Membranous complexes characteristic of melanocytes derived from patients with Hermansky-Pudlak syndrome type 1 are macroautophagosomal entities of the lysosomal compartment

Pigment Cell Res. 2005 Dec;18(6):417-26. doi: 10.1111/j.1600-0749.2005.00265.x.

Abstract

Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder resulting from mutations in a family of genes required for efficient transport of lysosomal-related proteins from the trans-Golgi network to a target organelle. To date, there are several genetically distinct forms of HPS. Many forms of HPS exhibit aberrant trafficking of melanosome-targeted proteins resulting in incomplete melanosome biogenesis responsible for oculocutaneous albinism observed in patients. In HPS-1, melanosome-targeted proteins are localized to characteristic membranous complexes, which have morphologic similarities to macroautophagosomes. In this report, we evaluated the hypothesis that HPS-1-specific membranous complexes comprise a component of the lysosomal compartment of melanocytes. Using indirect immunofluorescence, an increase in co-localization of misrouted tyrosinase with cathepsin-L, a lysosomal cysteine protease, occurred in HPS-1 melanocytes. In addition, ribophorin II, an integral endoplasmic reticulum protein that is also a component of macroautophagosomes, and LC3, a specific marker of macrophagosomes, demonstrated localization to membranous complexes in HPS-1 melanocytes. At the electron microscopic level, the membranous complexes exhibited acid phosphatase activity and localization of exogenously supplied horseradish peroxidase (HRP)-conjugated gold particles, indicating incorporation of lysosomal and endosomal components to membranous complexes, respectively. These results confirm that membranous complexes of HPS-1 melanocytes are macroautophagosomal representatives of the lysosomal compartment.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Acid Phosphatase / metabolism
  • Autophagy
  • Biopsy
  • Cathepsin L
  • Cathepsins / metabolism
  • Cell Membrane / metabolism*
  • Cell Membrane / ultrastructure
  • Cysteine Endopeptidases / metabolism
  • Endosomes / metabolism
  • Fluorescent Antibody Technique, Indirect
  • Gold / chemistry
  • Hermanski-Pudlak Syndrome / metabolism*
  • Hermanski-Pudlak Syndrome / pathology
  • Humans
  • Lysosomes / metabolism*
  • Melanocytes / metabolism*
  • Melanocytes / ultrastructure
  • Membrane Proteins / metabolism
  • Microtubule-Associated Proteins / metabolism
  • Monophenol Monooxygenase / metabolism
  • Phagosomes / metabolism*
  • Protein Transport
  • Skin / metabolism

Substances

  • MAP1LC3A protein, human
  • Membrane Proteins
  • Microtubule-Associated Proteins
  • ribophorin
  • Gold
  • Monophenol Monooxygenase
  • Acid Phosphatase
  • Cathepsins
  • Cysteine Endopeptidases
  • CTSL protein, human
  • Cathepsin L