ROLE OF DNA METHYLTRANSFERASE 3B IN LUNG TUMORIGENESIS

描述（由申请人提供）：肺癌是美国和发达国家男性和女性癌症相关死亡的主要原因。据估计，2007年美国有超过16.3万人死于肺癌。由于总体5年生存率低于15%，迫切需要新的诊断和治疗策略；然而，我们对这种疾病的生物学理解的局限性阻碍了这些努力。表观遗传改变，特别是异常的DNA甲基化，在肺肿瘤发生中发挥着与遗传改变同样重要的作用。DNA甲基转移酶，特别是DNMT1和DNMT3B的失调与肿瘤发生过程中DNA甲基化模式的异常分布有关。我们已经确定了一个新的DNMT3B亚家族，DNMT3B，至少有7个转录变体。我们还发现，很大一部分肺癌只表达缺乏甲基转移酶酶结构域（DNMT3B-del）的DNMT3B，这表明DNMT3B在肺肿瘤发生中的作用扩大。我们进一步发现DNMT3B是DNMT3B在成人组织中的主要转录形式，并且DNMT3B变体的表达模式对于启动子特异性DNA甲基化调控至关重要。因此，我们假设DNMT3B在维持人类基因组中的DNA甲基化模式分布中起着至关重要的作用，并且DNMT3B的表达模式中断决定了肺肿瘤发生中具有启动子特异性的异常DNA甲基化。我们提出了4个具体目标：目的1：将原发性肺癌标本中DNMT3B和DNMT3B变体的表达模式与全局和启动子特异性DNA甲基化模式相关联；目的2：确定DNMT3B和DNMT3B在DNA甲基化控制和其他生物学特性方面的功能差异；目的3：确定具有或不具有DNA甲基转移酶结构域的主要DNMT3B变异的生物学特性；目的4：确定DNMT3B变异与肺肿瘤发生中DNA甲基化模式之间的因果关系。我们的长期目标是更好地了解这些异常DNA甲基转移酶的作用，并将这些知识应用于未来针对肺癌DNA甲基化的新诊断和治疗策略中。公共卫生相关性：我们发现了一个新的DNMT3B亚家族，称为DNMT3B，至少有7个变体。我们进一步发现，很大比例的肺癌只表达缺乏甲基转移酶酶结构域的DNMT3B，这表明DNMT3B在肺肿瘤发生中的作用超越了DNA甲基转移酶。DNMT3B是成人组织中DNMT3B转录的主要形式，DNMT3B变异体的表达模式对启动子DNA甲基化的启动子特异性调控至关重要。这里要验证的假设是DNMT3B在维持DNA甲基化模式在人类基因组中的分布中起着至关重要的作用，DNMT3B的表达模式中断决定了肺肿瘤发生过程中DNA甲基化异常。本提案中提出的研究将使我们了解DNMT3B变异在肺癌中的作用，从而开发新的诊断和治疗策略。

DESCRIPTION (provided by applicant): Lung cancer is the leading cause of cancer-related death among both men and women in the United States and developed countries. More than 163,000 deaths due to lung cancer in the U.S. were estimated in 2007. With an overall 5-year survival rate of less than 15%, novel diagnostic and therapeutic strategies are critically needed; however, limitations in our understanding of the biology of the disease have hampered these efforts. Epigenetic alterations, particularly aberrant DNA methylation, play as important a role as genetic alterations in lung tumorigenesis. Disregulation of DNA methyltransferases, particularly DNMT1 and DNMT3B, has been implicated in the abnormal distribution of DNA methylation patterns in tumorigenesis. We have identified a novel DNMT3B subfamily, DNMT3B, with at least 7 transcriptional variants. We also discovered that a significant portion of lung cancers expressed only DNMT3B lacking the methyltransferase enzymatic domain (DNMT3B-del), suggesting an expanded role of DNMT3B in lung tumorigenesis. We further showed that DNMT3B is the major form of DNMT3B transcription in adult tissues, and that expression patterns of DNMT3B variants are critical for promoter-specific regulation of DNA methylation. Therefore, we hypothesize that DNMT3B plays an essential role in maintaining DNA methylation pattern distributions in the human genome, and that disrupted expression patterns of the DNMT3Bs determine abnormal DNA methylation with promoter-specificity in lung tumorigenesis. We propose 4 specific aims: Aim 1: To correlate expression patterns of DNMT3B and DNMT3B variants to the global and promoter-specific DNA methylation patterns in primary lung cancer specimens; Aim 2: To determine functional differences between DNMT3B and DNMT3B in DNA methylation control and other biological properties; Aim 3: To determine biological properties of the major DNMT3B variants with or without the DNA methyltransferase enzymatic domains; and Aim 4: To determine the causal relationship between DNMT3B variants and DNA methylation patterns in lung tumorigenesis. Our long-term goals are to better understand the role of these aberrant DNA methyltransferases and to apply this knowledge in future novel diagnostic and therapeutic strategies targeting DNA methylation in lung cancer. PUBLIC HEALTH RELEVANCE: We have discovered a novel DNMT3B subfamily, termed DNMT3B with at least 7 variants. We further discovered that a large percent of lung cancers expressed only DNMT3B lacking of the methyltransferase enzymatic domain, suggesting a role of DNMT3B beyond a DNA methyltransferase in lung tumorigenesis. DNMT3B is the major form of DNMT3B transcription in adult tissues and the expression patterns of DNMT3B variants are critical in promoter-specific regulation of DNA methylation of promoters. The hypothesis to be tested here is that DNMT3B plays an essential role in maintaining distribution of DNA methylation patterns in human genome and disrupted expression patterns of the DNMT3Bs determine the abnormal DNA methylation in lung tumorigenesis. The studies proposed in this proposal will allow us understand the role of DNMT3B variants in lung cancer for development of novel diagnostic and therapeutic strategies.