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Department of Etiology and Carcinogenesis, Cancer Institute, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021 [C. Y., D. X., G. L., W. T., D. L.], and Department of Epidemiology, Peking University School of Oncology, Beijing Institute for Cancer Research, Beijing 100034 [K. P., L. Z.], China
| ABSTRACT |
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T) in the MMP2 promoter sequence disrupts an Sp1 site and thus results in strikingly lower promoter activity. We examined the relationship between this polymorphism and risk for lung cancer in 781 cases and 852 age- and sex-matched controls in a Chinese population. We found that the allele frequency of MMP2-1306C was significantly higher among cases than among controls (0.91 versus 0.83). Subjects with the CC genotype had an overall 2-fold increased risk for developing lung cancer [adjusted odds ratio (OR) 2.18; 95% confidence interval (CI), 1.702.79] compared with those with the CT or TT genotype. The elevated risk was observed evenly among different subtypes of this cancer. Stratified analysis indicated an additive interaction between the CC genotype and smoking on the elevated risk. The ORs of lung cancer for the CC genotype, smoking, and both factors combined were 2.38 (95% CI 1.643.45), 4.26 (95% CI 2.578.44), and 7.64 (95% CI 4.7412.33), respectively. Furthermore, when the data were stratified by the pack-years smoked, this joint effect was more evident and stronger in heavy smokers (OR 10.25, 95% CI 5.8018.09) than in light smokers (OR 5.55, 95% CI 3.349.22). These results demonstrate a significant association between the MMP2 1306C/T polymorphism and risk of developing lung cancer solely or in a manner of interaction with carcinogen exposure. | Introduction |
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MMP-2 (gelatinase A), among other MMPs, primarily hydrolyzes type IV collagen, the major structural component of basement membrane (4
, 9)
. Numerous studies have shown that MMP-2 is overexpressed in various human cancer tissues and is implicated in tumor initiation, invasion, angiogenesis, and metastasis (7
, 10, 11, 12, 13)
. However, cancers in which a role for MMP-2 has been demonstrated are generally characterized by various individual susceptibility, implying the role of genetic factors. Recently, a functional single nucleotide polymorphism in MMP2 has been reported (14)
. The 1306C
T transition in the MMP2 promoter sequence disrupts an Sp1-type promoter site (CCACC box), and thus displays a strikingly lower promoter activity with the T allele in an in vitro assay system (14)
. It has been suggested that the 1306C/T polymorphism in the MMP2 gene may be informative in a test of association with cancer development in which a role for MMP-2 is implicated. However, this functional polymorphism has not been examined in any cancer studies to date. If this polymorphism actually causes variations in transcription and expression of MMP2 in vivo, it might affect individual susceptibility to carcinogenesis. On the basis of this hypothesis, we have examined the contribution of the 1306C/T polymorphism in the MMP2 gene to the risk of lung cancer in a large molecular epidemiological study in a Chinese population.
| Materials and Methods |
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MMP-2 Genotyping.
Genomic DNA was isolated from the peripheral blood of the controls or from surgically resected normal tissues adjacent to the tumor of lung cancer patients. PCR-based DHPLC analysis was used to determine the MMP2 genotypes. The primers used to amplify a 295-bp fragment of MMP2 promoter containing 1306 C/T site were: MMP-2F, 5'-CTG ACC CCC AGT CCT ATC TGC C; and MMP-2R, 5'-TGT TGG GAA CGC CTG ACT TCA G (14)
. PCR was accomplished with a 25-µl reaction mixture containing
100 ng of DNA, 1.0 µM concentration of each primer, 0.2 mM dNTP, 2.0 mM MgCl2, 1.0 unit Taq DNA polymerase with 1 x reaction buffer (Promega, Madison, WI) and 2% DMSO. The reaction was conducted under the following conditions: an initial melting step of 2 min at 94°C, followed by 35 cycles of 30 s at 94°C, 30 s at 64°C, and 45 s at 72°C; and a final elongation of 7 min at 72°C.
DHPLC analysis was performed on a Transgenomic WAVE System (Transgenomic Inc.) identical with that described previously (16) . Briefly, each PCR product was applied to the DHPLC column, denatured for 1 min at 94°C, and then gradually reannealed by decreasing sample temperature from 94°C to 45°C over a period of 30 min to form homo- and/or heteroduplexes. PCR products were eluted with a linear acetonitrile gradient at a flow rate of 0.9 ml/min. The genotypes of MMP2 1306 C/T revealed by DHPLC analysis were further confirmed by DNA sequencing. Three different allelic PCR products were directly analyzed with an ABI PRISM 377 automatic sequencer using a dye terminator sequencing kit. Sequences were compared with a published MMP2 promoter sequence (17) .
To ensure quality control, genotyping was performed with blinding to case/control status; a 15% masked, random sample of cases and controls was tested twice by different persons; and the results were concordant for all masked duplicate sets.
Statistical Analysis.
The association between the MMP2 polymorphism and risk of lung cancer was estimated by ORs and their 95% CIs, which were calculated by unconditional logistic regression models. Smokers were considered current smokers if they smoked up to 1 year before the date of diagnosis for cases or up to the date of the interview for controls. Information was collected on the amount of cigarettes smoked per day, the age at which the subjects started smoking, and the age at which ex-smokers stopped smoking. Light or heavy smokers were categorized by the approximate 50th percentile pack-year value among controls, i.e., <27 or
27 pack-years [(cigarettes per day ÷ 20) x (years smoked)]. The ORs were adjusted for age, sex, and smoking status or pack-years smoked. We tested the null hypotheses of additivity and multiplicativity and evaluated the departures from additive and multiplicative interaction models (18)
. A more than additive interaction was indicated when OR11 > OR10 + OR01 - 1, where OR11 = OR when both factors are present, OR10 = OR when only factor 1 is present, and OR01 = OR when only factor 2 is present. A more than multiplicative interaction was suggested when OR11 > OR10 x OR01. The departures from these additive and multiplicative models were assessed by including main effect variables and their product terms in the logistic regression model. All analysis was conducted with Statistical Analysis System software (version 6.12; SAS Institute, Cary, NC).
| Results |
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T polymorphism in MMP2 revealed by DHPLC analysis was readily discerned. From the first DHPLC, we found the heterozygous genotype (CT) of MMP2 based on the appearance of the elution profiles with double peak pattern (Fig. 1a)
T mutation was confirmed by DNA sequencing (Fig. 1c)
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27 pack-years smoked, a significant interaction between the susceptible genotype and pack-years smoked existed in a clear dose-response manner; the ORs were 1.00, 2.23, and 5.32, respectively, for the TT or CT genotype but 2.38, 5.55, and 10.25, respectively, for the CC genotype (trend test, P < 0.0001).
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| Discussion |
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2-fold increased risk for this disease. In addition, we observed a possible additive interaction between this genetic polymorphism and tobacco smoking on risk of lung cancer, with the OR being 10.25 among heavy smokers who had the CC genotype. To our best knowledge, this is the first study to investigate the impact of the MMP2 polymorphism on susceptibility to cancer and provides a substantial evidence, for the first time, that MMP2 may play an important role in the development of lung cancer. Although the design of hospital-based case-control study has potential drawbacks such as selection bias, the results in this study, which had large sample size and included >90% of the eligible cases, solid and reproducible genotyping procedures, and significantly increased ORs with very small P values, are unlikely to be attributable to selection bias. The fact that genotype frequencies among the control population fit the Hardy-Weinberg law further supports the randomness of our control selection. Moreover, the observed effect of MMP2 polymorphism was not fluctuated by other potential predictive factors of lung cancer such as age, sex, and smoking. Hence, our results are unlikely to be biased by subject selection or unknown confounding factors.
These molecular epidemiological results are consistent with the previous findings showing that the C
T transition at 1306, which disrupts an Sp1-type promoter site (CCACC box) and results in a strikingly lower promoter activity with the T allele of the MMP2 gene (14)
. The Sp1 site, among other promoter elements such as AP-2, has been shown to be necessary for regulating constitutive expression of MMP-2 (19)
. Therefore, the presence of the Sp1 promoter site in the MMP2 1306C allele may enhance transcription, which has in fact been demonstrated in vitro in transient transfection experiments (14)
, so MMP-2 protein expression would be higher in individuals who carry the CC genotype than those who carry the TT or CT genotype. Because MMP-2 and other forms of MMPs may contribute in multiple ways to all stages of carcinogenesis (8)
, the increased level of this enzyme over a lifetime may render the hosts and their target tissues at increased susceptibility to cancer development. This postulation is strongly supported by experimental cancer models. It has been shown that when induced by carcinogenic stimulus, wild-type mice developed more cancers than mice that lack the Mmp2, -7, -9, or -11 gene (20, 21, 22)
, and the development of squamous cell carcinomas in mice that lack Mmp9, another form of gelatinase, could be restored by transplanting Mmp9-expressing bone marrow cells (21)
. In another experiment, cancer cells injected via vein were found to be more capable of colonizing the lungs of wild-type mice than the lungs of Mmp2-deficient mice (12)
. It is also documented that overexpression of MMPs in transgenic mice results in elevated cancer susceptibility (23
, 24)
.
The involvement of MMPs in carcinogenesis is biologically plausible because they can alter the cellular microenvironment and consequently affect the process of neoplastic transformation and cancer development. It has been shown that by cleaving IGF-binding proteins, MMPs can release IGFs (25)
. IGFs such as IGF-1 are well known to have a strong effect on stimulating cell proliferation and inhibiting apoptosis. High levels of circulating IGF-1 and low levels of IGF-binding protein 3 are associated with increased risk of several common cancers, including lung cancer (26)
. MMPs may also release the cell membrane-bound precursor of transforming growth factor
(27)
, another important growth factor involved in neoplastic transformation and cancer development. Moreover, MMPs are also involved in cleavage of a number of molecules on the cell surface, which may alter cell cycle checkpoint controls and conceivably promote genomic instability by affecting cell adhesion (28)
, may disrupt cell signaling, and may foster cancer cells to escape immunosurveillance (8)
. Taken together, these data provide very plausible molecular mechanisms through which the genetic polymorphism resulting in high expression of MMP-2 over a lifetime could increase cancer risk.
In our study, we found that the MMP2-1306CC genotype was significantly associated with lung cancer risk in nonsmokers; however, the risk rose markedly in smokers, particularly heavy smokers, suggesting an additive interaction between the MMP2 polymorphism and smoking. Several possibilities exist to explain these findings. Because MMPs expression can be induced by smoking (29 , 30) , one hypothesis is that, in addition to higher constitutive expression because of gain of an Sp1 promoter site, the inducibility by smoking of the C allele of MMP2 may also be higher than that of the T allele, which loses an Sp1 site. Given these conditions, it would be expected that subjects who smoked and carried the CC genotype were more susceptible to developing lung cancer. Alternatively, a higher risk of lung cancer among heavy smokers with the CC genotype may attribute to the occurrence of larger numbers of transformed cells caused by smoking in the target tissue, which, in turn, increases the possibility that one of these cells will become malignant under the condition of higher expression of MMP2. Another interesting finding in our present study was that the increased risk related to the MMP2 polymorphism was evenly observed in different subtypes of lung cancers, i.e., squamous cell carcinoma, adenocarcinoma, and other histological types of lung cancer. This result suggests that the MMP2 polymorphism might be a general, but not a specific, risk factor for common cancers, further supporting the likelihood that MMPs profoundly influence early tumor initiation and development.
In summary, this study demonstrated a significant association between the MMP2 1306C/T polymorphism and the risk of developing lung cancer solely or in a manner of interaction with tobacco smoking in a Chinese population. Because this is the first report demonstrating the contribution of the MMP2 polymorphism to lung cancer risk and because MMP2 is expressed in many types of cancer and normal stromal cells, additional studies on lung cancer and other types of common cancers would be warranted. Moreover, the possible role of the MMP2 1306C/T polymorphism in cancer invasiveness and metastasis should also be addressed.
| FOOTNOTES |
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1 Supported by Grants 39825122 and 39990570 from the National Natural Science Foundation and Grant G1998051204 from the State Key Basic Research Program. ![]()
2 To whom requests for reprints should be addressed, at Department of Etiology and Carcinogenesis, Cancer Institute, Chinese Academy of Medical Sciences, Beijing 100021, China. Phone: 86-10-677-22460; Fax: 86-10-677-13359; E-mail: dlin{at}public.bta.net.cn ![]()
3 The abbreviations used are: MMPs, matrix metalloproteinases; DHPLC, denaturing high performance liquid chromatography; OR, odds ratio; CI, confidence interval; IGF, insulin-like growth factor. ![]()
Received 8/ 8/02. Accepted 10/ 2/02.
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