We will continue our development of a detailed, quantitative model of the interaction of the polypeptide growth factor, epidermal growth factor (EGF) with human fibroblasts (HF cells). Using a combination of kinetic and biochemical approaches, we will investigate our recent observations that EGF is able to induce the selective translocation of membrane components to the cell surface and that EGF can regulate subsequent binding to its own receptors. Specifically, we will attempt to answer the following questions: What is the general mechanism by which EGF regulates binding to its own unoccupied receptors? Does EGF treatment induce the translocation of a specific subset of intracellular proteins to the cell surface, or simply accelerate the return of normally recycling proteins? Is the autoregulation of the EGF receptor related to the specific desensitization of the membrane protein translocation response? Can the binding, internalization and the rate of appearance of the EGF receptor at the cell surface be regulated by hormones that modify the response of the cells to EGF? The kinetic studies will use our previously developed computer-assisted techniques for dissecting the individual components of the EGF receptor system. Studies of the effect of EGF on cell surface composition will use double labeling of cell surface components followed by lectin-agarose chromatography and multi-step gel electrophoresis. The relationship between regulators of EGF function and effects of the EGF receptor system will be explored using a completely defined medium in which HF cells are very responsive to the growth-promoting effects of EGF. All of the quantitative information that is obtained from this study will be used to extend and refine our current quantitative model of EGF-cell interactions. This hierarchical model is designed to facilitate our understanding of the role of polypeptide growth factors and receptor dynamics in intercellular communication. Many human diseases involve a dysfunction in growth control and intercellular communication. These studies are expected to provide basic insights into the mechanisms of these processes.
