Chlamydia trachomatis modulates the expression of JAK-STAT signaling components to attenuate the type II interferon response of epithelial cells

Abstract

ABSTRACT Chlamydia trachomatis has adapted to subvert signaling in epithelial cells to ensure successful intracellular development. Interferon-γ (IFNγ) produced by recruited lymphocytes signals through the JAK/STAT pathway to restrict chlamydial growth in the genital tract. However, during Chlamydia infection in vitro, addition of IFNγ does not fully induce nuclear localization of its transcription factor STAT1 and expression of its target gene, IDO1. We hypothesize that this altered interferon response is a result of Chlamydia targeting components of the IFNγ-JAK/STAT pathway. To assess the ability of replicating Chlamydia to dampen interferon signaling, HEp2 human epithelial cells were infected with C. trachomatis serovar L2 for 24 hours prior to exposure to physiologically relevant levels of IFNγ (500 pg/mL). This novel approach enabled us to observe reduced phospho-activation of both STAT1 and its kinase Janus Kinase 2 (JAK2) in infected cells compared with mock-infected cells. Importantly, basal JAK2 and STAT1 transcript and protein levels were dampened by infection even in the absence of interferon, which could have implications for cytokine signaling beyond IFNγ. Additionally, target genes IRF1, GBP1, APOL3, IDO1, and SOCS1 were not fully induced in response to IFNγ exposure. Infection-dependent decreases in transcript, protein, and phosphoprotein were rescued when de novo bacterial protein synthesis was inhibited with chloramphenicol, restoring expression of IFNγ-target genes. Similar Chlamydia-dependent dampening of STAT1 and JAK2 transcript levels was observed in infected HeLa and END1 endocervical cells and in HEp2s infected with C. trachomatis serovar D, suggesting a conserved mechanism of dampening the interferon response by reducing the availability of key signaling components.IMPORTANCEAs an obligate intracellular pathogen that has evolved to infect the genital epithelium, Chlamydia has developed strategies to prevent detection and antimicrobial signaling in its host to ensure its survival and spread. A major player in clearing Chlamydia infections is the inflammatory cytokine interferon-γ (IFNγ), which is produced by immune cells that are recruited to the site of infection. Reports of IFNγ levels in endocervical specimens from Chlamydia-infected patients range from 1 to 350 pg/mL, while most in vitro studies of the effects of IFNγ on chlamydial growth have used 15–85-fold higher concentrations. By using physiologically relevant concentrations of IFNγ, we were able to assess Chlamydia’s ability to modulate its signaling. We found that Chlamydia decreases the expression of multiple components that are required for inducing gene expression by IFNγ, providing a possible mechanism by which Chlamydia trachomatis can attenuate the immune response in the female genital tract to cause long-term infections.

Keywords

• intracellular pathogen
• JAK-STAT
• interferon
• immune evasion
• Chlamydia