The Aberrant Promoter Methylation Of P16 And DAPK Gene And Their Protein Expression In Gastric Carcinoma

Objective At present, 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 an important role in both initiation and progression of GC. Recent researches demonstrated that the methylation of promoter CpG islands was an important mechanism that caused the inactivation of TSGs, except for mutation and deletion. and seems to play an important role in both initiation and progression of the carcinogenesis. In this study, the methylation level of p16 and DAPK gene promoter CpG islands in GC tissues, 5cm adjacent nonmalignant gastric mucosa, and normal gastric biopsy tissues were detected to explore the relationship between the promoter hypermethylation of these genes and the carcinogenesis of GC. The expression of p16 and DAPK protein were detected to analyse the relationship between the promoter hypermethylation and the loss of protein expression.Methods Samples were divided into three groups: 123 cases of GC tissues, corresponding 5cm adjacent nonmalignant gastric mucosa tissues, 30 cases of normal gastric biopsy tissues. Genomic DNA was extracted from tissues by using Phenol/CHCl2, and then treated with bisulfite. The methylation-specific PCR (MSP) was adopted to detect the promoter CpG islands hypermethylation of p16 and DAPK gene in the above-mentioned three kinds of specimens. The immunohistochemical method was used to dected the expession of p16 and DAPK protein.Results The methylation of p16 and DAPK gene promoter was not detected in 30 normal gastric biopsy tissues. In 123 cases of GC tissues, the positive rates of hypermethylation on promoter region of p16 and DAPK were 69.1% (85 /123) and 64.2% (79/123) respectively. In the corresponding adjacent nonmalignant gastric mucosa tissues, the positive rates of hypermethylation on promoter region of p16 and DAPK were detected in 7.3% (9/123) and 34.1% (42/123) respectively, the frequency of p16 and DAPK promoter methylation in tumor tissues were significantly higher than adjacent nonmalignant tissues (both P<0.05). Furthermore, the status of p16 and DAPK methylation in adjacent nonmalignant tissues were consistent with tumor tissues (Kp16=0.068, KDAPK=0.448, both P<0.05). The frequency of p16 promoter methylation in tumor tissues of GC patients was significantly associated with the extent of differentiation, depth of infiltration and lymph node metastasis (P<0.05), the frequency of DAPK promoter methylation was significantly associated with extent of differentiation and lymph node metastasis (P<0.05). However, no correlation was found between hypermthylation and other clinicopathologic parameters such as sex, age, clinical stage, size of tumor and location of tumor. In addition, the level of p16 and DAPK protein expression was significant negative correlated with the level of their promter methylation in tumor tissues.Conclusions Aberrant methylation of p16 and DAPK gene promoter is a frequent event in GC, promoter methylation is one of the important mechanism leading to the weak and loss of protein expression, it may play an important role in the occurrence and development of gastric cancer. The aberrant hypermethylation of p16 and DAPK gene promoter may provide useful information for assessment of the malignant degree and lymph node metastasis of gastric cancer.