Tyrosine phosphorylation is
key for signal transduction from
exogenous
stimuli, including
the defence against
pathogens
.
Conversely, p
athogens
can
s
ubvert protein phosphorylation
to
control host
immune response
s
and
facilitate
invasion
and
dissemination
.
The bacterial
23
effector
s
EspJ
and SeoC are
injected into host cells
though a type III secretion system
by
entero
pathogenic
and enterohaemorrhagic
Escherichia coli
(EPEC and EHEC)
,
Citrobacter
rodentium
and
Salmonella
enterica
where
they inhibit Src kinase by
coupled
amidation
and
ADP
-
ribosylation
.
C. rodentium
, which
is u
sed to
model EPEC and EHEC infections in
human, is a mouse pathogen
triggering
colonic crypt hyperplasia (CCH) and colitis.
Enumeration of bacterial shedding and CCH confirmed that EspJ affects neither tolerance nor
resistance to infection. However, compar
ing the proteomes of intestinal epithelial cells
isolated from mice infected with wildtype
C.
rodentium
or
C. rodentium
encoding
catalytically
inactive EspJ
revealed that
EspJ
-
induced ADP
-
ribosylation
regulates
multiple non
-
receptor tyrosine kinases
in
vivo
.
Investi
gati
ng the substrate repertoire of EspJ revealed
that in HeLa and A549 Src and Csk were significantly targeted; in polarised Caco2 cells EspJ
targeted Src and Csk
and the Src family kinase (SFK) Yes1, while in differentiated Thp1
EspJ modified
Csk, the SFKs Hck and Lyn, the Tec family kinases Tec and Btk, and the adapter tyrosine kinase Syk. Furthermore, Abl (HeLa and Caco2) and Lyn (Caco2) were enriched specifically in the EspJ
-
containing samples. Biochemical assays revealed that EspJ
, the onl
y bacterial ADP
-
ribosyltransferase which targets mammalian kinases,
control
s
immune responses and
the Src/Csk signalling axis.