Biophysical regulation of cell motility by adhesion ligands and growth factors : effect of spatial presentation of the ligand

Abstract

A key problem in biomedical engineering today is in understanding the mechanisms which control cellular functions such as cell proliferation, migration and differentiation. The ability to engineer tissue replacements requires understanding of the interactions between the cell and its environment - the surface with which it interfaces and the fluid medium surrounding it. We are interested in designing a biologically inspired substrata which controls mammalian cell migration based on principles of receptor/ligand interactions involved in its regulation. Recent studies have shown that integrin cell surface receptors for the extracellular matrix (ECM) proteins initiate signaling cascades, some of which are in common with those initiated by growth factors. We have quantitatively investigated the potential synergy between growth factors and ECM ligands in governance of cell motility. In initial experiments using a model system of the ECM protein fibronectin and epidermal growth factor (EGF), we found that locomotion speed of a mouse fibroblast cell line is affected by combinations of EGF and fibronectin in diverse ways that can be accounted for by a biophysical model for migration. Following on these finding, we have designed a minimalistic artificial matrix using the linear peptide sequence, arginine-glycine-aspartic acid (ROD), derived from fibronectin as the adhesion ligand, conjugated to a protein resistant poly (ethylene oxide) (PEO) surface. With this system, we have identified a role for the micro-level spatial presentation of the ROD peptide integrin ligand in stimulating migration. In addition, we have investigated the role of presentation of EGF as a soluble ligand in its governance of cell motility. We find that presentation of EGF in an autocrine manner in human mammary epithelial cells, where the cell simultaneously synthesizes the receptor and the ligand, results in the regulation of the directionality of cell motion. Formation of cell surface EGF/EGFR complexes in an autocrine manner causes an increased persistence of cell motion which is abrogated upon addition of EGF into the bulk extracellular media. These studies highlight the importance of quantitative deconstruction of a biological problem and have important ramifications for the rational design of cell receptor/ligand interactions to control cell behavior.