Samowitz W S, Slattery M L
Department of Pathology, University of Utah Health Sciences Center, Salt Lake City, Utah 84132, USA.
Genes Chromosomes Cancer. 1999 Oct;26(2):106-14.
The reproducibility of microsatellite instability from different regions of the same sporadic colon cancer has not been addressed. We therefore microdissected and extracted DNA from three to nine separate regions of 13 highly unstable sporadic colon cancers. Each region was then evaluated by polymerase chain reaction amplification of 17 microsatellites: 10 tetranucleotide repeats, 2 noncoding mononucleotide repeats (BAT-26 and BAT-40), and 5 coding mononucleotide repeats (TGFBRII, BAX, MSH3, MSH6, IGFIIR). Microsatellite instability showed 100% regional reproducibility with respect to either the panel of 10 tetranucleotide repeats or BAT-26, and nearly 100% reproducibility with BAT-40, although regional variation in the percent instability and the size of unstable alleles was present. TGFBRII was more frequently mutated than any other coding mononucleotide repeat; frame shifts in this gene were identified in nearly every region of every tumor. Each of the five coding repeats showed regional variability in at least one tumor, and 10 of the 13 tumors showed variability with at least one coding repeat. This variability took the form of different mutant alleles (TGFBRII, BAX, MSH3) or mutations present in some but not all regions of a tumor (MSH6, IGFIIR, BAX, MSH3). We conclude that the regional reproducibility of generalized microsatellite instability as measured by noncoding repeats indicates that sampling is not a problem in these highly unstable tumors, and that the mismatch repair deficiency phenotype is acquired in the very late adenoma stage or early cancer stage of sporadic colonic tumorigenesis. The high frequency of TGFBRII mutations is consistent with acquisition of these mutations at a similar stage of tumorigenesis. The regional variability with respect to the presence or absence of a mutation in the other four coding mononucleotide repeats could lead to sampling error and is consistent with a somewhat later time of acquisition of these mutations. Genes Chromosomes Cancer 26:106-114, 1999.
同一散发型结肠癌不同区域微卫星不稳定性的可重复性尚未得到研究。因此，我们对13例高度不稳定的散发型结肠癌的3至9个不同区域进行了显微切割并提取DNA。然后通过聚合酶链反应扩增17个微卫星对每个区域进行评估：10个四核苷酸重复序列、2个非编码单核苷酸重复序列（BAT-26和BAT-40）以及5个编码单核苷酸重复序列（TGFBRII、BAX、MSH3、MSH6、IGFIIR）。微卫星不稳定性在10个四核苷酸重复序列或BAT-26组成的检测组中显示出100%的区域可重复性，在BAT-40检测中显示出近100%的可重复性，尽管存在不稳定性百分比和不稳定等位基因大小的区域差异。TGFBRII比其他任何编码单核苷酸重复序列更频繁地发生突变；几乎在每个肿瘤的每个区域都鉴定出该基因的移码突变。五个编码重复序列中的每一个在至少一个肿瘤中都显示出区域变异性，并且13个肿瘤中的10个在至少一个编码重复序列中显示出变异性。这种变异性表现为不同的突变等位基因（TGFBRII、BAX、MSH3）或存在于肿瘤某些但并非所有区域的突变（MSH6、IGFIIR、BAX、MSH3）。我们得出结论，通过非编码重复序列测量的广义微卫星不稳定性的区域可重复性表明，在这些高度不稳定的肿瘤中采样不是问题，并且错配修复缺陷表型是在散发性结肠肿瘤发生的晚期腺瘤阶段或早期癌症阶段获得的。TGFBRII突变的高频率与在肿瘤发生的相似阶段获得这些突变一致。其他四个编码单核苷酸重复序列中突变存在与否的区域变异性可能导致采样误差，并且与这些突变的获得时间稍晚一致。《基因、染色体与癌症》26:106 - 114，1999年。
