Huynh, K. K. et al. LAMP proteins are required for fusion of lysosomes with phagosomes. EMBO J. 26, 313-324

Division of Cell Biology, The Hospital for Sick Children, Toronto, Canada.
The EMBO Journal (Impact Factor: 10.43). 02/2007; 26(2):313-24. DOI: 10.1038/sj.emboj.7601511
Source: PubMed


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.

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    • "Maturation of the phagosome follows a series of orderly events; the small GTPase Rab5A regulates fusion with early endosomes (Bucci et al., 1992), while Rab7A regulates their interaction with late endosomes and lysosomes (Harrison et al., 2003). LAMP-1 and LAMP-2 are recruited at a stage between the interaction with early and late endosomes (Huynh et al., 2007) and were recruited appropriately to S. aureus-containing phagosomes . However, we observed that the phagosomes containing S. aureus had reduced levels of LIMP-II, a marker of fusion with lysosomes (Kuronita et al., 2002). "
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    • "Additionally, early endosome antigen 1 (Eea1), a Rab5 effector, is present in very early phagosomes but disappears rapidly during maturation of the organelle [7]. Late phagosomes acquire markers such as lysosomal-associated membrane protein (LAMP)-1 and LAMP-2, which are required for acquisition of Rab7 and microbicidal properties [8]. These markers are important for phagosome fusion and maturation. "
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