Sorting membrane proteins into intralumenal vesicles that form within late endosomes is a fundamental process that regulates many biological pathways that rely on maintaining appropriate levels of a given set of cell surface membrane proteins. This is the pathway that guides the delivery and degradation of proteins in lysosomes. This pathway is driven by ubiquitin, which works as a sorting signal when attached to membrane protein cargo. This process controls the degradation of almost all cell surface membrane proteins and understanding this degradative process is significant since it impacts a wide array of normal and pathogenic processes that rely on proper activity of particular membrane proteins such as transporters and signaling receptors at the cell surface. The long-term goal of the competitive renewal proposal is to understand how this ubiquitin-dependent sorting pathway is controlled, and will lead to insights into how disease states such as cancer might be achieved when this process goes awry. To accomplish this we have devised aims to 1) discover how the major family of Nedd4- related ubiquitin ligases are programed to target different cell surface membrane proteins;2) discover how ubiquitinated membrane proteins are recognized by the endosomal sorting machinery and how that cargo plays an active role in organizing the sorting apparatus itself;and 3) discover new proteins that participate in the process of intralumenal vesicle formation using a series of genetic screens.

Public Health Relevance

The proposed research is relevant to public health because it focuses on how multiple cellular functions are regulated through the degradation of cell surface proteins that mediate growth, differentiation, signal- transduction, neuronal signaling, and nutrient uptake. Thus, the proposed research is relevant to mission of the NIH to increase understanding of fundamental life processes that in turn will lay the foundation for advances in disease diagnosis, treatment and prevention.

National Institute of Health (NIH)
Research Project (R01)
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Study Section
Membrane Biology and Protein Processing Study Section (MBPP)
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Ainsztein, Alexandra M
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University of Iowa
Schools of Medicine
Iowa City
United States
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Piper, Robert C; Dikic, Ivan; Lukacs, Gergely L (2014) Ubiquitin-dependent sorting in endocytosis. Cold Spring Harb Perspect Biol 6:
Ver Heul, Aaron M; Fowler, C Andrew; Ramaswamy, S et al. (2013) Ubiquitin regulates caspase recruitment domain-mediated signaling by nucleotide-binding oligomerization domain-containing proteins NOD1 and NOD2. J Biol Chem 288:6890-902
Pashkova, Natasha; Gakhar, Lokesh; Winistorfer, Stanley C et al. (2013) The yeast Alix homolog Bro1 functions as a ubiquitin receptor for protein sorting into multivesicular endosomes. Dev Cell 25:520-33
Kamadurai, Hari B; Qiu, Yu; Deng, Alan et al. (2013) Mechanism of ubiquitin ligation and lysine prioritization by a HECT E3. Elife 2:e00828
MacDonald, Chris; Buchkovich, Nicholas J; Stringer, Daniel K et al. (2012) Cargo ubiquitination is essential for multivesicular body intralumenal vesicle formation. EMBO Rep 13:331-8
Pashkova, Natasha; Piper, Robert C (2012) UBAP1: a new ESCRT member joins the cl_Ub. Structure 20:383-5
Stringer, Daniel K; Piper, Robert C (2011) A single ubiquitin is sufficient for cargo protein entry into MVBs in the absence of ESCRT ubiquitination. J Cell Biol 192:229-42
Piper, Robert C; Lehner, Paul J (2011) Endosomal transport via ubiquitination. Trends Cell Biol 21:647-55
Shields, S Brookhart; Piper, Robert C (2011) How ubiquitin functions with ESCRTs. Traffic 12:1306-17
Pashkova, Natasha; Gakhar, Lokesh; Winistorfer, Stanley C et al. (2010) WD40 repeat propellers define a ubiquitin-binding domain that regulates turnover of F box proteins. Mol Cell 40:433-43

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