Studies On The Relationship Between The Aberrant Promoter Methylation Of DAPK, E-cadherin And P16 Gene And Gastric Carcinoma

Objective Presently, the studies on the pathogenesis of gastric carcinoma(GC) mainly focus on the molecule and cytobiology area. The inactivation of certain genes including tumor suppressor genes (TSGs) play important roles in both initiation and progression of GC. More and more attentions have been paid to the aberrant methylation of promoter CpG islands, one of the various inactivation modes. Recent researches demonstrated that the methylation of promoter CpG islands was an important mechanism that caused the inactivation of TSGs and seems to play an important role in both initiation and progression of the carcinogenesis. In this study, the methylation level of tumour-related gene promoter CpG islands in GC tissues, 5cm adjacent nonmalignant gastric mucosa tissues, and nornal gastric mucosa tissues were detected to explore the relationship between the aberrant promoter hypermethylation of those genes and the carcinogenesis of GC.Methods Samples were divided into three groups: 47 cases of GC tissues, 5cm adjacent nonmalignant gastric mucosa tissues, 20 cases of normal gastric mucosa tissues. Genomic DNA was extracted from tissues by using Phenol/CHCl2, and then treated with bisulfite. The technique of methylation-specific PCR (MSP) was adopted to investigate the promoter CpG islands hypermethylation of death-associated protein kinase (DAPK) gene, epithelial cadherin (E-cadherin or CDH1) gene and p16 gene in the above-mentioned three kinds of specimens. The relationship between the frequency of hypermethylation of the genes and clinical data was analyzed.Results Only the methylation of p16 gene promoter was detected in one of the 20 normal gastric mucosa tissues. In 47 cases of GC tissues, the positive rates of hypermethylation on promoter region of DAPK, E-cadherin and p16 were 66.0% (31/47), 44.7% (21/47) and 63.8% (30/47) respectively. In the paired non-tumor gastric mucosa tissues, the positive rates of hypermethylation on promoter region of DAPK, E-cadherin and p16 were detected in 36.2% (17/47), 25.5% (12/47) and 12.8% (6/47) respectively. In summary 87.2% (35/40) of GC and 48.9% (23/47) of the non-tumor gastric mucosa tissues had hypermethylation of at least one gene. The samples of one gene, two genes and three genes methylation in tumor tissues were 12 (25.5%), 17 (36.2%) and 12 (25.5%). All of the three genes methylaion were detected in 2 (4.3%) 47 cases of non-tumor gastric mucosa tissues. There were 8 (17.0%) samples of two genes methylation and 13 (27.7%) samples of one gene methylation in the non-tumor gastric mucosa tissues. Hypermethylation of DAPK and p16 gene was more frequent in GC than in non-tumor gastric mucosa tissues (p<0.05), and the statistical association of DAPK and p16 gene methylation between GC and non-tumor tissues was found (K=0.296 and 0.153, p<0.05). The methylated index (MI) of GC was more frequent than that of the non-tumor tissues (t=5.139, p<0.01). Methylation of DAPK gene promoter in GC patients is correlated to lymph node metastasis, differentiation level and TNM phase (p<0.05),while the methylation of E-cadherin gene promoter in GC patients is correlated to infiltration depth, TNM phase and lymph node metastasis (p<0.05). Methylated p16 gene in GC patients did not correlate with other clinicopathological characteristics, such as gender, age, size of tumor, TNM phase, and so on.Conclusions Aberrant methylation of DAPK, E-cadherin and p16 gene promoter is a common event in GC, and the aberrant methylation of DAPK, E-cadherin gene promoter was associated with clinical-pathological characteristics of GC, so it suggests that this two genes play important roles in the process of carcinogensis. Detection of multiple genes hypermethylation may offer a new approach in the diagnosis of GC. The theoretical basis may also provide for the therapy of GC through changing the gene methylation level.