Enteropathogenic E. coli effector Map regulates the depletion of the tight junction proteins occludin and claudin-4 via cathepsin B and Rab13-mediated mechanisms

Infections by Enteropathogenic E. coli (EPEC) cause acute diarrheal disease in infants accounting for severe morbidity and mortality. One of the underlying causes of the disease is the break-down of the intestinal barrier maintained by the tight junctions (TJs). EPEC uses a type 3 secretion system to translocate more than twenty 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 and cause the leakage of charged ions and uncharged molecules through the barrier. We have reported earlier 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 EPEC effector Map modulates the lysosomal protease, cathepsin B to deplete claudins and occludin. Expression of mutant Map proteins that lacked the mitochondrial targeting sequence (MTS) completely restored the total levels of occludin and its localization at the TJs and partially restored claudin-4 levels and its junctional localization. We also identified a novel interaction of Map with the GTPase Rab13. As Rab13 has been reported to mediate the recycling of occludin to the plasma membrane, its interaction with Map has important implications for the loss of TJ integrity in EPEC pathogenesis. Occludin regulates the passage of water and uncharged solutes through TJs and Map may block its recycling to compromise the TJs thus causing excessive leakage through the barrier.