Numerical changes of chromosome 17p (p53locus) detected by FISH in gastric cancer

为进一步了解P53基因缺失在胃腺癌中的作用，采用双色荧光原位杂交(FISH)技术，对42例胃腺癌组织中的着丝粒17和P53基因(17p13.1)基因片段与间期癌细胞进行杂交，逐个细胞分析P53和17号染色体的拷贝数。用限制性片段长度多态方法检测YNZ22基因17p13.3的杂合性缺失(LOH)，用抗P53蛋白抗体(RSP53)免疫组织化学方法检测P53蛋白的核过度表达。当P53基因信号比着丝粒信号减少的部分(包括单体部分)超过所计数的细胞核的60%时，Delection被定义为。15例缺失病例中有11例同时存在P53蛋白的LOH和核过度表达。在这些病例中，等位基因丢失被认为是由于17p13.1的物理缺失造成的，其余基因点突变具有很高的暗示意义。5例既无缺失又无杂合性缺失的病例中有大量癌细胞过度表达P53蛋白。这表明突变型P53蛋白在这些病例中以显性负向方式发挥作用。10例无缺失的患者，着丝粒和P53探针均为二体，但均为杂合性缺失。其余12例均未见P53蛋白缺失、缺失或过表达，提示P53基因可能与肿瘤的恶性进展无关。结论：FISH技术是分析胃腺癌P53基因突变的有用工具。

To understand better the role of p53 deletion in gastric adenocarcinoma, 42 cases were examined by dual-color fluorescence in situ hybridization (FISH).Probes for centromere 17 and the p53 locus (17p13.1) were hybridized simultaneously to interphase cancer cells to analyze p53 and chromosome 17 copy numbers on a cell by cell basis. The result was compared with the loss of heterozygosity (LOH) for probe YNZ22 at 17p13.3 detected by restriction fragment length polymorphism, and nuclear overexpression of p53 proteins examined immunohistochemically with anti-p53 protein antibody (RSP53). Delection was difined as when the fraction with decreased number for p53 gene signals compared with centromeric signals including monosomy fractions exceeded 60% of cell nuclei counted. Eleven of 15 cases showing deletion also showed LOH and nuclear overexpression of p53 protein. In these cases allelic loss was thought to be caused by physical deletion of 17p13.1 and point mutation of the remaining gene was highly suggestive. Five cases with neither deletion nor LOH had large population of cancer cells over-expressing p53 protein. This suggested mutant form of the p53 protein functioned in a dominant negative fashion in these cases. Other 10 cases without deletion showed LOH in spite of being disomic for both the centromeric and p53 probes. Remaining 12 cases showed neither deletion, LOH nor overexpression of p53 protein, thus it was very likely that p53 gene were not implicated in malignant progression in these cases. It was concluded that FISH is a useful tool to analyze aberrations of p53 gene in gastric adenocarcinoma.