G-Protein Signaling in Chemotaxis

Much of our current understanding of chemotaxis-signaling pathways through G-protein-coupled receptors (GPCRs) is derived from studies on the social amoeba, Dictyostelium discoideum, and mammalian neutrophils. Chemotaxis is the directed migration of cells in response to concentration gradients of extracellular signals. In unicellular organisms, such as bacteria and amoebae, chemotaxis is frequently used as a foraging mechanism. Recent advances in the understanding of the molecular mechanisms that regulate chemotaxis have revealed the important and diverse roles played by G proteins. These studies not only highlight the critical function of G proteins as molecular switches, but also show how their signaling in the context of chemotactic signaling networks allows cells to translate the directional information of external concentration gradients into directional movement. Recent work also provides some insight into the mechanisms of PI3K and PTEN localization in Dictyostelium. Future work will need to examine how these signaling networks interact, and new models need to be developed that can account for both directional sensing and polarization.