Group A Streptococcus exploits human plasminogen for bacterial translocation across epithelial barrier via tricellular tight junctions

Tomoko Sumitomo,Miharu Higashino,Shigetada Kawabata,Masanobu Nakata,Masaya Yamaguchi

doi:10.1038/srep20069

Abstract

Group A Streptococcus (GAS) is a human-specific pathogen responsible for local suppurative and life-threatening invasive systemic diseases. Interaction of GAS with human plasminogen (PLG) is a salient characteristic for promoting their systemic dissemination. In the present study, a serotype M28 strain was found predominantly localized in tricellular tight junctions of epithelial cells cultured in the presence of PLG. Several lines of evidence indicated that interaction of PLG with tricellulin, a major component of tricellular tight junctions, is crucial for bacterial localization. A site-directed mutagenesis approach revealed that lysine residues at positions 217 and 252 within the extracellular loop of tricellulin play important roles in PLG-binding activity. Additionally, we demonstrated that PLG functions as a molecular bridge between tricellulin and streptococcal surface enolase (SEN). The wild type strain efficiently translocated across the epithelial monolayer, accompanied by cleavage of transmembrane junctional proteins. In contrast, amino acid substitutions in the PLG-binding motif of SEN markedly compromised those activities. Notably, the interaction of PLG with SEN was dependent on PLG species specificity, which influenced the efficiency of bacterial penetration. Our findings provide insight into the mechanism by which GAS exploits host PLG for acceleration of bacterial invasion into deeper tissues via tricellular tight junctions.

Highlights

IntroductionSeveral GAS surface proteins act as PLG receptors and play crucial roles in the initial stage of severe invasive GAS infection[12]
PLG had no effect on bacterial adherence to Caco-2 cells (Supplementary Fig. 1), GAS was prone to be localized at tTJs labeled with anti-tricellulin
GAS is able to acquire host PLG to the bacterial surface, which is known to play a crucial role in firm adherence to host epithelial cells[13]

Summary

Introduction

Several GAS surface proteins act as PLG receptors and play crucial roles in the initial stage of severe invasive GAS infection[12]. Interactions of PLG with surface-exposed GAS receptors are mediated by lysine-binding sites within the kringle domains. Pancholi et al reported that PLG is a determinant for pericellular invasion of GAS into human pharyngeal cells[13]. On the basis of their report and our previous findings, we postulated that a PLG-mediated interplay between GAS and tTJs components is involved in the paracellular tropism of bacterial tissue invasion. Our findings indicate that PLG functions as a molecular bridge between tricellulin and streptococcal surface enolase (SEN), the principal PLG-binding protein of GAS. Data in the present study imply that GAS exploits the PLG-binding properties of tricellulin to translocate via tTJs of the epithelial barrier

Methods

Results

Conclusion