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 (CteGI), CteG is activated (CteGA) in a Pgp4-dependent manner, which could occur within chlamydiae or after delivery of CteG into the host cell cytoplasm. Premature CteGA-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 CteGA is alleviated by an unknown mechanism and host cell lysis is triggered.