MUTATIONS CAUSED BY LINE 1 TRANSPOSONS IN BREAST CANCER

乳腺癌中 1 号线转座子引起的突变

• 批准号: 6167584
• 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
• 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/6167584
• 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

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遗传改变。 导致乳腺癌DNA损伤的机制尚不清楚。 LINE-1（L1 H）转座是一种诱变过程，尚未被研究为乳腺癌的原因。 人类基因组平均包含100，000个L1 H序列;大多数是无功能的，但30-60个具有潜在的转座能力。活性元件通过一个涉及RNA中间体并将新的L1 H插入基因组的过程来扩增自身。 当插入发生在一个敏感的遗传位点时，结果是一个新的突变。 已经描述了由L1 H插入引起的疾病的实例。 我们假设L1 Hs逆转录转座是一个重要的突变机制，无论是散发性或遗传性乳腺癌的发展，或两者兼而有之。有几条证据支持这一假设。 1)大部分遗传性乳腺癌是BRCA 1或BRCA 2基因突变的结果。 BRCA 1/2蛋白参与DNA双链断裂（DSB）的修复。 L1 Hs转座涉及在整合位点形成DSB;在DSB修复途径改变的细胞中，转座率可能会提高。 2)L1 H的转座需要L1 H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L1 H。 相比之下，由L1 H第一开放阅读框编码的蛋白质p40存在于大多数乳腺癌和乳腺癌衍生的细胞培养系中。这表明在正常细胞中抑制L1 H转座的对照在乳腺癌中已经失活。 3)已经报道了患有癌症的个体（包括患有乳腺癌的患者）中的体细胞L1 H转座，并且已经在乳腺癌细胞系中观察到反转录转座。如果L1 H转座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L1 H插入位点。 这些位点被称为线插入二态性，或LID。 我们将使用一种称为L1显示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LID的存在。 将散发性和遗传性乳腺癌患者中LID的相对频率与正常个体中LID的频率进行比较。 研究人群中LID频率的显著差异表明L1 H转座在乳腺癌发展中的作用。 它还表明，抑制高危患者中L1 H编码的逆转录酶可能会降低乳腺癌的发病率。