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Molecular Oncology, Markers, Clinical Correlates |
Department of Surgery and Surgical Basic Science, Graduate School of Medicine, Kyoto University, Kyoto 606-8507 [Y. D., Y. S., M. M., A. K., J. K., I. K., Y. H., M. I.], and Department V of Oncology and Department of Thoracic Surgery, Kitano Hospital, Tazuke Kofukai Medical Research Institute, Osaka 530-8480 [M. M., H. H.], Japan
| ABSTRACT |
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Experimental Design: We performed reverse transcription-PCR analysis for CCR7 in 20 esophageal SCC cell lines and immunohistochemical analysis of 96 esophageal SCC samples. We then performed a cell migration assay, F-actin polymerization, and a phagokinetic assay on esophageal SCC cell lines in the presence of CCL21, a ligand of CCR7.
Results: CCR7 mRNA was detected in 9 of 20 esophageal SCC cell lines. Immunoreactive CCR7 was found mainly in esophageal cancer cells. High CCR7 expression was significantly correlated with esophageal SCC lymphatic permeation, lymph node metastasis, tumor depth, and tumor-node-metastasis stage and was associated with poor survival. In vitro studies demonstrated that CCL21 significantly increased the cell migration ability of esophageal SCC cell lines, and pseudopodia formation was induced by CCL21 stimulation. Furthermore, CCL21 markedly enhanced the motility of esophageal carcinoma cell lines by the phagokinetic assay.
Conclusions: The results suggested that the CCR7/CCL21 receptor ligand system may play a role in the lymph node metastasis of esophageal SCC.
| INTRODUCTION |
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Chemokines belong to the small molecule chemoattractive cytokine family and are grouped into CXC chemokines and CC chemokines on the basis of the characteristic presence of four conserved cysteine residues (3, 4, 5) . Chemokines mediate their chemical effect on target cells through G-protein-coupled receptors, which are characterized structurally by seven transmembrane spanning domains and are involved in the attraction and activation of mononuclear and polymorphonuclear leukocytes. Chemokines and their receptors play important roles in angiogenesis and tumor growth (6) , however, the role of chemokine receptors in metastasis has only recently been explored (7) . Of interest, CCR73 is expressed by human adult T-cell leukemia cells with lymph node involvement (8) , and CCR7 up-regulation in classical Hodgkins disease correlates with lymphoid organ dissemination (9) . In addition, some human breast and melanoma cell lines also express functional CCR7 (10) . Recently, Mashino et al. (11) found that CCR7 is associated with lymph node metastasis of gastric carcinoma. Furthermore, the expression of a single chemokine, CCR7, by murine melanoma cells increases metastasis to the lymph nodes (12) , raising the possibility that cancer cells may use normal mechanisms of lymph node homing for metastasis dissemination.
To clarify the role of CCR7 in esophageal SCC, we investigated the CCR7 expression using RT-PCR and performed immunohistochemical analysis. We also evaluated the experimental chemotactic activity and motility in the presence of CCL21 in esophageal cancer cell lines.
| MATERIALS AND METHODS |
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RT-PCR.
Total RNA was purified from esophageal squamous cancer cell lines by the AGPC method. Five µg of total RNA were reverse transcribed at 37°C for 60 min in a total 15-µl reaction volume using a first-strand cDNA synthesis kit (Amersham Pharmacia Biotech). cDNA was incubated at 95°C for 5 min to inactivate the reverse transcriptase and served as template DNA for 33 cycles of amplification using the PCR-200 DNA engine (MJ Research, Inc.). PCR was performed in a standard 50-µl reaction mixture, consisting of 10 mM Tris-HCl, 50 mM potassium chloride, 1.5 mM magnesium chloride (pH = 8.3), 0.2 mM deoxynucleoside triphosphates, 50 pmol of each sense and antisense primer, and 2.5 units of TaqDNA polymerase (Life Technologies, Inc.). Amplification was performed for 30 s at 94°C, 1 min at 55°C, and an extension step was carried out for 2 min at 72°C. As a negative control, the RNA template was omitted from the reaction. The amplification products were separated on 2% agarose gels and visualized by ethidium bromide staining. PCR primers for CCR7 cDNA were as follows: forward primer 5'-TCCTTCTCATCAGCAAGCTGTC-3' and reverse primer 5'-GAGGCAGCCCAGGTCCTTGAAG-3'. According to the CCR7 gene structure, a PCR product of 529 bp was obtained. For GAPDH, the forward primer was 5'-TGGTATCGTGGAAGGACTCATGAC-3', and the reverse primer was 5'-ATGCCAGTGAGCTTCCCGTTCAGC-3'. A single 189-bp band amplified with primers specific for GAPDH with the same cDNA was detected and used as an internal control under identical conditions.
Immunohistochemical Staining.
Immunohistochemical staining was performed using the avidin-biotin complex method. Tissue sections were deparafinized and rehydrated in water. Endogenous peroxidase was blocked with 0.3% hydrogen peroxide for 30 min. Sections were rehydrated, washed, and incubated with a blocking reagent, 5% normal horse serum with 1% BSA in PBS, for 30 min at room temperature to block nonspecific antibody reactions. Sections were incubated overnight at 4°C with antihuman CCR7 monoclonal antibody (BD Phar-Mingen). After four rinses in PBS, sections were incubated for 2 h at room temperature with biotinylated antimouse IgG, followed by four washes with PBS, and then reacted with the avidin-biotin system for 3 min using 0.03% 3,3'-diaminobenzidine tetrahydrochloride as a chromogen. Sections were counterstained with Mayers hematoxylin. For negative controls, blocking reagent without primary antibody was used as a substitute for the primary antibody of CCR7.
Evaluation of Immunostaining.
Specimens were considered immunopositive for CCR7 when
1% of the tumor cells had clear evidence of immunostaining. The percentage of positive tumor cells was graded as follows: 0, none; 1, 124%; 2, 2549%; 3, 5074%; and 4, 75100%. Immunostaining intensity was rated as follows: 0, none; 1, weak; 2, moderate; and 3, intense. In addition, an immunoreactive score was calculated by multiplying of the score of percentage positive cells and the score of staining intensity as reported previously (16)
. For example, a specimen containing 40% CCR7-immunopositive tumor cells with strong intensity received a score of 2 x 3 = 6. In the case of heterogeneous staining intensities within a sample, each component was scored independently, and the results were summed. Immunostaining was evaluated by two authors (Y. D., A. K.) blinded to patient outcome and other clinical findings. Cases that were evaluated differently after discussion between the two researchers were excluded.
Fluorescence Microscopy.
For F-actin location, esophageal cancer cell lines were incubated with 300 ng/ml CCL21 for 20 min, fixed for 20 min in paraformaldehyde in PBS, put on ice, permeabilized for 5 min in 0.2% Triton X-100, incubated with 5 mU/ml FITC-phalloidin (Molecular Probes) for 30 min, washed three times with PBS, and mounted with Antifade (Molecular Probes). Fixed cells were analyzed by confocal microscopy.
Migration Assay for Esophageal Cancer Cell Lines.
Cell migration assays were performed in triplicate using 6.5-mm diameter chambers with 12-µm pore filters (Transwell, 24-well culture plates; Costar, Boston, MA). KYSE cell lines were suspended at 1 x 105 cells/ml in serum-free media (RPMI 1640 containing 1% BSA), and 500 µl of the cell suspension were added to the upper chamber. CCL21(300 ng/ml) was placed in the lower well. The chambers were incubated for 12 h at 37°C in a humid atmosphere of 5% CO2, after which, the cells on the upper surface of the filter were removed using a cotton wool swab. The cells that had migrated to the lower surface were stained using DiffQuik (Dade Behring, Dudingen, Switzerland). For each transwell, the number of cells that had migrated in five medium-power fields (x20) was counted.
Phagokinetic Assay.
For the phagokinetic assay (17)
, 1000 trypsinized cells were plated on uniform carpets of gold particles prepared on glass coverslips coated with BSA and incubated for 24 h. The phagokinetic tracks were visualized by low-power, dark-field microscopy using side illumination. The area cleared of gold particles was measured after photography, and the mean value for 20 cells was calculated in each experiment.
Statistical Analysis.
Relationships between the immunostaining results of CCR7 and clinical factors were analyzed using the Pearsons
2 test and Fishers exact test. Survival curves of the patients were calculated using the Kaplan-Meier method and analyzed using the log-rank test and Breslow-Gehan-Wilcoxon test. Coxs proportional hazard model was used for multivariate analysis. For the multivariate analysis, cases with an immunoreactive score
8 were designated "1," and cases with an immunoreactive score < 7 were designated "0." pT, pN, histological grade, age, and gender were divided into the following categories: (pT1:0, pT2, pT3, pT4:0); (pN0:0, pN1:1); (G1, G2:0, G3, G4:1), (<63 years old: 0;
63 years: 1); and (female: 0, male: 1). Results of the migration assay and the phagokinetic assay were assessed with the Students t test.
StatView J-4.5 (Abacus Concepts, Inc., Berkeley, CA) and JMP version 4 (SAS Institute, Inc., Cary, NC) were used for statistical analysis. Differences with P < 0.05 were accepted as significant.
| RESULTS |
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| DISCUSSION |
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It has been demonstrated that activated dendritic cells home to lymph nodes through lymphatic vessels by a CCR7-dependent mechanism, and CCL21 and its receptor CCR7 play crucial roles in the homing of lymphocytes into the secondary lymphoid organs. A natural mutation in mice, designated plt (for paucity of lymph node T cells), which results in the loss of one of the forms of mCCL21 and disruption of the CCR7 gene, causes impaired homing of native T cells to the secondary lymphoid organs (26, 27, 28) . Thus, the abundant expression of the homeostatic chemokine CCL21 in lymph nodes makes it a likely candidate to attract CCR7-positive tumor cells.
We asked whether the expression of CCR7 could play a role in esophageal lymph node metastasis. In this study, we used an immunohistochemical method to examine the CCR7 expression in esophageal SCC. Immunoreactive CCR7 was found in the cytoplasm and cell membrane of esophageal SCC cancer cells, and CCR7 protein was found mainly in the cancer cells, although it was not expressed in normal esophageal epithelium. Of more importance, the strong CCR7 protein expression observed in esophageal lymph node metastasis was consistent with findings in gastric carcinoma (11) . High CCR7 expression was associated with lymphatic permeation, lymph node metastasis, tumor depth, and TNM stage. Next, we found that some esophageal SCC cell lines expressed functionally active CCR7, which triggered pseudopodia formation. Furthermore, CCR7 enhanced the motility and directional migration of the esophageal SCC cell lines in the presence of CCL21. Taken together with the distinct tissue distribution of its ligand, CCL21, which is produced constitutively by the lymphatic endothelial cells (29) and T-cell paracortical regions in the lymph node (27) , these findings suggested that CCR7 may play a role in lymph node metastasis in esophageal SCC.
The role of CCR7 in metastasis has also been explored in other malignant diseases. In a study of ATLL, Hasegawa et al. (8) showed that ATLL cells from patients with lymph node involvement had increased expression of CCR7 and enhanced functional response to CCL21, suggesting that the expression of CCR7 may alter the trafficking patterns of ATLL cells by recruiting these cells via CCL21-enriched high endothelial venules within the lymph node. Till et al. (30) showed that CCR7 engagement by CCL21 and/or CCL19-stimulated chronic lymphocytic leukemia cell entry into the lymph nodes. Muller et al. (10) showed that chemokines and their receptors such as CXCR4 and CCR7 had a critical role in determining the metastatic destination of breast cancer cells and melanoma cell lines.
Given that the rate of genetic mutations in cancer cells is much higher than that in normal cells, perhaps genetic or transcriptional changes lead to the enhanced expression of CCR7, as demonstrated by Muller et al. (10) . On the basis of our understanding of dendritic cell migration, it is conceptually clear how CCR7 expression may work to recruit tumor cells to lymphatic channels that constitutively express CCL21 (29) . After passive transport of tumor cells to the draining lymph nodes, CCR7 may help to retain malignant cells in the lymph nodes where the CCR7 ligands CCL21 and CCL19 are rich. Recently, Wiley et al. (12) demonstrated that the expression of a single chemokine, CCR7, by B16 murine melanoma cells increased metastasis to the regional lymph nodes. This strongly supported the hypothesis that malignant cells may use CCR7 in lymph node metastasis dissemination.
Our data suggested that CCR7/CCL21 was associated with esophageal lymph node metastasis. However, the possibility cannot be ruled out that other chemokines such as CXCR4 may be involved in esophageal lymph node metastasis because CXCL12, a ligand of CXCR4, is also abundantly expressed in the lymph nodes (10) and enhances the migration and invasion of breast cancer, melanoma, pancreatic cancer, prostate cancer, and ovarian epithelial tumors (10 , 31, 32, 33) . Next, it should be clarified whether CXCR4 plays a role in esophageal SCC lymph node metastasis.
There is increasing evidence that the inflammatory cells, cytokines, and chemokines found in human tumors are more likely to contribute to tumor growth, progression, and immunosuppression than they are to mount an effective antitumor response (34) . Over the past 10 years, study of the cytokine and chemokine networks has led to the development of a range of antagonists for the treatment of inflammation and allergy. We suggest that such agents may also be of benefit in the treatment of malignant disease.
In summary, our investigations suggested that CCR7 could be associated with lymph node metastasis of esophageal SCC. The mechanism by which the tumor cells escape from the lymphocyte immune response in the lymph node metastasis should be further clarified.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 This work was supported, in part, by from the Japanese Ministry of Education, Science and Culture Grants-in-Aid 07671386, 07457271, and 0971301. ![]()
2 To whom requests for reprints should be addressed, at Department of Surgery & Surgical Basic Science, Graduate School of Medicine, Kyoto University, Kawaracho 54 Shogoin Sakyo-KU, Kyoto 606-8507, Japan. Phone: 81-75-751-3227; Fax: 81-75-751-4390; E-mail: shimada{at}kuhp.kyoto-u.ac.jp ![]()
3 The abbreviations used are: CCR7, CC chemokine receptor 7; SCC, squamous cell carcinoma; RT-PCR, reverse transcription-PCR; TNM, tumor-node-metastasis; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; ATLL, adult T-cell leukemia/lymphoma; AGPC, acid guanidium-phenol-chloroform. ![]()
Received 8/27/02; revised 4/10/03; accepted 4/21/03.
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