The HOPS Proteins hVps41 and hVps39 Are Required for Homotypic and Heterotypic Late Endosome Fusion

The homotypic fusion and protein sorting (HOPS) complex is a multisubunit tethering complex that in yeast regulates membrane fusion events with the vacuole, the yeast lysosome. Mammalian homologs of all HOPS components have been found, but little is known about their function. Here, we studied the r...

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Bibliographic Details
Published in:Traffic (Copenhagen, Denmark) Denmark), 2013-02, Vol.14 (2), p.219-232
Main Authors: Pols, Maaike S., Brink, Corlinda, Gosavi, Prajakta, Oorschot, Viola, Klumperman, Judith
Format: Article
Language:English
Subjects:
Cathepsin B - metabolism
Cellular biology
Endocytosis
endosomes
Endosomes - metabolism
HeLa Cells
HOPS
Humans
Hydrogen-Ion Concentration
Intracellular Membranes - metabolism
Intracellular Signaling Peptides and Proteins - genetics
Intracellular Signaling Peptides and Proteins - metabolism
lysosomes
Lysosomes - metabolism
Membrane Fusion - genetics
Proteins
Proteolysis
RNA, Small Interfering
VAMP7
Vesicular Transport Proteins - genetics
Vesicular Transport Proteins - metabolism
Vps39
Vps41
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Summary:The homotypic fusion and protein sorting (HOPS) complex is a multisubunit tethering complex that in yeast regulates membrane fusion events with the vacuole, the yeast lysosome. Mammalian homologs of all HOPS components have been found, but little is known about their function. Here, we studied the role of hVps41 and hVps39, two components of the putative human HOPS complex, in the endo‐lysosomal pathway of human cells. By expressing hemagglutinin (HA)‐tagged constructs, we show by immunoelectron microscopy (immunoEM) that both hVps41 and hVps39 associate with the limiting membrane of late endosomes as well as lysosomes. Small interference RNA (siRNA)‐mediated knockdown of hVps41 or hVps39 resulted in an accumulation of late endosomes, a depletion in the number of lysosomes and a block in the degradation of endocytosed cargo. Lysosomal pH and cathepsin B activity remained unaltered in these conditions. By immunoEM we found that hVps41 or hVps39 knockdown impairs homotypic fusion between late endosomes as well as heterotypic fusion between late endosomes and lysosomes. Thus, our data show that both hVps41 and hVps39 are required for late endosomal–lysosomal fusion events and the delivery of endocytic cargo to lysosomes in human cells.
ISSN:1398-9219
1600-0854
DOI:10.1111/tra.12027