Open Journal of Applied Sciences, 2012, 2, 1-10
doi:10.4236/ojapps.2012.21001 Published Online March 2012 (http://www.SciRP.org/journal/ojapps)
p54nrb, a PSF Protein Partner, Contributes to Meningitic
Escherichia coli K1-Mediated Pathogenicities
Lina He1, Feng Chi1, Tao Bo1,2, Lin Wang1,3, Chunhua Wu1, Ambrose Jong1, Shenghe Huang1*
1 Department of Pediatrics, Saban Research Institute of Children’s Hospital Los Angeles,
University of Southern California, Los Angeles, USA
2 Department of Pediatrics, Division of Neonatology, The Second Xiangya Hospital, Central South University, Changsha, China
3Department of Histology and Embryology, School of Basic Medical Science, Wuhan University, Wuhan, China
Email: *shhuang@hsc.usc.edu
Received January 14, 2012; revised February 16, 2012; accepted February 27, 2012
ABSTRACT
IbeA is an important invasion determinant contributing to Escherichia coli K1 entry into brain microvascular endothe-
lial cells (BMEC) that is a key step in the pathogenesis of E. coli meningitis. Our previous studies have shown that
IbeA-induced signaling and E. coli K1 invasion is mediated by two IbeA-binding proteins, vimentin, which is constitu-
tively present in the surface of human BMECs (HBMECs), and PSF, which is inducibly expressed in both mesenchymal
(endothelium) and non-mesenchymal (epithelium) cells. However, it is unknown whether p54nrb, a PSF partner protein,
could contribute to the pathogenesis of E. coli K1 meningitis. Here, we reported that a 54-kDa protein was identified by
copurification with PSF through IbeA-affinity chromatography as an IbeA-binding protein, which is identical to p54nrb.
Both p54nrb and PSF are RNA-binding proteins and share significant sequence homology. The specific interaction be-
tween IbeA and p54nrb was confirmed by Western blot and ligand overlay assays. Recombinant p54nrb blocked E. coli
K1 invasion of human BMEC very effectively. Overexpressed p54nrb as a GFP fusion protein in the transfected 293T
cells significantly enhanced E. coli K1 invasion. Furthermore, higher levels of surface p54nrb in the transfected 293T
cells were detected by flow cytometry. These results suggest that the IbeA invasion protein of E. coli K1 interacts with
p54nrb for bacterial invasion of human cells.
Keywords: Meningitis; Escherichia coli; BMEC; IbeA; p54nrb; Invasion Protein; Receptor; Protein Interaction
1. Introduction
Despite the availability of effective bactericidal antibiot-
ics over the last sixty years neonatal bacterial meningitis
remains an important cause of high mortality and mor-
bidity [1-4]. Escherichia coli is the most common cause
of neonatal meningitis [2] and the K1 encapsulated strains
are most commonly acquired by neonates via vertical
transmission from the maternal genital tract in utero or
during passage through the birth canal [2]. Most cases of
bacterial meningitis in newborns develop as a result of
hematogenous spread. One of the most important issues
in the pathogenesis of E. coli meningitis is how circulat-
ing pathogens cross the blood-brain barrier (BBB). Strains
causing meningitis possess traits that distinguish them
from commensal strains of E. coli and other pathogenic
strains such as those causing diarrhea and urinary tract
infection. Characteristically, meningitic strains of E. coli
are composed of a restricted number of O serogroups (O1,
O2, O7, O18, O83), produce S fimbriae, express IbeA,
and predominately carry K1 capsule (over 84%) [1-3].
The presence of these features implies that meningitic
strains possess a defined set of virulence determinants that
allow the bacterium to penetrate the BBB and enter the
central nervous system. An in vitro brain microvascular
endothelial cells (BMEC) culture model with characteris-
tics of the BBB has been established for dissecting the
molecular and cellular mechanisms of E. coli crossing of
the BBB. Using this cell culture model, we and others
have shown that efficient penetration of E. coli across the
BBB is mediated by multiple factors. Several genetic de-
terminants, including ibeA, ibeB, yijP, aslA, traJ, cnfI and
ompA, are required for E. coli crossing of the BBB [1-4].
However, the ibeA gene encoding a 50-kDa protein has
been found to be unique to pathogenic E. coli K1 strains
(e.g., C5 and RS218), while laboratory strains of E. coli
K-12 (e.g., DH5 and HB101) as well as noninvasive E.
coli K1 (e.g., E412) lack ibeA [1-3,5-8].
In support of the role of IbeA in E. coli K1 invasion,
bacterial entry of human BMECs involves a complex in-
terplay of IbeA with the host cell receptors and is associ-
ated with activation of specific signaling pathways [9-11].
Receptor-mediated mechanisms also play an important
*Corresponding autho
r
.
Copyright © 2012 SciRes. OJAppS
L. N. HE ET AL.
2
role in biological functions of nicotine [12]. The in-
volvement of α7 nicotinic acetylcholine receptors (α7
nAChRs) and IbeA-binding proteins (IBPs) in nicotine-
sion process.
In summary, the data presented in this report establish
that p54nrb is the 55-kDa IbeA-binding protein, IBP55,
which mediates E. coli K1 invasion of BMEC. Further
work is needed to examine how vimentin, PSF and
p54nrb coordinately contribute to IbeA-induced signal
transduction and subsequently E. coli K1 entry into the
host cells.
5. Acknowledgements
We thank Dr. Kwang S Kim for providing brain endothe-
lial cells, Dr. Prasadarao V. Nemani for the polyclonal
antibody against IBP55, Dr. Yanming Zou for Western
blot and ligand overlay assays, Dr. Zhi-Hua Xie (Pro-
teinX Lab) for protein purification, Dr. Yu-Zhou Yang
for anti-His and anti-GST monoclonal antibodies, and Dr.
James G. Patton for p54nrb and PSF constructs. This
project is financially supported by Public Health Service
grants R01-AI40635 (S.H.H.) and R01-NS047599 (A.J.),
and China Natural Science Foundation grant 81070514
(L.W).
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Abbreviations
PSF, polypyrimidine tract-binding protein (PTB)-asso-
ciated splicing factor; BMEC, brain microvascular en-
dothelial cells; p54nrb, 54-kDa nuclear RNA-binding
protein; CSF, cerebrospinal fluid; BBB, blood-brain bar-
rier; IBP55, 55-kDa IbeA-binding protein; IBP100,
100-kDa IbeA-binding protein.