遗传性非腺瘤病性结直肠癌结肠腺瘤病基因突变研究

目的 分析遗传性非腺瘤病性结直肠癌(hereditary non-polyposis colorectal cancers，HNPCC)结肠腺瘤病(adenomatous polyposis coli，APC)基因突变的特点及错配修复缺陷对其影响。方法 采用体外蛋白合成试验和序列分析确定19例HNPCC病例APC体细胞突变。结果 19例病例中有11例(13个突变点)发生APC突变，发生率为58％(11／19)，其中移码突变9个，无义突变4个，移码突变占多数(69％)。所有移码突变表现为1—2个碱基的缺失或插入，大多(7／9)发生在简单核苷酸重复序列，特别是单腺苷酸重复序列(A)n(5／9)。检出的由单个碱基替换而导致的无义突变都发生在CpG岛，表现为C向T的转换。结论 多于半数的HNPCC发生APC突变，其突变多发生在编码区单核苷酸重复序列(移码突变)或CpG岛(点突变)上，提示APC基因失活在HNPCC为常见的分子事件；错配修复缺陷所致的微卫星DNA不稳定性等内源性机理可能对APC突变产生影响。

Mutational studies of adenomatous polyposis coli gene in carcinomas from patients with hereditary non-polyposis colorectal cancers

Objective To analyze the mutational features of adenomatous polyposis coli (APC) gene and to explore the effect of mismatch repair (MMR) deficiency on its mutations in hereditary non polyposis colorectal cancers (HNPCC). Methods PCR based in vitro synthesized protein test (IVSP) assay and sequencing analysis were used to confirm somatic mutations of whole APC gene in 19 HNPCC patients. Results Eleven cases with thirteen mutations were determined. The frequency of APC mutation was 58%(11/19). The exhibiting mutations consisted of 9 frameshift mutations and 4 nonsense ones , indicating the existence of more frameshift mutations (69%). All of frameshift mutations were deletion or insertion of 1 2 bp and most of them (7/9) happened at simple nucleotide repeat sequences, particularly within (A)n tracts (5/9). All of four nonsense mutations resulted from C to T transitions at CpG sites. Conclusion Mutational inactivations of APC gene were detected in more than half of HNPCC patients in this study, indicating that APC mutation is a common molecular event in the tumorigenesis of HNPCC. According to the location of frameshift mutations at simple nucleotide repeat sequences and point mutations at CpG sites, it was suggested that endogenous mechanisms like MMR deficiency might exert an effect on the nature of APC mutations in most HNPCC.