NleH effectors interact with Bax inhibitor-1 to block apoptosis during enteropathogenic Escherichia coli infection

Abstract

The human pathogens enteropathogenic (EPEC) and enterohemorrhagic Escherichia coli and the related mouse pathogen Citrobacter rodentium subvert a variety of host cell signaling pathways via their plethora of type III secreted effectors, including triggering of an early apoptotic response. EPEC-infected cells do not develop late apoptotic symptoms, however. In this study we demonstrate that the NleH family effectors, homologs of the Shigella effector kinase OspG, blocks apoptosis. During EPEC infection, NleH effectors inhibit elevation of cytosolic Ca 2+ concentrations, nuclear condensation, caspase-3 activation, and membrane blebbing and promote cell survival. NleH1 alone is sufficient to prevent procaspase-3 cleavage induced by the proapoptotic compounds staurosporine, brefeldin A, and tunicamycin. Using C. rodentium, we found that NleH inhibits procaspase-3 cleavage at the bacterial attachment sites in vivo. A yeast two-hybrid screen identified the endoplasmic reticulum six-transmembrane protein Bax inhibitor-1 (BI-1) as an NleH-interacting partner. We mapped the NleH-binding site to the N-terminal 40 amino acids of BI-1. Knockdown of BI-1 resulted in the loss of NleH's antiapoptotic activity. These results indicate that NleH effectors are inhibitors of apoptosis that may act through BI-1 to carry out their cytoprotective function.Citrobacter rodentium | type 3 secretion system | enterohemorrhagic E. coli | OspG | Shigella

Infection strategies of enteric pathogenic Escherichia coli

“…182 The action of these pro-apoptotic effectors is balanced by the translocation of anti-apoptotic effectors such as NleH and NleD. NleH inhibits intrinsic apoptotic pathways via its direct interaction with the anti-apoptotic protein Bax inhibitor-1 (BI-1) 185 while NleD inactivates JNK leading to the suppression of the downstream transcription factor AP-1 which activates several proapoptotic proteins. 186 Additionally, other T3SS effectors indirectly contribute to the inhibition of apoptosis through their ability to promote host cell survival mechanisms.…”

Bax Inhibitor 1 in apoptosis and disease

“…Among the effector proteins, EPEC and EHEC inject into the cell are proteins called NleH. These proteins have recently been shown to bind BI-1 and to inhibit apoptosis for the benefit of the pathogen (Hemrajani et al, 2010). For example, NleH binds BI-1 and decreased the cytoplasmic Ca 2 þ released during infection, thereby blocking Ca 2 þ -mediated apoptotic signalling.…”

The Inflammatory Response during Enterohemorrhagic Escherichia coli Infection

“…Given the possible additional role of NleH in cell death signaling (117), the mechanism of action of NleH and its contribution to EPEC/EHEC pathogenesis warrant further investigation.…”