The Type III Secretion Effector CteG Mediates Host Cell Lytic Exit of Chlamydia trachomatis

Abstract

Chlamydia trachomatis is an obligate intracellular bacterium causing ocular and urogenital infections in humans that are a significant burden worldwide. The completion of its characteristic infectious cycle relies on the manipulation of several host cell processes by numerous chlamydial type III secretion effector proteins. We previously identified the C. trachomatis CteG effector and showed it localizes at the host cell plasma membrane at late stages of infection. Here, we showed that, from 48 h post-infection, mammalian cells infected by wild-type C. trachomatis contained more infectious chlamydiae in the culture supernatant than cells infected by a CteG-deficient strain. This phenotype was CteG-dependent as it could be complemented in cells infected by the CteG-deficient strain carrying a plasmid encoding CteG. Furthermore, we detected a CteG-dependent defect on host cell cytotoxicity, indicating that CteG mediates chlamydial lytic exit. Previous studies showed that Pgp4, a global regulator of transcription encoded in the C. trachomatis virulence plasmid, also mediates chlamydial lytic exit. However, by using C. trachomatis strains encoding or lacking Pgp4, we showed that production and localization of CteG are not regulated by Pgp4. A C. trachomatis strain lacking both CteG and Pgp4 was as defective in promoting host cell cytotoxicity as mutant strains lacking only CteG or Pgp4. Furthermore, CteG overproduction in a plasmid suppressed the host cell cytotoxic defect of CteG- and Pgp4-deficient chlamydiae. Overall, we revealed the first chlamydial type III secretion effector involved in host cell lytic exit. Our data indicates that CteG and Pgp4 participate in a single cascade of events, but involving multiple layers of regulation, leading to lysis of host cells and release of the infectious chlamydiae.

The Chlamydia trachomatis IncM Protein Interferes with Host Cell Cytokinesis, Centrosome Positioning, and Golgi Distribution and Contributes to the Stability of the Pathogen-Containing Vacuole

“…Besides Incs, the chlamydial CPAF protease has been shown to inhibit host cell cytokinesis in C. trachomatis-infected cells (33,35). Finally, another chlamydial non-Inc effector (CteG) (60,61) We also found that inclusions containing IncM-deficient chlamydiae are morphologically different and less stable than inclusions of IncM-producing chlamydiae, a phenotype which is detectable at late stages of the developmental cycle (from 48 h postinfection). Other Incs have also been shown to play a role in inclusion stabilityinclusions of CT229/CpoS-, IncC-, InaC-or CT383-deficient C. trachomatis are also less stable; however, in these cases, increased inclusion lysis followed by host cell death is detectable from 18 to 24 h post-infection (25, 58), earlier than for IncM.…”

“…Other Incs have also been shown to play a role in inclusion stabilityinclusions of CT229/CpoS-, IncC-, InaC-or CT383-deficient C. trachomatis are also less stable; however, in these cases, increased inclusion lysis followed by host cell death is detectable from 18 to 24 h post-infection (25, 58), earlier than for IncM. While the distinct morphology of IncM-deficient inclusions does indicate a role of IncM in mediating inclusion stability, we cannot formally exclude that the two observations are unlinked, e.g., that IncM participates instead in a putative mechanism that prevents untimely chlamydial lytic exit (61). Thus, several Incs may cooperate to promote inclusion stability and ensure host cell survival throughout the chlamydial developmental cycle.…”

“…Cell cytotoxicity assays. The supernatants of infected HeLa cells were assayed for released LDH with the CytoScan TM LDH Cytotoxicity Assay kit (G-Biosciences), as described (61).…”

“…The multiplicity of infection and time post-infection used in these assays were based in optimization experiments described recently (61). In brief, the amount of LDH activity released from uninfected cells and detected in uninfected cells after lysis with 1 % (v/v) Triton X-100 were determined and correspond to the minimal and maximal values,…”

The Chlamydia trachomatis type III-secreted effector protein CteG induces centrosome amplification through interactions with centrin-2

“…As CteG is important for centrosome amplification ( Fig. 3 ) and lytic exit ( 39 ), we next sought to determine whether CteG, and by extension supernumerary centrosomes, are important for chlamydial infection. While no growth defect was noted in HeLa or A2EN cells, a significant decrease in infectious progeny from cteG::aadA was noted compared to WT L2- and CteG comp-infected primary human cervical cells ( Fig.…”