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Regular Articles |


From the Departments of Biochemistry and Molecular
Biology*
and Physiology and
Biophysics,
Immunology Research Group,
University of Calgary, Calgary, Alberta, Canada
| Abstract |
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|
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(TNF-
). BT-20 and SK-BR-3
cells only expressed ICAM-1 or VCAM-1 after stimulation with TNF-
.
Eosinophils constitutively bound to MDA-MB-435S cells, but not
to BT-20 cells. Stimulation with TNF-
slightly enhanced eosinophil
adhesion to MDA-MB-435S cells and dramatically increased adhesion to
BT-20 cells. Greater than 80% of eosinophil adhesion to these cell
lines was blocked with an anti-
4-integrin monoclonal antibody. Both
MDA-MB-435S and BT-20 cells also released eosinophil activator(s).
Supernatants from TNF-
-treated, but not
control-treated, cell lines increased eosinophil adhesion
to fibronectin and increased eosinophil transmigration across
fibronectin-coated transwell plates. Enzyme-linked immunosorbent assays
showed that TNF-
-stimulated breast carcinoma cells released the
chemokine regulated on activation, T cell expressed and
secreted (RANTES). Addition of an anti-RANTES antibody to breast
carcinoma cell supernatants partially blocked eosinophil activation
suggesting that RANTES in these supernatants was participating in
eosinophil activation. These data show that TNF-
-stimulated breast
carcinoma cells express mediators that can both bind and activate
eosinophils, suggesting a mechanism for eosinophil localization
to breast carcinoma sites.
| Introduction |
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|
|
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The mechanisms used by eosinophils to
adhere to activated endothelium may provide insights into how these
cells interact with carcinoma cells. Eosinophils, like other
leukocytes, respond to both adhesion and activation signals provided by
the endothelium. These signals result in leukocyte adhesion to the
vessel wall, activation, and transmigration into the
tissue.9
The first step in this process involves the rapid
tethering of eosinophils to P-selectin,10,11
E-selectin,10
or vascular cell adhesion molecule-1
(VCAM-1)11,12
expressed on activated endothelial cells.
Once eosinophils have bound to the endothelium, chemoattractants
activate eosinophils leading to firm adhesion mediated by
4-integrins binding to VCAM-1 as well as ß2-integrins likely
interacting with intercellular adhesion molecule-1
(ICAM-1).12,13
These chemoattractants include chemokines
such as eotaxin and regulated on activation, normal T cells expressed
and secreted (RANTES) as well as lipid mediators such as
platelet-activating factor and leukotrienes.1
Once bound
and activated, eosinophils migrate into inflamed tissue.1
Many of the adhesion and activation molecules expressed by stimulated endothelium have now been shown to be expressed by tumor cells. P-selectin and E-selectin are associated with many types of tumors; however, expression of the selectins is restricted to the vascular endothelium associated with the tumors.14,15 Similar observations have been made for VCAM-1, with increased expression found on tumor-associated endothelium.16,17 Although VCAM-1 is expressed on some mesotheliomas,18 VCAM-1 expression on tumors of epithelial origin has not been clearly demonstrated. Charpin et al17 found some focal expression of VCAM-1 on breast carcinoma epithelial cells; yet most of the VCAM-1 expression was found on stromal endothelial cells. In contrast, ICAM-1 is expressed both by tumor endothelium as well as by tumor cells of epithelial origin.16,19,20 This has been demonstrated using both tissue sections as well as tumor cell lines. Many have speculated that ICAM-1 and VCAM-1 expression may favor adhesive interactions with leukocytes, thus facilitating leukocyte tumor infiltration.
In this study we first examined the synthesis and expression of
adhesion proteins by human breast carcinoma cell lines, then determined
if expression of these adhesion proteins could be modulated by exposure
to tumor necrosis factor-
(TNF-
). Finally we assayed for
eosinophil adhesion and activation. We found that human breast
carcinoma cells express ICAM-1 and VCAM-1 on their surfaces and bind
eosinophils. These cell lines also release eosinophil activators
including the CC chemokine RANTES when exposed to TNF-
.
| Materials and Methods |
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Human TNF-
and enzyme-linked immunosorbent assay (ELISA) kits
for eotaxin, macrophage inflammatory protein-1
(MIP-1
), and
RANTES were from R & D Systems, Inc. (Minneapolis, MN). Hanks
balanced salt solution with Ca2+ and
Mg2+ (HBSS), lymphoprep 1077, Dulbeccos
modified Eagles medium, Media 199 (M199), fetal bovine serum,
Superscript II, and TRIzol reagent were from Life Technologies, Inc.
(Grand Island, NY). PCR Master Mix was from Qiagen (Mississagua,
Canada). All plasticware was from Becton Dickinson (Franklin Lakes,
NJ). Human serum albumin (HSA) was from Immuno US (Rochester, MI).
Enhanced chemiluminescence reagents were from Amersham
(Buckinghamshire, England). All other chemicals were from BDH, Inc.
(Toronto, Canada).
The anti-human P-selectin monoclonal antibodies (mAbs) S12 and G1 (both
IgG1-
) were prepared and characterized
as described.21,22
The blocking anti-human E-selectin mAb
ES1 (IgG1-
) was prepared and characterized as
described.23
Both the P-selectin and E-selectin mAbs were
kindly provided by Dr. Rodger McEver (University of Oklahoma, Oklahoma
City, OK). Anti-CD16 and anti-CD3 mAbs conjugated to paramagnetic beads
were purchased from Miltenyi (Auburn, CA). All other mAbs were
purchased from Serotec (Oxford, England). All antibodies were used
according to manufactures instructions or as described.
Cell Culture and Isolation
MDA-MB-435S, BT-20, SK-BR-3, and MDA-MB-468 were kindly provided by Drs. Patrick Lee and Karl Riabowol (University of Calgary, Calgary, Canada) and were maintained in Dulbeccos modified Eagles medium with 10% fetal bovine serum and antibiotics. Granulocytes were isolated from normal human donors by dextran sedimentation, hypotonic lysis, and density centrifugation on lymphoprep 1077 as described.24 Eosinophils were isolated from granulocytes by negative selection with anti-CD16 and anti-CD3 microbeads using magnetic cell separation as described.10 Eosinophils isolated in this way maintain an unactivated phenotype10,12 and were >95% pure as assessed by Kimura staining.
Reverse Transcription-Polymerase Chain Reaction (RT-PCR)
Stimulated cells were washed once with M199 and immediately lysed
in TRIzol reagent (Life Technologies, Inc.) and total RNA was extracted
according to the manufacturers instructions. RNA concentrations were
determined using a GeneQuant spectrophotometer (Pharmacia, Pascataway,
NJ). Reverse transcription using Superscript II (Life Technologies,
Inc.) was performed according to manufacturers instructions. PCR was
performed with Qiagen Master Mix using 2 µl of the RT reaction as
template cDNA and the appropriate primer pairs. The primers were as
follows: ß-actin forward 5'-CATGGATGATGATATCGCCG-3' and reverse
5'-ACAG-CCTGGATAGCAACGTA-3' (417 bp); ICAM-1 forward
5'-GGCAAGAACCTTACCCTACG-3' and reverse
5'-GAGA-CCTCTGGCTTCGTCAG-3' (586 bp); and VCAM-1 forward
5'-AGGGGACCACATCTACGCT-3' and reverse
5'-ACAGAGCTCCCATTCACGA-3' (1043 bp). Thirty-five PCR cycles
with 1 minute at 94°C, 1 minute at 55°C, and 1 minute at
72°C were used for amplification. PCR products were electrophoresed
through 2% agarose gels containing 0.5 µg/ml ethidium bromide and
were visualized using UV light. ß-Actin was used as positive control
for mRNA amplification. Control and TNF-
-stimulated endothelial
cells were used as positive and negative controls for adhesion molecule
mRNA expression.
Determination of Adhesion Protein Expression
Confluent monolayers of breast carcinoma cell lines were washed
and stimulated for 4 or 24 hours with either M199 with 0.5% HSA
(M199/A) alone or M199/A containing 20 ng/ml TNF-
. Total protein
expression in control and TNF-
-stimulated cell lines was determined
by Western blotting as described.25
Surface expression of
adhesion proteins on control and TNF-
-stimulated cell lines was
determined using a modified ELISA as described.26
Briefly,
stimulated cells were washed once with ice cold HBSS, fixed for 30
minutes at 4°C with 1% paraformaldehyde in HBSS, and then blocked
with HBSS/1%HSA for at least 30 minutes at 37°C. Surface expression
of adhesion proteins was then determined by adding saturating amounts
of mAb in HBSS/1%HSA and incubating for 30 minutes at 37°C. Cells
were washed three times with HBSS and then incubated with a 1/1000
dilution of a peroxidase-conjugated goat anti-mouse IgG secondary
antibody (Amersham, Buckinghamshire, England) for 30 minutes at 37°C.
mAb binding was determined using a trimethyl-benzadine one-step
substrate (DAKO, Carpinteria, CA) and quantified by reading absorbance
at 450 nm. Background expression was determined by using an
isotype-matched nonimmune IgG. Control and TNF-
-stimulated
endothelial cells were used as positive and negative controls for
adhesion molecule expression.
Adhesion Assay
Cell lines grown in 24-well plates were washed and stimulated for
24 hours with either M199/A alone or M199/A containing 20 ng/ml
TNF-
. The supernatant was removed and used in eosinophil activation
assays. The cells were washed once with HBSS and 250 µl eosinophils
(2 x 106/ml) were added to each well. After
15 minutes at 37°C, the nonadherent eosinophils were removed and the
cells were washed twice with HBSS to remove loosely adherent
eosinophils. Adherent eosinophils were quantified by counting three
random fields using a 20x objective and NIH Image similar to
previously described.12
In eosinophil activation
experiments, 24- or 48-well plates were coated with either 0.2%
gelatin or 25 µg/ml fibronectin. Two hundred twenty-five microliters
of eosinophils (12 x 106/ml) were placed
in each well and then 25 µl of supernatant from control or
TNF-
-stimulated cell lines was added. After 10 minutes at 37°C,
the nonadherent eosinophils were removed and the plates were washed
twice with HBSS to remove loosely adherent eosinophils. Adherent
eosinophils were quantified by assaying for eosinophil peroxidase
activity. HBSS/A alone was used as a negative control and HBSS/A
containing 10-7 mol/L formyl-Met-Leu-Phe
(fMLP) was used as a positive control. In some experiments
either cell lines, eosinophils, or both were pretreated for 10 minutes
with mAbs. mAbs were used at concentrations previously shown to be
optimal.11,12
Transmigration Assay
Eosinophil transmigration was determined using 3-µm pore transwell plates (Corning Costar Corporation, Cambridge, MA). Briefly, both the membranes and the bottom of the plates were coated with 25 µg/ml fibronectin. Supernatant was diluted 1:10 in HBSS/A and added to the lower chamber. Eosinophils (4 x 106/ml) were added to the upper chamber. After 90 minutes at 37°C, eosinophils that had migrated to the lower chamber were determined by counting three low-powered fields as described above. HBSS/A alone was used a negative control and HBSS/A containing 10-7 mol/L fMLP was used as a positive control.
ELISA for Eotaxin, MIP-1
, and RANTES
Supernatants from control or TNF-
-stimulated cell lines were
collected and chemokine levels were determined by ELISA according to
manufacturers instructions.
Statistics
All experiments were performed at least three times and the data are presented as mean and SEM of those replicates. Statistical differences between experimental groups were evaluated using either paired or unpaired Students t-test. P values < 0.05 were considered significant.
| Results |
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|
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In this study, four human breast carcinoma cell lines were
examined under baseline conditions or after stimulation with TNF-
,
since this cytokine is a key regulator of adhesion molecule expression
in both endothelial cells and epithelial cell lines.27-30
We first used RT-PCR to determine if these cells synthesized mRNA for
various adhesion molecules. MDA-MB-435S and MDA-MB-468 cells
both constitutively expressed high levels of mRNA for ICAM-1 (Figure 1A)
. Stimulation with TNF-
did not
increase this expression (Figure 1A)
. In contrast, BT-20 and SKBR-3
cells expressed only nominal levels of ICAM-1 under baseline
conditions, but stimulation with TNF-
for 24 hours dramatically
increased mRNA expression (Figure 1A)
. MDA-MB-468 cells also expressed
high constitutive levels of mRNA for VCAM-1; whereas, all of the other
cell lines had only low levels of VCAM-1 message with TNF-
stimulation dramatically increasing expression (Figure 1A)
. None of the
cell lines examined showed clear mRNA expression for either P-selectin
or E-selectin (data not shown).
|
mRNA expression of these adhesion molecules led us to examine
protein expression. In these experiments, cell lines were treated with
buffer alone or with buffer containing TNF-
for either 4 or 24
hours. The cells were then scraped and the Triton X-100 soluble
proteins were separated by SDS-PAGE and Western blotted using the
appropriate mAbs. We found robust, constitutive expression of both
ICAM-1 and VCAM-1 in MDA-MB-435S and MDA-MB-468 cells but not
on the other cell lines examined (Figure 1B)
. Treatment of
MDA-MB-435S and MDA-MB-468 cells with TNF-
led to a slight
increase in the expression of both ICAM-1 and VCAM-1 (Figure 1B)
.
Although BT-20 and SK-BR-3 cells did show low level constitutive
expression of mRNA for ICAM-1 and VCAM-1, neither protein was expressed
in these cell lines under control conditions (Figure 1B)
. Stimulation
of these cells with TNF-
for 24 hours dramatically induced the
expression of both ICAM-1 and VCAM-1 by BT-20 and SKBR-3 cells (Figure 1B)
. These data represent the first description of VCAM-1 expression by
tumor cell lines of epithelial origin.
Figure 1
shows that breast carcinoma cells can express constitutive or
induced protein for ICAM-1 and VCAM-1; however, Western blots cannot
assess whether these proteins are present on the cell surface. We
addressed this question by using a modified ELISA technique to evaluate
adhesion molecule surface expression. Similar to the Western blotting,
both ICAM-1 and VCAM-1 were constitutively expressed on the surface of
MDA-MB-435S and MDA-MB-468 cells (Figure 2A
and data not shown). Although Western
blotting showed an increase in ICAM-1 and VCAM-1 expression with
TNF-
treatment, no significant change in the surface expression of
these proteins was observed after TNF-
stimulation (Figure 2A)
.
Neither ICAM-1 or VCAM-1 were constitutively expressed on the surface
of BT-20 (Figure 2B)
or SK-BR-3 cells (data not shown). Instead there
was a dramatic increase in the surface expression of both of these
proteins when cells were stimulated with TNF-
(Figure 2B
and data
not shown). These data were consistent with the Western blotting
results.
|
Eosinophils Bind to Breast Carcinoma Cell Lines via
4- and
ß2-Integrins
The remaining experiments in this study focus on the
MDA-MB-435S cells and the BT-20 cells, since they represented
the two phenotypes observed. We next determined if these breast
carcinoma cell lines were able to support eosinophil adhesion. Freshly
isolated eosinophils were added to either control or TNF-
-treated
carcinoma cells. After 15 minutes the nonadherent and loosely adherent
eosinophils were removed and the adherent eosinophils were counted
using microscopy. We found that eosinophils constitutively bound both
to MDA-MB-435S cells and to the surrounding extracellular
matrix. Stimulation with TNF-
resulted in a modest, but significant
increase in eosinophil adhesion (Figure 3)
. In contrast, few eosinophils bound to
unstimulated BT-20 cells (Figure 3)
; however, there was a significant
increase in eosinophil adhesion to BT-20 cells stimulated with TNF-
,
with virtually all adhesion occurring directly on the cells (Figure 3)
.
Thus eosinophils can bind directly to breast carcinoma cells.
|
4-integrin mAb was the
only antibody that alone reduced constitutive eosinophil adhesion to
MDA-MB-435S cells (Figure 4A)
4-integrin mAb also blocked most eosinophil
adhesion to TNF-
-stimulated MDA-MB-435S cells (Figure 4B)
-stimulated cells;
however, neither ICAM-1 nor VCAM-1 mAbs alone had any effect on
eosinophil adhesion (Figure 4B)
|
4-integrins both
attenuated eosinophil adhesion to TNF-
-stimulated BT-20 cells,
although inhibition was greater with the anti-
4-integrin mAb (Figure 4C)
Breast Carcinoma Cell Lines Stimulated with TNF-
Release
Eosinophil Activators
Deposition of eosinophil granule proteins at tumor sites suggests
that mechanisms exist not only for eosinophil adhesion, but also for
their activation.5,33
Furthermore, the observation that
eosinophils were adhering both to MDA-MB-435S cells as well
as to the exposed matrix suggested a role for eosinophil activators.
This issue was addressed by harvesting the supernatants from either
MDA-MB-435S or BT-20 cells treated with buffer alone or
treated with TNF-
, then determining if there was a mediator in these
supernatants that could increase eosinophil adhesion to either gelatin-
or fibronectin-coated surfaces. These surfaces were used to assess
increased adhesivness of the ß2-integrins or the
4-integrins,
respectively. Freshly isolated eosinophils were added to plates coated
with gelatin or fibronectin. Eosinophils were then stimulated with a
1:10 dilution of supernatants from control or TNF-
-treated breast
carcinoma cell lines.
Supernatants from 24-hour TNF-
-treated, but not control-treated,
MDA-MB-435S cells increased eosinophil adhesion to
fibronectin with little increase in binding to gelatin (Figure 5A)
. This was not because of the presence
of TNF-
alone as neither TNF-
alone (data not shown) nor the
4-hour TNF-
supernatant increased eosinophil adhesion in this assay
(Figure 5A)
. As expected, an anti-
4-integrin mAb blocked eosinophil
adhesion to fibronectin (88.2 ± 3.3% inhibition;
n = 3). Thus, MDA-MB-435S cells
constitutively express adhesion proteins on their surface and can bind
eosinophils, but only after stimulation with TNF-
for 24 hours do
these cells release mediator(s) that can activate eosinophils.
|
stimulation. Unlike the
MDA-MB-435S cells, the supernatants from BT-20 cells treated
with TNF-
increased eosinophil adhesion to both gelatin and
fibronectin (Figure 5B)
supernatants were able to increase
eosinophil adhesion on fibronectin; whereas only the 24-hour
supernatant had pro-adhesive effects on gelatin (Figure 5B)
4-integrin
blocked adhesion to fibronectin (91.6 ± 4.2% inhibition;
n = 3). In addition, an anti-ß2-integrin blocked most
adhesion to gelatin (79.4 ± 1.9% inhibition; n =
3). These data suggest that mediators released from BT-20 cells
activate both the ß2- and
4-integrins on eosinophils promoting
adhesion to both gelatin and fibronectin, whereas the mediators
released from MDA-MB-435S cells only activate the
4-integrins promoting adhesion only to fibronectin.
We used an eosinophil transmigration assay to determine if the
mediators present in these supernatants were also chemotactic for
eosinophils. Eosinophils were placed in the upper chamber of a
transwell plate and supernatant from control or TNF-
-treated cells
was diluted 1:10 and placed in the lower chamber. Supernatants from
buffer-treated cells had no effect on eosinophil transmigration (Figure 6)
. In contrast, supernatants from both
MDA-MB-435S and BT-20 cells treated with TNF-
elicited
eosinophil transmigration (Figure 6)
. TNF-
alone at the same
concentration present in the diluted supernatant (2 ng/ml) induced only
minimal transmigration (Figure 6)
. Thus supernatants from
TNF-
-stimulated breast carcinoma cells contain eosinophil
chemotactic factors.
|
-stimulated MDA-MB-435S and BT-20
cells contained the CC chemokine RANTES (Figure 7)
was released by these breast carcinoma cell lines (data not
shown). To determine whether the RANTES present in the supernatant was
participating in eosinophil activation, we examined the ability of an
anti-RANTES antibody to block eosinophil adhesion to fibronectin. An
anti-RANTES antibody was able to attenuate eosinophil adhesion in
response to both MDA-MB-435S supernatants (30.0 ± 3.3%
inhibition, n = 3) and to BT-20 supernatants (40.6
± 14.4% inhibition, n = 3). Experiments using 10-fold
excess antibody resulted in similar inhibition, suggesting that this
antibody was used at saturating concentrations. These data show that
RANTES participates in eosinophil activation in response to breast
carcinoma supernatants; however, the incomplete inhibition with this
antibody suggests that additional eosinophil activators are likely
present. Studies are ongoing to identify these additional mediators.
|
| Discussion |
|---|
|
|
|---|
Several families of adhesion molecules are involved in the localization
of eosinophils into sites of inflammation. Endothelial cells stimulated
with either TNF-
11
or interleukin-412
have
increased expression of both selectins and Ig superfamily proteins that
act to tether and firmly bind eosinophils to these surfaces. Once
eosinophils are bound to the endothelium, directed localization of
eosinophils into tumor sites likely involves the combined actions of
chemoattractants and adhesion molecules present on tumor cells
themselves. Increased expression of selectins has been observed at
tumor sites as compared to normal tissue samples; however, this
expression is associated with the tumor endothelium.14,15
In contrast, ICAM-1 is expressed both by the tumor endothelium as well
as by tumor cells themselves.16,19,20
Increased expression
of ICAM-1 has been seen in tissue samples of breast carcinomas and is
associated with an improved prognosis.36
The mechanisms by
which ICAM-1 expression leads to decreased tumor size are unknown, but
may involve localization of leukocytes to the tumor.
In this study we used several human breast carcinoma cell lines including MDA-MB-435S, BT-20, SK-BR-3, and MDA-MB-468 to determine whether the expression of known adhesion molecules may result in eosinophil adhesion. All of the cell lines used in this study are adenocarcinomas of the breast, meaning that the tumors arose from glandular epithelial cells. The major difference between the four cell lines lies in their tumorigenicity. With MDA-MB-435S as the exception, all of the cell lines used are capable of forming tumors in nude mice. Morphologically, MDA-MB-435S also differ by growing in spindle shape, whereas the other cell lines form uniform monolayers. All of these cell lines are extensively used in breast cancer research and concentrating on the MDA-MB-435S and BT-20 cell lines allowed us to identify the differences in adhesion molecule expression, cell activation, and chemokine expression between these two characteristically different cell lines.
We examined adhesion molecule expression before and after stimulation
with TNF-
. TNF-
is a multifunctional cytokine that has been shown
to be produced by tumor-associated macrophages.37,38
TNF-
has many effects on tumors cells in vitro including
the induction of either necrotic or apoptotic cell death in some types
of tumors. TNF-
, along with interleukin-1 and interleukin-6, has
also been demonstrated to induce ICAM-1 expression on several types of
epithelial tumors including breast carcinomas.29,30,39
In
contrast, VCAM-1 has not been examined with respect to induction with
TNF-
; however, in other studies VCAM-1 has not been shown to be
expressed by breast carcinoma cells.14
RT-PCR, Western blotting, and cell surface ELISAs were used to examine
adhesion molecule expression on several breast carcinoma cell lines.
Two of the cell lines examined, MDA-MB-435S and MDA-MB-468,
constitutively expressed ICAM-1 and VCAM-1 (Figure 1)
. This expression
was enhanced after exposure to TNF-
. The other cell lines examined
only expressed these adhesion molecules after stimulation with TNF-
.
Although ICAM-1 expression was expected based on previous studies, the
expression of VCAM-1 was not expected. Using RT-PCR we amplified a band
for VCAM-1 at the expected size (1043 bp). Since mRNA levels do not
always correlate with protein expression, we also performed Western
blots and detected a protein with a molecular weight of
110 kd. One
explanation for the differences between our data (this study) and
others who have examined VCAM-1 protein expression14,17
may lie in the immunogenicity of the VCAM-1 expressed by breast
carcinoma cells. This may be attributable to either differential
splicing or posttranslational modifications of VCAM-1. VCAM-1 can be
alternatively spliced resulting in either a 6 domain or 7 domain form
of the molecule in endothelial cells.40
We found evidence
for this type of splicing with VCAM-1 expressed by
MDA-MB-435S cells by Western blotting where a doublet was
clearly observed (Figure 1B)
. Furthermore, Abe et al41
have demonstrated that endothelial cells treated with a combination of
interleukin-4 and TNF-
express VCAM-1 based on Western blotting and
ELISAs, but this VCAM-1 does not recognize its ligand on circulating T
cells. To further support this hypothesis, we found that only one of
three commercially available mAbs to VCAM-1 recognized the molecule
expressed on breast carcinoma cells, whereas, all three recognized
VCAM-1 present on TNF-
-stimulated endothelial cells (data not
shown).
Breast carcinoma cells bind eosinophils through interactions with
4-integrins. Although
4-integrins bind to BT-20 cells via VCAM-1
this may not be the case with MDA-MB-435S cells, because our
VCAM-1 mAb has no effect on eosinophil adhesion. Other ligands for the
4-integrins include alternate epitopes on VCAM-1 not recognized by
our mAb as well as extracellular matrix components such as fibronectin.
Interestingly, we found that eosinophils did bind to the exposed matrix
of MDA-MB-435S cells. This adhesion was partially dependent
on ß2-integrins, suggesting that the cell line was releasing an
eosinophil activator. By testing the ability of breast carcinoma cell
supernatants for the ability to stimulate eosinophil adhesion to
extracellular matrix proteins, we showed that these cell lines
release potent eosinophil activators including the CC chemokine RANTES.
Although RANTES is a potent eosinophil chemoattractant, it also exerts
its effects on T cells and monocytes. Thus these breast carcinoma cells
release mediators that are potentially able to bring several cell types
into the tissue. An anti-RANTES antibody only blocked 30 to 40% of
eosinophil adhesion suggesting that other mediators are released by
these breast carcinoma cell lines. Studies are currently underway to
identify and characterize these additional mediators.
The expression of adhesion and activation molecules by breast carcinoma
cells may provide a mechanism for localizing eosinophils to tumor
sites. Once localized at these sites, the role for eosinophils is
unclear. There are several studies that suggest that eosinophil tumor
infiltration is associated with improved prognosis.3,7,35
There are an equal number of studies showing either no role for
eosinophils or an association with a poor prognosis.42-44
Recently it has been suggested that eosinophils may not play a direct
role in tumor cell clearance, but may instead participate in tissue
remodeling.4,45
Eosinophils can synthesize cytokines,
growth factors, and proteases that are associated with both tissue
remodeling and angiogenesis. These include transforming growth
factors-
and -ß1,46-48
vascular endothelial cell
growth factor,49
and matrix
metalloprotease-9.50,51
Thus, the role of eosinophils in
tumor biology may be directed less toward direct tumoricidal activity
and more to modulation of the tumor microenvironment.
| Acknowledgements |
|---|
| Footnotes |
|---|
Supported by grants from the Canadian Breast Cancer Foundation, Alberta Chapter, the Honda Run for the Cure and the Medical Research Council of Canada (MT-14180). Dr. K. D. Patel is supported both by a scholarship from the Medical Research Council of Canada and a scholarship from the Alberta Heritage Foundation for Medical Research.
Accepted for publication March 7, 2000.
| References |
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