Metazoan cell biology of the HOPS tethering complex

Abstract

Membrane fusion with vacuoles, the lysosome equivalent of the yeast Saccharomyces cerevisiae, is among the best understood membrane fusion events. Our precise understanding of this fusion machinery stems from powerful genetics and elegant in vitro reconstitution assays. Central to vacuolar membrane fusion is the multi-subunit tether the HO motypic fusion and Protein Sorting (HOPS) complex, a complex of proteins that organizes other necessary components of the fusion machinery. We lack a similarly detailed molecular understanding of membrane fusion with lysosomes or lysosome-related organelles in metazoans. However, it is likely that fundamental principles of how rabs, SNAREs and HOPS tethers work to fuse membranes with lysosomes and related organelles are conserved between Saccharomyces cerevisiae and metazoans. Here, we discuss emerging differences in the coat-dependent mechanisms that govern HOPS complex subcellular distribution between Saccharomyces cerevisiae and metazoans. These differences reside upstream of the membrane fusion event. We propose that the differences in how coats segregate class C Vps/HOPS tethers to organelles and domains of metazoan cells are adaptations to complex architectures that characterize metazoan cells such as those of neuronal and epithelial tissues.

Notch signaling from the endosome requires a conserved dileucine motif

“…On the basis of our findings, we propose that the Notch dileucine motif is actively recognized by AP-3 on tubular early endosomes (Peden et al ., 2004), which in concert with HOPS (Angers and Merz, 2009; Salazar et al ., 2009; Zlatic et al ., 2011a, b), delivers Notch to the lysosome limiting membrane for signaling. This raises several interesting questions: What role does Notch signaling from the lysosome play in development and/or homeostasis?…”

CORVET and HOPS tethering complexes–coordinators of endosome and lysosome fusion

“…Metazoan HOPS has been extensively characterized in mammalian cells, Drosophila and Caenorhabditis elegans, whereas specific information on metazoan CORVET is still fragmentary (reviewed by Fairn and Grinstein, 2012;Pols et al, 2012;Zlatic et al, 2011b;Solinger et al, 2013). As metazoan cells have evolved additional isoforms of subunits, we consider it a major challenge to decipher from the literature which analyzed reactions indeed require metazoan HOPS and which might depend instead on the admittedly poorly described metazoan CORVET.…”

Inhibitory effect of SPE‐39 due to tyrosine phosphorylation and ubiquitination on the function of Vps33B in the EGF‐stimulated cells

“…This is in part because the levels of E-cadherin at the adherens junctions and the level of CEACAM5 at the apical membrane protein are regulated by Vps33B and SPE-39. Reducing the expression of each protein by knockdown or knockout induced degradation of the apical membrane protein, because of its mis-sorting to basolateral membranes and into the late endosomes and lysosomes [7]. For proper maintenance of this pathway, the expression levels of each protein must be correctly regulated.…”

“…An anti-SPE-39 rabbit polyclonal antibody was raised against peptides having an additional cysteine residue at the N-terminal end of the SPE-39 amino acid sequence, KGDEEEYWNSSKF (amino acids [5][6][7][8][9][10][11][12][13][14][15][16][17]. The peptides were coupled to keyhole limpet hemocyanin and used to immunize rabbits.…”

“…The human ortholog of SPE-39 (hSPE-39) is also known to associate with both subtypes of Vps33A and Vps33B in mammalian cells [4,7]. Furthermore, other research groups found hSPE-39 mutations, but not Vps33B mutations in individuals with ARC.…”