Escherichia coli O157:H7 suppresses host autophagy and promotes epithelial adhesion via Tir-mediated and cAMP-independent activation of protein kinase A

Abstract

Autophagy is a pivotal innate immune response that not only degrades cytosolic components, but also serves as one of the critical antimicrobial mechanisms eliminating intracellular pathogens. However, its role in host defense against extracellular pathogens is largely unknown. Here we showed that E. coli O157:H7 altered autophagy to evade host defense and facilitate adhesion. Enhancing host cell autophagy with tumor necrosis factor (TNF), host starvation or rapamycin reduced the adherence of E. coli O157:H7 to HT-29 cells. As a key regulator of autophagy, protein kinase A (PKA) was activated by E. coli O157:H7 infection. PKA inhibition by H89 abrogated E. coli O157:H7 inhibition of autophagy and prevented bacterial epithelial adhesion. Thus, PKA had a mediatory role in blocking autophagy and E. coli O157:H7 epithelial adhesion. Furthermore, deletion of translocated intimin receptor (tir) prevented PKA activation, whereas ectopic tir expression in a Δtir mutant strain restored its ability to activate PKA and inhibited autophagy in host cells. This indicated that Tir and PKA played pivotal roles in manipulating host autophagy during infection. Consistent with autophagy inhibition, E. coli O157:H7 infection inhibited endoplasmic reticulum (ER) stress in HT-29 cells, which was reversed by TNF, starvation, or H89 treatment. Additionally, E. coli O157:H7-induced PKA activation suppressed extracellular signal-regulated kinase 1/2 (ERK1/2) activation and enhanced phosphatidylinositol 3-kinase/Akt (PI3K/Akt) signaling, thereby repressing autophagic signaling. Conversely, PKA inhibition prevented downregulation of ERK1/2 signaling due to E. coli O157:H7 infection. In summary, E. coli O157:H7 inhibited host autophagy via Tir-mediated PKA activation that favored bacterial persistence on intestinal epithelial cell surfaces.

Suppressing autophagy: a strategy by Escherichia coli O157:H7 for its survival on host epithelial cells

“…We observed a robust PKA activation in response to E. coli O157:H7 infection but not in tir deletion mutant (Δ tir ) strain infected cells, indicating Tir mediated PKA activation. We further showed that PKA activation was essential for E. coli O157:H7-induced autophagy inhibition, blocking PKA abolished E. coli O157:H7 ability to inhibit autophagy 6 . Correspondingly, cholera toxin and edema toxin from Vibrio cholerae and Bacillus anthracis , respectively, induce PKA hyperactivation and reduce autophagosome formation 8 .…”

“…The ER stress sensor inositol-requiring enzyme 1α (IRE1α) is one of the mediators of UPR and has been implicated in ER stress-induced autophagy 11 . In our recent publication, upon E. coli O157:H7 infection, IRE1-α was decreased 6 , which may reduce autophagy-induced cell death and benefit bacterial survival. Accumulating studies have indicated that autophagy-induced cell death is a host strategy to inhibit bacterial replication.…”

“…1 ). E. coli O157:H7 infection inhibited autophagy activity in colonic epithelial cells, which was abolished by tir deletion and was further restored by complementary tir plasmid expression 6 .

Fig.

…”

“…Recent publications show that Shiga toxin serves as an autophagy inducer in immune cells and intestinal epithelial cells, likely through the induction of endoplasmic reticulum (ER) stress 4 , 5 ; Shiga toxin 2 induces DNA-damage-inducible transcript 3 (DDIT3) activation and Akt1 inactivation, further leading to autophagic cell death 4 . Our recent publication in Cell Death Discovery reported that E. coli O157:H7 subverted host autophagic response to promote epithelial adhesion, which was mediated by T3SS effector, Tir 6 (Fig. 1 ).…”

Lactobacillus johnsonii L531 Ameliorates Escherichia coli-Induced Cell Damage via Inhibiting NLRP3 Inflammasome Activity and Promoting ATG5/ATG16L1-Mediated Autophagy in Porcine Mammary Epithelial Cells

“…Given that pathogen infections represent one of the major threats to the health of animals and human beings, thus, autophagy pathway is necessary to outcome host-microbe interactions. For example, E. coli O157:H7 dampens autophagy via a Tir-dependent pathway mechanism while autophagy activation suppresses the adhesion of E. coli O157:H7 to intestinal epithelial cells [ 25 ]. Moreover, recent evidence highlighted the cross-talk between autophagy and NLRP3 inflammasome activation [ 26 ].…”