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 ALP-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 ALP-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 ALP-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. (C) 2012 Elsevier Inc. All rights reserved.