Background: Mouse double minute 2 (MDM2) is a negative regulator of p53. In the present study, we examined MDM2 transcriptional activity and messenger RNA (mRNA) expression in lung tumors with respect to MDM2 SNP309 genotypes and p53 mutation status, and the effects of MDM2 SNP309 genotypes and p53 mutation status on lung cancer prognosis.
Methods: p53-null lung cancer cells were cotransfected with MDM2 P2 reporter construct containing the TT or GG genotype and wild-type or mutant p53 plasmids for luciferase reporter assay. Genomic DNA from 306 lung tumors and adjacent normal tissues was used to determine p53 mutation and MDM2 genotype by direct sequencing and polymerase chain reaction (PCR) restriction fragment length polymorphism. Real-time reverse-transcriptase PCR was applied to determine MDM2 mRNA levels. Overall survival was also calculated.
Results: Transcriptional activity of the MDM2 promoter containing the SNP309 GG genotype was significantly lower than that containing the TT genotype in p53-null lung cancer cells cotransfected with wild-type p53 expression plasmid under mithramycin A treatment. MDM2 mRNA levels in tumors with the SNP309 TG and GG genotypes were higher than those in tumors with the TT genotype, particularly in wild-type p53 tumors. Stage I patients with MDM2 SNP309 GG also had better overall survival than TT carriers, especially wild-type p53 patients (hazard ratio = 0.34; 95% confidence interval 0.15-0.80). Similar results were not observed in late-stage patients.
Conclusions: MDM2 SNP309 was associated with MDM2 transcripts, mRNA levels, and survival in stage I non-small-cell lung cancer patients with wild-type p53 tumors.