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Molecular Oncology, Markers, Clinical Correlates |
Section of General Thoracic Surgery, Department of Surgery [C. J. M., M. D. I., G. C., M. B. O., D. G. B.], Section of Pulmonary Medicine and Critical Care, Department of Medicine [D. A. A.], Biostatistics [C-C. H.], Pathology [T. J. G., D. G. T.], Pediatrics [D. E. M., S. H.], University of Michigan, Ann Arbor, Michigan 48109
| ABSTRACT |
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Experimental Design: Sixty-three stage I lung adenocarcinomas were analyzed for gene expression using Affymetrix oligonucleotide microarrays. Tumors were stratified into ALR+ and ALR- groups and compared for statistically significant differences in gene expression. Identified candidate genes were validated using both ELISA and immunohistochemistry. Follow-up data for these patients were collected and used to assess patient prognosis.
Results: Of the 63 tumors studied, 27 were ALR+ and 36 were ALR-. A total of 303 genes showed significant differences in gene expression between the two populations (t test, P < 0.02). Three of the genes overexpressed by ALR+ tumors were the chemokines: small inducible cytokine A4 (MIP-1ß), RANTES, and interferon inducible protein 10 (IP-10). Immunohistochemistry analysis showed that the tumor cells expressed these cytokines. ELISA showed that MIP-1ß and RANTES were overexpressed at the protein level by ALR+ tumors. Univariate Cox proportional hazards analysis showed that RANTES was a predictor of survival in stage I lung adenocarcinomas (P = 0.002).
Conclusion: When tested in the Cox univariate proportional hazards model, RANTES expression by lung adenocarcinoma cells is a predictor of survival in stage I NSCLC patients and may be useful as a prognostic factor in lung cancer.
| INTRODUCTION |
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Patients who have an ALR+ within their NSCLC tumor demonstrate an improved prognosis compared with those patients without ALR (ALR-). This relationship is especially true for tumors with high levels of intratumoral CD3+ and S100+ cells (7) . This relationship has also been shown for stage I NSCLC tumors with peritumoral B-lymphocytes (8) and for advanced lung cancer patients (9) .
The mechanisms underlying the presence or absence of lymphocytic infiltration within a lung tumor mass are unknown. The immune system may tolerate a tumor because of the tumors failure to produce the needed "danger" signals required for recognition and inflammation (10) . On the other hand, tumors may also secrete signals that actively down-regulate the immune response and allow the tumor to escape immune surveillance (11) . Regardless of how these cells arrive in the tumor, stimulation of peritumoral lymphocytes results in the release of tumoricidal cytokines (12) . Some therapies have tried to harness the antitumor activity of the immune system by providing stimulation to these peritumoral lymphocytes (13) . Other experiments have used fusion antibodies that target tumor antigens and contain a superantigen to activate T cells by linking the T-cell receptor to the MHC class II receptor on an antigen-presenting cell (14) . To date, immune therapies for lung cancer are experimental and have achieved limited success.
Chemokines, a structurally similar but functionally diverse family of molecules, are principally produced by, and target cells of, the immune system (15) . Chemokines are also produced by a variety of normal tissues including lung tissue. These lung-derived chemokines are produced by pulmonary epithelium, especially in the setting of acute injury from infectious or chemical insult (16 , 17) . The effect of chemokines on other cells is usually dependent on the presence of chemokine receptors on those target cells. Such cell surface receptors have been found on a variety of cells including endothelial, neuronal, smooth muscle, and epithelial cells (18) .
In addition to normal tissues, a variety of tumors have been shown to secrete chemokines (19 , 20) . These molecules are now known to affect the behavior of cells in tumors. Chemokine receptors are expressed by breast cancer cells and are thought to be responsible for the distinct pattern of metastasis in breast cancer (21) . Chemokines and their receptors have also been implicated in the migration of ovarian cancer cells (22) .
Some chemokines with ascribed "antitumor" activity, particularly RANTES, IP-10, MCP-1, and MIP-3
, have been used in animal trials in an attempt to induce tumor-specific immune responses (23
, 24) . In NSCLC, chemokines secreted by the tumor cells are responsible for the infiltration of macrophages (25)
. Sharma et al., (26)
has shown that secondary lymphoid organ (SLO) chemokine reduced tumor burden and increased CD4, CD8, and dendritic cell infiltrates in the tumors when injected into mice with metastatic pulmonary adenocarcinoma.
The aim of this study was to identify differences in gene expression between lung adenocarcinomas that correlate with ALR. Global gene expression in stage I tumors was examined using oligonucleotide microarrays. Differences in tumor cell expression of genes with known chemotactic, or immune-activating potential, may provide additional avenues for immune therapy in the future, or markers for prognosis that may direct therapy and more accurately stratify patients based on risk profile.
| MATERIALS AND METHODS |
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At least two of the original H&E-stained slides of each tumor were evaluated for the presence of lymphocytic response. Tumors were divided by the study surgical pathologist (T. J. G.) into two broad categories based on the absence or presence of a significant peritumoral and intratumoral lymphocytic infiltrate that was readily apparent at low magnification (ALR- versus ALR+).
RNA Isolation and Oligonucleotide Microarray Analysis.
RNA isolation and oligonucleotide microarray analysis was carried out according to the methods of Giordano et al., (27)
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Statistical Methods.
Trimming of the dataset was performed by excluding genes from analysis if the Affymetrix measure of their 75th percentile value was less than 100. Restriction of the dataset in this manner reduced the number of probe sets from 7129 to 4578. Tumors were divided into two groups: those with ALR+ and those without (ALR-). Next, using Microsoft Excel, we performed a Students t test to compare the ALR+ and ALR- groups. To restrict the dataset further, a P of <0.02 was considered statistically significant. An average-linkage hierarchical clustering of an uncentered Pearson correlation similarity matrix was applied to the list of significant genes with the program Cluster, and figures were generated with the program TreeView (Eisen Lab Software; Stanford, Palo Alto, CA). From the clusters generated, genes that were overexpressed by the ALR+ group were further analyzed. With the use of the Locus Link website,4
genes in this group were subcategorized into functional classes. Genes with functional potential to incite ALR were chosen for validation. A correlation analysis between mRNA expression and protein expression was performed using the Spearman method. Survival analysis was performed using the Cox univariate proportional hazard regression model. Median gene expression for all tumors for a given gene was used as a cutoff value to designate "high expression" or "low expression" groups.
IHC.
IHC was performed on tissue microarrays containing 90 lung adenocarcinomas to simultaneously examine the majority of cases in the study. From the diagnosed adenocarcinomas, the areas of the tumor that best represented the overall morphology were selected and a tissue microarray (TMA) block was constructed according to the method of Kononen et al., (28)
. Deparaffinized sections, along with sections from a commercially available normal-tissue tissue microarray block (NO50; Clinomics Laboratories, Pittsfield, MA) were microwave pretreated in citric acid buffer for antigen retrieval. The sections were incubated with blocking solution for 60 min at room temperature before being exposed to the primary antibodies. The antibodies used included: anti-MIP-1ß, anti-RANTES (R&D Systems, Minneapolis, MN), and anti-IP-10 (Santa Cruz Biotechnologies, Santa Cruz, CA). The antibodies were incubated with the tissue microarrays overnight at 4°C. The immunocomplex was visualized by the immunoglobulin enzyme bridge technique using Vector ABC-kit (Vector Laboratories, Burlingame, CA), with 3,3-diaminobenzidine tetrachloride as the enzyme substrate. Sections were lightly stained with hematoxylin and permanently mounted.
ELISA.
Of these same tumor specimens, 25 had sufficient tumor material to perform protein-based assays. This included 12 in the ALR+ group and 13 in the ALR- group. Samples of tumor and normal lung distal to tumor were homogenized and sonicated in anti-protease buffer on recovery from the operating room. Specimens were centrifuged at 900 x g for 15 min, filtered through 0.45-µm Sterile Acrodiscs (Gelman Sciences, Ann Arbor, MI), and frozen at -70°C until thawed for assay by a specific antibody (MIP-1ß, RANTES, IP-10). Proteins were quantitated using a modification of a double ligand method as described previously (29)
. All of the antibodies were polyclonal goat antihuman as listed above. The IP-10 antibody used for the ELISA was purchased from R&D Systems. Briefly, flat-bottomed 96-well microtiter plates (Nunc Immuno-Plate I 96-F) were coated with 50 µl/well containing the primary antibody [1 ng/µl in 0.6 M NaCl, 0.26 M H3B04, and 0.08 N NaOH (pH 9.6)] for 24 h at 4°C and then washed with PBS (pH 7.5), 0.05% Tween 20 (wash buffer). Microtiter plate nonspecific binding sites were blocked with 2% BSA in PBS and incubated for 60 min at 37°C. Plates were rinsed three times with wash buffer. Fifty µl of tumor homogenate were added (neat and 1:10 dilution), followed by incubation for 1 h at 37°C. Plates were washed three times, 50 µl/well biotinylated polyclonal rabbit anti-IP-10 [3.5 ng/µl in PBS (pH 7.5), 0.05% Tween 20, and 2% FCS] were added, and plates were incubated for 45 min at 37°C. Plates were washed three times, streptavidin-peroxidase conjugate (Bio-Rad Laboratories, Richmond, CA) added, and the plates incubated for 30 min at 37°C. Plates were washed three times and chromogen substrate (Bio-Rad Laboratories, Richmond, CA) added. The plates were incubated at room temperature to the desired extinction, and the reaction terminated with 50 µl/well H2SO4 (3 M) solution. Plates were read at 490 nm in an automated microplate reader (Bio-Tek Instruments, Inc., Winooski, VT). Standards were dilutions of IP-10 from 100 ng/ml to 1 pg/ml (50 µl/well). This protocol consistently detected protein (MIP-1ß, RANTES, IP-10) concentrations greater than 50 pg/ml in a linear fashion. Tissue samples were run in parallel for total protein content (Pierce, Rockford, IL), and results were expressed as nanograms of protein per milligram.
| RESULTS |
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6800 genes and included tumors of various cell differentiations and derivations. Tumors were stratified into 27 with ALR+ and 36 ALR-. Pathological and demographic data for the two groups are represented in Table 1
0.02 was used as a cutoff.
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MIP-1ß, RANTES, and IP-10 protein expression was then examined using an immunohistochemical analysis of tissue microarrays containing the majority of the stage I tumors in this study. These arrays also contained samples of normal lung, squamous cell carcinoma, advanced-stage lung adenocarcinoma, and adenocarcinoma cell line samples. For all three of the proteins tested, there was little to no staining in the normal sample, with the exception of positive-staining alveolar macrophages (Fig. 2A)
. The A549 lung adenocarcinoma cell line showed positive cytoplasmic staining for all three proteins. Similarly MIP-1ß, RANTES, and IP-10 antibodies stained the cytoplasm of tumor cells, and these IHC results demonstrated that the expression of these gene products are localized to the adenocarcinoma cells. There was no appreciable staining for IP-10, RANTES, or MIP-1ß within lymphocytes (Fig. 2, BD)
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| DISCUSSION |
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IP-10, MIP-1ß, and RANTES, are known chemotactic cytokines. IP-10 is a chemotactic cytokine that can activate the immune system but that also inhibits angiogenesis. Monocytes/macrophages, T-lymphocytes, endothelial cells, fibroblasts, and keratinocytes produce and secrete IP-10 (30)
. As an
-chemokine, IP-10 is primarily chemotactic for Th-1 lymphocytes and macrophages but has little effect on basophils or eosinophils (31)
. From our data, the mRNA expression of IP-10 was higher in the ALR+ group; however, this pattern was not supported by the protein expression as evidenced by the ELISA data. This result may have been influenced by the relatively small sample size tested by ELISA. IHC staining of all stage I tumors did show a higher number of strongly staining tumors in the ALR+ group; however, there was no correlation between the strength of staining and the mRNA level. One explanation for this discrepancy may be that, if only a small number of cells account for the high mRNA expression in a given tumor, this difference in expression may not be reflected in the protein staining. Another possibility is that it is difficult to determine quantitative information regarding protein expression levels using IHC alone. IP-10 may also be induced because of some interaction between lymphocytes and tumor cells. IFN
up-regulates IP-10 expression. As evidenced by the array data, IFN
levels in both ALR+ and ALR- tumors are very low. IP-10 is not a product of the lymphocytes themselves, as indicated by the IHC results. The presence of a significant amount of lymphocytes in a tumor in the ALR+ tumor group, as well as the tumor/immune system interplay, may account for the higher level of IP-10 message and may potentially account for the difference in expression between the ALR+ and ALR- groups. In a murine model, IP-10 has been implicated as the key player in the tumor-protective immunity conferred by IL-12 by affecting Th-1 type CD8+ cells (32)
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MIP-1ß is produced by mononuclear cells, endothelial cells, and mast cells. It functions as a chemotactic and activating factor of the immune system and serves to inhibit the CD4+/CCR5-mediated HIV cell entry (30) . MIP-1ß is a ß chemokine and affects all leukocytes except neutrophils (31) . In one study, MIP-1ß was implicated as the major chemotactic cytokine responsible for macrophage chemotaxis and activation during acute lung injury (15) . MIP-1ß was also shown to be produced by NSCLC and was highly correlated with macrophage chemotaxis (25) .
RANTES is another known chemotactic cytokine that is produced by many cell types including T-lymphocytes, monocytes, platelets, eosinophils, epithelial cells, dendritic cells, and mast cells (30) . In cell cultures of bronchial epithelial cells infected with influenza A, the transcription and translation of RANTES is increased within 24 h after infection (33) . In vivo studies have shown the release of RANTES in lung to be a response to a variety of noxious stimuli including bacterial and viral infection, and chemotherapy (34, 35, 36) . Although it typically works through the CCR5 receptor, multiple RANTES molecules can form a complex that can directly stimulate T cells, outside of the usual receptor (37) . This direct stimulation is a reminder that RANTES, as do other chemokines, exerts its effects in a dose-dependent fashion. Arenberg et al. (25) showed that NSCLC cells produced RANTES but that RANTES levels did not correlate significantly with macrophage chemotaxis. RANTES, like MIP-1ß, is a ß chemokine and affects all leukocytes except neutrophils (31) . RANTES has been used as a prognostic indicator in both breast and cervical cancers (38) . However, in contrast to the findings of our study, higher levels of RANTES in those malignancies are correlated with a poor outcome. The reason for this difference in tumor behavior is unknown and may be worthy of future study.
In viewing this study in the context of previous studies, it is very possible that MIP-1ß and RANTES could be signals to incite an ALR. In the tumors that were ALR+, both RANTES and MIP-1ß mRNA were significantly increased. Similarly, the protein levels of these gene products, as confirmed by ELISA, were increased in the tumors with ALR. Immunohistochemical analysis shows that RANTES and MIP-1ß are produced by NSCLC tumor cells and are not associated with lymphocytes.
When the types of inflammatory cells that infiltrate lung tumors are considered, RANTES is seen as an even more plausible signal for ALR. Controversy regarding the type of cells that infiltrate lung tumors exists in the literature. There are reports that both Th-1 and Th-2 profiles exist (39 , 40) . One study that looked at the lymphocytes themselves concluded that the predominant peritumoral lymphocyte in NSCLC is an activated memory T cell that is capable of synthesizing Th-1 cytokines (4) . RANTES was first described as a chemoattractant for memory T cells in vitro (41) . Other more recent data suggest that, in certain lung tumors, the CD4+, CD25+ T cells predominate; these may function to depress the host immune system and allow for tumor progression (42) . One possible future direction for investigation would be to try to further characterize the T-cell population in each tumor and correlate the various T-cell profiles to the gene expression profile of each tumor to determine a more causal relationship among chemokine expression, T-cell population, and tumor behavior. Our data suggest that RANTES is a major chemotactic signal for infiltrating lymphocytes and is produced by NSCLC cells.
The proper antitumor cytokine milieu is surely the result of lymphocytes that recognize the danger of tumor tissue and, in turn, start an inflammatory cascade to destroy the tumor. RANTES expression by the tumor itself may be one possible event to aid in the initiation of this inflammatory cascade in lung adenocarcinoma. Although the Th-1 (IL-2 and IFN
) and Th-2 (IL-4, IL-5, IL-9, and IL-13) representative cytokines are on the oligonucleotide arrays, their expression levels were found to be extremely low (data not shown). In addition, there was no discernable difference in the expression of any of these cytokines between the ALR+ and ALR- groups. Given these limitations, the prevalence of a Th-1 or Th-2 profile in the peritumoral lymphocytes of NSCLC tumors could not be determined.
If RANTES and MIP-1ß represent signals needed to incite ALR, it is unclear as to why some tumors produce these cytokines and others do not. MIP-1ß is located at 17q21 and RANTES is located at 17q11.2-q12. Chromosome 17p is a known region of loss in NSCLC that also includes the region in which the p53 tumor suppressor gene resides. It is possible that a portion of chromosome 17 could be lost in those tumors with lower levels of RANTES and MIP-1ß. Alternatively, these differences may reflect regulation of gene transcription.
Regardless of the mechanism for the differential expression of these genes, it is clear that, in the case of RANTES, overexpression of this gene is associated with improved prognosis in NSCLC. Patients with a lower expression of this gene had an increased mortality using Cox modeling. If RANTES is a key signal to help promote chemotaxis of lymphocytes to a tumor, it may have potential therapeutic benefit. Irrespective of its therapeutic potential, RANTES could be considered a prognostic factor and may help to further stratify patients with stage I NSCLC. In recent studies, the use of genetic profiling and gene microarray technology has yielded families of genes that have delineated the various phenotypes of lung cancer as well as stratifying high- and low-risk expression profiles (43, 44, 45) . Like those studies, this study also has been able to show a global difference in gene expression profiles between stage I tumors that are ALR+ and those that are ALR-. In concentrating on and further investigating genes that may play a role in recruiting lymphocytes, this study has shown RANTES to predict survival in stage I patients. Recognition of high-risk stage I patients may afford the use of adjuvant therapies in an attempt to positively impact survival in NSCLC patients.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 Supported by National Cancer Institute Grant U19 CA-85953. ![]()
2 To whom requests for reprints should be addressed, at General Thoracic Surgery, MSRB II B560, University of Michigan, Ann Arbor, MI 48109-0686. E-mail: dgbeer{at}umich.edu ![]()
3 The abbreviations used are: NSCLC, non-small cell lung cancer; ALR, active lymphocytic response; RANTES, regulated upon activation, normal T-cell-expressed and -secreted; MIP-1ß, small inducible cytokine A4; IP-10, interferon inducible protein 10; IHC, immunohistochemistry; IL, interleukin; FCS, fetal calf serum. ![]()
4 Internet address: http://www.ncbi.nlm.nih.gov/LocusLink/index.html. ![]()
Received 3/11/02; revised 7/31/02; accepted 8/12/02.
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