EspFu-Mediated Actin Assembly Enhances Enteropathogenic Escherichia coli Adherence and Activates Host Cell Inflammatory Signaling Pathways

Abstract

The translocation of effectors into the host cell through type 3 secretion systems (T3SS) is a sophisticated strategy employed by pathogenic bacteria to subvert host responses and facilitate colonization. Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) utilize the Tir and EspFu (also known as TccP) effectors to remodel the host cytoskeleton, culminating in the formation of attaching and effacing (AE) lesions on enterocytes. While some EPEC strains require tyrosine phosphorylation of Tir and recruitment of the host Nck to trigger actin polymerization, EHEC and certain EPEC strains, whose Tir is not phosphorylated, rely on the effector EspFu for efficient actin remodeling. Here, we investigated the role played by Tir-Nck and Tir-EspFu actin polymerization pathways during the infection of epithelial cells, as well as the host transcriptional response to the AE lesion formation induced by EPEC. We found that EspFu-mediated actin assembly promotes bacterial attachment and epithelial colonization more efficiently than Tir-Nck. Moreover, we showed that both actin polymerization mechanisms can activate inflammatory pathways and reverse the anti-inflammatory response induced by EPEC in epithelial cells. However, this activity is remarkably more evident in infections with EspFu-expressing EPEC strains. This study demonstrates the complex interactions between effector-mediated actin remodeling and inflammation. Different strains carry different combinations of these two effectors, highlighting the plasticity of pathogenic E. coli enteric infections. IMPORTANCE EPEC is among the leading causes of diarrheal disease worldwide. The colonization of the gut mucosa by EPEC results in actin pedestal formation at the site of bacterial attachment. These pedestals are referred to as attaching and effacing (AE) lesions. Here, we exploit the different molecular mechanisms used by EPEC to induce AE lesions on epithelial cells, showing that the effector EspFu is associated with increased bacterial attachment and enhanced epithelial colonization compared to the Tir-Nck pathway. Moreover, we also showed that actin pedestal formation can counterbalance the anti-inflammatory activity induced by EPEC, especially when driven by EspFu. Collectively, our findings provide new insights into virulence mechanisms employed by EPEC to colonize epithelial cells, as well as the host response to this enteric pathogen.

Distribution of PDLIM1 at actin‐rich structures generated by invasive and adherent bacterial pathogens

“…Actin pedestal formation is further modulated by an array of additional injected bacterial effectors (Larzábal, Marques Da Silva, Riviere, & Cataldi, 2018; Singh, Davidson, Hume, & Koronakis, 2019; Tapia, Kralicek, & Hecht, 2020; Young et al, 2014). Interestingly, some EPEC strains utilize the injected effector EspFu to promote bacterial attachment and actin pedestal generation independently of the canonical Tir pathway (Campellone, Robbins, & Leong, 2004; Martins et al, 2020). Like L .…”

“…Actin pedestal formation is further modulated by an array of additional injected bacterial effectors (Larzábal, Marques Da Silva, Riviere, & Cataldi, 2018;Singh, Davidson, Hume, & Koronakis, 2019;Tapia, Kralicek, & Hecht, 2020;Young et al, 2014). Interestingly, some EPEC strains utilize the injected effector EspFu to promote bacterial attachment and actin pedestal generation independently of the canonical Tir pathway (Campellone, Robbins, & Leong, 2004;Martins et al, 2020). Like L. monocytogenes comet/rocket tails, EPEC pedestals are motile and propagate infection by enabling the attached bacteria to move (or "surf") across the top of the epithelium (Sanger, Chang, Ashton, Kaper, & Sanger, 1996;Velle & Campellone, 2017).…”

Shiga toxin remodels the intestinal epithelial transcriptional response to Enterohemorrhagic Escherichia coli

“…All serotypes share two primary virulence factors: the 'LEE' pathogenicity island that encodes a type III secretion system (T3SS), and prophages that encode one or more Shiga toxins [10]. The activities of EHEC's T3SS effector proteins mediate the pathogen's tight adherence to the colonic mucosa [11], and can promote or antagonize the inflammatory response in epithelial cells [12][13][14][15].…”

Shiga toxin remodels the intestinal epithelial transcriptional response to Enterohemorrhagic Escherichia coli

“…All serotypes classified as EHEC share two primary virulence factors: the 'LEE' pathogenicity island that encodes a type III secretion system (T3SS), and prophages that encode one or more Shiga toxins (12)(13)(14). The activities of EHEC's T3SS effector proteins mediate the pathogen's tight adherence to the colonic mucosa (15), and can promote or antagonize the inflammatory response in epithelial cells (16)(17)(18)(19)(20).…”