Absence of Specific Chlamydia trachomatis Inclusion Membrane Proteins Triggers Premature Inclusion Membrane Lysis and Host Cell Death

Abstract

Summary Chlamydia trachomatis is a human pathogen associated with significant morbidity worldwide. As obligate intracellular parasites, chlamydiae must survive within eukaryotic cells for sufficient time to complete their developmental cycle. To promote host cell survival, chlamydiae express poorly understood anti-apoptotic factors. Using recently developed genetic tools, we show that three inclusion membrane proteins (Incs) out of eleven examined are required for inclusion membrane stability and avoidance of host cell death pathways. In the absence of specific Incs, premature inclusion lysis results in recognition by autophagolysosomes, activation of intrinsic apoptosis, and premature termination of the chlamydial developmental cycle. Inhibition of autophagy or knockdown of STING prevented host cell death and activation of intrinsic apoptosis. Significantly these findings emphasize the importance of Incs in the establishment of a replicative compartment that sequesters the pathogen from host surveillance systems.

Safe haven under constant attack-TheChlamydia-containing vacuole

“…By targeted gene disruption of individual Inc proteins in Ctr , mutants of IncC, CT383, and CT229/CpoS exhibited a significant growth defect and premature inclusion lysis followed by host cell death. These results were further confirmed in mouse genital infection studies (Weber et al, ). Independent studies identified several Rab proteins as interaction partners of CT229/CpoS, and inhibition of host cell protein biosynthesis or anterograde vesicular trafficking rescued the growth defect of CT229/CpoS mutants and prevented host cell death (Rzomp, Moorhead, & Scidmore, ; Sixt et al, ; Weber et al, ).…”

“…With the establishment of genetic tools for Chlamydia within the last years (Sixt et al, ), new insights in the role of Inc proteins during infection were obtained. Some Inc proteins specifically regulate interaction with host cell proteins and compartments (see above) whereas others are crucial for inclusion stability and evasion from cell‐autonomous host defence (Weber et al, ).…”

“…Just recently, three additional Inc proteins have been identified that mediate inclusion stability (Sixt et al, ; Weber et al, ). By targeted gene disruption of individual Inc proteins in Ctr , mutants of IncC, CT383, and CT229/CpoS exhibited a significant growth defect and premature inclusion lysis followed by host cell death.…”

IncV, a FFAT motif-containing Chlamydia protein, tethers the endoplasmic reticulum to the pathogen-containing vacuole

“…Finally, we tested if IncV is required for the formation of ER-inclusion MCS by using an incV::bla mutant (43). We confirmed that the mutant harbors an intron insertion between nucleotide position 99 and 100 of the incV ORF, which is predicted to lead to the production of a truncated peptide containing the first 33 aa of IncV (Fig.…”

“…However, it is unknown if Inc proteins can also act as structural components to bring and maintain the ER and the inclusion membrane in close apposition. C. trachomatis encodes more than 50 putative Incs and only some of them have known functions in C. trachomatis infection (24,28,(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43). Recently, Mirrashidi et al (37) determined the Inc-human interactome from uninfected cells expressing C. trachomatis Inc proteins.…”