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November 2015


Recurrent urinary tract infections (UTIs) caused by uropathogenic E. coli (UPEC) are common and morbid infections with limited therapeutic options. Previous studies have demonstrated that persistent intracellular infection of bladder epithelial cells (BEC) by UPEC contributes to recurrent UTI in mouse models of infection. However, the mechanisms employed by UPEC to survive within BEC are incompletely understood. In this study we aimed to understand the role of host vesicular trafficking proteins in the intracellular survival of UPEC. Using a cell culture model of intracellular UPEC infection, we found that the small GTPase Rab35 facilitates UPEC survival in UPEC-containing vacuoles (UCV) within BEC. Rab35 plays a role in endosomal recycling of transferrin receptor (TfR), the key protein responsible for transferrin–mediated cellular iron uptake. UPEC enhance the expression of both Rab35 and TfR and recruit these proteins to the UCV, thereby supplying UPEC with the essential nutrient iron. Accordingly, Rab35 or TfR depleted cells showed significantly lower intracellular iron levels and reduced ability to support UPEC survival. In the absence of Rab35, UPEC are preferentially trafficked to degradative lysosomes and killed. Furthermore, in an in vivo murine model of persistent intracellular infection, Rab35 also colocalizes with intracellular UPEC. We propose a model in which UPEC subverts two different vesicular trafficking pathways (endosomal recycling and degradative lysosomal fusion) by modulating Rab35, thereby simultaneously enhancing iron acquisition and avoiding lysosomal degradation of the UCV within bladder epithelial cells. Our findings reveal a novel survival mechanism of intracellular UPEC and suggest a potential avenue for therapeutic intervention against recurrent UTI.


© 2015 Dikshit et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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VCU Microbiology and Immunology Publications

S1_Fig.tif (2181 kB)
A. Selective recruitment of Rab GTPases to UCV at 24 h post-infection.

S1_Table.xlsx (10 kB)
Sequences of primers used in the study.

S2_Fig.tif (2093 kB)
A. In vivo QIRs are positive for both LAMP1 and Rab35.

S3_Fig.tif (878 kB)
Iron is required for UPEC growth in the cell-free system.

S4_Fig.tif (1081 kB)
A. Transferrin receptor, but not Rab35 is required for the maintenance of labile iron pool (LIP) at 4 h post-UPEC infection.

S5_Fig.tif (169 kB)
Rab14 is not required for the survival of UPEC within BEC 5637.

S6_Fig.tif (994 kB)
LC3 colocalizes with UCV during intracellular infection of BEC.