Specific Behavior of Intracellular Streptococcus pyogenes That Has Undergone Autophagic Degradation Is Associated with Bacterial Streptolysin O and Host Small G Proteins Rab5 and Rab7

Atsuo Sakurai,Shigeyuki Hamada,Seikou Shintani,Chihiro Aikawa,Junko Funao,Ichiro Nakagawa,Takashi Ooshima,Fumito Maruyama,Nobuo Okahashi,Takashi Nozawa

doi:10.1074/jbc.m109.100131

Abstract

Streptococcus pyogenes (group A streptococcus (GAS)) is a pathogen that invades non-phagocytic host cells, and causes a variety of acute infections such as pharyngitis. Our group previously reported that intracellular GAS is effectively degraded by the host-cell autophagic machinery, and that a cholesterol-dependent cytolysin, streptolysin O (SLO), is associated with bacterial escape from endosomes in epithelial cells. However, the details of both the intracellular behavior of GAS and the process leading to its autophagic degradation remain unknown. In this study, we found that two host small G proteins, Rab5 and Rab7, were associated with the pathway of autophagosome formation and the fate of intracellular GAS. Rab5 was involved in bacterial invasion and endosome fusion. Rab7 was clearly multifunctional, with roles in bacterial invasion, endosome maturation, and autophagosome formation. In addition, this study showed that the bacterial cytolysin SLO supported the escape of GAS into the cytoplasm from endosomes, and surprisingly, a SLO-deficient mutant of GAS was viable longer than the wild-type strain although it failed to escape the endosomes. This intracellular behavior of GAS is unique and distinct from that of other types of bacterial invaders. Our results provide a new picture of GAS infection and host-cell responses in epithelial cells.

Highlights

Streptococcus pyogenes (group A streptococcus (GAS)) is a pathogen that invades non-phagocytic host cells, and causes a variety of acute infections such as pharyngitis
It is known that streptolysin O (SLO) and LLO share 60% amino acid identity, and that their three-dimensional structures and inant-active; DN, dominant-negative; LC3, microtubule-associated protein 1 light chain 3; lysosome-associated membrane protein-1 (LAMP-1), lysosome associated membrane protein-1; PI, propidium iodide; PBS, phosphate-buffered saline
We examined the behavior of GAS within host epithelial cells prior to bacterial elimination by the autophagic pathway

Summary

Introduction

Streptococcus pyogenes (group A streptococcus (GAS)) is a pathogen that invades non-phagocytic host cells, and causes a variety of acute infections such as pharyngitis. Our group previously reported that intracellular GAS is effectively degraded by the host-cell autophagic machinery, and that a cholesterol-dependent cytolysin, streptolysin O (SLO), is associated with bacterial escape from endosomes in epithelial cells. This study showed that the bacterial cytolysin SLO supported the escape of GAS into the cytoplasm from endosomes, and surprisingly, a SLOdeficient mutant of GAS was viable longer than the wild-type strain it failed to escape the endosomes This intracellular behavior of GAS is unique and distinct from that of other types of bacterial invaders. The autophagic machinery is thought to act to remove these bacteria It is still unclear under what circumstances the intracellular bacteria are sequestered by autophagosomes and what events in the infected cells lead to the degradation of bacteria by autophagy. The influences of Rab and Rab should be analyzed in detail during GAS infection

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Conclusion