HECT E3 Ubiquitin Ligase-Regulated Txnip Degradation Facilitates TLR2-Mediated Inflammation During Group A Streptococcal Infection.

Po-Chun Tseng,Chia-Ling Chen,Yee-Shin Lin,Chih-Feng Kuo,Chiou-Feng Lin,Jiunn-Jong Wu,Miao-Huei Cheng,Chih-Peng Chang,Shu-Wen Wan,Chi-Chen Huang

doi:10.3389/fimmu.2019.02147

Abstract

Thioredoxin-interacting protein (Txnip) inhibits the activity of thioredoxin (Trx) to modulate inflammatory responses. The burden of inflammation caused by microbial infection is strongly associated with disease severity; however, the role of Txnip in bacterial infection remains unclear. In Group A Streptococcus (GAS)-infected macrophages, Txnip was degraded independent of glucose consumption and streptococcal cysteine protease expression. Treatment with proteasome inhibitors reversed GAS-induced Txnip degradation. The activation of Toll-like receptor 2 (TLR2) initiated Txnip degradation, while no further Txnip degradation was observed in TLR2-deficient bone marrow-derived macrophages. NADPH oxidase-regulated NF-κB activation and pro-inflammatory activation were induced and accompanied by Txnip degradation during GAS infection. Silencing Txnip prompted TLR2-mediated inducible nitric oxide synthase (iNOS)/NO, TNF-α, and IL-6 production whereas the blockage of Txnip degradation by pharmacologically inhibiting the HECT E3 ubiquitin ligase with heclin and AMP-dependent protein kinase with dorsomorphin effectively reduced such effects. Our findings reveal that TLR2/NADPH oxidase-mediated Txnip proteasomal degradation facilitates pro-inflammatory cytokine production during GAS infection.

Highlights

Recognition of Toll-like receptors (TLRs), the most important pathogen recognition receptors expressed on innate immune cells, with pathogen-associated molecular patterns can rapidly initiate the coordinated activation of transcriptional factors and result in the effective expression of pro-inflammatory mediators [1]
Murine macrophage RAW264.7 cells were infected with different multiplicities of infection (MOIs) of Group A Streptococcus (GAS) for 1 h, and the protein expression of Thioredoxin-interacting protein (Txnip) was determined at different times post-infection
There were no significant differences of glucose consumption between non-infected and infected cells within 2 h post-infection, while Txnip had already been degraded in GAS infection (Figure 1C)

Summary

Introduction

Recognition of Toll-like receptors (TLRs), the most important pathogen recognition receptors expressed on innate immune cells, with pathogen-associated molecular patterns can rapidly initiate the coordinated activation of transcriptional factors and result in the effective expression of pro-inflammatory mediators [1]. Txnip Degradation in GAS Infection pro-inflammatory cytokines is mostly regulated by TLR-myeloid differentiation factor 88 (MyD88) signaling [2, 3]. Group A Streptococcus (GAS) infection causes various diseases ranging from mild pharyngitis and impetigo to severe necrotizing fasciitis and streptococcal toxic shock syndrome (STSS) [4]. In STSS, the excessive production of various cytokines is thought to be responsible for severe systemic effects, and serum levels of TNF-α and IL-6 show the highest correlation with disease severity [5, 6]. In addition to the proapoptotic role of Txnip under stress, it plays a crucial role in the induction of reactive oxygen species (ROS)-mediated NLRP3 inflammasomes whereby initiating inflammatory responses [12, 15, 16]

Methods

Results

Conclusion