Leishmania promastigotes require lipophosphoglycan to actively modulate the fusion properties of phagosomes at an early step of phagocytosis

Abstract

SummaryThe lipophosphoglycan (LPG) of Leishmania promastigotes plays key roles in parasite survival in both insect and mammalian hosts. Evidence suggests that LPG decreases phagosome fusion properties at the onset of infection in macrophages. The mechanisms of action of this molecule are, however, poorly understood. In the present study, we used a panoply of Leishmania mutants displaying modi®ed LPG structures to determine more precisely how LPG modulates phagosome±endosome fusion. Using an in vivo fusion assay measuring, at the electron microscope, the transfer of solute materials from endosomes to phagosomes, we provided further evidence that the repeating Gal(b1,4)Man(a1-PO 4 ) units of LPG are responsible for the alteration in phagosome fusion. The inhibitory effect of LPG on phagosome fusion was shown to be more potent towards late endocytic organelles and lysosomes than early endosomes, explaining how Leishmania promastigotes can avoid degradation in hydrolase-enriched compartments. The involvement of other repeating unit-containing molecules, including the secreted acid phosphatase, in the inhibition process was ruled out, as an LPG-defective mutant (lpg1 À ) which secretes repeating unit-containing glycoconjugates was present in highly fusogenic phagosomes. In L. major, oligosaccharide side-chains of LPG did not contribute to the inhibition process, as Spock, an L. major mutant lacking LPG side-chains, blocked fusion to the same extent as wild-type parasites. Finally, dead parasites internalized from the culture medium were not as ef®cient as live parasites in altering phagosome±endosome fusion, despite the presence of LPG. However, the killing of parasites with vital dyes after their sequestration in phagosomes had no effect on the fusion properties of this organelle. Collectively, these results suggest that living promastigotes displaying full-length cell surface LPG can actively in¯uence macrophages at an early stage of phagocytosis to generate phagosomes with poor fusogenic properties.

Erlin-1 and erlin-2 are novel members of the prohibitin family of proteins that define lipid-raft-like domains of the ER

“…Bars, 10 m. Salzer and Prohaska, 2001;Snyers et al, 1998). However, they differ in their subcellular distributions, which include the plasma membrane, phagosomes, lipid droplets, Golgi vesicles, mitochondria, the nucleus and now the ER (Dermine et al, 2000;Garin et al, 2001;Gkantiragas et al, 2001;Green et al, 2004;Morrow et al, 2002;Salzer and Prohaska, 2001;Tatsuta et al, 2005;Umlauf et al, 2004). Proteins with a PHB domain are highly conserved throughout evolution and are found within diverse kingdoms including those of plants, bacteria and animals (Morrow and Parton, 2005;Tavernarakis et al, 1999).…”

Biogenesis of Leishmania major -Harboring Vacuoles in Murine Dendritic Cells

“…These findings are reminiscent of the situation with macrophages, for which it has been demonstrated that promastigotes, unlike amastigotes, are located in phagosomes that poorly fuse with late endocytic/lysosomal compartments. This phenomenon could be linked to the stage-specific expression of lipophosphoglycan, the predominant surface glycoconjugate of promastigotes (8,9,19). The promastigote-containing phagosomes with low fusogenic activity were shown to display an impaired recruitment of Rab7 (29).…”

A critical role for lipophosphoglycan in proinflammatory responses of dendritic cells to Leishmania mexicana

“…LPG expression is thought to enhance resistance against toxic serum components such as complement [42][43][44], and in the case of L. donovani and L. major, LPG expression contributes to early promastigote survival in macrophages [45,46]. Upon infection the parasites quickly undergo metamorphosis from promastigotes to amastigotes, which depending on the species, express very little or no LPG [5].…”