The Human Centrosomal Protein CCDC146 Binds Chlamydia trachomatis Inclusion Membrane Protein CT288 and Is Recruited to the Periphery of the Chlamydia-Containing Vacuole.

Filipe Almeida,Sara V Pais,Inês Serrano Pereira,Maria P Luís,Luís Jaime Mota

doi:10.3389/fcimb.2018.00254

Abstract

Chlamydia trachomatis is an obligate intracellular human pathogen causing mainly ocular and genital infections of significant clinical and public health impact. C. trachomatis multiplies intracellularly in a membrane bound vacuole, known as inclusion. Both extracellularly and from within the inclusion, C. trachomatis uses a type III secretion system to deliver several effector proteins into the cytoplasm of host cells. A large proportion of these effectors, the inclusion membrane (Inc) proteins, are exposed to the host cell cytosol but possess a characteristic hydrophobic domain mediating their insertion in the inclusion membrane. By yeast two-hybrid, we found that C. trachomatis Inc CT288 interacts with the human centrosomal protein CCDC146 (coiled-coil domain-containing protein 146). The interaction was also detected by co-immunoprecipitation in mammalian cells either ectopically expressing CCDC146 and CT288 or ectopically expressing CCDC146 and infected by a C. trachomatis strain expressing epitope-tagged and inclusion membrane-localized CT288. In uninfected mammalian cells, ectopically expressed full-length CCDC146 (955 amino acid residues) localized at the centrosome; but in cells infected by wild-type C. trachomatis, its centrosomal localization was less evident and CCDC146 accumulated around the inclusion. Recruitment of CCDC146 to the inclusion periphery did not require intact host Golgi, microtubules or microfilaments, but was dependent on chlamydial protein synthesis. Full-length CCDC146 also accumulated at the periphery of the inclusion in cells infected by a C. trachomatis ct288 mutant; however, a C-terminal fragment of CCDC146 (residues 692–955), which interacts with CT288, showed differences in localization at the periphery of the inclusion in cells infected by wild-type or ct288 mutant C. trachomatis. This suggests a model in which chlamydial proteins other than CT288 recruit CCDC146 to the periphery of the inclusion, where the CT288-CCDC146 interaction might contribute to modulate the function of this host protein.

Highlights

Chlamydiae are a large group of obligate intracellular bacteria, including human and animal pathogens, and symbionts of free-living amoebae
We examined the localization of ectopically expressed EGFP-CCDC146FL, or EGFP alone as control, in cells infected by C. trachomatis L2 strain 434/Bu (L2/434) harboring pCT288-2HA
We found that the human centrosomal protein CCDC146 can bind the C. trachomatis Inc protein CT288 and is recruited to the periphery of the inclusion membrane in cells infected by C. trachomatis

Summary

Introduction

Chlamydiae are a large group of obligate intracellular bacteria, including human and animal pathogens, and symbionts of free-living amoebae. Among Chlamydiae, C. trachomatis is an important human pathogen causing ocular and genital infections. C. trachomatis ocular strains (serovars A–C) are the leading cause of infectious blindness (trachoma; Taylor et al, 2014), urogenital strains (serovars D–K) are the most common cause of bacterially sexually transmitted diseases worldwide, and lymphogranuloma venereum (LGV) strains (serovars L1–L3) cause invasive urogenital or anorectal infection (O’Connell and Ferone, 2016). Attachment of EBs to host cells leads to bacterial invasion with the formation of a Chlamydia-containing vacuole known as inclusion. RBs divide, while membrane and nutrients are routed to the inclusion by interaction with host cell vesicular and non-vesicular transport pathways. Most RBs differentiate back into EBs, which exit the host cell and can infect neighboring cells [reviewed by (Elwell et al, 2016) and references therein]

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