Interrogative Cell Signaling
Biological organisms must respond appropriately to their environment to survive. The information-gathering systems of single-cell organisms, such as protozoa and bacteria, have evolved to respond to a range of stimuli, allowing them to locate food and avoid extremes of temperature or light. Individual cells of a multi-cellular organism must cooperate and participate in functions that extend far beyond survival. To this end, cell communication couples the behavior of a cell to the requirements of the organism.
Traditionally, cell communication has been studied in the context of how cells receive information generated by other cells. It has become increasingly clear, however, that cells are able to actively interrogate their extracellular environment by the regulated shedding of growth factors, proteases, and adhesion molecules. Shed molecules can be retrieved by the cells that produced them or stimulate neighboring cells. In this way, a signal can be transmitted to an entire cell population. The role of regulated protein shedding in cell communication has only recently been described, but it appears to be a fundamental, evolutionarily ancient mechanism involved in tissue remodeling, embryogenesis, stress responses, and tissue homeostasis. Significantly, disruptions in this signaling system appear to be associated with many types of cancer.
Despite its importance, interrogative cell signaling has been scarcely investigated, mainly because of the technical difficulties. Shed molecules are produced in exceedingly small amounts, and they are produced and consumed in the vicinity of individual cells. We do not know the spectrum of molecules that are actively shed by cells, and we do not know their fate. Most important, we have a very poor understanding of the molecular mechanisms involved in shedding itself. Which enzymes are involved? What is the basis of their specificity? How are they regulated? What biological processes do they control?
Understanding these fundamental questions is critical to understanding interrogative cell signaling. However, answering these questions requires new approaches to detect and quantify shed proteins. We must be able to genetically alter model cells to study molecular structure-function relationships. New imaging technologies must be developed to measure the interaction of molecules at the cell surface. Finally, we need testable physiochemical models of extracellular signaling networks to allow us to dissect the workings of these complex cellular circuits.
Despite the technical difficulties associated with investigating interrogative cell signaling, it has features that make it very amenable to experimental investigations. The extracellular nature of the process provides easy access to many of its components. It can be interrupted by the use of antibodies, and the network status can be evaluated serially by sampling the extracellular medium. Imaging technologies can also be used to follow dynamic elements of the process. Because it is extracellular and can be selectively disrupted, interrogative cell signaling can also potentially be manipulated to control cell behavior.
The goal of the Biomolecular Systems Initiative's (BSI's) Interrogative Cell Signaling study is to use a systems approach to understand the role of regulated shedding in the ability of cells to detect their immediate microenvironment, referred to as context detection. In fiscal year 2005, interrogative cell signaling projects at Pacific Northwest National Laboratory (PNNL) centered on developing the necessary tools, capabilities, and technologies to study this important, yet nascent research problem. Fiscal year 2006 efforts are focused on generating data to rigorously test hypotheses on the mechanisms of regulated shedding and the role that this process plays in receptor transactivation and autocrine signaling.
Interrogative Cell Signaling Supports Seven Projects
Three projects are focused on understanding the mechanisms that control regulated shedding and its functional role in cell behavior.
- Mechanisms of Regulated Ligand Shedding
- Transmodulation of Cell Reponses
- Regulation of Cell Surface Ligand Dynamics
Researchers working on capability development projects are making a reagent with applications to biodetection technologies and generating high-throughput assays to measure the activity of signaling pathways that are modulated by regulated shedding.
The goal of two data management projects is to build an infrastructure to store and manage the data generated by the experimental projects.
Our scientists are also developing an integrated model of multiple signaling pathways linked through regulated shedding.