Role of AP1 and Gadkin in the traffic of secretory endo-lysosomes

Mol Biol Cell. 2011 Jun 15;22(12):2068-82. doi: 10.1091/mbc.E11-03-0193. Epub 2011 Apr 27.

Abstract

Whereas lysosome-related organelles (LRO) of specialized cells display both exocytic and endocytic features, lysosomes in nonspecialized cells can also acquire the property to fuse with the plasma membrane upon an acute rise in cytosolic calcium. Here, we characterize this unconventional secretory pathway in fibroblast-like cells, by monitoring the appearance of Lamp1 on the plasma membrane and the release of lysosomal enzymes into the medium. After sequential ablation of endocytic compartments in living cells, we find that donor membranes primarily derive from a late compartment, but that an early compartment is also involved. Strikingly, this endo-secretory process is not affected by treatments that inhibit endosome dynamics (microtubule depolymerization, cholesterol accumulation, overexpression of Rab7 or its effector Rab-interacting lysosomal protein [RILP], overexpression of Rab5 mutants), but depends on Rab27a, a GTPase involved in LRO secretion, and is controlled by F-actin. Moreover, we find that this unconventional endo-secretory pathway requires the adaptor protein complexes AP1, Gadkin (which recruits AP1 by binding to the γ1 subunit), and AP2, but not AP3. We conclude that a specific fraction of the AP2-derived endocytic pathway is dedicated to secretory purposes under the control of AP1 and Gadkin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / immunology
  • Actins / metabolism
  • Adaptor Protein Complex 1 / metabolism*
  • Animals
  • Biological Transport
  • Cricetinae
  • Cytosol / metabolism
  • Endocytosis
  • Endosomes / metabolism*
  • Exocytosis
  • Fibroblasts / metabolism
  • Hexosaminidases / metabolism
  • Humans
  • Lysosomal Membrane Proteins / immunology
  • Lysosomal Membrane Proteins / metabolism
  • Lysosomes / metabolism*
  • Membrane Proteins / metabolism*
  • RNA Interference
  • rab GTP-Binding Proteins / metabolism
  • rab27 GTP-Binding Proteins

Substances

  • AP1AR protein, human
  • Actins
  • Adaptor Protein Complex 1
  • LAMP1 protein, human
  • Lysosomal Membrane Proteins
  • Membrane Proteins
  • rab27 GTP-Binding Proteins
  • Hexosaminidases
  • RAB27A protein, human
  • rab GTP-Binding Proteins