Expression of Francisella pathogenicity island protein intracellular growth locus E (IglE) in mammalian cells is involved in intracellular trafficking, possibly through microtubule organizing center

Abstract

Francisella tularensis is the causative agent of the infectious disease tularemia and is designated a category A bioterrorism agent. The type VI secretion system encoded by the Francisella pathogenicity island (FPI) is necessary for intracellular growth; however, the functions of FPI proteins are largely unknown. In this study, we found that the FPI protein intracellular growth locus E (IglE) showed a unique localization pattern compared to other FPI proteins. Deleting iglE from Francisella tularensis subsp. novicida (F. novicida) decreased intracellular growth. Immunoprecipitation and pull-down assays revealed that IglE was associated with β-tubulin. Additionally, GFP-fused IglE colocalized with microtubule organizing centers (MTOCs) in 293T cells. The iglE deletion mutant was transferred with dynein toward MTOCs and packed into lysosome-localizing areas. Conversely, the wild-type F. novicida exhibited intracellular growth distant from MTOCs. In addition, IglE expressed in 293T cells colocalized with dynein. These results suggest that IglE helps to prevent dynein- and MTOC-mediated intracellular trafficking in host cells to inhibit the transport of F. novicida toward lysosomes.

Keywords: Francisella; MTOCs; type VI secretion system.