The long-term goal of our laboratory is understand how signaling transduction by cell surface receptors isregulated. Ultimately, we would like to develop strategies for selectively activating or inhibiting these cellularactivities and bypass limitations of the receptor, such as low receptor number or receptor desensitization.Every extracellular ligand (growth factor, hormone, neurotransmitter, etc) binds to a unique cell surfacereceptor that induces intracellular, biochemical changes that are integrated to invoke a specific change in cellphysiology. While the exquisite specificity of this system has been long appreciated, the molecular mechanismby which it occurs is poorly understood. Understanding how an overlapping set of biochemical responsesproduces a specific physiology is the key to this problem. To better understand this important process, we areusing the prototypical receptor tyrosine kinase, the epidermal growth factor receptor (EGFR), as a model. TheEGFR is critical for many developmental and homeostatic processes; stimulation of the EGFR leads to avariety of cellular changes including cell proliferation, differentiation, migration, and viability. Further,overexpression of the EGFR is associated with many cancers. We, and others, believe that the magnitude and duration of signaling to these biochemical intermediatesdictates how cell physiology is altered. One way the magnitude and duration of receptor signaling is modulatedis through the internalization and degradation of the receptor following ligand binding. In addition to activatingintracellular signaling pathways, ligand binding also causes most cells surface receptors to internalize viaclathrin-coated pits. Once inside the cell, the ligand:receptor complex moves through a series of well-definedendocytic stages until it ultimately reaches the lysosome where it undergoes degradation. It has been shownpreviously by a number of groups that disrupting this process can alter the effect that activated EGFRs have onthe cell. However, these studies have been limited to distinguishing between cell surface and intracellularreceptors. The overarching hypothesis of our research is that the endocytic pathway is a key positive andnegative regulator of cell surface receptor signaling.
In Aim I, we will use cultured cells and selectively disrupt EGFR trafficking through the endocytic pathway.We will assess EGFR signaling at each of these endocytic stages. Further, we will determine whetherdifferences in signaling occur due to changes in the receptor itself, receptor:effector interactions, or theduration/magnitude of signaling.
Aim II, we will build on our recent findings that spatially restricting the EGFRin cancer cells (MDA-MB-468 mammary adenocarcinoma cells) dramatically changes cell growth and viabilityproperties. We will build on this model to determine which signals emanate from the cell surface and which areproduced within the cell. Finally, in Aim III, we will explore how the endocytic pathway negatively regulatesEGFR signaling. In these studies, we will determine the mechanism of signal inactivation and determine if it isunique for the receptor or effectors are inactivated in this same manner. Completion of these studies will reveal how EGFR signaling is regulated downstream of the receptor. Thiswill guide the production of more targeted therapies to inhibit EGFR signaling (i.e. cancer) or activation ofEGFR signaling (i.e. corneal wound healing).
The epidermal growth factor receptor (EGFR) is a fundamental cell surface protein that functions by detecting the presence of growth factors outside the cell and converting the information into biochemical changes within the cell. Proper function of the EGFR is necessary for development and homeostasis of the whole organism;overexpression/hyperactivation of the EGFR is associated with many cancers. The immediate goal of this research is to better understand the molecular mechanisms that regulate the biological pathological functions of the EGFR and use that information for treatment of diseases associated with the EGFR.
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