Recently we have shown that influenza A virus infection leads to activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway and that this cellular reaction is dependent on the expression of the viral nonstructural protein 1 (NS1). These data also suggested that PI3K activation confers a virus-supporting activity at intermediate stages of the infection cycle. So far it is not known which process is regulated by the kinase that supports virus replication. It is well established that upon infection with influenza A virus, the expression of the viral NS1 keeps the induction of beta interferon and the apoptotic response within a tolerable limit. On a molecular basis, this activity of NS1 has been suggested to preclude the activation of cellular double-stranded RNA receptors as well as impaired modulation of mRNA processing. Here we present a novel mode of action of the NS1 protein to suppress apoptosis induction. NS1 binds to and activates PI3K, which results in the activation of the PI3K effector Akt. This leads to a subsequent inhibition of caspase 9 and glycogen synthase-kinase 3␤ and limitation of the virus-induced cell death program. Thus, NS1 not only blocks but also activates signaling pathways to ensure efficient virus replication.

Nucleotide-binding oligomerization domain (Nod) proteins serve as intracellular pattern recognition molecules recognizing peptidoglycans. To further examine intracellular immune recognition, we used Listeria monocytogenes as an organism particularly amenable for studying innate immunity to intracellular pathogens. In contrast to wild-type L. monocytogenes, the nonpathogenic Listeria innocua, or L. monocytogenes mutants lacking internalin B or listeriolysin O, poorly invaded host cells and escaped into host cell cytoplasm, respectively, and were therefore used as controls. In this study, we show that only the invasive wild-type L. monocytogenes, but not the listeriolysin O- or internalin B-negative L. monocytogenes mutants or L. innocua, substantially induced IL-8 production in HUVEC. RNA interference and Nod1-overexpression experiments demonstrated that Nod1 is critically involved in chemokine secretion and NF-κB activation initiated by L. monocytogenes in human endothelial cells. Moreover, we show for the first time that Nod1 mediated activation of p38 MAPK signaling induced by L. monocytogenes. Finally, L. monocytogenes- and Nod1-induced IL-8 production was blocked by a specific p38 inhibitor. In conclusion, L. monocytogenes induced a Nod1-dependent activation of p38 MAPK signaling and NF-κB which resulted in IL-8 production in endothelial cells. Thus, Nod1 is an important component of a cytoplasmic surveillance pathway.

Epigenetic histone modifications contribute to the regulation of eukaryotic gene transcription. The role of epigenetic regulation in immunity to intracellular pathogens is poorly understood. We tested the hypothesis that epigenetic histone modifications influence cytokine expression by intracellular bacteria. Intracellular Listeria monocytogenes, but not noninvasive Listeria innocua, induced release of distinct CC and CXC chemokines, as well as Th1 and Th2 cytokines and growth factors by endothelial cells. Cytokine expression was in part dependent on p38 MAPK and MEK1. We analyzed global histone modification and modifications in detail at the gene promoter of IL-8, which depended on both kinase pathways, and of IFN-γ, which was not blocked by kinase inhibition. Intracellular Listeria induced time-dependent acetylation (lysine 8) of histone H4 and phosphorylation/acetylation (serine 10/lysine 14) of histone H3 globally and at the il8 promoter in HUVEC, as well as recruitment of the histone acetylase CREB-binding protein. Inhibitors of p38 MAPK and MEK1 reduced lysine 8 acetylation of histone H4 and serine 10/lysine 14 phosphorylation/acetylation of histone H3 in Listeria-infected endothelial cells and disappearance of histone deacetylase 1 at the il8 promoter in HUVEC. In contrast, IFN-γ gene transcription was activated by Listeria monocytogenes independent of p38 MAPK and MEK1, and histone phosphorylation/acetylation remained unchanged in infected cells at the IFN-γ promoter. Specific inhibition of histone deacetylases by trichostatin A increased Listeria-induced expression of IL-8, but not of IFN-γ, underlining the specific physiological impact of histone acetylation. In conclusion, MAPK-dependent epigenetic modifications differentially contributed to L. monocytogenes-induced cytokine expression by human endothelial cells.

(COPD) and may also contribute to the pathogenesis of COPD. Little is known about M. catarrhalis-bronchial epithelium interaction. We investigated activation of M. catarrhalis infected bronchial epithelial cells and characterized the signal transduction pathways. Moreover, we tested the hypothesis that the M. catarrhalis-induced cytokine expression is regulated by acetylation of histone residues and controlled by histone deacetylase activity (HDAC). We demonstrated that M. catarrhalis induced a strong time-and dose-dependent inflammatory response in the bronchial epithelial cell line (BEAS-2B), characterized by the release of IL-8 and GM-CSF. For this cytokine liberation activation of the ERK and p38 mitogen-activated protein (MAP) kinases and transcription factor NF-B was required. Furthermore, M. catarrhalis-infected bronchial epithelial cells showed an enhanced acetylation of histone H3 and H4 globally and at the promoter of the il8 gene. Preventing histone deacetylation by the histone deacetylase inhibitor trichostatin A augmented the M. catarrhalis-induced IL-8 response. After exposure to M. catarrhalis, we found a decrease in global histone deacetylase expression and activity. Our findings suggest that M. catarrhalisinduced activation of il8 gene transcription was caused by interference with epigenetic mechanisms regulating il8 gene accessibility. Our findings provide insight into important molecular and cellular mechanisms of M. catarrhalis-induced activation of human bronchial epithelium. chronic obstructive pulmonary disease; bronchial epithelium; immune response; mitogen-activated protein kinase; nuclear factor-B