ALTERATIONS OF LEVEL OF TOTAL GENOMIC DNA METHYLATION AND PATTERN OF C-MYC, C-HA-RAS ONCOGENE METHYLATION IN HUMAN GASTRIC CARCINOGENESIS

Objective. To investigate the status of DNA methylation in gastric car cinogenesis. Methods. We analysed methylation pattern of c-myc, c-Ha-r as oncogenes by southern blot hybridization. DNA from cancerous, parac ancerous and nun-cancerous area of surgically resected samples in 21 c ases of advanced gastric cancer were digested with MspI/HpaII and hybr idized with the two genomic P-32 labelled probes. In addition, the lev el of total genomic DNA methylation was measured by incubating DNA wit h H-3-S-Adenosylmethionine (H-3-SAM) in the presence of a methylase wh ich methylates all the cytosine residues that are in the double CpG (c ytosine-guanine). Results, The results indicated that both c-myc and c -Ha-ras oncogene fragments containing CCGG sequence were hypomethylate d in DNA samples from cancerous (10/21 and 5/10) and paracancerous (13 /21 and 4/10) areas. Moreover, the level of total genomic DNA methylat ion in cancerous tissue was significantly lower than that in non-cance rous and paracancerous mucosa tissues (P<0.05). The results from two m ethods are incompletely alike. Conclusion. These results supported a s trong correlation between DNA hypomethylation and gastric carcinogenes is; particularly methylated pattern of c-myc and c-Ha-ras oncogenes fr agments containing CCGG sequence was abnormal in gastric mucosa tissue from gastric cancerous and paracancerous areas.