Lothe R A, Peltomäki P, Tommerup N, Fosså S D, Stenwig A E, Børresen A L, Nesland J M
Department of Genetics, Norwegian Radium Hospital, Oslo, Norway.
Lab Invest. 1995 Nov;73(5):606-14.
An isochromosome for the short arm of chromosome 12, i(12p), is the most common and characteristic cytogenetic aberration in testicular germ cell tumors. Little is known about the molecular genetic abnormalities of these neoplasms.
A total of 32 loci were studied in DNA from 31 primary testicular germ cell tumors and compared with corresponding normal DNA. The loci map to 17 different chromosome arms, including seven that contain known tumor suppressor genes. Southern blot analysis and PCR-based methods were used. Several microsatellite loci were included to investigate instability (seen as new alleles) at repeat loci. The TP53 tumor suppressor gene was analyzed for point mutations by constant denaturant gel electrophoresis and for expression by immunohistochemistry. Histologic sections of the tumor biopsies were evaluated with regard to components and percentage of intact tumor cells. The growth fraction, representing one component of proliferative activity of the tumor, was assessed by the Ki-67 index.
Changes were found at all chromosome arms investigated but at very different frequencies, 5-56% of all tumors. The most frequently affected chromosome arms, those showing loss of heterozygosity or allelic imbalance in more than 40% of the tumors, were 2q, 3p, 3q, 11p, 12p, 18q, and 22q. Complete loss of one allele was often seen at 3p and 11p loci, whereas allelic imbalances dominated on the 2p, 3q, 12p, 18q, and 22q loci tested. No mutations were detected within four known mutational hot spots of TP53, but positive immunostaining with two TP53 Ab was seen in 9 of 14 tumors. Most tumors (26 of 31) showed positive immunostaining with Ki-67. Microsatellite instability was not observed.
High frequencies of loss of heterozygosity and allelic imbalance at several loci indicate that inactivation of several tumor suppressor genes may be of importance in developing testicular germ cell tumors. The increase in copynumber of 12p alleles seen in several tumors is likely to reflect one or more 12p isochromosomes. Our findings do not indicate that TP53 plays any major pathogenic role in this tumor type, nor was there any indication that defect repair genes, causing microsatellite instability in other cancers, participate in the progression of testicular cancer.
12号染色体短臂等臂染色体i(12p)是睾丸生殖细胞肿瘤中最常见且具有特征性的细胞遗传学异常。关于这些肿瘤的分子遗传学异常知之甚少。
对31例原发性睾丸生殖细胞肿瘤的DNA中的32个基因座进行了研究，并与相应的正常DNA进行比较。这些基因座定位于17条不同的染色体臂，其中包括7条含有已知肿瘤抑制基因的染色体臂。采用了Southern印迹分析和基于PCR的方法。纳入了几个微卫星基因座以研究重复基因座处的不稳定性（表现为新的等位基因）。通过恒定变性剂凝胶电泳分析TP53肿瘤抑制基因的点突变，并通过免疫组织化学分析其表达。对肿瘤活检组织的组织学切片进行了肿瘤细胞成分和完整率的评估。通过Ki-67指数评估代表肿瘤增殖活性一个组成部分的生长分数。
在所研究的所有染色体臂上均发现了变化，但频率差异很大，占所有肿瘤的5%-56%。受影响最频繁的染色体臂，即在超过40%的肿瘤中显示杂合性缺失或等位基因失衡的染色体臂，为2q、3p、3q、11p、12p、18q和22q。在3p和11p基因座经常可见一个等位基因的完全缺失，而在所检测的2p、3q、12p、18q和22q基因座上，等位基因失衡占主导。在TP53的四个已知突变热点内未检测到突变，但在14例肿瘤中的9例中观察到两种TP53抗体的阳性免疫染色。大多数肿瘤（31例中的26例）Ki-67免疫染色呈阳性。未观察到微卫星不稳定性。
几个基因座处高频率的杂合性缺失和等位基因失衡表明，几个肿瘤抑制基因的失活可能在睾丸生殖细胞肿瘤的发生中起重要作用。在几个肿瘤中观察到的12p等位基因拷贝数增加可能反映了一条或多条12号染色体短臂等臂染色体。我们的研究结果并未表明TP53在这种肿瘤类型中起任何主要的致病作用，也没有迹象表明在其他癌症中导致微卫星不稳定性的缺陷修复基因参与了睾丸癌的进展。
