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CUTTING EDGE |
Department of Biochemistry and Cell Biology, National Institute of Infectious Diseases, Tokyo, Japan
| Abstract |
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| Introduction |
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B (5, 6, 7). Subsequently, using generated
TLR4-deficient mice, TLR4 was unequivocally demonstrated to be involved
in LPS responses (7). Furthermore, TLR4 was suggested to
be involved in ligand-specific recognition of LPS (8, 9),
although direct binding of TLR4 with LPS on the cell surface has not
beendemonstrated. However, expression of TLR4 alone is not sufficient
for LPS responsiveness to be conferred on a mouse pro B cell line,
Ba/F3 cells (10). In addition to TLR4, the expression of
MD-2, which associates with the extracellular domain of TLR4, is
required for LPS responsiveness to be conferred on Ba/F3 cells
(10). In fact, there is a TLR4-MD-2 complex on the surface
of mouse peritoneal macrophages, and the complex on the macrophages has
been shown to be involved in LPS responses (11).
Taxol, a diterpene purified from the bark of the Western yew
(Taxus brevifolia) (12), is an antitumor agent
that blocks mitosis by binding and stabilizing microtubules (13, 14). Although the structure of Taxol is quite different from
that of the LPS lipid A moiety, which is responsible for many LPS
responses (15), Taxol has been shown to exhibit many
LPS-mimetic activities as to murine macrophages, such as induction of
TNF secretion (16), NO production (17), and
NF-
B activation (18). Taxol was suggested to share a
receptor and/or signaling molecule with LPS because these LPS-mimetic
activities of Taxol were not detected in macrophages from
LPS-hyporesponsive C3H/HeJ mice (16, 17, 18). Interestingly,
the LPS-mimetic activities of Taxol were species specific; Taxol did
not mimic the action of LPS on human LPS-responsive cells including
macrophages (19, 20). By using stable transfectants
expressing MD-2 and/or TLR4, we found that mouse TLR4-MD-2 mediates
LPS-mimetic signal transduction by Taxol and that the species-specific
LPS-mimetic action of Taxol was based on the species difference between
mouse and human TLR4-MD-2 (21). In this study, we
investigated the molecular basis for the species-specific LPS-mimetic
action of Taxol and found that Gln22 of mouse MD-2 is
essential for LPS-mimetic Taxol signaling but not for LPS
signaling.
| Materials and Methods |
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Taxol from Taxus brevifolia was purchased from Sigma (St. Louis, MO). LPS prepared from Escherichia coli 0111:B4 was purchased from List Biological Laboratories (Campbell, CA). All other chemicals used were of reagent grade or better.
Stable transfectants and cell culture
Human embryonic kidney (HEK) 293 cells stably expressing a
recombinant mouse TLR4 bearing a FLAG (Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys)
and a 6x His epitope at its C terminus were generated by introducing
the mouse TLR4 expression construct prepared as described previously
(11). Expression of the recombinant mouse TLR4 was
confirmed by immunoblotting with Tetra-His Ab (Qiagen, Chatsworth, CA).
The stable HEK293 transfectant expressing the recombinant mouse TLR4
and HEK293 cells were transfected with p55Ig
luc, an
NF-
B-dependent luciferase reporter construct (22), the
resultant stable transfectants being named 293/mTLR4/luc and 293/luc,
respectively. Introduction of p55Ig
luc was confirmed by the increase
of luciferase activity on PMA stimulation. The transfectants were
purified by limited dilution. The stable HEK293 transfectants were
maintained in DMEM (Sigma) supplemented with 10% heat-inactivated FBS,
penicillin G (100 U/ml), and streptomycin sulfate (100 µg/ml) at
37°C.
Transient transfection
Cells (3 x 104) were seeded into the wells of a 24-well dish (Costar, Cambridge, MA), containing 1 ml of cell culture medium. After cultivation overnight, the cells were transfected with plasmids (0.3 µg/well) using FuGENE 6 transfection reagent (Boehringer Mannheim, Indianapolis, IN). The plasmids used for transfection were purified with a Wizard PureFection Plasmid DNA Purification System (Promega, Madison, WI).
Luciferase assay
Luciferase activity in cell lysates was measured with a luciferase assay system (Promega) as described previously (21).
Expression constructs
Human (10) or mouse (11) MD-2 cDNA was cloned into the XhoI and NotI sites of an expression vector, pEFBOS (23), by PCR-based introduction of restriction sites. Human/mouse chimeric MD-2 (cMD-2) cDNAs and mutant MD-2 cDNAs were generated by PCR-based overlap extension (24). The sequences of the PCR primers are available upon request. cMD-2 cDNAs and mutant MD-2 cDNAs were cloned into the XhoI and NotI sites of pEFBOS. The inserts of the expression constructs were verified by sequencing with an ABI PRISM Genetic Analyzer (Applied Biosystems, Foster City, CA). The stuffer region of pEFBOS was eliminated by digestion with XbaI, and the resulting construct was named pEFBOS(-).
| Results and Discussion |
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Coexpression of mouse TLR4 and mouse MD-2 conferred LPS and Taxol
responsiveness on a mouse pro-B cell line, Ba/F3 cells, but
coexpression of human TLR4 and human MD-2 conferred LPS responsiveness
alone (21). To further explore the molecular basis for
this species-specific action of Taxol, we previously examined whether
or not a Ba/F3 stable transfectant expressing mouse TLR4 (named
Ba/mTLR4) acquired Taxol or LPS responsiveness on the additional
expression of human MD-2. However, the effects of human MD-2 expression
on Taxol and LPS responsiveness in Ba/mTLR4 cells were unclear
(21), partly because NF-
B was slightly activated when
Ba/mTLR4 cells were stimulated with Taxol or LPS (11, 21).
Because we found that LPS and Taxol were incapable of inducing any
NF-
B activation in HEK293 cells expressing mouse TLR4
(293/mTLR4/luc) (Fig. 1
), we examined
whether expression of human or mouse MD-2 confers LPS or Taxol
responsiveness on 293/mTLR4/luc cells by measuring NF-
B activation.
As shown in Fig. 1
, 293/mTLR4/luc cells expressing mouse MD-2 responded
well to both Taxol and LPS stimulation, but 293/mTLR4/luc cells
expressing human MD-2 responded to LPS stimulation but not to Taxol
stimulation. These results show that human MD-2 does not have the
ability to confer Taxol responsiveness on mouse TLR4, although it has
the ability to confer LPS responsiveness on mouse TLR4.
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The amino acid sequence (160 aa) encoded by mouse MD-2 cDNA
exhibited 64% identity with that (160 aa) encoded by human MD-2 cDNA
(11). To determine whether there is a domain(s) of mouse
MD-2 responsible for conferring Taxol responsiveness on mouse TLR4,
constructs for expressing mouse/human cMD-2 proteins (Fig. 2
A) were generated, and their
ability to confer Taxol responsiveness was examined. The 293/mTLR4/luc
cells expressing cMD2-2, -3, -4, -5, or -6 did not respond to Taxol
stimulation, and those expressing cMD2-1 slightly responded to Taxol
stimulation (Fig. 2
B). In contrast, all of the transfectants
expressing cMD-2 proteins responded to LPS stimulation (Fig. 2
B). These results suggested that the ability of mouse MD-2
to confer Taxol responsiveness on mouse TLR4 is not due to a particular
domain of mouse MD-2.
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Although only nine amino acid residues were different between the
amino acid sequences of mouse MD-2 and cMD21 (Figs. 2
A and
3A), the ability of mouse MD-2
to confer Taxol responsiveness was apparently different from that of
cMD21, the fold induction of reporter activity on Taxol stimulation
being 14- and 3.2-fold in 293/mTLR4/luc cells expressing mouse MD-2 and
cMD21, respectively (Fig. 2
B). To determine which of the
nine different amino acid residues were important for Taxol signaling,
we generated mutant mouse MD-2 expression constructs in which
Pro13, Ser18,
Glu19, or Gln22 was
replaced with the corresponding amino acid residue of human MD-2, and
then their ability to confer Taxol and LPS responsiveness was examined
(Fig. 3
B). Although P13S-, S18A-, and E19Q-mouse MD-2
exhibited similar abilities to confer Taxol responsiveness on
293/mTLR4/luc cells to that of mouse MD-2, Q22Y-mouse MD-2 had an
apparently lower ability to confer Taxol responsiveness than mouse
MD-2, the fold induction of reporter activity on 10 µM Taxol
stimulation being 9.4- and 2.7-fold in 293/mTLR4/luc cells expressing
mouse MD-2 and Q22Y-mouse MD-2, respectively (Fig. 3
B). With
regard to the effect of the Taxol concentration on NF-
B activation,
1 µM Taxol induced NF-
B activation in the cells expressing mouse
MD-2, whereas 10 µM Taxol was required to induce NF-
B activation
in the cells expressing Q22Y-mouse MD-2, just like in the cells
expressing cMD21 (Fig. 3
C). Furthermore, the cells
expressing Y22Q-cMD21, in which Tyr22 of
cMD21 was replaced with mouse type Gln22,
showed similar sensitivity to Taxol to that of the cells expressing
mouse MD-2 (Fig. 3
C). In contrast, the sensitivity to LPS
was similar between the cells expressing mouse MD-2 and those
expressing Q22Y-mouse MD-2 (Fig. 3
, B and C).
These results, taken together, indicate that
Gln22 of mouse MD-2 is involved in the
species-specific LPS-mimetic action of Taxol.
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B activation in the 293/mTLR4 cells
expressing Q22E-mouse MD-2 was similar to that in those expressing
mouse MD-2 (Fig. 4
B activation was similar among these cells expressing mutant
mouse MD-2 proteins. These results, taken together, suggest that
Gln22 is an essential residue for Taxol
signaling.
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| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Masahiro Nishijima, National Institute of Infectious Diseases, Toyama, 1-23-1, Shinjuku-ku, Tokyo 162-8640, Japan. ![]()
3 Abbreviations used in this paper: TLR, Toll-like receptor; HEK, human embryonic kidney; cMD-2, chimeric MD-2. ![]()
Received for publication October 11, 2000. Accepted for publication October 27, 2000.
| References |
|---|
|
|
|---|
B translocation in murine macrophages. Infect. Immun. 64:878.[Abstract]
and tumor necrosis factor-
production. J. Lab. Clin. Med. 122:374.[Medline]
B p50 homodimers. Genes Dev. 7:1354.This article has been cited by other articles:
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||||
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G. D. Snyder, R. E. Oberley-Deegan, K. L. Goss, S. A. Romig-Martin, L. L. Stoll, J. M. Snyder, and N. L. Weintraub Surfactant protein D is expressed and modulates inflammatory responses in human coronary artery smooth muscle cells Am J Physiol Heart Circ Physiol, May 1, 2008; 294(5): H2053 - H2059. [Abstract] [Full Text] [PDF] |
||||
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||||
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S. M Zimmer, S. M Zughaier, Y.-L. Tzeng, and D. S Stephens Human MD-2 discrimination of meningococcal lipid A structures and activation of TLR4 Glycobiology, August 1, 2007; 17(8): 847 - 856. [Abstract] [Full Text] [PDF] |
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