Cell signaling is at the core of most biological processes from the simplest to the most complex. In addition to unicellular organisms possessing the essential ability to receive inputs with regard to nutrient availability and noxious stimuli, the cells in multicellular organisms require signaling from adjacent, as well as distant cells to maintain normal internal function, including growth, differentiation, and homeostasis. Conversely, the etiology of many disease processes, such as those involving immune system dysfunction and tumor development, have been traced to aberrant cell signaling....