Role of Rab7 and RILP on signaling receptor trafficking and telomere length.

This is a national project funded by the Associazione Italiana per la ricerca sul cancro (AIRC). ABSTRACT: Diversification of membrane-bound compartments in eukaryotic cells was accompanied by elaboration of complex molecular machineries mediating communication between compartments and delivery of molecules to specific intracellular destinations. Various human diseases are caused by alteration of membrane trafficking. Therefore, understanding the molecular and cellular mechanisms underlying the endocytic and exocytic pathways is crucial to develop treatments. In particular, endocytosis is the mechanism used by eukaryotic cells to internalize cell surface lipids, surface receptors and their ligands, and various soluble molecules from the extracellular milieu, and it is tightly connected with signaling. Signaling molecules as hormones, growth factors, cytokines and mitogens bind to signal transducing cell surface receptors triggering cascades of signal transduction. Binding to ligands activates the receptors and increases their rate of internalization. Endocytosis of signaling receptors causes receptor clearance from the plasma membrane and represents a mechanism for signal attenuation and receptor degradation. Recent evidence indicate that endocytosis, beside its attenuation function, has a central and direct role in cellular homeostasis and control of proliferation. Indeed, it is now clear that the effect of a signaling cascade does not rely exclusively on the activation of signaling molecules but also on where and how long the signal is produced. Endocytic organelles, as endosomes and caveolae, represents important signaling platforms for propagation of intracellular signals, being responsible for spatial and temporal regulation of signaling. Emerging evidence indicate that some Rab proteins play a key role in these processes. Rab proteins are small GTPases heavily involved in the regulation of membrane traffic. Indeed, Rab proteins regulate, through the action of their effectors, formation of vesicles, movement of vesicles on cytoskeleton tracks, tethering and fusion of vesicles with target compartments. The endocytic trafficking of several hormones, growth factor and chemochine receptors is regulated by Rab proteins. As dysregulation of receptor signaling is associated with cancer, also dysregulation of endosomal Rab proteins may be a generalized component of human tumors. Indeed, for instance, Rab25 determines aggressiveness of ovarian and breast cancer while Rab7 prevents growth factor-independent cell survival. In addition, altered expression of many Rab proteins has been found in different kind of tumors. Despite the extraordinary importance of defining the interplay between receptor signaling and endocytic membrane traffic, our knowledge on this topic is still limited. Our lab is working since many years on the role of endosomal Rab proteins. In particular, we have isolated and functionally characterized Rab7 and its effector RILP and we recently discovered that RILP interacts with VPS22, a component of the Endosomal Sorting Complex Required for Transport II (ESCRT-II). The ESCRT complexes are responsible for targeting to lysosomal degradation monoubiquitinated signaling receptors. The goal of the present application is to investigate the role of Rab7 and its effector RILP in controlling signal transduction pathways, looking, in particular, at the effects due to the interaction with VPS22 on EGF and neurotrophins receptors trafficking. These receptors play a major role in tumor biology and increased knowledge about these pathways will result in future development of novel drugs against cancer.