genomewide characterization of host-pathogen interactions by ...

Maren Depke
Results
Host Cell Gene Expression Pattern in an in vitro Infection Model
Enzymes catalyzing synthesis or degradation reactions of lipids are in certain cases also
related to signal transduction and regulatory processes in the cell. In this context, a cumulation of
increased expression values in infected samples 6.5 h after start of infection was noticeable
(Fig. R.4.11).
Phosphatidylinositol-4-kinase and phosphoinositide-3-kinase subunits (PI4K2B, 2.1; PIK3CA,
1.7; PIK3R1, 1.7; PIK3R3, 2.4) belong to the group of genes coding for enzymes involved in lipid
messenger reactions. These enzymes catalyze reactions ending with the production of
phosphatidylinositol-trisphosphate (PIP 3 ), a messenger involved in activation of protein kinase
AKT/PKB. Phospholipases C (PLCB4, 2.9; PLCG2, 3.9; PLCH1, 2.0) generate the messengers
inositol-trisphosphate (IP 3 ) and diacylglycerol (DAG). Cytosolic phospholipase A2 gamma
(PLA2G4C, 2.7) releases among others arachidonic acid, which can serve as messenger with the
function of directly activating ion channels and protein kinase C (Ordway et al. 1991, Khan WA et
al. 1995, Bonventre 1992) or can be processed to eicosanoid mediators like prostaglandins
(Laye/Gill 2003). Interestingly, the acyl-CoA synthetase (ACSL3, 1.7) with preference for
arachidonate, myristate and eicosapentaenoate was increased, too. This might indicate an
inactivation process for the messenger arachidonic acid. Furthermore, PRKD1 (2.0) and PRKD2
(2.5), coding for protein kinase D alias protein kinase C isoform µ, were induced, too (not shown).
Three more genes showed an increase of gene expression 6.5 h after start of infection: Serine
palmitoyltransferase subunit (SPTLC2, 1.8) and ketodihydrosphingosine reductase (KDSR, 1.6),
which are part of ceramide biosynthesis, and alkaline ceramidase (ACER2, 4.1), an enzyme of
ceramide degradation to sphingosine. Noticeably, both final products ceramide and sphingosine
are associated with apoptosis.
3-phosphoinositide
biosynthesis
phospholipases
activation of
fatty acid by CoA
ceramide
biosynthesis
sphingosine
metabolism
preference for
arachidonate,
myristate,
eicosapentaenoate
palmityl-CoA
ceramide
PIP 3
IP 3 + DAG
arachidonic
acid
arachidonyl-
CoA
ceramide
sphingosine
activation of
AKT/PKB
activation of
calcium-channels
and PKC
activity regulation
of ion channels
and PKC
inactivation of
arachidonic acid
apoptosis
Fig. R.4.11: Induction of enzyme genes related to lipid messenger production.
Lipid metabolism related genes were chosen with the help of omics-viewer(s) of BIOCYC (SRI International, CA, USA, http://biocyc.org)
and manually added to and arranged in the Ingenuity Pathway Analysis path designer tool (IPA, www.ingenuity.com). Red color
indicates induction of gene expression in infected samples at the 6.5 h time point, and more intense color shows a higher absolute
fold change. Genes coding for enzymes, which are involved in lipid messenger reactions, were induced: phosphatidylinositol 4-kinase
type 2 beta (PI4K2B), phosphoinositide-3-kinase, catalytic, alpha polypeptide (PIK3CA), phosphoinositide-3-kinase, regulatory subunit
1/alpha (PIK3R1), and phosphoinositide-3-kinase, regulatory subunit 3/gamma (PIK3R3). These enzymes catalyze reactions ending
with the production of phosphatidylinositol-trisphosphate (PIP 3), a messenger involved in activation of protein kinase AKT/PKB.
Phospholipase C, beta 4 (PLCB4), phosphatidylinositol-specific phospholipase C, gamma 2 (PLCG2), and phospholipase C, eta 1 (PLCH1)
generate the messengers inositol-trisphosphate (IP 3) and diacylglycerol (DAG), cytosolic, calcium-independent phospholipase A2,
group IV C (PLA2G4C) generates the messenger arachidonic acid. Acyl-CoA synthetase long-chain family member 3 (ACSL3) was
increased, too. This might indicate in inactivation process for the messenger arachidonic acid.
Serine palmitoyltransferase, long chain base subunit 2 (SPTLC2) and 3-ketodihydrosphingosine reductase (KDSR), which are part of
ceramide biosynthesis, and alkaline ceramidase 2 (ACER2), an enzyme of ceramide degradation to sphingosine, showed a higher
expression in infected samples than in controls at the 6.5 h time point.
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