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

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.