Biological functions of melanoma antigen (MAGE) proteins

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The abundance and subcellular localization of proteins contributes to the ctivities that take place inside cells. Both protein stability and localization are determined in part by post-translational modification. The proposed research specifically considers the role of the reversible attachment of a 76 residue ubiquitin protein to substrate proteins, which dynamically changes the stability, activity, or subcellular localization of the ubiquitinated protein. For example, cell cycle proteins undergo highly regulated ubiquitination and deubiquitination, fine tuning their stability, activity and localization. However, the proteins that perform the reversible ubiquitination / deubiquitination processes, and other proteins that modify the activity of these ubiquitin ligases and deubiquitinases are poorly understood. Our previous research has demonstrated that Melanoma Antigen Gene (MAGE) proteins regulate the ubiquitination and deubiquitination of proteins important for a variety of physiological processes. In particular, the L2 member of the MAGE family of proteins (MAGEL2) regulates the intracellular localization and stability of other proteins. Our team found that MAGEL2 forms a functional complex with E3 ubiquitin ligases (e.g. RBX1-SCF) and deubiquitinases (e.g. USP7), thereby regulating circadian rhythm processes through effects on the activity and stability of master clock components. We found that MAGEL2 regulates the stability of BBS proteins important for the function of centrosomes and of cilia, subcellular organelles that sense and respond to signals in the extracellular environment. We found that MAGEL2 and another MAGE protein, namely necdin, regulate the intracellular shuttling of the leptin receptor through processes dependent on ESCRT (endosomal sorting complexes required for transport) machinery. Our research program objective is to explore the mechanisms for regulation of intracellular shuttling and stability of proteins by protein ubiquitination. The importance of MAGE proteins in this process is evident from the observations that mutation in the genes encoding MAGE proteins cause disease in humans (MAGEL2 in Schaaf-Yang syndrome, MAGED2 in antenatal Bartter syndrome, MAGEG1 in a chromosome breakage syndrome), with phenotypes in mouse MAGE gene knockouts as well. We will use molecular and cellular models to determine the role of MAGE proteins, which are components of ubiquitination (Ub) complexes. Specifically, we will use protein-protein interaction techniques to identify components of the MAGE-ubiquitin ligase-deubiquitinase complexes; determine how MAGE proteins fine tune cellular processes using cell lines in culture and 3) examine how genes and proteins important in cellular processes are regulated by ubiquitination in tissues. Ultimately, this research will explore how modification of proteins by ubiquitination and deubiquitination fine tunes the activity of proteins in the cell.