Linda C. McPhail
The research in my laboratory is focused on elucidation of cellular signal transduction mechanisms involved in the activation of NADPH oxidase, an enzyme responsible for the generation of toxic oxygen radicals in many cell types. NADPH oxidase is found in high levels in phagocytic cells, like neutrophils and monocytes, where the elicited production of oxygen radicals plays critical roles in both protection against microbial infections and in damage to tissue in a variety of diseases, including degenerative neurological diseases, arthritis, stroke, and myocardial infarction. Homologs of NADPH oxidase have now been discovered in many cell types, including smooth muscle cells, kidney cells, thyroid cells, endothelial cells, and epithelial cells. These enzymes are present at low levels (compared to phagocytic cells) and may be involved in both host defense and cell signaling by reactive oxygen species. Thus, a mechanistic understanding of the regulation of NADPH oxidase could ultimately be used for design of therapeutic approaches to control the activity of this enzyme in a wide variety of disease situations. Mechanisms involved in NADPH oxidase activation include phosphorylation of components, lipid binding to components, activation of GTP-hydrolyzing proteins, and assembly of enzyme components from various intracellular compartments to form an active complex. We are exploring these mechanisms using site-directed mutagenesis of NADPH oxidase components and various analytical and functional assays. Our current focus is on dissecting the structure/function relationship of protein phosphorylation and lipid binding events in the regulation of two NADPH oxidase components – the soluble p47phox and the integral membrane protein flavocytochrome b558. A working model depicting the phosphorylation events and the lipid-binding interactions we believe are taking place is shown below. In addition, a new project is studying the interaction between neutrophils and pathogens, to determine the biochemical mechanisms by which pathogens alter neutrophil function during host defense and inflammation. Techniques used in my laboratory include: mutagenesis, expression of recombinant proteins, Western blotting, lipid-binding assays, protein:protein interaction assays, cell culture and blood cell isolation, flow cytometry, transfection of cultured cells, enzymatic assays (NADPH oxidase, protein kinase, phospholipase D), and functional assays (chemotaxis, degranulation, bactericidal activity).