# Enteropathogenic E. coli effector Map interacts with Rab13 and regulates the depletion of the tight junction proteins occludin and claudins via cathepsin B-mediated mechanisms

## TL;DR

This study shows how a protein from a harmful E. coli strain breaks down intestinal barriers, leading to diarrhea in infants.

## Contribution

The paper reveals a new interaction between the EPEC effector Map and Rab13, and identifies cathepsin B as a key player in tight junction protein depletion.

## Key findings

- Inhibiting cathepsin B reduces the depletion of claudin-1, claudin-4, and occludin caused by the Map effector.
- A mutant Map lacking the mitochondrial targeting sequence partially prevents occludin and claudin-4 depletion.
- Map interacts with Rab13, which is involved in occludin recycling and intestinal barrier integrity.

## Abstract

Infections by enteropathogenic Escherichia coli (EPEC) cause acute diarrheal disease in infants accounting for severe morbidity and mortality. One of the underlying causes of the disease is the breakdown of the intestinal barrier maintained by the tight junctions (TJs). EPEC uses a type 3 secretion system to translocate more than 20 effectors into infected cells, which disrupt several functions of the host cells. The effectors EspF, Map, EspG1/G2 and NleA have been reported to disrupt the TJs causing the leakage of charged ions and uncharged molecules through the barrier. We have previously reported that EspF and Map cause the depletion of TJ proteins claudin-1, claudin-4 and occludin through both transcriptional and post-transcriptional mechanisms. Here, we show that the inhibition of the lysosomal protease cathepsin B, in cells expressing the EPEC effector Map, reduces the depletion of claudin-1, claudin-4 and occludin. Further, we show that the expression of a mutant Map protein lacking the mitochondrial targeting sequence inhibits the depletion of occludin and its delocalization from the TJs and partially rescues claudin-4 levels and its junctional localization. We also identified a novel interaction of Map with the GTPase Rab13. Rab13 has been reported to mediate the recycling of occludin to the plasma membrane. Since occludin regulates the passage of macromolecules through the intestinal TJ barrier, the interaction of Map with Rab13 may have important implications for the loss of TJ integrity and excessive leakage through the intestinal barrier in EPEC pathogenesis.

Summary: Enteropathogenic E. coli infection causes acute diarrheal disease in infants. This paper shows that the EPEC effector Map interacts with the recycling endosome marker Rab13 and disrupts the intestinal barrier by cathepsin B-mediated depletion of tight junction proteins.