Dataset Information

Nucleolin, a shuttle protein promoting infection of human monocytes by Francisella tularensis.

ABSTRACT:

Background

Francisella tularensis is a highly virulent facultative intracellular bacterium, disseminating in vivo mainly within host mononuclear phagocytes. After entry into macrophages, F. tularensis initially resides in a phagosomal compartment, whose maturation is then arrested. Bacteria escape rapidly into the cytoplasm, where they replicate freely. We recently demonstrated that nucleolin, an eukaryotic protein able to traffic from the nucleus to the cell surface, acted as a surface receptor for F. tularensis LVS on human monocyte-like THP-1 cells.

Methodology/principal findings

Here, we followed the fate of nucleolin once F. tularensis has been endocytosed. We first confirmed by siRNA silencing experiments that expression of nucleolin protein was essential for binding of LVS on human macrophage-type THP-1 cells. We then showed that nucleolin co-localized with intracellular bacteria in the phagosomal compartment. Strikingly, in that compartment, nucleolin also co-localized with LAMP-1, a late endosomal marker. Co-immunoprecipation assays further demonstrated an interaction of nucleolin with LAMP-1. Co-localization of nucleolin with LVS was no longer detectable at 24 h when bacteria were multiplying in the cytoplasm. In contrast, with an iglC mutant of LVS, which remains trapped into the phagosomal compartment, or with inert particles, nucleolin/bacteria co-localization remained almost constant.

Conclusions/significance

We herein confirm the importance of nucleolin expression for LVS binding and its specificity as nucleolin is not involved in binding of another intracellular pathogen as L. monocytogenes or an inert particle. Association of nucleolin with F. tularensis during infection continues intracellularly after endocytosis of the bacteria. The present work therefore unravels for the first time the presence of nucleolin in the phagosomal compartment of macrophages.

SUBMITTER: Barel M

PROVIDER: S-EPMC2995743 | biostudies-literature | 2010 Dec

REPOSITORIES: biostudies-literature

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Publications

Nucleolin, a shuttle protein promoting infection of human monocytes by Francisella tularensis.

Barel Monique M Meibom Karin K Charbit Alain A

PloS one 20101201 12

<h4>Background</h4>Francisella tularensis is a highly virulent facultative intracellular bacterium, disseminating in vivo mainly within host mononuclear phagocytes. After entry into macrophages, F. tularensis initially resides in a phagosomal compartment, whose maturation is then arrested. Bacteria escape rapidly into the cytoplasm, where they replicate freely. We recently demonstrated that nucleolin, an eukaryotic protein able to traffic from the nucleus to the cell surface, acted as a surface ...[more]

PMID: 21152024

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Project description:The ?-proteobacterium Francisella tularensis causes seasonal tick-transmitted tularemia outbreaks in natural rabbit hosts and incidental infections in humans in the south-central United States. Although Dermacentor variabilis is considered a primary vector for F. tularensis, Amblyomma americanum is the most abundant tick species in this endemic region. A systematic study of F. tularensis colonization of A. americanum was undertaken to better understand its potential to serve as an overwintering reservoir for F. tularensis and as a bridging vector for human infections. Colony-reared A. americanum were artificially fed F. tularensis subspecies holarctica strain LVS via glass capillaries and colonization levels determined. Capillary-fed larva and nymph were initially infected with 10(4) CFU/tick which declined prior to molting for both stages, but rebounded post-molting in nymphs and persisted in 53% at 10(3) to 10(8) CFU/nymph at 168 days post-capillary feeding (longest sampling time in the study). In contrast, only 18% of adults molted from colonized nymphs maintained LVS colonization at 10(1) to 10(5) CFU/adult at 168 days post-capillary feeding (longest sampling time). For adults, LVS initially colonized the gut and disseminated to salivary glands by 24 h and had an ID50 of <5CFU in mice. Francisella tularensis infected the ovaries of gravid females, but transmission to eggs was infrequent and transovarial transmission to hatched larvae was not observed. The prolonged persistence of F. tularensis in A. americanum nymphs supports A. americanum as an overwintering reservoir for F. tularensis from which seasonal epizootics may originate; however, although the rapid dissemination of F. tularensis from gut to salivary glands in adults A. americanum is compatible with intermittent feeding adult males acting as bridging vectors for incidental F. tularensis infections of humans, acquisition of F. tularensis by adults may be unlikely based on adult feeding preference for larger mammals which are not involved in maintenance of sylvatic tularemia.

Dataset Information

Nucleolin, a shuttle protein promoting infection of human monocytes by Francisella tularensis.

Background

Methodology/principal findings

Conclusions/significance

Publications

Nucleolin, a shuttle protein promoting infection of human monocytes by Francisella tularensis.

Similar Datasets

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