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

Yansong Xue,Carolyn J Hovde,Haiqing Sheng,Mei-Jun Zhu,Min Du

doi:10.1038/cddiscovery.2017.55

Yansong Xue, Carolyn J Hovde + Show 3 more

Open Access

https://doi.org/10.1038/cddiscovery.2017.55

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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.

Highlights

Autophagy is a crucial process for degrading intracellular proteins and organelles[1] and, recently, it is recognized as a critical selfdefense mechanism to microbial infection.[2]
We found that EDL993 Δtir mutant strain was not able to suppress extracellular signal-regulated kinase 1/2 (ERK1/2) signaling in HT-29 cells upon infection; neither was EDL993 WT able to suppress ERK1/2 signaling in HT-29 cells treated with protein kinase A (PKA) inhibitor, showing that the abrogated ERK1/2 activation was associated with E. coli O157:H7 Tir-induced PKA activation and autophagy inhibition
Autophagy plays an important role in host defense against bacterial infection; in this study, we demonstrate that E. coli O157:H7 has evolved strategies to block host autophagic response partially via activation of PKA

Summary

Introduction

Autophagy is a crucial process for degrading intracellular proteins and organelles[1] and, recently, it is recognized as a critical selfdefense mechanism to microbial infection.[2]. Invasive pathogens have evolved different mechanisms to evade the trap by autophagy. Listeria monocytogenes and Shigella flexneri can escape autophagic capture by blocking the recruitment of autophagic proteins such as Beclin[1] and Atg[7] and subsequently inhibiting the maturation of the phagosomes.[4,5] On the other hand, autophagic vacuole may be utilized by pathogens as a shelter that protects the invading microorganisms from lysis and facilitates their growth inside the host cells.[6] Porphyromonas gingivalis can replicate in vacuoles by degrading autophagic proteins into amino acids that serve as nutritional sources.[7]

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