Purified Streptococcus pneumoniae Endopeptidase O (PepO) Enhances Particle Uptake by Macrophages in a Toll-Like Receptor 2- and miR-155-Dependent Manner

Abstract

Insights into the host-microbial virulence factor interaction, especially the immune signaling mechanisms, could provide novel prevention and treatment options for pneumococcal diseases. Streptococcus pneumoniae endopeptidase O (PepO) is a newly discovered and ubiquitously expressed pneumococcal virulence protein. A PepO-mutant strain showed impaired adherence to and invasion of host cells compared with the isogenic wild-type strain. It is still unknown whether PepO is involved in the host defense response to pneumococcal infection. Here, we demonstrated that PepO could enhance phagocytosis of Streptococcus pneumoniae and Staphylococcus aureus by peritoneal exudate macrophages (PEMs). Further studies showed that PepO stimulation upregulated the expression of microRNA-155 (miR-155) in PEMs in a time-and dose-dependent manner. PepO-induced enhanced phagocytosis was decreased in cells transfected with an inhibitor of miR-155, while it was increased in cells transfected with a mimic of miR-155. We also revealed that PepO-induced upregulation of miR-155 in PEMs was mediated by Toll-like receptor 2 (TLR2)-NF-B signaling and that the increased expression of miR-155 downregulated expression of SHIP1. Taken together, these results indicate that PepO induces upregulation of miR-155 in PEMs, contributing to enhanced phagocytosis and host defense response to pneumococci and Staphylococcus aureus.

Streptococcus pneumoniae Endopeptidase O Promotes the Clearance of Staphylococcus aureus and Streptococcus pneumoniae via SH2 Domain-Containing Inositol Phosphatase 1-Mediated Complement Receptor 3 Upregulation

“…Our previous study has proven that PepO stimulation leads to the down regulation of SHIP1 in macrophages (Yao et al, 2017 ). It is still unclear that whether the down regulation of SHIP1 mediates the enhanced phagocytosis of S. aureus and S. pneumoniae by PepO-stimulated macrophages.…”

“…Preparation of PepO protein has been described in details previously (Yao et al, 2017 ). The Ni 2+ -charged column chromatograph used for PepO purification was purchased from GE Healthcare (Buckinghamshire, United Kingdom).…”

“…on the down regulation of SHIP1 and the up regulation of CR3 (Yao et al, 2017). To determine whether the enhanced clearance of S. aureus and D39 in PepO-treated mice is associated with SHIP1 and CR3, we detected the expression of SHIP1 and CR3 in cells from bronchoalveolar lavage fluids.…”

“…Streptococcus pneumoniae endopeptidase O (PepO) is a ubiquitously expressed pneumococcal virulence protein (Agarwal et al, 2013 ). Our previous work has proven that PepO enhances the phagocytic function of macrophages in a miR-155 dependent manner (Yao et al, 2017 ), and macrophages play an important role in the clearance of respiratory pathogens (Lovewell et al, 2014 ; Byrne et al, 2015 ; Eichinger et al, 2015 ; Lemon et al, 2015 ), indicating that PepO may protect against respiratory pathogens partially through immunomodulation. Even so, the exact molecular mechanisms involved in this process are still unclear.…”

Streptococcus pneumoniae evades host cell phagocytosis and limits host mortality through its cell wall anchoring protein PfbA

“…Human macrophages challenged with S. pneumoniae induce a negative feedback loop, preventing excessive inflammation via miR-146a and potentially other miRNAs on the TLR2-MyD88 axis (50). On the other hand, pneumococcal endopeptidase O enhances macrophage phagocytosis in a TLR2- and miR-155-dependent manner (58). Furthermore, miR-9 is induced by TLR agonists and functions in feedback control of the NF-κB-dependent responses in human monocytes and neutrophils (59).…”