Figure 5.

C. trachomatis mediates host cell lysis via a common pathway involving both CteG and Pgp4. (A) HeLa cells were infected with C. trachomatis L2/434 carrying pVector[Pgp4⁺] (CteG⁺/Pgp4⁺), L2/434 carrying pVector[Pgp4^-] (CteG⁺/Pgp4^-), cteG::aadA carrying pVector[Pgp4⁺] (CteG^-/Pgp4⁺), or cteG::aadA carrying pVector[Pgp4^-] (CteG^-/Pgp4^-) for 72 h at an MOI of 0.3, and the LDH released by lysed host cells was measured using a CytoScan™ LDH Cytotoxicity Assay kit (G-Biosciences). (B) As in panel A, but HeLa 229 cells were also infected with cteG::aadA carrying pCteG-2HA[Pgp4⁺] (also named pCteG-2HA in Table 1 and in Figures 1 – 3 ; CteG-2HA⁺/Pgp4⁺), or cteG::aadA carrying pCteG-2HA[Pgp4^-] (CteG-2HA⁺/Pgp4^-). Statistical significance was assessed by using ordinary one-way ANOVA and Tukey post-test analysis. In (A, B), data correspond to mean ± standard error of the mean (n = 4 in panel A and n = 7 in panel B; ns, non-significant; *p<0.01; **p<0.0001). (C) Hypothetical model for the mode of action of CteG and Pgp4 in promoting host cell lysis. After CteG is produced by chamydiae in an inactive form (CteG_I), CteG is activated (CteG_A) in a Pgp4-dependent manner, which could occur within chlamydiae or after delivery of CteG into the host cell cytoplasm. Premature CteG_A-mediated host cell lysis is prevented by the action of an unknown inhibitory factor, which could be another chlamydial effector or a host cell factor. At late stages of infection, the effect of this inhibitor in CteG_A is alleviated by an unknown mechanism and host cell lysis is triggered.