Ito T, Seyama T, Mizuno T, Tsuyama N, Hayashi Y, Dohi K, Nakamura N, Akiyama M
Department of Radiobiology, Radiation Effects Research Foundation, Hiroshima.
Jpn J Cancer Res. 1993 May;84(5):526-31. doi: 10.1111/j.1349-7006.1993.tb00171.x.
To identify the genetic events that must be involved in thyroid tumor progression, we initially investigated p53 gene alterations in 10 papillary adenocarcinomas, 4 follicular adenocarcinomas, and 8 undifferentiated carcinomas. Base substitutional mutations in exons 5 to 8 and loss of heterozygosity (LOH) of the p53 gene were not detected in papillary or follicular adenocarcinomas. However, 7 of 8 undifferentiated carcinomas were carrying base substitutional mutations, and LOH was detected in 3 of 5 informative cases. Furthermore, to verify that the p53 gene alterations are truly involved in tumor progression, DNA from individual foci of the four undifferentiated carcinomas coexisting with a differentiated focus and from one follicular adenocarcinoma with an undifferentiated focus was analyzed by direct sequencing and polymerase-chain-reaction-restriction-fragment-length polymorphism (PCR-RFLP). Base substitutional mutations in the p53 gene from exons 5 to 8 were identified exclusively in the undifferentiated foci, but not in the differentiated foci. LOH was observed in 3 of 4 informative undifferentiated foci. In one of these positive cases, LOH was observed in both papillary adenocarcinoma and undifferentiated carcinoma. However, a p53 gene mutation at codon 248 was detected in the undifferentiated carcinoma but not in the papillary adenocarcinoma. The results imply that LOH occurs first in papillary adenocarcinoma followed by a p53 mutation during the transition from papillary adenocarcinoma to undifferentiated carcinoma. Maintenance of LOH during tumor progression excludes the possibility that these different histological foci are derived from different origins and represents molecular evidence that undifferentiated carcinoma is very likely derived from preexisting papillary adenocarcinoma. Furthermore, these results strongly suggest that the mutated p53 gene plays a crucial role in de-differentiation during the progression of thyroid tumors.
为了确定甲状腺肿瘤进展过程中必然涉及的基因事件，我们首先研究了10例乳头状腺癌、4例滤泡状腺癌和8例未分化癌中的p53基因改变情况。在乳头状或滤泡状腺癌中未检测到外显子5至8的碱基置换突变以及p53基因的杂合性缺失（LOH）。然而，8例未分化癌中有7例携带碱基置换突变，在5例信息充分的病例中有3例检测到LOH。此外，为了验证p53基因改变确实参与肿瘤进展，通过直接测序和聚合酶链反应 - 限制性片段长度多态性（PCR - RFLP）分析了与分化灶共存的4例未分化癌的单个病灶以及1例伴有未分化灶的滤泡状腺癌的DNA。外显子5至8的p53基因碱基置换突变仅在未分化灶中被鉴定出来，而在分化灶中未检测到。在4例信息充分的未分化灶中有3例观察到LOH。在其中1例阳性病例中，在乳头状腺癌和未分化癌中均观察到LOH。然而，在未分化癌中检测到密码子248处的p53基因突变，而在乳头状腺癌中未检测到。结果表明，在从乳头状腺癌向未分化癌转变过程中，LOH首先发生在乳头状腺癌中，随后出现p53突变。肿瘤进展过程中LOH的维持排除了这些不同组织学病灶源自不同起源的可能性，并提供了分子证据，表明未分化癌很可能源自先前存在的乳头状腺癌。此外，这些结果强烈表明，突变的p53基因在甲状腺肿瘤进展过程中的去分化过程中起关键作用。
