The long-term goal of this proposal is to define molecular mechanisms that regulate the trafficking of integral membrane proteins to the lysosome for degradation. Recent evidence indicates that modification of transmembrane proteins by ubiquitin is sufficient for protein sorting into this pathway. The ESCRT machinery, a set of conserved endosomal protein complexes, is proposed to directly bind to ubiquitinylated membrane proteins and govern their entry into vesicles that bud into the lumen of specialized multivesicular endosomes (MVEs). This process is particularly important for the downregulation of hormone receptors to prevent constitutive signaling, which can lead to developmental abnormalities and disease. How the ESCRT machinery coordinates the efficient capture and transport of ubiquitinylated substrates to MVEs will be addressed in this proposal. The C. elegans germline and early embryo are powerful model systems to study membrane dynamics in an intact, developing animal. Specific proteins can be efficiently depleted from oocytes using RNA interference. Additionally, oocyte maturation and fertilization reproducibly trigger the internalization and degradation of multiple transmembrane proteins, providing an ideal, physiologically relevant system for studying lysosomal protein transport. C. elegans is highly amenable to genetic manipulation and can be engineered to stably express fluorescently tagged proteins, including cell surface receptors that can be monitored by live cell microscopy. Taking advantage of this unique combination of attributes, the specific aims of this proposal are: 1) to determine mechanisms by which the ESCRT machinery recognizes substrates, 2) to define the role of PTH-2, a newly discovered ESCRT-0 binding protein, and 3) to define mechanisms that regulate cargo entry into the ESCRT pathway. Our preliminary genetic and biochemical studies have uncovered new components of the lysosomal transport pathway that associate with the ESCRT machinery. The significance of these interactions will be tested using a combination of fluorescence microscopy-based functional assays, biophysical measurements, and in vitro reconstitution experiments. These studies will provide a framework for future investigation into highly related pathways in mammalian cells.

Public Health Relevance

The directed movement of proteins and membranes between different cellular locations is a fundamental process required for the proper functioning of all eukaryotic cells. Many diseases including cancer, neurodegenerative disorders such as Parkinson's disease and Huntington's disease, and immune dysfunction can be caused by intracellular protein transport defects. The proposed research will determine how membrane trafficking pathways are appropriately regulated, enhancing our fundamental understanding of this process, which should facilitate the future identification of therapeutic targets for disease intervention.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Membrane Biology and Protein Processing (MBPP)
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Ainsztein, Alexandra M
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University of Wisconsin Madison
Schools of Medicine
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Wang, Lei; Audhya, Anjon (2014) In vivo imaging of C. elegans endocytosis. Methods 68:518-28
Schuh, Amber L; Audhya, Anjon (2014) The ESCRT machinery: from the plasma membrane to endosomes and back again. Crit Rev Biochem Mol Biol 49:242-61
Bahmanyar, Shirin; Biggs, Ronald; Schuh, Amber L et al. (2014) Spatial control of phospholipid flux restricts endoplasmic reticulum sheet formation to allow nuclear envelope breakdown. Genes Dev 28:121-6
Wickert, Lisa E; Karta, Maya R; Audhya, Anjon et al. (2014) Simvastatin attenuates rhinovirus-induced interferon and CXCL10 secretion from monocytic cells in vitro. J Leukoc Biol 95:951-9
Shen, Qing-Tao; Schuh, Amber L; Zheng, Yuqing et al. (2014) Structural analysis and modeling reveals new mechanisms governing ESCRT-III spiral filament assembly. J Cell Biol 206:763-77
Wan, Jun; Zhu, Fen; Zasadil, Lauren M et al. (2014) A Golgi-localized pool of the mitotic checkpoint component Mad1 controls integrin secretion and cell migration. Curr Biol 24:2687-92
Green, Rebecca A; Mayers, Jonathan R; Wang, Shaohe et al. (2013) The midbody ring scaffolds the abscission machinery in the absence of midbody microtubules. J Cell Biol 203:505-20
Mayers, Jonathan R; Wang, Lei; Pramanik, Jhuma et al. (2013) Regulation of ubiquitin-dependent cargo sorting by multiple endocytic adaptors at the plasma membrane. Proc Natl Acad Sci U S A 110:11857-62
Hanna, Michael; Wang, Lei; Audhya, Anjon (2013) Worming our way in and out of the Caenorhabditis elegans germline and developing embryo. Traffic 14:471-8
Beetz, Christian; Johnson, Adam; Schuh, Amber L et al. (2013) Inhibition of TFG function causes hereditary axon degeneration by impairing endoplasmic reticulum structure. Proc Natl Acad Sci U S A 110:5091-6

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