Identifikation von TNFAIP2 als Wirtsfaktor in der Legionellen-Infektion durch genomweite Chromatinanalyse

Eukaryotic gene expression is tightly controlled by epigenetic mechanisms, such as histone modifications and chromatin remodeling and thus, these mechanisms are good targets for pathogens during infection. Recent studies show that bacteria manipulate the host chromatin structure by diverse mechanisms, thereby imposing a specific transcriptional profile and in most cases dampening the host innate immune response. Understanding of bacterial-induced epigenetic deregulations in the physiopathology of infec-tious diseases may have important therapeutic implications. Pneumonia is an acute inflammatory lung disease provoked by infection with different pathogens, e.g. Legionella pneumophila (L. pneumophila). The human alveolar epithelium and macrophages constitute the main cellular targets for inhaled microorganisms and play a key role in the initiation of the innate immune response and the defence against respiratory infection. L. pneumophila is a motile, rod-shaped, gram-negative, aerobic and intracellular pathogen, which possesses the ability to manipulate the host immune defence to enable efficient bacterial replication within lung tissue. Published data demonstrate that L. pneumophila modifies the epigenetics landscape at pro-inflammatory gene promoters, such as the IL-8 gene promoter and the IL-6 gene promoter, by inducing diverse histone modifications (Schmeck et al., 2008; Lorenz et al., 2011). Herein, using ChIP-Seq we looked at the effect on H4Ac upon Legionella pneumophila infection and identified a factor called TNFAIP2 whose acetylation is induced after infection. Briefly, TNFAIP2-mRNA and protein expression is induced by L. pneumophila Corby and Streptococcus pneumoniae in human and mouse cells, respectively. In contrast, its expression cannot be induced by human (Pan/99 (H3N2)), nor by avian (Dk/Alb (H12N5)) influenza virus in A549 cells. Furthermore, L. p.-induced TNFAIP2-mRNA expression depends on bacterial Typ IV secretion system and on the activation of TLR2 and TLR5. Using specific MAP-kinase and NF-κB inhibitors we could show that L. p.-induced TNFAIP2 expression is dependent on NF-κB. Binding of the NF-κB subunit p65 to the TNFAIP2 gene promoter could be confirmed by ChIP analysis and occurs at a distal NF-κB binding site. Knockdown of TNFAIP2 leads to reduced intracellular replication of L. pneumophila in human alveolar epithelial cells and to a vast number of differentially expressed genes, with some of them belonging e.g. to the immunsystem and cytoskeleton, respectively. Finally, using Maldi-TOF analysis we could show some putative interaction partners and thus speculate on the function of TNFAIP2. In summary, regulatory mechanisms orchestrating the expression of TNFAIP2 could be determined and on this basis possible function of TNFAIP2 in pneumonia could be hypothesized. We conclude that TNFAIP2 may have a fundamental role in the immune response to L. pneumophila and therefore represents an interesting therapeutic target.