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MUTATIONS CAUSED BY LINE 1 TRANSPOSONS IN BREAST CANCER

乳腺癌中 1 号线转座子引起的突变

基本信息

批准号：
6378012
负责人：
Gary D Swergold
金额：
$ 12.79万
依托单位：
COLUMBIA UNIVERSITY HEALTH SCIENCES
依托单位国家：
美国
项目类别：
财政年份：
2000
资助国家：
美国
起止时间：
2000-08-10 至 2002-07-31
项目状态：
已结题

来源：
https://reporter.nih.gov/project-details/6378012
关键词：
RNA directed DNA polymerase brca gene breast neoplasms clinical research female gene mutation human subject messenger RNA molecular cloning neoplasm /cancer genetics nucleic acid sequence open reading frames polymerase chain reaction transposon /insertion element women's health

项目摘要

Breast cancer cells must accumulate a series of genetic alterations before causing clinical disease. The mechanisms responsible for causing DNA damage in breast cancer are not known. LINE-1 (L1Hs) transposition is a mutagenic process that has not yet been investigated as a cause of breast cancer. The average human genome contains 100,000 L1Hs sequences; most are nonfunctional but 30-60 are potentially capable of transposition. Active elements amplify themselves by a process that involves an RNA intermediate and inserts a new L1Hs into the genome. When insertion occurs into a sensitive genetic locus the result is a new mutation. Examples of disease caused by L1Hs insertions have been described. We hypothesize that L1Hs retrotransposition is an important mechanism of mutagenesis in the development of either sporadic or hereditary breast cancer, or both. Several lines of evidence support this hypothesis. 1) A large fraction of hereditary breast cancers are the result of mutations in either the BRCA1 or BRCA2 genes. The BRCA1/2 proteins are involved in the repair of DNA double strand breaks (DSB). L1Hs transposition involves the formation of a DSB at the integration site; transposition rates may be enhanced in cells with altered pathways of DSB repair. 2) Trasposition by L1Hs requires the transcription and translation of L1Hs-encoded proteins. Differentiated cells, and most malignant cell types, do not transcribe or translate L1Hs. In contrast, p40, the protein encoded by the L1Hs first open reading frame, is present in most breast cancers and breast cancer-derived cell culture lines. This suggests that the controls that inhibit L1Hs transposition in normal cells have been deactivated in breast cancers. 3) Somatic L1Hs transposition in individuals with cancer, including a patient with breast cancer, have been reported, and retrotransposition has been observed in a breast cancer cell line. If L1Hs transposition is an important prelude to breast cancer, DNA isolated from patients' tumor cells will have L1Hs insertion sites that are not present in DNA isolated from the same patients' normal cells. These sites are called LINE Insertion Dimorphisms, or LIDs. We will use a new technique called L1 display to look for the presence of LIDs in paired blood and tumor DNA samples obtained from breast cancer patients. The relative frequency of LIDs in patients with sporadic and hereditary breast cancers will be compared with the frequency of LIDs in normal individuals. A significant difference in the frequency of LIDs in the study populations will suggest a role for L1Hs transposition in the development of breast cancer. It will also suggest that inhibiting the L1Hs encoded reverse transcriptase in high-risk patients may lower their incidence of breast cancer.

乳腺癌细胞在引起临床疾病之前必须积累一系列的基因改变。导致乳腺癌DNA损伤的机制尚不清楚。LINE-1(L1Hs)转座是一种突变过程，尚未被作为乳腺癌的原因进行研究。人类基因组平均包含10万个L1Hs序列；大多数是无功能的，但有30-60个有潜在的转座能力。活性元素通过涉及RNA中间体的过程放大自己，并将新的L1H插入到基因组中。当插入到一个敏感的基因位置时，结果是一个新的突变。描述了由L1Hs插入引起的疾病的例子。我们推测，L1Hs逆转录转位是散发性或遗传性乳腺癌，或两者兼有的重要突变机制。有几条证据支持这一假设。1)很大一部分遗传性乳腺癌是BRCA1或BRCA2基因突变的结果。BRCA1/2蛋白参与DNA双链断裂的修复。L1Hs转座涉及在整合部位形成DSB；在DSB修复途径改变的细胞中，转座速率可能会增加。2)L1Hs的转位需要L1Hs编码蛋白的转录和翻译。分化细胞和大多数恶性细胞类型不转录或翻译L1Hs。相比之下，由L1Hs第一个开放阅读框架编码的蛋白质p40存在于大多数乳腺癌和乳腺癌来源的细胞培养系中。这表明，在乳腺癌中，抑制正常细胞中L1Hs转位的控制组已经失活。3)已有报道在包括乳腺癌患者在内的癌症患者中发生体细胞L1Hs转座，并在一种乳腺癌细胞系中观察到逆转座。如果L1Hs易位是乳腺癌的重要前奏，那么从患者肿瘤细胞中分离的DNA将具有从相同患者正常细胞中分离的DNA中不存在的L1Hs插入位点。这些位置被称为行插入二态，或LID。我们将使用一种名为L1 Display的新技术来寻找从乳腺癌患者获得的配对血液和肿瘤DNA样本中是否存在LID。散发性和遗传性乳腺癌患者LIDs的相对频率将与正常人的LIDs频率进行比较。研究人群中L1Hs易位频率的显著差异将提示L1Hs易位在乳腺癌发生中的作用。它还表明，在高危患者中抑制L1Hs编码的逆转录酶可能会降低他们的乳腺癌发病率。