Single nucleotide polymorphisms of IGFBP-3 gene and lung cancer risk in a Korean population

Insulin-like growth factor binding protein-3 (IGFBP-3) is a putative tumor suppressor and inhibits the mitogenic and antiapoptotic activity of insulin-like growth factor (IGF) by blocking the binding to its receptors or by IGF-independent manner. Epidemiological studies have suggested that serum level of IGFBP-3 is associated with lung cancer risk. The present study was conducted to evaluate the association between single nucleotide polymorphisms (SNPs) of the IGFBP-3 gene and susceptibility to lung cancer and the effect of the SNPs on the serum levels of IGFBP-3, total IGF-I and free IGF-I in a Korean population. After a preliminary study for polymorphism screening of the promoter region of the IGFBP-3 gene in randomly selected 41 lung cancer patients, two polymorphisms (-1590 C>A; -202 A>C) were identified with PCR-based restriction fragment length polymorphism (PCR-RFLP) and SNaPshot primer extension assay in 415 Korean lung cancer patients and 415 matched normal controls. Although the genotype and allele frequency distribution of each SNP did not differ significantly between cases and controls in the single-locus analysis, we found that the polymorphisms of -1590A and -202C were associated with increased risk for lung cancer in females (-1590 C>A; adjusted OR=2.11, 95% CI=1.08-4.12, -202 A>C; adjusted OR=1.96, 95% CI=1.02-3.75, respectively) and never-smokers (-1590 C>A; adjusted OR=2.06, 95% CI=1.12-3.78, -202 A>C; adjusted OR=1.99, 95% CI=1.10-3.62, respectively) in a dominant model after stratification for gender and smoking history. Haplotype analysis showed that carriers of A-C had significantly higher risk for lung cancer in females (dominant aOR=2.05, 95% CI=1.14-3.68) and in never-smokers (codominant aOR=1.71, 95% CI=1.11-2.64 and dominant aOR=1.99, 95% CI=1.17-3.40). Functional analysis in H1703 cell line using DNA fragments containing A-C haplotype of the promoter region showed significantly decreased transcriptional activity. Furthermore, there was a negative correlation between the number of polymorphic alleles in -1590/-202 loci and serum levels of IGFBP-3 in lung cancer patients, but it was not statistically significant in the test for linear trend. These results suggest that IGFBP-3 promoter polymorphisms of -1590 C>A and -202 A>C might be a genetic risk factor for lung cancer by means of decreased IGFBP-3 expression among females or never-smoking Koreans.