Reactivation of embryonic growth programs in liver cancer

描述(申请人提供)：异时性基因编码产物，其在组织中的表达随时间变化，暂时调节发育变化和器官生长[1]。例如，许多异时性基因在胎儿组织中表达，但在成人组织中不表达，因此它们促进胎儿组织的快速生长，并在出生后被关闭。癌症可以重新激活成人组织中的这些异时性基因，使肿瘤得以增殖[2]。这些基因在正常和恶性生物学中的作用还不是很清楚，因为不能在体外研究发育时间，而且这些基因中很少有在体内被系统研究的。LIN28是一种异时RNA结合蛋白，以抑制let-7microRNAs(MiRNAs)的生物发生而闻名，miRNAs是一种古老的肿瘤抑制因子，它抑制癌基因的翻译以损害细胞生长[3，4]。在过去的四年里，我通过使用允许LIN28和LET-7在时间上特定的获得或丢失的小鼠模型，揭示了异时基因的重要作用。我发现，适度增加Lin28a的表达显著增加了小鼠的生长、身高和青春期时间，显示了从蠕虫到小鼠的发育时间的保守作用[5]。接下来，我们证明了LIN28和LET-7是哺乳动物葡萄糖代谢的调节者，与糖尿病的发病机制有关。最近，我们发现，成人重新激活Lin28a会促进再生能力，这让人想起胚胎组织[7]。LIN28的S能够在时间上整合胚胎代谢、细胞增殖和组织生长，这增加了它也通过这些机制促进成人肿瘤发生的可能性。我们将重点关注小鼠的肝癌模型，因为Lin28b在多达40%的儿童和成人肝癌中过度表达，而且肝癌是一个主要的全球性问题，治疗选择有限[8，9]。在初步研究中，我们发现Lin28b的过度表达足以诱导成年小鼠发生肝癌。我们还发现，MYC的过度表达会导致Lin28b的高表达和let-7的低表达，我们的数据表明Lin28b在这些肝癌的发展中是必需的。在目标1中，我们将测试正在进行的Lin28b表达是否对肿瘤的维持或生长是必需的，然后我们将评估Lin28b缺失的代谢后果。在AIM 2中，我们将确定let-7 miRNAs的抑制是否对肝脏肿瘤的发展是必要的，并将评估可能起作用的代谢和再生机制。我们还表明，已知的let-7靶点和mRNA翻译调节因子Igf2mRNA结合蛋白1和3(Imp1和Imp3)在Lin28b过表达的肿瘤中被有效诱导。在AIM3中，我们将测试Imp1和Imp3的表达对肝肿瘤的生长是必要的还是充分的，以及Imp1/3的变化是否介导了Lin28对代谢的影响。这一提议有可能剖析通常调节生长、新陈代谢和再生的异时通路在癌症中的作用。

DESCRIPTION (provided by applicant): Heterochronic genes encode products whose expression changes over time in tissues, temporally regulating developmental changes and organ growth [1]. For example, many heterochronic genes are expressed in fetal, but not adult tissues such that they promote the rapid growth of fetal tissues and are shut off postnatally. Cancers can reactivate these heterochronic genes in adult tissues to enable neoplastic proliferation [2]. The role of these genes in normal and malignant biology is not well understood because developmental timing cannot be studied in vitro, and few of these genes have been systematically investigated in vivo. Lin28 is a heterochronic RNA-binding protein known for its ability to inhibit the biogenesis of let-7 microRNAs (miRNAs), ancient tumor suppressors that suppress the translation of oncogenes to impair cellular growth [3, 4]. Over the last 4 years I have uncovered important roles for heterochronic genes by using murine models that allow temporally specific gain or loss of Lin28 and let-7. I found that modestly increased expression of Lin28a substantially increased mouse growth, height, and time to puberty, demonstrating a conserved role in developmental timing from worms to mice [5]. Next, we showed that Lin28 and let-7 are regulators of mammalian glucose metabolism, implicating heterochronic genes in the pathogenesis of diabetes [6]. More recently, we showed that adult reactivation of Lin28a promotes regeneration capabilities reminiscent of embryonic tissue [7]. Lin28's ability to temporally integrate embryonic metabolism, cell proliferation, and tissue growth raises the possibility that it also promotes adult tumorigenesis through these mechanisms. We will focus on mouse models of liver tumors because LIN28B is overexpressed in up to 40% of pediatric and adult liver cancers, and because liver cancer is a major global problem with limited treatment options [8, 9]. In preliminary studies, we find that LIN28B overexpression is sufficient to induce liver cancer in adult mice. We have also found that MYC overexpression produces liver tumors with high Lin28b and low let-7 expression, and our data suggest that Lin28b is required for the development of these liver cancers. In AIM 1, we will test whether ongoing Lin28b expression is required for tumor maintenance or growth, then we will assess the metabolic consequences of Lin28b loss. In AIM 2, we will determine if the suppression of let-7 miRNAs is necessary for the development of liver tumors, and we will assess the metabolic and regenerative mechanisms that might be responsible. We have also shown that Igf2 mRNA-binding proteins 1 and 3 (Imp1 and Imp3), which are known let-7 targets and regulators of mRNA translation, are potently induced in LIN28B overexpressing tumors. In AIM3, we will test whether Imp1 and Imp3 expression are necessary or sufficient for the growth of liver tumors and whether changes in Imp1/3 mediate effects of Lin28 on metabolism. This proposal has the potential to dissect the role in cancer of a heterochronic pathway that normally regulates growth, metabolism, and regeneration.