| The endosomal system in eukaryotes was originally perceived to serve as a conduit for internalized nutrients to the cytoplasm of the cell, and certain micro-organisms were shown to highjack the system to gain access to the cytoplasm for replication. It is now clear that endocytosis is about more than just eating and drinking. A few examples of the complex processes in which the endosomal system has an essential role include gradient formation of morphogens, asymmetric cell division, generation and maintenance of cell polarity, intracellular signaling, cell migration, and expression of many biologically important molecules including channel proteins and receptors. By taking reductionist and 'omic' approaches we will understand in the future how endocytosis affects development, cell polarity and migration, and vice versa. Recent progress has shown that membrane transport and signal transduction are related more strongly than was originally anticipated. This has become particularly clear for kinase/phosphatase dependent signaling pathways that control many of the proteins that regulate endocytic internalization and sorting. Main objective: Our long term objective is to identify and characterize signaling pathways that regulate membrane recycling through the endo-lysosomal system. This application describes our strategy to define the molecular principles organizing recycling pathways from endosomes to the plasma membrane. The mechanisms operating these conduits, however have not been established yet. A key feature in this process is the employment of the binary switch of rab and ARF GTPases. Previously we made seminal observations that rab4 and its effectors are important regulators of membrane recycling from endosomes. For that matter, analysis of the rab4 effector network provides an excellent strategy to gain insight in the molecular machinery underlying a faithful operation of the recycling pathway. Our specific aims are: 1. To determine regulatory mechanisms that selectively act on recycling pathways 2. To define the function of AP-1/rab4 in formation of recycling carriers Innovative aspects: We aim to eludidate a poorly understood general process, that is how proteins and membrane recycle from endosomes to the plasma membrane. Although the pathway is present in a rudimentary form in yeast its significance is particularly clear in higher eukaryotes where the endosomal recycling pathway is committed to a multitude of specialized tasks akin to multicellular organisms. Research in this area provides good opportunities since it presents a niche in the field of membrane biology that will provide novel opportunities. We will use a combination of state of the art methods of biophysical chemistry, bioinformatics and biochemistry. Our research already yielded, seminal molecular insights in organizational aspects of the endosome, that shaped thinking in related areas of research such as eg G protein coupled receptor signaling, and the control of integrin-dependent cell motility. |
