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Departments of 1 Biochemistry, 2 Preventive Medicine, and 3 Anatomic Pathology, School of Medicine; 4 Department of Internal Medicine, Kyungpook National University Hospital; 5 Cancer Research Institute, and 6 Health Promotion Research Center, Kyungpook National University, Daegu, Korea
Requests for reprints: Jae Yong Park, Department of Internal Medicine, School of Medicine, Kyungpook National University, Samduk 2Ga 50, Daegu, 700-412, Korea. Phone: 82-53-420-5536; Fax: 82-53-426-2046. E-mail: jaeyong{at}kyungpook.ac.kr
| Abstract |
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| Introduction |
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Angiogenesis is an essential process in the development, growth and metastasis of malignant tumors (3-5). Vascular endothelial growth factor (VEGF) is an important regulator of angiogenesis, and several studies have shown that its increased expression is associated with the grade of angiogenesis and with a poor prognosis in various human cancers, including lung cancer (6-8).
The VEGF gene is located on chromosome 6p21.3 and consists of eight exons that exhibit alternate splicing to form a family of proteins (9, 10). Several polymorphisms have been described in the VEFG gene. Some of these variants [460T > C, 116G > A and +405C > G (transcription start site counted as +1) in the promoter or 5'-untranslated region and 936C > T in the 3'-untranslated region] have been associated with variations in VEGF protein production (11-13) and have reported to be involved in several disorders in which angiogenesis is critical in the development of disease (14-17).
In spite of the importance of the VEGF gene in lung cancer carcinogenesis, no investigation of the role of VEGF polymorphisms in relation to lung cancer has been undertaken. In the present study, we conducted a case-control study to evaluate the association between three VEGF polymorphisms [460T > C, +405C > G (634 from translation start site), and 936C > T] and lung cancer. The 116G > A (1154 from translation start site) polymorphism was rare in the preliminary study consisting of 50 cases and 50 controls (the frequencies of polymorphic allele, 2% and 3%, respectively) and was not analyzed further.
| Materials and Methods |
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VEGF Genotyping
Genomic DNA was extracted from peripheral blood lymphocytes by proteinase K digestion and phenol/chloroform extraction. The VEGF 460T > C, +405C > G, and 936C > T genotypes were determined using a PCR-RFLP assay. PCR primers were designed based on the Genbank reference sequence (accession no. NT_007592). The PCR primers used for 460T > C, +405C > G, and 936C > T polymorphisms were 5'-CCTCTTTAGCCAGAGCCGGGG-3' (forward) and 5'-TGGCCTTCTCCCCGCTCCGAC-3' (reverse); 5'-CGACGGCTTGGGGAGATTGC-3' (forward) and 5'-GGGCGGTGTCTGTCTGTCTG-3' (reverse); and 5'-AGGGTTCGGGAACCAGATC-3' (forward) and 5'-CTCGGTGATTTAGCAGCAAG-3' (reverse), respectively. PCR reactions were done in a 20-µL reaction volume containing 100 ng genomic DNA, 25 pmol/L each primer, 0.2 mmol/L deoxynucleotide triphosphates, 10 mmol/L Tris-HCl (pH 8.3), 50 mmol/L KCl, 1.5 mmol/L MgCl2, and 1 unit of Taq polymerase (Takara Shuzo Co., Otsu, Shiga, Japan). PCR cycle conditions consisted of an initial denaturation step at 94°C for 5 minutes followed by 35 cycles of 30 seconds at 94°C, 30 seconds at 62°C; 30 seconds at 72°C, and a final elongation at 72°C for 10 minutes. The PCR products were digested overnight with the appropriate restriction enzymes (New England BioLabs, Beverly, MA). The restriction enzymes for the 460T > C, +405C > G, and 936C > T genotypes were BsaHI, BsmFI, and NlaIII, respectively. The digested PCR products were resolved on 6% acrylamide gel and stained with ethidium bromide for visualization under UV light. For quality control, genotyping analysis was done blind with respect to case/control status and was repeated twice for all subjects. To confirm the genotyping results, selected PCR-amplified DNA samples (n = 2, for each genotype) were examined by DNA sequencing.
Statistical Analysis
Cases and controls were compared using the Student's t test for continuous variables and the
2 test for categorical variables. Hardy-Weinberg equilibrium of alleles at individual loci was tested using a goodness-of-fit
2 test with one degree of freedom to compare the observed genotype frequencies with the expected genotype frequencies among the subjects. Haplotypes and their frequencies were estimated using Bayesian algorithm in the phase program (20), which is available at http://www.stat.washington.edu/stephens/phase.html.. Unconditional logistic regression analysis was used to calculate odds ratio (OR) and 95% confidence interval (95% CI), with adjustment for possible confounders (sex, as a nominal variable and age and pack-years, as continuous variables). A referent (to the homozygotes of wild-type allele) and 3 alternative models (codominant, dominant, and recessive for the variant allele) were used in the analyses. When multiple comparisons are made, corrected Ps (Pc values) were also calculated for multiple testing using Bonferroni's inequality method. All analyses were done using Statistical Analysis Software for Windows, version 8.12 (SAS Institute, Cary, NC).
| Results |
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| Discussion |
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In agreement with previous reports (11, 13), the 460T > C and +405C > G polymorphisms in the 5' region of the VEGF promoter were in linkage disequilibrium. However, the frequencies of 460C and +405G alleles among healthy Koreans were 0.257 and 0.519, respectively, which differed from those (0.474 and 0.291, respectively) of 115 mixed race healthy individuals in previous study (11) done in the United Kingdom. The frequencies of haplotype 460T/+405C, 460T/+405G, 460C/+405C, and 460C/+405G among the controls in the present study were 0.462, 0.280, 0.019, and 0.239, respectively, which also differed from those (0.287, 0.187, 0.004, and 0.522, respectively) of the previous study (11). In the present study, the frequency of 936C > T polymorphism among controls was 0.206, which was lower than that (0.294) found in healthy Austrians (17), and was higher than those of Japanese (0.148-0.158; ref. 21, 22) and Caucasians (0.12-0.13; refs. 14, 23).
A few studies have reported that these three VEGF polymorphisms are associated with VEGF production, but the results are inconsistent. Awata et al. (21) reported that individuals with the +405CC genotype had a higher fasting serum VEGF level than those with other genotypes, and that they carried an increased risk of diabetic retinopathy. On the other hand, Watson et al. (11) reported that the +405G allele is associated with higher lipopolysaccharide-stimulated VEGF production by peripheral blood mononuclear cells than the +405C allele. Stevens et al. (13) also reported that haplotype 460C/+405G has a higher promoter activity than haplotype 460T/+405C. For the 936C > T polymorphism, Renner et al. (12) reported that the 936T allele is associated with lower VEGF plasma levels. Krippl et al. (17) also reported that the 936T allele is associated with low VEGF plasma levels and a decreased risk of breast cancer. In contrast, in a Japanese study, no relation was found between this polymorphism and VEGF serum levels (21). In the present study, the +405C > G and 936C>T polymorphisms were associated with a significantly reduced risk of SCC. Consistent with these results, by further haplotype analysis, haplotype CGT containing 78% of +405G/936T in the study population showed a similar protective effect on the risk of SCC, whereas haplotype TCC containing 96% of +405C/936C in the population showed an increased SCC risk. Our findings that the +405GG genotype and the combined 936 CT + TT genotype are associated with a significantly reduced risk for SCC are in agreement with some reports (12, 17, 21) but are in disagreement with others (11, 13). Different results in different populations may be due to the different genetic backgrounds.
In the current study, none of the VEGF polymorphisms studied (-460T > C, +405C > G, and 936C > T) significantly influenced susceptibility to lung cancer except SCC. However, haplotypes TCT and TGT were significantly associated with the risk of lung cancer, overall and for each histologic type. This finding may be because each polymorphism alone is insufficient to influence the susceptibility to lung cancer, but that the set of the three polymorphisms (haplotype) effect on lung cancer risk due to a combined effect on gene function. Another possible explanation is that the effect of the VEGF haplotypes on lung cancer risk may be due to linkage disequilibrium with other functional variants in the VEGF gene (13, 15, 24). However, it is possible that such a finding is attributable to chance because the number of TCT and TGT haplotypes was small. Thus, additional studies with more subjects will be needed to confirm this finding.
In conclusion, we found that the VEGF haplotypes of three polymorphisms (460T > C, +405C > G, and 936C > T) are associated with the risk of lung cancer, especially SCC. These results suggest that the VEGF gene may contribute to an inherited predisposition to lung cancer, although additional studies with larger sample sizes are required to confirm our findings. Future studies of other VEGF sequence variants and on their biological functions are also needed to understand the role of the VEGF polymorphisms and haplotypes in determining the risk of lung cancer. Moreover, since genetic polymorphisms often vary between ethnic groups, further studies are needed to clarify the association between the VEGF polymorphism and lung cancer in diverse ethnic populations.
| Footnotes |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 6/24/04; revised 9/23/04; accepted 10/ 8/04.
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