Molecular Mechanisms of Signaling in the ERK Pathway

Abstract

In order to respond to their environment, cells must sense extracellular stimuli and translate these signals into intracellular actions. The transmission of signals is mediated by complex networks of interacting proteins. The proper function of these networks is required for cells to respond to their surroundings, making them the foundation of critical processes including development, tissue growth and repair, immunity, and maintaining homeostasis. The study of these systems has yielded a wealth of knowledge. Biophysical and biochemical tools have enabled the understanding of molecular structures and individual reactions in enzymatic networks. However, we are often unable to predict how perturbations to these systems at the molecular level translate to larger-scale changes in signaling. This is critical, as small changes can have broad implications for the larger network.

Extracellular Signal-Regulated Kinase (ERK) is a critical enzyme that integrates signals from a number of stimuli and coordinates many different cellular responses, from proliferation to differentiation and death. Because ERK is so crucial to proper cellular function, disruptions to ERK pathway signaling are common in the development of disease. ERK has been studied extensively, and a great deal is known about ERK signaling on a wide range of scales, from its molecular structure to its role in the development and life cycle of organisms. However, there remains a divide between understanding ERK signaling at the level of tissues and organisms and the molecular mechanisms of the reactions underlying these events.

The work presented in this dissertation seeks to address the molecular origins of poorly understood phenomena in the ERK network. We used a novel approach to map the binding interface between ERK and an important substrate, the transcriptional repressor Capicua, which has been implicated in neurodegenerative diseases and cancers. Next, we uncovered the effects of point mutations in MEK, the enzyme that activates ERK, on the kinetics of complex phosphorylation reactions at multiple levels of pathway regulation. This work illustrates the value of understanding the molecular basis of network phenomena in cell signaling networks using the ERK pathway as a model system.