Functional analysis of polymorphisms in the COX-2 gene and risk of lung cancer

Abstract

The enzyme cyclooxygenase 2 (COX-2) is known to be involved in tumorigenesis and metastasis in certain types of cancer. Nevertheless, the prognostic value of COX-2 overexpression and its polymorphisms in patients with non-small cell lung cancer (NSCLC) have yet to be fully elucidated. The aim of the present study was to investigate the association between the three most commonly studied COX-2 gene polymorphisms (-1195 G/A, -765 G/C and 8473 T/C) with COX-2 expression and lung cancer risk in a Brazilian cohort. In the present hospital based, case-control retrospective study, 104 patients with NSCLC and 202 cancer free control subjects were genotyped for -1195 G/A, -765 G/C and 8473 T/C polymorphisms using allelic discrimination with a reverse transcription quantitative polymerase chain reaction method. COX-2 mRNA expression was analyzed in surgically resected tumors from 34 patients with NSCLC. The results revealed that COX-2 expression levels were higher in tumor tissue compared with normal lung tissue. However, this overexpression of COX-2 was not associated with the patient outcome, and furthermore, none of the analyzed polymorphisms were associated with the risk of developing lung cancer, COX-2 overexpression, or the overall survival of the patients with NSCLC. Taken together, the findings described in the present study do not support a major role for COX-2 polymorphisms and COX-2 overexpression in lung carcinogenesis within the Brazilian population.

Keywords: cohort; cyclooxygenase 2; lung cancer; polymorphism; tumorigenesis.

Figure 1.

Overall survival curves of patients according to the (A) −1195 G/C, (B) −765 G/C and (C) 8473 T/C COX2 polymorphisms and the mRNA expression of COX2. The polymorphisms were grouped according to the variant allele: Homozygous for the variant allele compared with homozygous for the wild-type and heterozygous, and subjects were genotyped using allelic discrimination by a reverse transcription quantitative polymerase chain reaction method. Survival over time (months) was determined as shown in A, B and C. (D) The 34 patients with non-small cell lung cancer in which COX2 expression had been previously obtained were stratified into high and low-expression groups according to the median. The survival over time (months) was determined.

Figure 2.

Relative mRNA expression of COX2 by RTPCR according to tumor vs. (A) normal tissue and according to the three COX2 polymorphisms, (B) −1195 G/A, (C) −765 G/C and (D) 8473 T/C. Relative gene expression quantification for COX2, with β-actin as an internal reference gene, was performed. Significance of the mean differences between tumor tissue and the control cDNA from normal lung tissue was estimated on log-transformed normalized expression levels, as shown in (A). (BCD) The relative mRNA expression of COX2 correlated with the COX2 polymorphisms, (B) −1195 G/A, (C) −765 G/C and (D) 8473 T/C.