1. Understanding molecular mechanisms underlying breast cancer risk due to breast density.
Patients with “dense” breast tissue have a four- to six-fold increased risk of developing breast carcinomas. In fact, 1/3 of all breast cancer cases are attributed to breast density, making it one of the greatest risk factors for carcinoma. Increased breast density is associated with a significant increase in the deposition of connective tissue, or ECM components, most notably the protein, collagen. We have been developing model systems to understand why increased breast density results in an increased risk for developing breast carcinoma. We find in a simple in vitro model that increasing the density of collagen in the matrix is sufficient to disrupt breast epithelial differentiation, suggesting that matrix density is itself an important regulator of cellular behavior. Additionally, we are employing a mouse strain engineered to have more collagen in its connective tissue. We find evidence for changes in collagen organization, termed Tumor Associated Collagen Signatures (TACS), that occur during tumor progression. We are investigating whether this signature can be developed as a tool to aid in diagnosing human breast carcinoma at an earlier stage.
2. Molecular signaling events related to cell interactions with the ECM.
Cells interact with the ECM through a variety of cell surface receptors, the best understood of which are members of the integrin family. Much remains to be determined regarding the specific molecular players and signaling pathways downstream of integrins, and how these pathways are involved in the progression of various diseases. Therefore, part of the focus of the lab is to investigate signaling events through the integrin family of receptors. A second aspect of this work is to investigate how small GTPases of the Ras superfamily, some of which are known or suspected oncogenes, affect the response of cells to the ECM. Specifically, we have focused on R-Ras and Rho, which we find alter the way breast epithelial cells respond to the ECM, promoting cellular migration and invasion. We are particularly interested in studying signaling events using state of the art imaging approaches to understand how small GTPases function in a spatial and temporal manner during cell migration.
3. Intravital Imaging to recognize cell-cell and cell-matrix interactions in a native environment
Our ability to understand cancer has been significantly enhanced by the techniques of multiphoton fluorescence excitation microscopy (MPM) and second harmonic generation imaging (SHG). Applying these techniques using the rodent mammary imaging window allows us to study tumor formation, progression, and metastasis within single animals. Through the use of animal models that express extrinsic flourophores and the characterization of endogenous fluorescence we are able to identify specific cell types and examine the interplay between the immune system and cancer. The use of ported imaging windows allows access to the tumor microenvironment in vivo to characterize the collagen structure in normal glands and around tumors. These procedures helps us better understand the physical relationship between cells and the collagen fibers found during breast cancer progression.
4. Inflammation and immunosuppressive signaling within the collagen dense tumor microenvironment
Our lab demonstrated that breast carcinoma is among several solid tumors in which it is clear there is a role for the extracellular matrix in tumor progression. Further investigation into mammary tumor progression identified several inflammatory signals and mediators of immunosuppression that are dramatically increased when tumors arise in a collagen dense microenvironment, including carcinoma associated fibroblasts (CAFs) and expression of programmed death ligand-1 (PD-L1). It is well documented that CAFs can regulate the immune response within the tumor microenvironment by secreting multiple factors that either inhibit or enhance tumor growth. The cytokines found in the collagen dense tumor microenvironment activate CAFs toward an immunosuppressive phenotypeto subsequently enhance tumor progression. Thus, we seek to investigate collagen density in the breast tumor microenvironment as a predictive biomarker for immune therapy.