Caenorhabditis elegans HOPS and CCZ-1 mediate trafficking to lysosome-related organelles independently of RAB-7 and SAND-1

• Published in: Molecular biology of the cell 2014-04, Vol.25 (7), p.1073-1096
• Main Authors: Delahaye, Jared L, Foster, Olivia K, Vine, Annalise, Saxton, Daniel S, Curtin, Thomas P, Somhegyi, Hannah, Salesky, Rebecca, Hermann, Greg J
• Format: Article
• Language: English
• Subjects: Animals; Caenorhabditis elegans - cytology; Caenorhabditis elegans - embryology; Caenorhabditis elegans - metabolism; Caenorhabditis elegans Proteins - metabolism; Cytoplasmic Granules - metabolism; Embryo, Nonmammalian - cytology; Embryo, Nonmammalian - metabolism; Endosomes - metabolism; Fluorescence; Green Fluorescent Proteins - metabolism; Intestines - cytology; Intestines - embryology; Intestines - metabolism; Lysosomes - metabolism; Multiprotein Complexes - metabolism; Mutant Proteins - metabolism; Protein Transport; rab GTP-Binding Proteins - metabolism; Suppression, Genetic; Vesicular Transport Proteins - metabolism
• ISSN: 1059-1524; 1939-4586
• DOI: 10.1091/mbc.E13-09-0521

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.