title: Caenorhabditis elegans HOPS and CCZ-1 mediate trafficking to lysosome-related organelles independently of RAB-7 and SAND-1.
abstract: As early endosomes mature, the SAND-1/CCZ-1 complex acts as a guanine nucleotide exchange factor (GEF) for RAB-7 to promote the activity of its effector, HOPS, which facilitates late endosome-lysosome fusion and the consumption of AP-3-containing vesicles. We show that CCZ-1 and the HOPS complex are essential for the biogenesis of gut granules, cell type-specific, lysosome-related organelles (LROs) that coexist with conventional lysosomes in Caenorhabditis elegans intestinal cells. The HOPS subunit VPS-18 promotes the trafficking of gut granule proteins away from lysosomes and functions downstream of or in parallel to the AP-3 adaptor. CCZ-1 also acts independently of AP-3, and ccz-1 mutants mistraffic gut granule proteins. Our results indicate that SAND-1 does not participate in the formation of gut granules. In the absence of RAB-7 activity, gut granules are generated; however, their size and protein composition are subtly altered. These observations suggest that CCZ-1 acts in partnership with a protein other than SAND-1 as a GEF for an alternate Rab to promote gut granule biogenesis. Point mutations in GLO-1, a Rab32/38-related protein, predicted to increase spontaneous guanine nucleotide exchange, specifically suppress the loss of gut granules by ccz-1 and glo-3 mutants. GLO-3 is known to be required for gut granule formation and has homology to SAND-1/Mon1-related proteins, suggesting that CCZ-1 functions with GLO-3 upstream of the GLO-1 Rab, possibly as a GLO-1 GEF. These results support LRO formation occurring via processes similar to conventional lysosome biogenesis, albeit with key molecular differences.
authors: Department of Biology, Lewis & Clark College, Portland, OR 97219 Program in Biochemistry and Molecular Biology, Lewis & Clark College, Portland, OR 97219.
authors: Jared L
authors: JL
authors: Delahaye
authors: Olivia K
authors: OK
authors: Foster
authors: Annalise
authors: A
authors: Vine
authors: Daniel S
authors: DS
authors: Saxton
authors: Thomas P
authors: TP
authors: Curtin
authors: Hannah
authors: H
authors: Somhegyi
authors: Rebecca
authors: R
authors: Salesky
authors: Greg J
authors: GJ
authors: Hermann
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D005453:Fluorescence; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000166:cytology / Q000196:embryology; D008247:Lysosomes / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D021381:Protein Transport; D013489:Suppression, Genetic; D033921:Vesicular Transport Proteins / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000378:metabolism*; D000090802:rab7 GTP-Binding Proteins
chemical_list: C549250:CCZ-1 protein, C elegans; D029742:Caenorhabditis elegans Proteins; D046912:Multiprotein Complexes; D050505:Mutant Proteins; C506114:SAND-1 protein, C elegans; D033921:Vesicular Transport Proteins; D000090802:rab7 GTP-Binding Proteins; D049452:Green Fluorescent Proteins; C000593038:RAB-7 protein, C elegans; D020691:rab GTP-Binding Proteins