The Endosomal Sorting Complex Required for Transport (ESCRT) machinery is a set of interacting protein complexes responsible for cargo selection and biogenesis of intralumenal vesicles inside endosomal multivesicular bodies, also known as late endosomes. Evolutionary conservation and the discovery that ESCRTs are required for topologically equivalent processes including viral budding, cytokinetic abscission, and nuclear envelope closure led to the now widely accepted concept that ESCRTs are uniquely involved in membrane fission for reactions that share this topology. ESCRT-III proteins act by changing conformation and polymerizing into membrane-remodeling filaments that spiral on the inside ? negatively curved ? surface of membrane tubules, ultimately pulling the tubules closed to drive membrane fission and release. Intriguingly, there are twelve ESCRT-III proteins in humans that are not functionally interchangeable. Beyond identification of different molecular binding partners, there has been little structural distinction among these proteins to explain their unique physiological importance. We recently made the surprising discovery that two human ESCRT-III proteins ? CHMP1B and IST1 ? assemble into filaments that spiral around the outside ? positively curved ? surface of membrane tubules, forming external coats in vitro and in vivo. This unexpected preference for positively curved membrane tubules challenges the dogma that the membrane deforming and fission activity associated with ESCRT-III filaments is limited to a single topology and prompts us to reconsider established paradigms for ESCRT-III function. This project will (1) define the topology preference of particular ESCRT-III homo- and heteropolymers polymers and the corresponding distribution of endogenous ESCRT-III proteins across the endosomal system, (2) establish the role(s) of representative ESCRT-III proteins in distinct endosomal cargo trafficking pathways, and (3) compare the effects of depleting different ESCRT-III proteins on endosomal and lysosomal morphology. This work will expand our understanding of the ESCRT-III membrane remodeling system with significant implications for future studies of trafficking and organization within the endolysosomal system.

Public Health Relevance

The Endosomal Sorting Complex Required for Transport (ESCRT) machinery is known for its fundamental but topologically restricted roles in remodeling cellular membranes to enable membrane protein degradation, HIV budding, and cell division. Our proposed work will test a more general model of ESCRT-mediated membrane remodeling in which different combinations of proteins function in topologically distinct reactions to also regulate endosomal recycling and organelle fission. Defects in these latter processes may contribute to a large number of diseases, including cancers and neurodegeneration as well as specific forms of Hereditary Spastic Paraplegia and Chediak-Higashi syndrome.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM122434-04
Application #
9872173
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Maas, Stefan
Project Start
2017-01-01
Project End
2020-11-30
Budget Start
2019-12-01
Budget End
2020-11-30
Support Year
4
Fiscal Year
2020
Total Cost
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Biochemistry
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
Skowyra, Michael L; Schlesinger, Paul H; Naismith, Teresa V et al. (2018) Triggered recruitment of ESCRT machinery promotes endolysosomal repair. Science 360:
Mittal, Ekansh; Skowyra, Michael L; Uwase, Grace et al. (2018) Mycobacterium tuberculosis Type VII Secretion System Effectors Differentially Impact the ESCRT Endomembrane Damage Response. MBio 9:
Rimer, Jamie M; Lee, Jiyeon; Holley, Christopher L et al. (2018) Long-range function of secreted small nucleolar RNAs that direct 2'-O-methylation. J Biol Chem 293:13284-13296
Jackson, Charles E; Scruggs, Benjamin S; Schaffer, Jean E et al. (2017) Effects of Inhibiting VPS4 Support a General Role for ESCRTs in Extracellular Vesicle Biogenesis. Biophys J 113:1342-1352