Functional analysis of Coxiella burnetii type IV effector protein AnkG-induced inhibition of host cell apoptosis

• Applicant: Professorin Dr. Anja Lührmann
• Subject Area: Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398099936

Coxiella burnetii is an obligate intracellular Gram-negative pathogen with worldwide prevalence, except in New Zealand. Roughly, 40% of infected humans develop acute Q fever, a mild flu-like illness, which can develop into an interstitial pneumonia or hepatitis. 2 - 5 % of all infected individuals develop chronic Q fever years after primary infection. Chronic Q fever mainly manifests as endocarditis and is potentially fatal. So far, factors that account for the chronicity of Q fever remain largely unknown. However, it is known that the ability to prevent host cell death is essential to establish a persistent infection. To interfere with host cell viability C. burnetii requires a type IV secretion system (T4SS), used to inject effector proteins into the host cell cytosol to interfere with host cell pathways. So far, only four T4SS effector proteins, AnkG, CaeA, CaeB and IcaA, have been identified to facilitate host cell survival. The present grant application focuses on the further characterization of the molecular mechanism of action of the anti-apoptotic effector protein AnkG. In our previous studies, we could demonstrate that AnkG is a strain specific virulence factor. Furthermore, we showed by co- and RNA-immunoprecipitation that AnkG binds to the host cell DExD box RNA helicase 21 (DDX21) as well as to the 7SK, a cellular small nuclear RNA. AnkG interferes with the function of the 7SK small nuclear ribonucleoprotein (7SK snRNP) complex, an important regulator of the positive transcription elongation factor b (P-TEFb), leading to significant changes in host cell transcription and ensuring host cell survival. Importantly, AnkG activity is essential for efficient intracellular replication of C. burnetii and its ability to inhibit apoptosis.As DDX21 and P-TEFb are both essential for AnkG-mediated inhibition of host cell apoptosis, the overarching goal of the present project is to investigate further the molecular mechanism of action of AnkG and its role in pathogenesis. First, we will characterize transcriptional activity of AnkG in more detail and determine the role of DDX21 and the 7SK snRNP during C. burnetii infection. Our preliminary data suggest that AnkG might alter the subcellular localization and activation of the transcription factor TFEB, a master regulator of autophagy and lysosomal biogenesis. Therefore, we will investigate the AnkG-mediated nuclear translocation of TFEB and its functional consequence for C. burnetii-containing vacuole formation.

• DFG Programme: Research Grants