5/15/2023 0 Comments Coccinella burnetii![]() ![]() Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was detected as a loading control. A fraction of the cell lysates separated by sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) were probed for the expression of the testing genes by immunoblotting with a Flag-specific antibody ( Lower). Luciferase activity was measured, and the fold of induction was calculated using control samples transfected with the empty vector ( Upper). HEK293T cells transfected with plasmids carrying the indicated Coxiella genes and a luciferase-based NF-κB reporter were induced with PMA for 4 h. ( A) Identification of Coxiella proteins capable of inhibiting NF-κB activation. Identification of cbu0513 (CinF) as an inhibitor of NF-κB activation. Results Identification of Cbu0513 as an Inhibitor of NF-κB Activation.įig. burnetii protein Cbu0513 (designated as a Coxiella inhibitor of NF-κB, CinF) as an inhibitor of NF-κB activation triggered by immune stimuli by functioning as a protein phosphatase that dephosphorylates IκBα, thus making it resistant to proteasome-mediated degradation. Yet, a transposon insertion mutant of NopA did not display detectable defects in intracellular bacterial replication ( 25), suggesting the existence of additional effectors involved in modulating the NF-κB signaling pathway. In line with this hypothesis, a recent study shows that the Dot/Icm effector NopA (Cbu1217) interferes with the nuclear import of NF-κB components by directly binding to Ran GTPase ( 25). burnetii induces robust NF-κB activation, but such activation appears to be suppressed at later phases of infection, likely by proteins injected by the Dot/Icm transporter ( 24). Signaling events regulated by the nuclear transcription factor NF-κB are important in immunity, cell proliferation, and apoptosis and thus, are common targets of pathogens ( 23). In support of this notion, the effector IcaA has been shown to inhibit caspase-11–mediated activation of the NLRP3 inflammasome trigged by cytosolic LPS from gram-negative bacteria such as Escherichia coli and L. burnetii strains does not trigger robust immune responses, likely because of immune suppression by its Dot/Icm effectors ( 12). Like other obligate pathogens, infection by phase II C. burnetii was long considered an obligate bacterial pathogen before the development of a cell-free culture protocol ( 21). burnetii have been shown to modulate cellular processes such as cell death ( 17), vesicle trafficking ( 18), gene expression ( 19), and autophagy ( 20). burnetii pathogenesis owning to the requirement of less stringent containment measures.ĭot/Icm effectors of C. Phase II strains are still comparably competent in intracellular replication in cultured cells or isolated primary macrophages ( 9) and thus are extremely useful in the study of C. The loss of a set of genes involved in the addition of terminal O antigen sugars to the LPS gave rise to phase II strains with marked reduction in virulence on immune competent animals ( 7, 8). This smooth LPS also prevents the activation of dendritic cells ( 6). burnetii elaborate LPS molecules that contain a tetra-acylated lipid A with long fatty acid chains, which plays an important role in immune evasion by mediating resistance to complement ( 5). Virulent wild-type strains (phase I) of C. burnetii often lead to an acute self-limiting illness characterized by headache and fever or chronic diseases such as endocarditis and hepatitis ( 4). burnetii utilizes a protein adapted from sugar metabolism to subvert host immunity. The IκBα phosphatase activity is essential for the role of CinF in C. Instead, it functions as a protein phosphatase that specifically dephosphorylates and stabilizes IκBα. Further study reveals that unlike its ortholog from Sulfolobus tokodaii, CinF does not exhibit FBP phosphatase activity. CinF is highly similar to a fructose-1,6-bisphosphate (FBP) aldolase/phosphatase present in diverse bacteria. Here, by a cell-based functional screening, we identified the effector Cbu0513 (designated as CinF) as an inhibitor of NF-κB signaling. A large cohort of such effectors has been identified, but the function of most of them remain elusive. Biogenesis of this compartment requires effectors of its Dot/Icm type IV secretion system. Coxiella burnetii is a bacterial pathogen that replicates within host cells by establishing a membrane-bound niche called the Coxiella-containing vacuole. ![]()
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