Coxiella burnetii induces apoptosis during early stage infection via a caspase-independent pathway in human monocytic THP-1 cells.
The ability of Coxiella burnetii to modulate host cell death may be a critical factor in disease development. In this study, human monocytic THP-1 cells were used to examine the ability of C. burnetii Nine Mile phase II (NMII) to modulate apoptotic signaling. Typical apoptotic cell morphological changes and DNA fragmentation were detected in NMII infected cells at an early stage of infection. FACS analysis using Annexin-V-PI double staining showed the induction of a significant number of apoptotic cells at an early stage of NMII infection. Double staining of apoptotic cell DNA and intracellular C. burnetii indicates that NMII infected cells undergoing apoptosis. Interestingly, caspase-3 was not cleaved in NMII infected cells and the caspase-inhibitor Z-VAD-fmk did not prevent NMII induced apoptosis. Surprisingly, the caspase-3 downstream substrate PARP was cleaved in NMII infected cells. These results suggest that NMII induces apoptosis during an early stage of infection through a caspase-independent pathway in THP-1 cells. In addition, NMII-infected monocytes were unable to prevent exogenous staurosporine-induced apoptotic death. Western blot analysis indicated that NMII infection induced the translocation of AIF from mitochondria into the nucleus. Cytochrome c release and cytosol-to-mitochondrial translocation of the pore-forming protein Bax in NMII infected cells occurred at 24 h post infection. These data suggest that NMII infection induced caspase-independent apoptosis through a mechanism involving cytochrome c release, cytosol-to-mitochondrial translocation of Bax and nuclear translocation of AIF in THP-1 monocytes. Furthermore, NMII infection increased TNF-α production and neutralization of TNF-α in NMII infected cells partially blocked PARP cleavage, suggesting TNF-α may play a role in the upstream signaling involved in NMII induced apoptosis. Antibiotic inhibition of C. burnetii RNA synthesis blocked NMII infection-induced PARP activation. These results suggest that both intracellular C. burnetii replication and secreted TNF-α contribute to NMII infection-triggered apoptosis during an early stage of infection.
Department of Microbial and Molecular Pathogenesis, College of Medicine, Texas A & M Health Science Center, Bryan, Texas, United States of America.
Yan
Y
Zhang
Guoquan
G
Zhang
Laura R
LR
Hendrix
Vernon L
VL
Tesh
James E
JE
Samuel
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D061945:Caspase Inhibitors; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D016997:Coxiella burnetii / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D045304:Cytochromes c / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D042541:Intracellular Space / Q000187:drug effects / Q000382:microbiology; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000378:metabolism; D009000:Monocytes / Q000187:drug effects / Q000201:enzymology* / Q000382:microbiology* / Q000473:pathology; D009500:Neutralization Tests; D010539:Permeability / Q000187:drug effects; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D011778:Q Fever / Q000382:microbiology* / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D000590:Amino Acid Chloromethyl Ketones; D017304:Annexin A5; D051033:Apoptosis Inducing Factor; D061945:Caspase Inhibitors; D014409:Tumor Necrosis Factor-alpha; D051028:bcl-2-Associated X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D045304:Cytochromes c; D011065:Poly(ADP-ribose) Polymerases; D053148:Caspase 3