AFP-producing adenocarcinoma is a variant of adenocarcinoma with high 
malignancy. Production of AFP suggests enteroblastic or hepatoid differentiation 
of cancer cells. GATA4 is a key molecule involved in the prenatal development of 
the stomach and liver. GATA4 is epigenetically silenced by hypermethylation of 
primer region in many types of cancers including gastric cancer. The aim of this 
study is to investigate the expression and epigenetic regulation of GATA4 in 
AFP-producing adenocarcinoma. Immunohistochemical analysis revealed that GATA4 
was positive in 3/8 cases of AFP-producing gastric adenocarcinomas and in 28/30 
cases of common type adenocarcinomas. Epigenetic modification of GATA4 promoter 
region was investigated with 3 AFP-producing and 4 common-type gastric cancer 
cell lines. GATA4 mRNA was detected in 1/3 of AFP-producing and 2/4 of 
common-type gastric cancer cell lines by RT-PCR. Methylation-specific PCR 
revealed no GATA4 methylation in any of the AFP-producing gastric cancers, 
whereas methylation was consistent with GATA4 expression in the common-type 
gastric cancers. Chromatin immunoprecipitation assay for AFP-producing gastric 
cancers revealed that histones H3 and H4 were hypoacetylated in the 
GATA4-negative cells, while they were hyperacetylated in the GATA4-positive 
cells. Treatment with trichostain A, an inhibitor for histone deacetylase, 
induced acetylation of histones H3 and H4, and tri-methylation of lysine 4 of 
histone H3, which was associated with the active transcription of GATA4 in 
GATA4-negative AFP-producing cells. These results indicated that histone 
deacetylation is a silencing mechanism for GATA4 expression in AFP-producing 
gastric cancer cells. Differences between AFP-producing gastric cancer and 
common-type gastric cancer in terms of the mechanism of GATA4 regulation may be 
reflected in the phenotypic deviation of AFP-producing gastric cancer from 
common-type gastric cancer.