Reactivation of embryonic growth programs in liver cancer

描述（由申请人提供）：异时基因编码的产物在组织中的表达随时间变化，在时间上调节发育变化和器官生长[1]。例如，许多异时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关闭。癌症可以在成人组织中重新激活这些异时基因，使肿瘤增殖[2]。这些基因在正常和恶性生物学中的作用尚不清楚，因为发育时间不能在体外研究，并且很少有这些基因在体内进行了系统研究。Lin 28是一种异时RNA结合蛋白，已知其能够抑制let-7 microRNA（miRNA）的生物发生，let-7 microRNA是抑制癌基因翻译以损害细胞生长的古老肿瘤抑制因子[3，4]。在过去的4年里，我已经发现了重要的作用，异时基因通过使用小鼠模型，允许时间特异性增益或损失的Lin 28和let-7。我发现适度增加Lin 28 a的表达显著增加了小鼠的生长、身高和青春期时间，证明了从蠕虫到小鼠的发育时间中的保守作用[5]。接下来，我们证明了Lin 28和let-7是哺乳动物葡萄糖代谢的调节因子，暗示了糖尿病发病机制中的异时基因[6]。最近，我们发现，成年人重新激活Lin 28 a促进再生能力，让人想起胚胎组织[7]。Lin 28在时间上整合胚胎代谢、细胞增殖和组织生长的能力提高了它也通过这些机制促进成人肿瘤发生的可能性。我们将专注于肝脏肿瘤的小鼠模型，因为LIN 28 B在高达40%的儿童和成人肝癌中过表达，并且因为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LIN 28 B过表达足以在成年小鼠中诱导肝癌。我们还发现MYC过表达产生具有高Lin 28 b和低let-7表达的肝肿瘤，我们的数据表明Lin 28 b是这些肝癌发展所必需的。在AIM 1中，我们将测试持续的Lin 28 b表达是否是肿瘤维持或生长所必需的，然后我们将评估Lin 28 b损失的代谢后果。在AIM 2中，我们将确定let-7 miRNAs的抑制是否是肝肿瘤发展所必需的，我们将评估可能负责的代谢和再生机制。我们还表明，Igf 2 mRNA结合蛋白1和3（Imp 1和Imp3），这是已知的let-7靶点和mRNA翻译的调节因子，在LIN 28 B过表达肿瘤中被有效诱导。在AIM 3中，我们将测试Imp 1和Imp3表达是否是肝肿瘤生长所必需或足够的，以及Imp 1/3的变化是否介导Lin 28对代谢的影响。这一建议有可能剖析在癌症中的作用的异时途径，通常调节生长，代谢和再生。

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.