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The DnaJ-domain protein RME-8 functions in endosomal trafficking

Martine Girard1, Viviane Poupon, Francois Blondeau

  • 1Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal QC H3A 2B4, Canada.

The Journal of Biological Chemistry
|September 24, 2005
PubMed

Insights

Researchers identified the RME-8 protein, a DnaJ co-chaperone, involved in mammalian endosomal trafficking. Knockdown of RME-8 affects epidermal growth factor uptake and lysosomal protein sorting.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Protein Biochemistry

Background:

  • Receptor-mediated endocytosis is crucial for cellular uptake of various molecules.
  • DnaJ domain proteins are known molecular chaperones involved in protein folding and trafficking.
  • The endosomal system plays a key role in sorting and directing internalized cargo to their destinations.

Purpose of the Study:

  • To identify and characterize the mammalian homolog of Caenorhabditis elegans RME-8.
  • To investigate the function of mammalian RME-8 in intracellular trafficking pathways.
  • To determine the role of RME-8 as a co-chaperone in endosomal protein regulation.

Main Methods:

  • Proteomic analysis of clathrin-coated vesicles from rat liver.
  • Affinity selection assays to identify binding partners.
  • Small interfering RNA (siRNA)-mediated knockdown of RME-8.
  • Confocal microscopy to assess co-localization with endosomal markers.
  • Analysis of transferrin, epidermal growth factor, cation-independent mannose 6-phosphate receptor, and cathepsin D trafficking.

Main Results:

  • Mammalian RME-8, a DnaJ domain-containing protein, was identified and found to have broad tissue distribution.
  • Hsc70 was identified as the major binding partner for RME-8's DnaJ domain.
  • RME-8 is associated with microsomal membranes and co-localizes with endosomal markers.
  • RME-8 knockdown reduced epidermal growth factor internalization and altered trafficking of the cation-independent mannose 6-phosphate receptor and cathepsin D.
  • Transferrin endocytosis was unaffected by RME-8 knockdown.

Conclusions:

  • Mammalian RME-8 functions in intracellular trafficking, particularly within the endosomal system.
  • RME-8 acts as a DnaJ domain-bearing co-chaperone on endosomes, influencing the trafficking of specific receptors and lysosomal enzymes.
  • This study provides the first evidence for a functional role of a DnaJ co-chaperone in endosomal protein sorting and trafficking.

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