Somatic mutations of the APC gene in eight cancer cell lines, twelve adenomas and sixteen intestinal metaplasias of the stomach were examined. The expression of the APC mRNA and protein in eight cancer cell lines was also investigated. PCR-SSCP analysis detected mutations of the APC gene in 25% (2 out of 8) of cancer cell lines, 42% (5 out of 12) of gastric adenomas, 6% (1 out of 16) of intestinal metaplasia mucosae. Direct sequencing analysis confirmed nonsense mutations in one cancer cell line, one adenoma and one intestinal metaplasia mucosa resulted in truncation of the product, frameshift mutations in one adenoma and silent mutations in one cancer cell line and three adenomas. In addition, the KATO-III cell line, which was established from signet ring cell carcinoma, expressed very low level of APC mRNA and its APC protein could not be detected. On the other hand, the expression level of variant APC mRNA transcript which lacks exon 7 was relatively high in KATO-III. It is supposed that the variant APC mRNA transcript might contribute to the inactivation of the APC gene. These data overall provide strong evidence that changes in the APC gene play an important role in the early event of stomach carcinogenesis, especially in intestinal type gastric cancer.

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