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Genetic Alterations in the Human Tcf-4 Gene in Japanese Patients with Sporadic Gastrointestinal Cancers with Microsatellite Instability

Disruption of the APC/β-catenin/Tcf pathway has been proposed as an important step in the development of cancer. The Tcf-4 transcription factor gene was reported to be one of the targets of microsatellite instability (MSI) in colorectal cancers in with MSI. We carried out a sequencing analysis of the Tcf-4 gene in 41 Japanese patients with gastrointestinal tumors with MSI as well as in cancer cell lines. Three of 21 (14.3%) colorectal tumors with MSI contained a mutant Tcf-4 gene encoding 1-bp deletion in an (A)9 repeat, leading to carboxyl terminal truncation of Tcf-4 protein. No Tcf-4 mutations were detected in 20 gastric tumors with MSI, or in gastric cancer cell lines. Additionally, we found a novel transcript of the Tcf-4 gene which contained a segment of 73 bp in front of the (A)9 repeat of the Tcf-4 coding sequence. Sequencing analysis revealed that the inserted fragment was 60% homologous to that of exon IXA of the Tcf-1 gene. It is of interest that this insertion resulted in truncation of Tcf-4, similar to the 1-bp deletion in the (A)9 repeat. Therefore, in part of the Japanese colorectal tumors with MSI, frameshift mutations in Tcf-4 may be of functional significance. Functional alterations in the Tcf-4 signaling network in gastrointestinal tumorigenesis require further investigations.