Extracellular Matrix Mechanobiology Of Breast Tumor Stroma

Abstract

The extracellular matrix (ECM) is a complex fibrillar structure that provides biochemical and mechanical cues to cells. Fibronectin (Fn) is a fundamental ECM protein implicated in cell signaling and behavior in both physiological and pathological conditions. Fn comprises 3 types of repeating modules (I, II, III), which contain binding sites for cells, ECM components, and growth factors. Its type III repeating modules lack disulfide bonds and under cell traction or ECM strain, extend and unfold to expose cryptic binding sites or disrupt exposed binding sites. Therefore, Fn is considered as a mechanotransducer, in which cell-induced conformational changes alter its biological behavior. Fn is known to be up-regulated in tumor stroma. However, how Fn is altered and its role in tumorigenesis is unclear. The results herein demonstrate how invasive breast cancer cell secretion activates pre-adipocytes to deposit an initial Fn matrix that is stiffer and more unfolded than its healthy counterpart to mediate an integrin switch in downstream cell attachment. These newly attached cells, in response to the altered ECM, enhance pro-angiogenic secretion. Furthermore, Fn binds to collagen I (Col I), another major ECM protein. Col I is known to be dependent on previous Fn matrices. Col I is a key proponent in mediating invasive breast cancer, found to be more crosslinked, stiffer, and exhibiting enhanced remodeling to create ECM tracks for increased cell migration. How altered Fn mediates changes in downstream Col I deposition is yet unclear. ! The results herein show how invasive breast cancer cell secretion enhances activated preadipocytes ability to remodel the initially deposited Fn ECM. This altered Fn ECM, through proteolytic activity, is replaced by a dense, dysregulated Fn-Col ECM. The findings of this dissertation highlight how breast cancer cell secretions alter stromal ECM deposition and remodeling. This work combined physical science tools with biochemical tools to evaluate the importance of tumor stroma. These findings may provide insight into the development of breast tumor therapies to prevent tumor progression into the surrounding stroma for eventual metastasis. ii