engleski

The many ways of Francisella intracellular trafficking

The F. tularensis-containing phagosome (FCP) matures to a late endosome-like phagosome prior to bacterial escape into the cytosol of human macrophages. It is not known whether the FCP acquires the vATPase proton pump and becomes acidified prior to bacteria escape into the cytosol. We have utilized a fluorescence microscopy-based phagosome integrity assay for differential labeling of vacuolar vs. cytosolic bacteria using anti-bacterial antibodies loaded into the cytosol of live primary human monocyte-derived macrophages (hMDMs). Our data show that within the first 15 min post-infection, ~90% of the FCPs acquire the proton vATPase pump and the lysomotropic dye, LysoTracker, which concentrates in acidic vesicles, similar to the Listeria monocytogenes control. Acquisition of the proton vATPase pump and the lysomotropic dye is gradually lost by 30-60 min post-infection, which coincides with bacterial escape into the cytosol of hMDMs. When the iglD mutant-containing phagosomes were examined, our data showed that ~80% of them acquired the proton vATPase pump by 15 min post-infection, followed by a rapid decrease to ~ 40% at 30 min after infection, consistent with rapid escape of this mutant into the cytosol. In contrast, 85% of the iglC mutant-containing phagosomes, which fuse to lysosomes, persistenly acquired and retained the proton vATPase pump at 15-60 min. Importantly, specific inhibition of the proton vATPase pump blocks escape of the wild type strain of F. tularensis and the iglD mutant into the cytosol of hMDMs, similar to L. monocytogenes. Therefore, within few minutes of its biogenesis, the FCP rapidly acquires the proton vATPase pump and becomes acidified, and this acidification is essential for subsequent bacterial escape into the macrophage cytosol.

Trafficking; Francisella; vATPase

nije evidentirano