Bartonella type IV secretion effector BepC induces stress fiber formation through activation of GEF-H1

Chunyan Wang,Congli Yuan,Yuhao Cai,Tianyun Ding,Xiaoyun Liu,Meng Wang,Jiaqi Fu,Haoran Zhang,Jane E Koehler,Jiezhang Jiang,Zhao-Qing Luo

doi:10.1371/journal.ppat.1009065

Abstract

Bartonella T4SS effector BepC was reported to mediate internalization of big Bartonella aggregates into host cells by modulating F-actin polymerization. After that, BepC was indicated to induce host cell fragmentation, an interesting cell phenotype that is characterized by failure of rear-end retraction during cell migration, and subsequent dragging and fragmentation of cells. Here, we found that expression of BepC resulted in significant stress fiber formation and contractile cell morphology, which depended on combination of the N-terminus FIC (filamentation induced by c-AMP) domain and C-terminus BID (Bartonella intracellular delivery) domain of BepC. The FIC domain played a key role in BepC-induced stress fiber formation and cell fragmentation because deletion of FIC signature motif or mutation of two conserved amino acid residues abolished BepC-induced cell fragmentation. Immunoprecipitation confirmed the interaction of BepC with GEF-H1 (a microtubule-associated RhoA guanosine exchange factor), and siRNA-mediated depletion of GEF-H1 prevented BepC-induced stress fiber formation. Interaction with BepC caused the dissociation of GEF-H1 from microtubules and activation of RhoA to induce formation of stress fibers. The ROCK (Rho-associated protein kinase) inhibitor Y27632 completely blocked BepC effects on stress fiber formation and cell contractility. Moreover, stress fiber formation by BepC increased the stability of focal adhesions, which consequently impeded rear-edge detachment. Overall, our study revealed that BepC-induced stress fiber formation was achieved through the GEF-H1/RhoA/ROCK pathway.

Highlights

Bartonella species are facultative intracellular pathogens that are highly adapted to their specific mammalian hosts and vector reservoirs [1,2]
Bartonella effector proteins (Beps) are multi-domain proteins that mainly possess an N-terminal FIC domain that confers posttranslational modifications (PTMs) to substrates in host cells, and a C-terminal BID (Bartonella intracellular delivery) domain that acts as a signal for T4SS translocation
We identified that BepC exploited a guanine nucleotide exchange factor (GEF) of Rho GTPase, GEF-H1, to induce stress fiber formation and maturation of focal adhesion

Summary

Introduction

Bartonella species are facultative intracellular pathogens that are highly adapted to their specific mammalian hosts and vector reservoirs [1,2]. Beps are multi-domain proteins that mainly possess an N-terminal FIC (filamentation induced by c-AMP) domain that confers posttranslational modifications (PTMs) to substrates in host cells, and a C-terminal BID (Bartonella intracellular delivery) domain that acts as a signal for T4SS translocation. BepE ensures the migration of dendritic cells to deliver Bartonella from derma to the bloodstream because BepE antagonizes BepC-induced host cell cytotoxicity [6]. This cytotoxic effect is characterized as disturbance of rear-edge detachment during the migration of infected migratory cells, and such cells become elongated and fragmented. The mechanism how BepC modulates F-actin cytoskeleton and subsequent cell fragmentation, remains elusive

Methods

Results

Conclusion