Subverted transferrin trafficking in Leishmania-?infected macrophages |
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Authors: | Valéria M Borges Marcos A Vannier-Santos Wanderley de Souza |
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Institution: | Laboratório de Ultraestrutura Celular Hertha Meyer, Programa de Biologia Celular e Parasitologia, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, CCS, Bl. G, Ilha do Fund?o 21949-900, Rio de Janeiro, Brasil e-mail: wsouza@ibccf.biof.ufrj.br, Fax: +55-21-2602364,
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Abstract: | The intracellular fate of human transferrin (HTf) in macrophages infected by Leishmania was investigated. Binding of HTf-gold complexes at 4 °C was competitively inhibited by native holoHTf but not by apoHTf.
Infected and uninfected macrophages displayed rather distinct HTf trafficking. Pulse-chase experiments using uninfected macrophages
loaded with 15-nm gold-conjugated bovine serum albumin (BSA) and then incubated with 5-nm gold-conjugated HTf revealed a remarkable
segregation of these tracers in distinct compartments. Nevertheless, Leishmania-infected macrophages presented extensive particle colocalization at both 60 min and 18 h. Light and electron microscopy immunolabeling
indicated that HTf was delivered to the parasitophorous vacuole, formed patches on the amastigote surface, and was endocytosed
via the flagellar pocket. Double-staining assays showed the colocalization of biotinylated HTf and its receptor in association
with the parasitophorous vacuole. To approach the Tf-binding sites of amastigotes we performed HTf-fluorescein isothiocyanate
(FITC) assays. Staining was diffuse at 4 °C and punctate at 35 °C, and only the former was sensitive to ethidium bromide,
indicating an eventual temperature-dependent endocytic process. Within parasites, HTf was found in cysteine-proteinase-rich
structures, suggesting that the protein can be endocytosed by intracellular amastigotes and sorted to the parasite endosomal-lysosomal
compartments rather than being recycled. The treatment of infected macrophages with holoHTf, but not apoHTf, promoted the
parasite's intracellular survival. These results suggest that Leishmania amastigotes can exploit and subvert the host-cell endocytic system and indicate the role of Tf-carried iron in the outcome
of leishmanial infection.
Received: 20 May 1998 / Accepted: 18 June 1998 |
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