ESCRTs function directly on the lysosome membrane to downregulate ubiquitinated lysosomal membrane proteins

Abstract

The lysosome plays an important role in maintaining cellular nutrient homeostasis. Regulation of nutrient storage can occur by the ubiquitination of certain transporters that are then sorted into the lysosome lumen for degradation. To better understand the underlying mechanism of this process, we performed genetic screens to identify components of the sorting machinery required for vacuole membrane protein degradation. These screens uncovered genes that encode a ubiquitin ligase complex, components of the PtdIns 3-kinase complex, and the ESCRT machinery. We developed a novel ubiquitination system, Rapamycin-Induced Degradation (RapiDeg), to test the sorting defects caused by these mutants. These tests revealed that ubiquitinated vacuole membrane proteins recruit ESCRTs to the vacuole surface, where they mediate cargo sorting and direct cargo delivery into the vacuole lumen. Our findings demonstrate that the ESCRTs can function at both the late endosome and the vacuole membrane to mediate cargo sorting and intra-luminal vesicle formation.DOI: http://dx.doi.org/10.7554/eLife.26403.001

Three Distinct Types of Microautophagy Based on Membrane Dynamics and Molecular Machineries

“…Microlipophagy requires ESCRT components, but not the core Atg proteins for the autophagosome formation, when it is induced either by inhibition of phosphatidylcholine biosynthesis or by diauxic shift of the culture (Figure D). Furthermore, microautophagy for the degradation of vacuolar membrane proteins utilizes the ESCRT machinery under different culture conditions . These findings seem reasonable in light of the direct activity of the ESCRT machinery on membrane curvature and formation of luminal vesicles in endosomes, membrane dynamics that are similar to the invagination process of microautophagy.…”

“…The target organelles of these microautophagic pathways include the cytoplasm, ER, portions of the nucleus (piecemeal microautophagy of the nucleus, or PMN), mitochondria, and lipid droplets . In addition, recent studies demonstrated that vacuolar membrane proteins are degraded through this type of microautophagy . Below we summarize three aspects of the molecular machineries discovered in these yeast studies.…”

Structures, Functions, and Dynamics of ESCRT-III/Vps4 Membrane Remodeling and Fission Complexes

“…The budding of enveloped viruses from the plasma membrane appears to be an analogous vesiculation process, as the bud neck is again narrow and the ESCRT-III/Vps4 machinery accumulates and is released rapidly (Baumgartel et al 2011, Bleck et al 2014, Feng et al 2013, Jouvenet et al 2011). Other analogous ESCRT-dependent vesiculation processes include ILV budding directly into the vacuole (the yeast equivalent of the lysosome) (Zhu et al 2017, Caspi & Dekker 2018), shedding microvesicle release from the plasma membrane (Choudhuri et al 2014, Matusek et al 2014, Nabhan et al 2012), and possibly also nuclear egress of the Herpes viral core particle (Lee et al 2012) and vesicle secretion at the ciliary transition zone (Diener et al 2015, Wood et al 2013). …”

Virulence‐associated protein A fromRhodococcus equiis an intercompartmental pH‐neutralising virulence factor

“…We were surprised to observe an unexpected accumulation of strongly LAMP1-positive membranes within the RCV, particularly at late times of infection ( Figure S6). Alternatively, vesicles containing LAMP1 and vATPase may bud from the boundary phagosome membrane into the phagosome lumen similar as described for yeast vacuole transmembrane proteins (McNally, Karim, & Brett, 2017;Zhu, Jorgensen, Li, Chuang, & Emr, 2017) or for microautophagy (Dunn, 1994), depleting the RCV membrane of certain proteins. Alternatively, vesicles containing LAMP1 and vATPase may bud from the boundary phagosome membrane into the phagosome lumen similar as described for yeast vacuole transmembrane proteins (McNally, Karim, & Brett, 2017;Zhu, Jorgensen, Li, Chuang, & Emr, 2017) or for microautophagy (Dunn, 1994), depleting the RCV membrane of certain proteins.…”