[APC mutation analysis in sporadic colorectal cancer].
APC gene, responsible for familial adenomatous polyposiscoli, is one of the tumor suppressor genes involved in tumorigenesis of sporadic colorectal cancer. Because the majority of APC mutations are located in the 5' end of exon 15 and 95% of them generate stop codon, a coupled in vitro transcription and translation system (IVSP) was used to detect somatic APC mutation of exon 15 in sporadic colorectal cancer. Forty-nine mutated sporadic cases containing 59 truncated bands (9 cases with 2 bands) were identified. The results of the study showed: 1. APC frameshift mutations were more frequent than point mutations (60% vs 40%). Most of the frameshift mutations (32/35) were deletion or insertion of 1-2 bp, whereas 16 of all 23 point mutations presented C-to-T transitions. Mutations (57/59) were mostly but unevenly distributed in segment 2 and 3 of exon 15, while in segment 3, 69% (45/59) of all the mutations were predominantly located in mutation cluster region (codon 1286-1531). In seven of the 9 cases with 2 mutations their close proximity with each other is suggestive of the possibility of mutations at 2 independent alleles. The similarities between APC somatic and germline mutations suggest that APC gene might well have some common functions during the tumorigenesis of sporadic and hereditary coloretal cancer.