Abstract: OBJECTIVE: We investigated the promoter and exon1 methylation of mothers against decapentaplegic homolog 4 (Smad4) and its correlation with protein expression of TGF-β1 in gastric cardia adenocarcinoma (GCA). METHODS：Methylation-specific PCR approach，RT-PCR and immunohistochemistry methods were used to examine the methylation status of the 5' CpG island，mRNA and protein expression of Smad4. Immunohistochemistry method was used to detect the protein expression of TGF-β1 in tumors and corresponding normal tissues. RESULTS：For the promoter site，Smad4 was methylated in 6/110 (5.5%) tumor specimens. For the 5' UTR of exon1，Smad4 was methylated in 24.5% (27/110) tumor specimens. Both were significantly higher than that in corresponding normal tissues (P<0.05). Methylation frequency of Smad4 in the 5' UTR of exon1 was significantly higher than that in the promoter site (P<0.01). Smad4 mRNA and protein expression of tumor tissues were significantly lower than that in corresponding normal tissues and was inversely correlated with its methylation status. Seventy-two of 110 (65.5%) tumor tisssues demonstrated positive immunostaining for TGF-β1 and the frequency of positive TGF-β1 protein expression was significantly higher than that in corresponding normal tissues (P<0.01). The protein expressions of TGF-β1 were significantly different among various stages and differentiations of GCA (P<0.05). The protein expression of Smad4 was inversely correlated with TGF-β1 in GCA. CONCLUSION：Hypermethylation of Smad4 in 5' UTR of exon1 and the higher protein expression of TGF-β1 may play important roles in the development of gastric cardia adenocarcinoma.

Key words: gastric cardia adenocarcinoma, DNA methylation, Smad4 gene, TGF-β1 gene