EGF-induced Formation of Clathrin Coated Pits

Growth factor receptors control cellular growth and differentiation by transmitting signals from outside the cell to the cell interior, particularly the nucleus. Signal transmission can be modulated in several ways. To control signalling, down-regulation of receptors from the cell surface is important. This happens by endocytosis and sorting to lysosomes, where degradation occurs. Receptor down-regulation is important to prevent tonic mitogenic stimulation of cells. Receptor tyrosin kinases (RTKs) have li gand-binding capacity as well as intrinsic tyrosin kinase activity. Upon ligand binding, the RTK is autophosphorylated, and signaling cascades are initiated. Our studies will be concentrated on mechanisms controlling initial steps in endocytosis of the EG F receptor (EGFR). Upon ligand binding, the EGFR is translocated to clathrin coated pits at the plasma membrane from where endocytosis occurs. We have discovered that the ligand-bound and activated EGFR in fact induces its own coated pits by downstream si gnaling. The kinase activity in some way controls recruitment of clathrin adaptor proteins as well as cargo-binding proteins to the plasma membrane. We have developed conditions enabling us to study generation of EGF-induced clathrin coated pits. We will therefore in detail study the composition of these plasma membrane microdomains as well as the signaling cascades required to orchestrate the building of these microdomains. We will further investigate whether EGF-induced EGFR-containing clathrin coated p its form cholesterol-dependently.