MECHANISMS OF INTERNALIZATION AND TRAFFICKING OF THE TUMOR SUPPRESSOR AND LYSOSOMAL MEMBRANE PROTEIN TMEM127

Endocytosis is a conserved pathway that internalizes macromolecules and transmembrane proteins and sortsthem through the endo-lysosomal system to their destinations. This process is often dysregulated in manydiseases including cancers, metabolic disorders and neurodegenerative diseases. Elucidating the endocyticmechanisms of transmembrane proteins will improve our understanding of biological processes, diseaseprognosis and therapeutic strategies. Our lab has identified the poorly known transmembrane protein,TMEM127, which we discovered to be mutated in hereditary neuroendocrine tumors, as a tumor suppressor, anegative regulator of mTOR signaling and a lysosomal membrane protein. However, the function andregulation of TMEM127 remain poorly defined. Our previous studies show that TMEM127 localizes to theplasma membrane and to endo-lysosomal vesicles and that its localization changes in response to nutrientconditions. Specifically, the lysosomal localization of TMEM127 increases upon amino acid stimulation. At thelysosome, TMEM127 interacts with the amino acid-sensitive, lysosomal-anchored, mTOR activating complexwhich leads to dampened mTOR signaling. How TMEM127 senses amino acids and whether TMEM127translocation to the lysosome originates from the plasma membrane, or an endosomal compartment, isunknown. Recently, we observed that several C-terminally truncated TMEM127 mutants predominantly localizeto the plasma membrane suggesting that an endocytic signal is lost after truncation. We also recently observedthat TMEM127 co-localizes with clathrin, but not caveolin, two mediators of endocytosis, indicating thatclathrin-mediated endocytosis (CME) may be involved. These observations implicate a novel endocyticmechanism involved in TMEM127 internalization and trafficking to the lysosome. The objective of this proposalis to define these endocytic mechanisms. In Aim 1, we will identify the endocytic motif responsible forTMEM127 internalization and trafficking. In Aim 2, we will determine if TMEM127 internalization occurs throughCME. In Aim 3, we will determine if TMEM127 internalizes in response to amino acids. Successful completionof this proposal will provide novel insights into the endocytic mechanisms regulating TMEM127 and itsresponse to amino acids, which could have broad implications for human health including a betterunderstanding of cancers with TMEM127 mutations or increased mTOR signaling and disorders affectingmetabolic and lysosomal homeostasis.