The Putative Type III Secreted Chlamydia abortus Virulence-Associated Protein CAB063 Targets Lamin and Induces Apoptosis

Abstract

Since intracellular survival of all chlamydiae depends on the manipulation of the host cell through type III secreted effector proteins, their characterization is crucial for the understanding of chlamydial pathogenesis. We functionally characterized the putative type III secreted Chlamydia abortus protein CAB063, describe its intracellular localization and identified pro-and eukaryotic binding partners. Based on an experimental infection model and plasmid transfections, we investigated the subcellular localization of CAB063 by immunofluorescence microscopy, immunoelectron microscopy, and Western blot analysis. Pro-and eukaryotic targets were identified by co-immunofluorescence, coimmunoprecipitation, and mass spectrometry. Transmission electron microscopy and flow cytometry were used for morphological and functional investigations on host cell apoptosis. CAB063 localized in the nuclear membrane of the host cell nucleus and we identified the chaperone HSP70 and lamin A/C as pro-and eukaryotic targets, respectively. CAB063-dependent morphological alterations of the host cell nucleus correlated with increased apoptosis rates of infected and CAB063-transfected cells. We provide evidence that CAB063 is a chaperone-folded type III secreted C. abortus virulence factor that targets lamin thereby altering the host cell nuclear membrane structure. This process may be responsible for an increased apoptosis rate at the end of the chlamydial developmental cycle, at which CAB063 is physiologically expressed.

Genome organization and genomics in Chlamydia: whole genome sequencing increases understanding of chlamydial virulence, evolution, and phylogeny

“…The secreted T3SS effectors are recognised as virulence factors in Chlamydiae ( Peters et al., 2007 ; Bachmann et al., 2014 ; Mueller et al., 2014 ; Mojica et al., 2015 ). While for some species, like C. trachomatis and C. psittaci , T3SS effectors have been experimentally confirmed and/or functionally characterised ( Mojica et al., 2015 ; da Cunha et al., 2017 ; Marschall et al., 2020 ). For other less characterised chlamydial species WGS analyses is used to identify and decipher their roles ( Hölzer et al., 2020 ; Heijne et al., 2021 ; White et al., 2021 ).…”

The Hypothetical Inclusion Membrane Protein CPSIT_0846 Regulates Mitochondrial-Mediated Host Cell Apoptosis via the ERK/JNK Signaling Pathway

“…generation of EBs is formed, some Chlamydial effector proteins can promote host cell apoptosis, such as CPSIT_0959 in C. psittaci, which helps the release of offspring EBs, and ultimately promotes EBs to infect neighboring host cells Sun et al, 2017;Weber et al, 2017;Wen et al, 2019;Marschall et al, 2020). Whether they are to promote or inhibit host cell apoptosis, all of these are the way that Chlamydia has evolved in order to survive in the host cell.…”

“…In the development cycle, Chlamydia produces a large number of effector proteins, some of which can inhibit host cell apoptosis to maintain a suitable living environment and help them obtain nutrients. When the new generation of EBs is formed, some Chlamydial effector proteins can promote host cell apoptosis, such as CPSIT_0959 in C. psittaci , which helps the release of offspring EBs, and ultimately promotes EBs to infect neighboring host cells ( Sixt and Kroemer, 2017 ; Sun et al., 2017 ; Weber et al., 2017 ; Wen et al., 2019 ; Marschall et al., 2020 ). Whether they are to promote or inhibit host cell apoptosis, all of these are the way that Chlamydia has evolved in order to survive in the host cell.…”

Animal and Public Health Significance of Chlamydiosis

“…After getting entry into the host cell, the elementary body converts into the reticulate body, which is non-infectious but metabolically active. Reticulate bodies start to multiply by asexual binary fission in nonfusogenic vacuoles, which are also named as inclusions (Marschall et al 2020). These elementary bodies keep growing until inclusions fill the cytoplasm of the host cell.…”