Reprogramming of microRNA expression via E2F1 downregulation promotes Salmonella infection both in infected and bystander cells

Abstract

Cells infected with pathogens can contribute to clearing infections by releasing signals that instruct neighbouring cells to mount a pro-inflammatory cytokine response, or by other mechanisms that reduce bystander cells’ susceptibility to infection. Here, we show the opposite effect: epithelial cells infected with Salmonella Typhimurium secrete host factors that facilitate the infection of bystander cells. We find that the endoplasmic reticulum stress response is activated in both infected and bystander cells, and this leads to activation of JNK pathway, downregulation of transcription factor E2F1, and consequent reprogramming of microRNA expression in a time-dependent manner. These changes are not elicited by infection with other bacterial pathogens, such as Shigella flexneri or Listeria monocytogenes. Remarkably, the protein HMGB1 present in the secretome of Salmonella-infected cells is responsible for the activation of the IRE1 branch of the endoplasmic reticulum stress response in non-infected, neighbouring cells. Furthermore, E2F1 downregulation and the associated microRNA alterations promote Salmonella replication within infected cells and prime bystander cells for more efficient infection.

5’isomiR-183-5p|+2 elicits tumor suppressor activity in a negative feedback loop with E2F1

“…Along this line, we validated that the expression of mature miR-183 and its precursor pri-miR-183 was indeed regulated by E2F1. This is in line with recent miRNA sequencing data demonstrating a 60% decrease in expression of miR-183-5p upon knockdown of E2F1 in HeLa cells [ 58 ]. Of note, the oncogenic miRNAs miR-182 and miR-96 originating from the same primary transcript as miR-183 are coordinately downregulated by knockdown of E2F1 in this dataset.…”

Computational prediction and experimental validation of Salmonella Typhimurium SopE-mediated fine-tuning of autophagy in intestinal epithelial cells

“…Cross-talk between infected and uninfected neighbouring cells has previously been described for many bacterial or viral pathogens, for example through cytokines signalling (Milivojevic et al, 2017;Bost et al, 2020), or directly through uptake of pathogen effector proteins from infected to uninfected cells (Guidi et al, 2013). S. Typhimurium was also shown to cause a reprogramming of microRNAs in infected cells, affecting also bystander cells (Aguilar et al, 2021). Endoplasmic reticulum stress response is activated in bystander cells, affecting many genes' expression; in particular downregulating key transcription factors, such as E2F1.…”

“…S . Typhimurium was also shown to cause a reprogramming of microRNAs in infected cells, affecting also bystander cells ( Aguilar et al., 2021 ). Endoplasmic reticulum stress response is activated in bystander cells, affecting many genes’ expression; in particular downregulating key transcription factors, such as E2F1.…”

Study of microRNA expression in Salmonella Typhimurium-infected porcine ileum reveals miR-194a-5p as an important regulator of the TLR4-mediated inflammatory response

“…For example, let-7i-3p is downregulated in porcine ileum, and has been shown to control Salmonella adhesion and intracellular replication [ 8 ]; also, miR-15a-5p, miR-15b-5p, miR-22, miR-16-5p, miR-421, miR-744 and let-7i-5p (E2F1-dependent miRNAs) were downregulated in S . Typhimurium infected porcine ileum and colon, promoting bacterial replication [ 9 ].…”

“…Previous studies have shown that microRNAs (miRNAs), which are conserved small non-coding post-transcriptional regulators of gene expression [ 5 ], modulate the development and function of immune cells and can have pro- or anti-inflammatory effects during bacterial infections [ 6 , 7 ]. The regulation of the transcriptional response by miRNAs in Salmonella infection is still mostly unclear, but several miRNAs such as let-7i or miR-15 have been shown to modulate certain host immune functions [ 8 , 9 ]. In a previous study, we described the transcriptomic response in the porcine ileum 2 days after infection with S .…”