Unravelling Mechanisms of Endosomal Signaling with Designer Nanomaterials

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Abstract Endosomes, the membrane compartments inside living cells, are increasingly recognized as discrete “hubs” that regulate the network of cell signaling circuits in space and time. Physical phenomena like the clustering of proteins on endosome membranes and the active transport of endosomes are hypothesized to play a key role in these regulatory mechanisms. Unfortunately however, the direct evidence needed to support this level of mechanistic understanding of endosome signaling is lacking. Over the last four years, the research program of my lab has focused on exploring the wealth of physical phenomena involved in the endocytic process. We have uncovered new physical mechanisms of endocytosis in immune cells, but the questions we pose are of general relevance to many kinds of cells. We aim to test the general hypothesis that endosomes are a specialized platform for the spatiotemporal regulation of cellular signal transduction. This proposal highlights two of our developing project areas that are designed to test this hypothesis by identifying the biophysical mechanisms of endosome signaling regulation. Both are enabled by our established biophysical tools that allow us to manipulate and analyze the signaling activities and dynamics of endosomes in living cells. One research direction focuses on the mechanisms of signaling crosstalk on endosome membranes. Our ultimate goal for this research direction is to identify mechanisms by which physical interactions between endosomal receptors lead to their signaling crosstalk. By developing a novel approach that physically manipulates interactions between receptors on endosome membranes, we will establish the quantitative relationship between receptor clusters on endosomes, their signaling crosstalk, and the end-point cell response. The other research project addresses the functional roles of endosome trafficking in signaling. Our ultimate goal for this second research direction is to determine mechanisms under which the transport and subcellular location of endosomes regulate their signaling functions. By developing a particle reporter system that will allow us to magnetically control trafficking of single endosomes and simultaneously detect their signaling activities, we will reveal direct connection between the dynamical, mechanical and biochemical activities of individual endosomes. The proposed research directions are enabled by the novel integration of nanomaterial engineering, quantitative physical measurements, and advanced optical techniques, with live cell experiments. In the long term, we will expand our research scope from endosome signaling in immune cells to that in other cell types. Our ongoing and future research directions share the overarching goal of establishing a quantitative understanding of endosome signaling in living cells.