294:G1392-G1400, 2008. First published 10 April 2008;
Am J Physiol Gastrointest Liver Physiol
Dario Siccardi, Karen L. Mumy, Daniel M. Wall, Jeffrey D. Bien and Beth A. McCormick
P-glycoprotein in the intestinal epithelium
Salmonella enterica serovar Typhimurium modulates
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Salmonella enterica serovar Typhimurium modulates P-glycoprotein
in the intestinal epithelium
Dario Siccardi, Karen L. Mumy, Daniel M. Wall, Jeffrey D. Bien, and Beth A. McCormick
Mucosal Immunology Laboratory, Massachusetts General Hospital, Charlestown, Massachusetts and the Department
of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts
Submitted 21 December 2007; accepted in final form 6 April 2008
Siccardi D, Mumy KL, Wall DM, Bien JD, McCormick BA.
Salmonella enterica serovar Typhimurium modulates P-glycopro-
tein in the intestinal epithelium. Am J Physiol Gastrointest Liver
Physiol 294: G1392–G1400, 2008. First published April 10, 2008;
doi:10.1152/ajpgi.00599.2007.—Studies over the last decade have
shown that Salmonella enterica serovar Typhimurium (S. typhi-
murium) is able to preferentially locate to sites of tumor growth and
modulate (shrink) the growth of many cancers. Given this unique
association between S. typhimurium and cancer cells, the objective of
this study was to investigate the capacity of this microorganism to
modulate the plasma membrane multidrug resistance (MDR) protein
P-glycoprotein (P-gp), an ATP-binding cassette transporter responsi-
ble for effluxing many cancer drugs. Using an in vitro model of S.
typhimurium infection of polarized human cancer intestinal cell lines,
we have found that this enteric pathogen functionally downregulates
the efflux capabilities of P-gp. Specifically, we show that S. typhi-
murium infection of human intestinal cancer cells results in the
enhanced intracellular accumulation of a number of P-gp substrates
that corresponds to the posttranscriptional downregulation of P-gp
expression. Furthermore, cells expressing small interfering RNAs
against MDR1, the gene encoding P-gp, were significantly more
susceptible to the cytotoxic effects of bacterial infection. This result is
consistent with our observation that S. typhimurium was significantly
less able to invade cells overexpressing MDR1. Taken together, these
results reveal a novel role for P-gp in the maintenance of homeostasis
in the gastrointestinal tract in regard to bacterial infection. Thus the
regulation of P-gp by S. typhimurium has important implications not
only for the development of new cancer therapeutics aimed at revers-
ing drug resistance but also in the understanding of how microbes
have evolved diverse strategies to interact with their host.
ATP-binding cassette transporter; inflammation; multidrug resistance 1
BACTERIA HAVE BEEN INVESTIGATED as therapeutic agents for
tumors for over 150 years, when it was first observed by
William B. Coley that a fraction of cancer patients who
developed postoperative bacterial infections went into remis-
sion and were cured of their tumors (33). Although the mech-
anisms underlying this observation were unclear, it was known
even then that bacteria exhibit immunostimulatory properties.
Moreover, it has been understood for over half a century that
anaerobic bacteria can selectively grow within tumors. In 1997,
Pawelek et al. (27) reported that Salmonella could preferen-
tially infect and accumulate within implanted tumors in mice,
achieving tumor-to-normal-tissue ratios of ?1,000:1. It is clear
that such microbes have the potential to sidestep many of the
delivery barriers that hinder conventional chemotherapeutics.
In addition, the conditions that permit anaerobic bacterial
growth, such as impaired circulation and extensive necrosis,
are found in many tumors, supporting the ideology that bacte-
rial therapeutic conduits may serve as a unique portal to a wide
variety of malignancies (21).
Collectively, these observations suggest that Salmonella, or
aspects thereof, has the potential to be developed as clinically
useful anticancer agents. In particular, Salmonella enterica
serovar Typhimurium (S. typhimurium) produces self-limited
enteritis in most healthy adults, can easily be manipulated to
carry foreign genes, and infects both mice and humans, allow-
ing testing of appropriate animal models. This species also
exists as a facultative anaerobe, allowing for survival in both
oxygenated and hypoxic conditions, and thus it would be
expected that this organism could colonize both small meta-
static lesions as well as larger tumors with an internal anaer-
obic environment. Recently, Low and co-workers (22) took
advantage of these unique properties and developed a strain of
S. typhimurium (VNP20009) that is nonpathogenic in mice,
pigs, and humans and accumulates 2,000-fold more in tumors.
Although this strain was able to retard tumor growth and
prolong survival in mice, it was not successful at slowing
tumor growth in humans (22).
Given that S. typhimurium can localize to tumors and mod-
ulate numerous biochemical pathways of intestinal epithelial
cells, we reasoned that perhaps this enteric pathogen has
evolved mechanisms that interact/interfere with multidrug re-
sistance (MDR) transporters that complicate drug treatment.
Consequently, we have investigated one of the membrane
transport proteins that promote the expulsion of xenobiotics,
the well-characterized P-glycoprotein (P-gp), a 170-kDa ATP-
dependent multispecific drug transporter (16). Reports linking
overexpression of the MDR1 gene (leading to increased levels
of P-gp) to adverse treatment outcomes in many cancers,
including colon cancer, provided the evidence necessary to
implicate this MDR phenotype as an important biologic target
for pharmacologic modulation (15, 19). In this study, we
examined where the two paths of targeting the MDR pheno-
type, specifically the inherent anti-tumor properties of P-gp and
Salmonella, cross in regard to cancer therapeutics and host-
tumor/pathogen interactions. We demonstrate that apical col-
onization of colon cancer cell lines by wild-type S. typhi-
murium leads to a profound functional decrease in the MDR
protein transporter, P-gp. In a physiological context, this is
consistent with our observation that the presence of P-gp
adversely influences the ability of S. typhimurium to invade
host cells. This is the first observation to link a microorganism
Address for reprint requests and other correspondence: B. McCormick,
Dept. of Pediatric Gastroenterology and Nutrition, Massachusetts General
Hospital, 114 16thSt. (114-3503), Charlestown, MA 02129 (e-mail: mccormic
The costs of publication of this article were defrayed in part by the payment
of page charges. The article must therefore be hereby marked “advertisement”
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Am J Physiol Gastrointest Liver Physiol 294: G1392–G1400, 2008.
First published April 10, 2008; doi:10.1152/ajpgi.00599.2007.
0193-1857/08 $8.00 Copyright © 2008 the American Physiological Societyhttp://www.ajpgi.org G1392
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INTERACTION OF S. TYPHIMURIUM WITH P-GLYCOPROTEIN
AJP-Gastrointest Liver Physiol • VOL 294 • JUNE 2008 • www.ajpgi.org
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