The role of microdomains in EGF receptor activation and trafficking

Signal transduction by plasma membrane receptors is important in control of cellular growth and differentiation. Accumulating evidence suggests that the function of such receptors is controlled by their subcellular localization. Cellular membranes are not uniform, but consist of functionally different microdomains. Using the epidermal growth factor receptor (EGFR) as model, we will study the role of different microdomains in control of signal transduction and intracellular membrane traffic. We will study how localization of EGFR to caveolae and lipid rafts controls EGFR activation and how ubiquitination controls recruitment of EGFR to coated pits. Following endocytosis, EGFR is transferred to early endosomes from which it is either recycled or transported to lysosomes. Recycling or transport to late endosomes depends on sorting to different endosomal microdomains. Recycling endosomes are enriched in raft molecules and we will study colocalization of EGFR and such molecules. Transport of EGFR to lysosomes involves its translocation to inner membranes of multivesicular bodies. We have evidence that this depends on EGFR ubiquitination and retention in specific clathrin coated microdomains. This retention will be studied under conditions where EGFR ubiquitination is modified. In addition to localization and characterization of known proteins we aim to identify novel proteins involved in sorting of EGFR