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

为了更好地了解p53缺失在胃腺癌中的作用，我们对42例胃腺癌患者进行了双色荧光原位杂交（FISH）检测。将17号着丝粒和p53位点（17p13.1）的探针与间期癌细胞同时杂交，以细胞为单位分析p53和17号染色体的拷贝数。将结果与限制性片段长度多态性检测的YNZ22探针17p13.3位点杂合性缺失（LOH）进行比较，并使用抗p53蛋白抗体（RSP53）免疫组化检测p53蛋白的核过表达。当p53基因信号与包括单体在内的着丝体信号相比数量减少的部分超过细胞核计数的60%时，定义为缺失。15例缺失病例中有11例同时出现LOH和细胞核过表达p53蛋白。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，剩余基因的点突变高度提示。5例既无缺失也无LOH的患者存在大量过表达p53蛋白的癌细胞。这表明p53蛋白的突变形式在这些病例中以显性阴性方式发挥作用。另外10例未缺失的病例显示LOH，尽管对着丝粒和p53探针都是二体的。其余12例患者均未出现p53蛋白缺失、LOH和过表达，因此p53基因很可能与这些病例的恶性进展无关。结论FISH是分析胃腺癌中p53基因畸变的有效工具。

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.