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，应用双色荧光原位杂交技术（FISH），将着丝粒17和p53基因位点（17p13.1）探针同时与间期癌细胞杂交，分析p53和17染色体拷贝数。用限制性片段长度多态性（RFLP）检测探针YNZ 22在17 p13.3位点的杂合性缺失（洛），用抗p53蛋白抗体（RSP 53）检测p53蛋白在细胞核的过表达。当p53基因信号与着丝粒信号相比数量减少的部分（包括单体部分）超过计数细胞核的60%时，定义为剔除。15例缺失型中有11例同时存在洛性缺失和p53蛋白核内过表达。在这些病例中，等位基因丢失被认为是由17p13.1的物理缺失引起的，其余基因的点突变是高度提示的。5例既无缺失也无洛的病例中有大量的癌细胞过度表达p53蛋白。这表明p53蛋白的突变形式在这些病例中以显性负性方式起作用。另外10例无缺失的病例尽管着丝粒和p53探针均为二体，但仍显示洛缺失。其余12例p53蛋白未出现缺失、洛缺失或过表达，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基因异常的有效方法。

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.