Takahashi T, D'Amico D, Chiba I, Buchhagen D L, Minna J D
National Cancer Institute, Navy Medical Oncology Branch, National Cancer Institute, Bethesda, Maryland 20814.
J Clin Invest. 1990 Jul;86(1):363-9. doi: 10.1172/JCI114710.
The p53 gene initially was thought to be an oncogene, but recent evidence suggests that wild-type p53 can function as a tumor suppressor gene in lung, colon, and breast cancer as well as less common malignancies. This study reports the first identification of intronic point mutations as a mechanism for inactivation of the p53 tumor suppressor gene. Abnormally sized p53 mRNAs found in a small cell and a non-small cell lung cancer cell line were characterized by sequence analysis of cDNA/PCR products, the RNase protection assay and immunoprecipitation. These mRNAs were found to represent aberrant splicing leading to the production of abnormal or no p53 protein. Sequence analysis of genomic DNA revealed that a point mutation at the splice acceptor site in the third intron or the splice donor site in the seventh intron accounts for the abnormal mRNA splicing. In one patient the same intronic point mutation was found in the tumor cell line derived from a bone marrow metastasis and in multiple liver metastases but not in normal DNA, indicating that it occurred as a somatic event before the development of these metastases. These findings further support the role of inactivation of the p53 gene in the pathogenesis of lung cancer and indicate the role of intronic point mutation in this process.
p53基因最初被认为是一种癌基因，但最近的证据表明，野生型p53在肺癌、结肠癌和乳腺癌以及一些罕见的恶性肿瘤中可作为肿瘤抑制基因发挥作用。本研究首次鉴定出内含子点突变是p53肿瘤抑制基因失活的一种机制。通过对cDNA/PCR产物进行序列分析、核糖核酸酶保护试验和免疫沉淀，对在一个小细胞肺癌细胞系和一个非小细胞肺癌细胞系中发现的大小异常的p53 mRNA进行了特征分析。发现这些mRNA代表异常剪接，导致产生异常的或无p53蛋白。基因组DNA序列分析显示，第三个内含子的剪接受体位点或第七个内含子的剪接供体位点的一个点突变导致了mRNA的异常剪接。在一名患者中，在源自骨髓转移灶和多个肝转移灶的肿瘤细胞系中发现了相同的内含子点突变，但在正常DNA中未发现，这表明该突变是在这些转移灶形成之前作为体细胞事件发生的。这些发现进一步支持了p53基因失活在肺癌发病机制中的作用，并表明内含子点突变在这一过程中的作用。
