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

Mol Biol Cell. 2014 Apr;25(7):1073-96. doi: 10.1091/mbc.E13-09-0521. Epub 2014 Feb 5.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • 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
  • Intestinal Mucosa / metabolism
  • Intestines / cytology
  • Intestines / embryology
  • Lysosomes / metabolism*
  • Multiprotein Complexes / metabolism*
  • Mutant Proteins / metabolism
  • Protein Transport
  • Suppression, Genetic
  • Vesicular Transport Proteins / metabolism*
  • rab GTP-Binding Proteins / metabolism*
  • rab7 GTP-Binding Proteins

Substances

  • CCZ-1 protein, C elegans
  • Caenorhabditis elegans Proteins
  • Multiprotein Complexes
  • Mutant Proteins
  • SAND-1 protein, C elegans
  • Vesicular Transport Proteins
  • rab7 GTP-Binding Proteins
  • Green Fluorescent Proteins
  • RAB-7 protein, C elegans
  • rab GTP-Binding Proteins