LAMP Proteins Are Required for Fusion of Lysosomes With Phagosomes

EMBO J. 2007 Jan 24;26(2):313-24. doi: 10.1038/sj.emboj.7601511.

Abstract

Lysosome-associated membrane proteins 1 and 2 (LAMP-1 and LAMP-2) are delivered to phagosomes during the maturation process. We used cells from LAMP-deficient mice to analyze the role of these proteins in phagosome maturation. Macrophages from LAMP-1- or LAMP-2-deficient mice displayed normal fusion of lysosomes with phagosomes. Because ablation of both the lamp-1 and lamp-2 genes yields an embryonic-lethal phenotype, we were unable to study macrophages from double knockouts. Instead, we reconstituted phagocytosis in murine embryonic fibroblasts (MEFs) by transfection of FcgammaIIA receptors. Phagosomes formed by FcgammaIIA-transfected MEFs obtained from LAMP-1- or LAMP-2- deficient mice acquired lysosomal markers. Remarkably, although FcgammaIIA-transfected MEFs from double-deficient mice ingested particles normally, phagosomal maturation was arrested. LAMP-1 and LAMP-2 double-deficient phagosomes acquired Rab5 and accumulated phosphatidylinositol 3-phosphate, but failed to recruit Rab7 and did not fuse with lysosomes. We attribute the deficiency to impaired organellar motility along microtubules. Time-lapse cinematography revealed that late endosomes/lysosomes as well as phagosomes lacking LAMP-1 and LAMP-2 had reduced ability to move toward the microtubule-organizing center, likely precluding their interaction with each other.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cells, Cultured
  • Lysosomal-Associated Membrane Protein 2 / genetics
  • Lysosomal-Associated Membrane Protein 2 / physiology
  • Lysosome-Associated Membrane Glycoproteins / genetics
  • Lysosome-Associated Membrane Glycoproteins / physiology*
  • Lysosomes / metabolism
  • Lysosomes / physiology*
  • Macrophages / physiology
  • Macrophages / ultrastructure
  • Membrane Fusion*
  • Mice
  • Mice, Knockout
  • Models, Biological
  • Phagocytosis / genetics
  • Phagosomes / metabolism
  • Phagosomes / physiology*
  • Transfection
  • rab GTP-Binding Proteins / metabolism

Substances

  • Lamp1 protein, mouse
  • Lysosomal-Associated Membrane Protein 2
  • Lysosome-Associated Membrane Glycoproteins
  • rab7 protein
  • rab GTP-Binding Proteins