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- Title
Anti-apoptotic signalling by the Dot/Icm secretion system of L. pneumophila.
- Authors
Abu-Zant, Alaeddin; Jones, Snake; Asare, Rexford; Suttles, Jill; Price, Christopher; Graham, James; Kwaik, Yousef Abu
- Abstract
The Dot/Icm type IV secretion system of Legionella pneumophila triggers robust activation of caspase-3 during early and exponential stages of proliferation within human macrophages, but apoptosis is delayed till late stages of infection, which is novel. As caspase-3 is the executioner of the cell, we tested the hypothesis that L. pneumophila triggers anti-apoptotic signalling within the infected human macrophages to halt caspase-3 from dismantling the cells. Here we show that during early and exponential replication, L. pneumophila-infected human monocyte-derived macrophages (hMDMs) exhibit a remarkable resistance to induction of apoptosis, in a Dot/Icm-dependent manner. Microarray analyses and real-time PCR reveal that during exponential intracellular replication, L. pneumophila triggers upregulation of 12 anti-apoptotic genes that are linked to activation of the nuclear transcription factor kappa-B (NF-κB). Our data show that L. pneumophila induces a Dot/Icm-dependent sustained nuclear translocation of the p50 and p65 subunits of NF-κB during exponential intracellular replication. Bacterial entry is essential both for the anti-apoptotic phenotype of infected hMDMs and for nuclear translocation of the p65. Using p65–/– and IKKα–/–β–/– double knockout mouse embryonic fibroblast cell lines, we show that nuclear translocation of NF-κB is required for the resistance of L. pneumophila-infected cells to apoptosis-inducing agents. In addition, the L. pneumophila-induced nuclear translocation of NF-κB requires the activity of IKKα and/or IKKβ. We conclude that although the Dot/Icm secretion system of L. pneumophila elicits an early robust activation of caspase-3 in human macrophages, it triggers a strong anti-apoptotic signalling cascade mediated, at least in part by NF-κB, which renders the cells refractory to external potent apoptotic stimuli.
- Subjects
MACROPHAGE activation; LEGIONELLA pneumophila; APOPTOSIS; CYSTEINE proteinases; PROTEIN microarrays; MOLECULAR microbiology; MOLECULAR biology
- Publication
Cellular Microbiology, 2007, Vol 9, Issue 1, p246
- ISSN
1462-5814
- Publication type
Article
- DOI
10.1111/j.1462-5822.2006.00785.x