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CUTTING EDGE |


*
Division of Clinical Immunology and Allergy, Johns Hopkins Asthma and Allergy Center, Baltimore, MD 21224;
Division of Otolaryngology, University of Chicago, Chicago, IL; and
LeukoSite Inc., Boston, MA 02142
| Abstract |
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stimulation of the
human primary bronchial epithelial cells as well as the epithelial cell
line, BEAS-2B; IFN-
potentiated the TNF-
-induced expression.
Western blots and flow cytometry confirmed the expression of CCR3
protein. This receptor is functional based on studies demonstrating
eotaxin-induced intracellular Ca2+ flux and tyrosine
phosphorylation of cellular proteins. The specificity
of this functional response was confirmed by blocking these signaling
events with anti-CCR3 mAb (7B11) or pertussis toxin. Furthermore,
125I-eotaxin binding assay confirmed that CCR3 expressed on
epithelial cells have the expected ligand specificity. These studies
indicate that airway epithelial cells express CCR3 and suggest that
CCR3 ligands may influence epithelial cell
functions. | Introduction |
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Chemokine receptors have been demonstrated on structural cells, such as smooth muscle and endothelial cells (10, 11). We now report that human airway epithelial cells express a functional CCR3. Epithelial cells play a significant role in the chemokine network, as a major source of both CXC and C-C chemokines (12). Among the C-C chemokines, epithelial cells produce the CCR3 agonists, RANTES, MCP-3, MCP-4, eotaxin, and eotaxin-2 (13, 14, 15, 16). These C-C chemokines may contribute to the accumulation and activation of eosinophils and other inflammatory cells in the allergic airway. The coexpression of CCR3 and its ligands suggest that epithelial cells may have a C-C chemokine autoregulatory pathway.
| Materials and Methods |
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Formalin-fixed, paraffin-embedded tissue sections were stained using Vectastain ABC-AP Kit and Red Substrate Kit (Vector Laboratories, Burlingame, CA). The mouse monoclonal blocking anti-CCR3 Ab (7B11; LeukoSite, Boston, MA) anti-eotaxin (2G6; LeukoSite), and anti-RANTES (3D3; Genentech, San Francisco, CA) were used with the isotype-matched (IgG2a; Coulter-Immunotech, Miami, FL) mouse Ig control.
Cell culture
The BEAS-2B and the 16-HBE cell lines were kindly donated by Drs. Curtis Harris and Dieter Gruenert, respectively (17, 18). Primary bronchial epithelial cells (PBEC) were isolated and purity confirmed as described (19, 20). Normal human bronchial epithelial cells (NHBE) were used as another source of primary epithelial cells (CC-2541; Clontech, Palo Alto, CA). BEAS-2B (passage 3340) and PBEC (passage 1) were cultured in Hanks F12/DMEM medium with 5% heat-inactivated FCS, 1% L-glutamine, 1% fungizone, penicillin (100 U/ml), and streptomycin (100 mg/ml). 16-HBE (passage 1822) were cultured in DMEM with 10% heat-inactivated FCS, 1% L-glutamine, 1% fungizone, penicillin (100 U/ml), and streptomycin (100 mg/ml), and NHBE (passage 13) were cultured in BEGM Bullet Kit (Clontech).
Northern blot analysis
Total RNA was extracted with RNAzol B (20). RNA (20 µg) was electrophoresed and blotted onto Genescreen plus nylon membranes (NEN Life Sciences, Boston, MA). Membranes were hybridized with a 32P-labeled cDNA probe encoding 0.3 kb of the CCR3 coding region, or a GAPDH probe (Clontech), and washed with high-stringency conditions (2x SSC, 0.1% SDS, 65°C, 15 min).
Western blot analysis for CCR3 protein
Cell lysates (10 µg/lane) were separated by SDS-PAGE and transferred to a Sequi-blot polyvinylidene difluoride membrane (Bio-Rad, Hercules, CA). Blots were blocked in 1x PBS/5% BSA/0.1% Tween 20 overnight and incubated with the anti-CCR3 Ab 7B11 (1 µg/ml) or with the rabbit polyclonal anti-CCR3 Ab H-52 (1 µg/ml; Santa Cruz Biotechnology, Santa Cruz, CA), washed with 1x PBS/0.1% Tween 20, and incubated with HRP-conjugated secondary Ab. Immunoreactive bands were visualized using ECL (Amersham, Arlington Heights, IL).
Stimulation, preparation of cytosolic extracts, and Western analysis
Epithelial cells were washed with serum-free media and preincubated with either anti-CCR3 Ab (7B11, 10 µg/ml) or IgG2a (10 µg/ml; Coulter) for 30 min on ice or pertussis toxin (1 µg/ml; Sigma, St. Louis, MO) for 1 h at 37°C. Cells were stimulated with eotaxin (R&D Systems, Minneapolis, MN) for up to 10 min. The reaction was quenched with cold 10 mM sodium orthovanadate (Sigma) and complete mini-protease inhibitor cocktail tablets (Boehringer Mannheim, Indianapolis, IN). The cells were harvested and lysed with lysis buffer (10 mM Tris, pH 7.4, 150 mM NaCl, 5 mM EDTA, 10% glycerol, 1% Triton X-100, 1 mM sodium orthovanadate, and protease inhibitor tablets). Protein concentrations were determined using the bicinchoninic acid assay (Pierce, Rockford, IL). Samples were boiled in 4x SDS buffer (0.5 M Tris, pH 6.8, 16% glycerol, 3% SDS, 8% 2-ME, 2 mg bromophenol blue) and 10 µg of protein loaded onto a 10% Tris-glycine SDS polyacrylamide gel. Proteins were transferred to a polyvinylidene difluoride membrane and washed in PBST (20 mM Tris, 137 mM NaCl, 0.2% Tween 20), and nonspecific binding was blocked with 5% BSA (Fisher Scientific, Pittsburgh, PA) in PBST. The membranes were incubated overnight (4°C) with p42/p44 anti-phospho-extracellular signal-related kinase (ERK) or p42/p44 anti-ERK (New England Biolabs, Beverly, MA) or anti-phosphotyrosine Ab, clone 4G10 (Upstate Biotechnology, Lake Placid, NY), all at 1/1000 dilution. Equal loading of cell lysates was reconfirmed by both amido black (Bio-Rad) and p42/p44 anti-ERK staining. Membranes were probed as noted in Western blot methods.
Flow cytometry
Epithelial cells were labeled by indirect immunofluorescence and analyzed using the EPICS Profile II flow cytometer (Coulter Electronics, Hialeah, FL) as described (21). Cells were incubated in saturating concentrations of the anti-CCR3 mAb 7B11, or an equivalent concentration of isotype-matched control Ig, washed, and then incubated with saturating dilutions of FITC-conjugated F(ab')2 goat anti-mouse IgG Ab (Tago, Burlingame, CA).
Cytosolic Ca2+ measurements
Cells were loaded with 4 mM fura-2AM (Molecular Probes, Eugene, OR) for 60 min at 37°C in Hanks F12/DMEM. Cells were then washed, incubated with HBSS buffer, and viewed under a Zeiss digital video microscope (Oberkochen, Germany) before and after stimulation with 10 nM eotaxin and a positive control, bradykinin (1 µM).
125I chemokine binding assay
Confluent BEAS-2B grown in 24-well plates were washed with
binding buffer (25 mM HEPES, 8 mM NaCl, 1 mM
MgCl2, 1 mM CaCl2, 0.5%
BSA, 0.1% sodium azide, pH 7.8) before incubation (90 min, room
temperature) with 11.5 x 105 cpm of
125I-eotaxin (Amersham) with increasing
concentrations of unlabeled eotaxin (R&D Systems) or 100 nM of either
macrophage inflammatory protein (MIP)-1
(BioSource, Camarillo, CA)
or IL-8 (PeproTech, Rocky Hill, NJ). Cells were washed in buffer (25 mM
HEPES, 1 mM MgCl2, 1 mM
CaCl2, 0.5 M NaCl, 0.1% sodium azide, pH 7.8)
and lysed in buffer with 1% Triton X-100. Free and bound ligands were
separated using the Brandel cell harvester (Bethesda, MD) and Whatman
GF/F filters (Tewksbury, MA), blocked with polyethylenimine (0.2%
solution, 1 h).
| Results |
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(100
ng/ml) and found induction of CCR3 mRNA by Northern blot analysis.
Treatment of cells with IFN-
for 24 h did not induce CCR3 mRNA;
however, IFN-
potentiated TNF-
-induced CCR3 mRNA expression,
which increased under such stimulation in a concentration-dependent
fashion (Fig. 2
-induced CCR3 expression up to 39%,
while IL-10 modestly up-regulated TNF-
-induced CCR3 up to 30%
(p = NS, not shown). CCR3 mRNA was weakly
detected in unstimulated BEAS-2B cells in one of three experiments. In
contrast with mRNA expression, the levels of CCR3 protein detected by
Western blot analysis of resting and TNF-
plus IFN-
-stimulated
BEAS-2B cells (Fig. 2
plus IFN-
(MFI fold control = 1.69 ± 0.19, n = 10).
Unstimulated 16-HBE cells (MFI fold control = 1.70 ± 0.13,
n = 12) and PBECs (MFI fold control = 1.52 ±
0.16, n = 3) expressed similar levels of CCR3 (Fig. 2
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,
which does not bind to CCR3, and the CXC chemokine IL-8 did not
displace radiolabeled eotaxin binding even at high concentrations
(100 nM).
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| Discussion |
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We noted concordant expression in the airway epithelium of CCR3 with
two of its ligands, eotaxin and RANTES. This suggests that in vivo,
CCR3 is dynamically regulated and that the expression of CCR3 and its
ligands share some common regulatory elements. In vitro analysis
of mRNA expression confirms this hypothesis, because CCR3 mRNA
expression was modulated by TNF-
and IFN-
, which also induces
eotaxin and RANTES mRNA expression in epithelial cells
(13). Despite the increase of CCR3 mRNA induced by these
stimuli, levels of CCR3 protein on the cell surface and from total cell
lysates did not appear to be significantly increased. The reason for
this discrepancy is yet to be established, but may be explained by
enhanced receptor turnover and degradation (24) in the
presence of its endogenous ligands. Alternatively, posttranscriptional
regulation or existence of receptor-activity modifying protein-like
proteins necessary for expression of mature membrane protein
(25) may exist. The coexpression of functional CCR3 and
some of its ligands in airway epithelium suggest that epithelial CCR3
may be involved in the regulation of the mucosal chemokine network by
enabling epithelial cells to respond in an autoregulatory or
juxtaregulatory fashion to CCR3 ligands.
Epithelial CCR3 is a functional G protein-coupled receptor and not merely a decoy receptor. Stimulation of both primary and immortalized epithelial cells with the CCR3-specific ligand, eotaxin, induced an intracellular Ca2+ flux and tyrosine phosphorylation. The latter function was inhibited by pertussis toxin or 7B11.
Expression of a functional CCR3 on epithelial cells indicates that the biological effects of the C-C chemokines in the airways may extend beyond migration and activation of hemopoietic cells. C-C chemokines may modulate several aspects of epithelial function, including cell migration, activation, proliferation, and apoptosis (10, 11, 26). We are exploring whether CCR3 ligands mediate epithelial cell migration and proliferation, which would be important in tissue remodeling. Chemokine receptors have been subverted for use as entry molecules by numerous intracellular pathogens such as malaria (27), HIV (28), and poxvirus (29); thus, epithelial CCR3 may play a role in microbial infections.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint request to Dr. Lisa A. Beck, Johns Hopkins Asthma and Allergy Center, 5501 Hopkins Bayview Circle, Baltimore, MD 21224-6801. ![]()
3 Abbreviations used in this paper: MCP, monocyte chemoattractant protein; ERK, extracellular signal-regulated kinase; NHBE, normal human bronchial epithelial cells; PBEC, primary bronchial epithelial cells; MIP, macrophage inflammatory protein; MFI, mean fluorescence intensity. ![]()
Received for publication December 13, 1999. Accepted for publication December 8, 2000.
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