Association Of P73 And MDM2 Polymorphisms With The Risk Of Epithelial Ovarian Cancer

Objective: Ovarian cancer (OC) is the most common cause of death of the gynecological malignancies in Chinese women. Epithelial ovarian cancer (EOC) originates from ovarian surface epithelium and occupies 90% of all ovarian tumors in women. Nevertheless, it is often asymptomatic and approximately 70% of all cases, when diagnosed, present an advanced stage of the disease. So the overall 5-year survival rate is only 25 to 30% currently. The study showed that genetic susceptibility that affect the function of pathways known to in?uence the neoplastic process may be particularly relevant. Therefor, it is the effective way to improve the survival rate of ovarian cancer to look for predisposing genes, high-risk group and early diagnosis method. p73 and murine double minute2 (MDM2), as the candidate tumor gene, have been the studyed focus in recent years.p73, as a candidate tumour suppressor gene, plays an important role in modulating cell-cycle control and sustaining cell stabilization. A dinucleotide single nucleotide polymorphisms (SNPs) at positions 4 and 14 of exon 2 (G4C14/A4T14) is regarded as a functional one, which possibly forms a stem-loop structure to influence the p73 translation. MDM2, as a proto-oncogene, is an important negative regulator of p73, which represses the transcriptional activity of p73 and thus attenuates its function. Based on the molecular interaction between p73 and MDM2 in cell-cycle control and apoptosis, this study was designed to investigate the association between single nucleotide polymorphisms (SNPs) in the promoter region of p73 and MDM2 genes and the risk of epithelial ovarian cancer. By this way, we hope to offer some evidences for the prevention and therapy of ovarian cancer at molecular level.Methods: This hospital-based case-control study included 257 patients with epithelial ovarian cancer and 257 healthy women as control. Five ml of venous blood from each subject was drawn in vacutainer tubes. The white blood cell DNA was extracted by using proteinase K-digestion followed by a salting out procedure. p73 G4C14/A4T14 and MDM2 309T/G and MDM2 Del1518+/- SNPs were genotyped by polymerase chain reaction-restrictive fragment length polymorphism (PCR-RFLP) analysis.Statistical analysis was performed using SPSS11.5 software package. Hardy-Weinberg analysis was performed by comparing the observed and expected genotype frequencies in study groups using Chi-square test. Between cases and controls, the t test was used to examine the difference of ages and ages of menarche and the Chi-square test was used to examine the difference of gravidity and parity. Univariate comparisons of allele and genotype distribution were performed using Chi-square test. The odds ratio (OR) and 95% confidence interval (CI) were calculated using an unconditional logistic regression model. The MDM2 309T/G and MDM2 Del1518+/- haplotype frequencies and linkage disequilibrium coefficient were estimated by using EH linkage software and 2ld software. Tests for the interaction between p73 and MDM2 genes were performed using the likelihood ratio test. P<0.05 was considered significant for all statistical analyses.Results:1 The genotype distributions of the p73 G4C14/A4T14 and MDM2 309T/G, Del1518+/- SNPs in control group did not significantly deviate from that expected for a Hardy-Weinberg equilibrium (χ2=0.00, 1.00 and 0.64, respectively, and all P values >0.05).2 There were no significant differences in allele frequencies and genotype distributions of the p73 G4C14/A4T14 polymorphism between cases and control women (P=0.55 and 0.20, respectively). Compared to the GC/AT+AT/AT genotypes, the GC/GC genotype had no association with the risk of epithelial ovarian cancer (OR=1.24, 95%CI=0.87～1.77). Stratification analysis showed no significant difference between the cases and control groups in allele or genotype distributions of p73 G4C14/A4T14 according to the pathological type, clinical stage and patient age of epithelial ovarian cancer (P>0.05).3 The frequencies of three genotypes (T/T, T/G and G/G) of MDM2 309T/G in ovarian cancer cases and controls were 30.0%, 46.7%, 23.3% and 21.8%, 47.1%, 31.1%,respectively, and there was significant difference between the two groups (P=0.046). The frequencies of the G allele of the MDM2 309T/G SNP were significantly lower in ovarian cancer cases (46.7%) than those in healthy controls (54.7%), there was statistical difference between the two groups (P=0.01). Compared with the T/T genotype, the G allelotype (T/G+G/G genotype) significantly decreased the risk of developing EOC (OR=0.65, 95%CI=0.44～0.97). Stratification analysis showed that subjects carrying G allelotype (T/G+G/G genotype) significantly decreased the risk of endometrioid ovarian cancer (OR=0.53, 95%CI=0.31～0.90) according to histological subtypes. When stratified by clinical stage, individuals with the G allelotype (T/G+G/G genotype) significantly had a relation on the reduced risk of the advanced ovarian cancer (OR=0.62,95%CI=0.40～0.97). Furthermore, the lower risk of ovarian cancer was associated with the G allelotype (T/G+G/G genotype) in subjects that were 50 or older, with odds ratio of 0.59 (95%CI=0.38～0.92).4 MDM2 Del1518+/- genotype and allele frequencies did not differ between the case group and the control group (P=0.68 and P=0.45). Compared to the (+/-)+(-/-) genotypes, the +/+ genotype did not significantly modify the risk of epithelial ovarian cancer with odds ratio of 1.17 (95%CI=0.83～1.65). But MDM2 Del1518+/+ genotype was associated with a trend for mucinous ovarian cancer by stratification analysis according to histological subtypes (OR=2.01, 95%CI=0.93～4.37). When stratified by clinical stage, individuals with the +/+ genotype tended to increased the risk of the earlier ovarian cancer (OR=1.64, 95%CI=0.99～2.72). No association was observed between the polymorphism and age at diagnosis.5 The results of the 2LD program analysis showed that the MDM2 309T/G and Del1518+/- polymorphisms displayed linkage disequilibrium (D'=0.57, P=0.00). The frequencies of four haplotypes (+1518/T309, +1518/G309, -1518/T309 and -1518/G309) of MDM2 309T/G and Del1518+/- were not significantly different between the case and control groups (P=0.07). Compared with the haplotype of +1518/T309, the +1518/G309 and -1518/G309 haplotypes both significantly decreased the risk of EOC (OR=0.73, 95%CI=0.55～0.98; OR=0.65, 95%CI=0.45～0.96).6 The gene-gene interaction between the p73 G4C14/A4T14 and MDM2 309T/G or Del1518+/- SNPs on the risk of EOC was analyzed using the likelihood ratio test. The results showed that there was a significant interaction between p73 G4C14/A4T14 and MDM2 309T/G (P=0.03, OR=0.89, 95%CI=0.80～0.99). However, the significant interaction of p73 G4C14- to-A4T14 and Del1518+/- was not observed (P=0.36). Compared with GC/GCp73 G4C14/A4T14-T/TMDM2 309T/G, subjects carrying (GC/AT+AT/AT)p73 G4C14/A4T14-(T/G+G/G)MDM2 309T/G significantly decreased the risk of EOC (OR=0.55, 95%CI=0.31～0.98).Conclusions:1 The p73 G4C14/A4T14 SNP may have no susceptibility to the epithelial ovarian cancer.2 MDM2 309G allele carriers significantly decreased the risk of epithelial ovarian cancer. Furthermore, there were significant association between MDM2 309T/G polymorphism and tumor histological subtypes, clinical stage and age. It may be a potentially protective factor for epithelial ovarian cancer.3 The MDM2 Del1518+/+ genotype tended to increase the risk of mucinous ovarian cancer or earlier ovarian cancer, but not associated with the age.4 The MDM2 309T/G and Del1518+/- SNPs showed linkage disequilibrium, the +1518/G309 and -1518/G309 haplotypes both significantly decreased the risk of EOC.5 There was a significant interaction between p73 G4C14/A4T14 and MDM2 309T/G. But the significant interaction of p73 G4C14/A4T14 and Del1518+/- was not observed. (GC/AT+AT/AT)p73 G4C14/A4T14-(T/G+G/G)MDM2 309T/G genetype significantly decreased the risk of EOC.