Biochemical characterization of MEK1 mutations in the RAS/MAPK pathway

Abstract

Signal transduction is the process by which a chemical signal is transmitted through a cell’s plasma membrane to stimulate a response within the cell. The Ras/MAPK (rat sarcoma/mitogen activated protein kinase) is an example of such a pathway that transmits extracellular signals to nuclear targets through a network of proteins. It is highly conserved across species, is involved in essentially all aspects of development, and is responsible for other important processes such as cell cycle regulation and tissue repair. Due to its critical function,genetic perturbations of the pathway can lead to a multitude of cancers and developmentalabnormalities. In this thesis, I focus on the biochemical effects of mutations in the Ras/MAPK pathway, specifically mutations in the MEK1 protein, a critical pathway component. My work provides two new insights into the effects of these pathogenic mutations. One, MEK1 variants were able to be phosphorylated faster than the wild type (WT) when reacted with Raf. And two, when phosphorylated, the activity of the MEK1 variants and WT reach similar levels, and this activity is higher than that of the unphosphorylated MEK1, either mutant or WT. Together, these findings suggest that the presence of a mutation in MEK1 affects its activation by Raf, the protein upstream of MEK1, and its activation of ERK, the protein downstream of MEK1. My findings can be summarized using a simple ODE based reaction model. My thesis underscores the importance of careful characterization of mutations and shows that studies of morphological effects on animal models do not provide a complete picture of the protein-protein interactions at the molecular level.