering with the stromal-epithelial crosstalk could be an attractive approach to cancer therapy.