Microsatellite instability in Japanese hereditary non-polyposis colorectal cancer does not induce mutation of a simple repeat sequence of the bax gene

The identification of frameshift mutations in the coding region of the bax gene in Western cases of hereditary non-polyposis colorectal cancer provided evidence that the disease could be caused by the disruption of a tumor suppressor gene associated with microsatellite instability. In order to determine whether this observation could be extended to Japanese colorectal cancers, we analyzed the simple repeat sequence of (G)8 in the bax gene of tumor genomes from 15 cases of Japanese hereditary non-polyposis colorectal cancer that showed microsatellite instability in at least one of four examined microsatellite loci. None of 15 tumor DNA samples had a frameshift mutation in this region of the bax gene. Our results suggest that direct disruption of the bax gene is not a major factor responsible for carcinogenesis in Japanese hereditary non-polyposis colorectal cancers even though microsatellite instability is present.