genomewide characterization of host-pathogen interactions by ...

Maren Depke
Discussion and Conclusions
found in the IFN-γ dependently regulated genes in BALB/c or C57BL/6 macrophages, when the
gene list was translated to murine homologues in Rosetta Resolver software with the help of the
EntrezGene HomoloGene database (http://www.ncbi.nlm.nih.gov/homologene). Some genes
even fit together in their regulation in both studies: S9 cells induced cytokine IL12A and
indoleamine 2,3-dioxygenase 1 (IDO1) upon infection, BMM induced the receptor Il12rb1 and
kynureninase (Kynu) after activation by IFN-γ.
An important mediator of inflammation is prostaglandin E 2 (PGE 2 ) whose production is mainly
mediated by prostaglandin-endoperoxide synthase (PTGS), which generates the inflammation
mediators prostaglandin (PG) G 2 and H 2 from arachidonic acid. From PGH 2 , the other
prostaglandins like PGE 2 are formed by different synthases (Spencer et al. 1998, Steer/Corbett
2003, Park JY et al. 2006). In this study, PTGS2 and PGE 2 receptors PTGER4 and PTGER2 were
induced at least at one analyzed time point. The mechanism of PTGS2 induction involves among
others NFκB (Newton et al. 1997, Lin et al. 2000, Tsatsanis et al. 2006). More specifically, it was
published that lipoteichoic acid (LTA) from S. aureus induced PTGS2 protein in human pulmonary
epithelial A549 cells and that this also led to PGE 2 production to which phospholipase A 2 (PLA2)
contributed (Lin et al. 2001). The authors demonstrate an induction of PTGS2 via a mechanism in
which LTA first activates phosphatidylcholine-phospholipase C or D (PC-PLC, PC-PLD), whose
product diacylglycerol (DAG) subsequently activates protein kinase C (PKC), which finally leads to
the activation of NFκB and NFκB-dependent PTGS2 (Lin et al. 2001).
In S. aureus RN1HG infected S9 cells, the induction of phospholipase A 2 (PLA2G4C),
phospholipase C (PLCB4, PLCG2, PLCH1), protein kinase C µ (PRKD1, PRKD2), and PTGS2 was
observed, which fits very well to the literature data. As it is known that NFκB activation results in
autoregulation and induction of its inhibitors (Sun et al. 1993, Le Bail et al. 1993, Liptay et al.
1994, Eto et al. 2003, Trinh et al. 2008), the induction of NFKBIZ can be regarded as indirect hint
for NFκB activity in infected S9 cells.
Airway epithelial cells have been used to study S. aureus in vitro infection before. In a farreaching
microarray and RT-PCR study, Moreilhon and coworkers analyzed the reaction of the
human airway glandular cell line MM-39 to the S. aureus 8325-4 strain in two settings: First,
diluted bacterial supernatants were added to the host cell culture. In a second experiment, PBSwashed
bacterial cells were used to infect the eukaryotic cell culture (Moreilhon et al. 2005).
Bacteria were cultivated in TSB, and when a concentration of 5E+08 cfu/ml was reached, cells or
supernatants were used for the infection experiments. This concentration corresponds to a time
point during exponential growth. Inoculation was performed with 10 % supernatant for a time
span from 1 h to 24 h or with a MOI of 50 for infection with viable staphylococci for 3 h. Thus,
additional to a different host cell line and S. aureus strain – whose known SigB-negative
phenotype (Kullik/Giachino 1997) probably is the main difference to the phenotypically SigBpositive
strain RN1HG – the experimental setting differed from the one used in this study. This
necessarily has impact on the comparability of the results. Furthermore, the strain 8325-4 was
observed to produce a lipase and protease sensitive lipoprotein inhibitor of internalization into
endothelial cells. Reduced internalization consequently led to a reduction of the endothelial cells’
cytokine production (Yao et al. 2000).
Moreilhon et al. observed distinct gene expression profiles of supernatant and viable
staphylococci treated host cells in which bacterial supernatant led to stronger alterations (higher
number as well as stronger magnitude) than washed viable staphylococci.
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