Arrested maturation ofNeisseria-containing phagosomes in the absence of the lysosome-associated membrane proteins, LAMP-1 and LAMP-2

Abstract

SummaryMature, microbicidal phagosomes are rich in the lysosome-associated membrane proteins, LAMP-1 and LAMP-2, two highly glycosylated proteins presumed to form a protective barrier lining the phagosomal membrane. Pathogenic Neisseria secrete a protease that selectively cleaves LAMP-1, suggesting a critical role for LAMP proteins in the microbicidal competence of phagosomes. To determine the requirement for LAMP proteins in bacterial phagocytosis, we employed embryonic fibroblasts isolated from knockout mice lacking lamp-1, lamp-2 or both genes, as well as small interfering RNA (siRNA)-mediated knockdown of LAMP expression in a human epithelial cell line. Like wild-type cells, those lacking either LAMP-1 or LAMP-2 alone formed phagosomes that gradually acquired microbicidal activity and curtailed bacterial growth. In contrast, LAMP-1 and LAMP-2 double-deficient fibroblasts failed to kill engulfed Neisseria gonorrhoeae. In these cells, maturation was arrested prior to the acquisition of Rab7. As a result, the Rab7-interacting lysosomal protein (RILP, a Rab7 effector) was not recruited to the phagosomes, which were consequently unable to undergo dynein/dynactin-mediated centripetal displacement along microtubules and remained in a predominantly peripheral location. The inability of such phagosomes to migrate towards lysosomes likely contributed to their incomplete maturation and inability to eliminate bacteria. These findings suggest that neisserial degradation of LAMP-1 is not sufficient to affect its survival within the phagosome, and establish LAMP proteins as critical components in the process whereby phagosomes acquire microbicidal capabilities.

Impaired Phagosomal Maturation in Neutrophils Leads to Periodontitis in Lysosomal-Associated Membrane Protein-2 Knockout Mice

“…We could also recently show that phagosomal maturation is not affected in LAMP-1-or LAMP-2-deficient macrophages (14,26).…”

Autophagy, and BiP level decrease are early key events in retrograde degeneration of motoneurons

“…Therefore, we analyzed by immunohistochemistry the distribution of a 110-kDa lysosomal membrane glycoprotein (Lamp-1), which has been reported to be essential for the correct fusion with the autophagosome. 33 Control animals revealed a weak immunostaining for Lamp-1, indicating basal lysosomal traffic (Figure 7). At 3 days after root avulsion, the Lamp-1 immunostaining increased substantially in MNs after both types of injury.…”

Synaptotagmin XI Regulates Phagocytosis and Cytokine Secretion in Macrophages

“…As phagosomes mature, they become highly acidic and acquire a panoply of highly microbicidal molecules, such as cathepsins and other acid hydrolases (8). Late phagosomes acquire markers such as the lysosomal-associated membrane proteins (LAMP)-1 and -2, which are required for acquisition of Rab7 (9) and of microbicidal properties (10). Crucial to the killing of many intracellular pathogens is the generation of reactive oxygen species (ROS) in the phagosome, which is produced mostly by the NADPH oxidase 2 complex (NOX2) (11,12) and mitochondria (13).…”