genomewide characterization of host-pathogen interactions by ...

Maren Depke
Discussion and Conclusions
tryptophanyl-tRNA need: Interferon inducible proteins with tryptophan-enriched sequences
require above average tryptophanyl-tRNA (Xue/Wong 1995). 3) expanded function of the
tryptophanyl-tRNA synthetase: Splice variants were shown to act anti-angiogenic (Tolstrup et al.
1995, Otani et al. 2002, Wakasugi et al. 2002).
It has been shown that bone marrow-derived myeloid dendritic cells (Hara et al. 2008) and
astrocytes (Speciale et al. 1989) take up exogenous kynurenine, which would be an explanation
for the induction of kynureninase in BMM after treatment with IFN-γ (this study).
It can be speculated that the induction of Kynu and Wars together in BMM after treatment
with IFN-γ might indicate a preparation of the BMM for their presence in inflamed tissue where
they might encounter a tryptophan depleted environment.
Interferons are described to induce a group of GTPases / GTP binding proteins of different
families which play a role in antimicrobial defense. Of each of the four families described in
literature (MacMicking 2004) examples were found in the BMM data set after IFN-γ treatment, in
part exhibiting the highest induction factors of the data set: p47 GTPases (Igtp, Iigp1, Irgm1,
Tgtp), p65 guanylate-binding proteins (Gbp1, Gbp2, Gbp3, Gbp4, Gbp5, Gbp6), Mx proteins (Mx1,
Mx2), and very large inducible GTPases (Gvin1). The observation of induction is entirely in
agreement with literature references and impressive in its entity. This group of GTPases provides
the host with resistance against viral and microbial pathogens by cell-autonomous resistance
mechanisms.
GTPase p47 and p65 cellular knockdown studies and experiments using knockout animals led
to a higher susceptibility during infection. These GTPases were described to be membraneassociated
via myristoylation, isoprenylation, or interaction with e. g. Golgi-proteins. GTPases of
the p47 family were recruited to phagosomes after infection. Thus, they target intracellular,
vacuolarized pathogens by a mechanism proposed to remodel the pathogen-containing
compartment and to increase the fusion with lysosomes. GTPases of the p65 family were
described to be involved in the control of virus infections. More recently, a publication reported a
role for p65 GTPases during defense against bacterial and protozoan infections (Shenoy et al.
2007, Taylor GA et al. 2007, Anderson SL et al. 1999, Carter et al. 2005, Degrandi et al. 2007). Mx
proteins, which intracellularly bind to virus particles, are part of the innate immune defense
against several RNA viruses. In mice, the location of the Mx protein type (nuclear Mx1, cytosolic
Mx2) correlates with the replication site of the viruses against which the Mx proteins provide
resistance (Haller/Kochs 2002, Haller et al. 2007). Finally, very large inducible GTPases (VLIG) are
proteins of approximately 280 kDa. Despite the big size, the protein is encoded in a single exon.
Mice harbor six different, but similar VLIG genes, which are organized in a gene cluster on
chromosome 7 (Klamp et al. 2003). The genomes of primates and carnivores do not include VLIG
sequences, which probably were lost during evolution since other vertebrata own VLIG (Li et al.
2009).
Literature data indicate that C57BL/6 BMM do not synthesize Gbp-1 protein after interferon
induction because they own a different allele of the Gbp-1 gene (Staeheli et al. 1984). Although
this study detected a 6-fold increase in Gbp-1 mRNA of C57BL/6 BMM after IFN-γ treatment,
even the induced mRNA level was still very low. This change in mRNA was not detectable on
protein level: LC-MS/MS data of Dinh Hoang Dang Khoa revealed equal protein abundance in
control and IFN-γ treated C57BL/6 BMM, which was in accordance with the phenotype described
in literature.
187