Investigating the tumor suppressive functions of the miR-34 family of microRNAs

描述（由申请人提供）：微小RNA（miRNA）是小的非编码RNA，充当转录后调节因子。microRNA失调是人类癌症的共同特征，并且许多miRNA具有致癌或肿瘤抑制特性。miR-34家族（miR-34 a、miR-34 b和miR-34 c）由于受p53直接调控并能在体外诱导细胞周期阻滞和凋亡而受到广泛关注。重要的是它的 在许多人类癌症中已经观察到失活。尽管越来越多的证据表明其作为肿瘤抑制剂的作用，但大多数（如果不是全部）先前关于miR-34的研究都是在体外或使用miR-34的非生理表达水平进行的，这易于产生人为结果。因此，其确切的功能，机制和功能相关的目标在体内仍然是未知的。这些知识空白阻碍了将其用于治疗干预。本申请的目的是研究miR-34家族的生理和肿瘤抑制特性。核心假设是miR-34家族的成员是p53反应的重要调节剂，并且是真正的肿瘤抑制剂。该提案旨在回答以下问题：1）miR-34表达的慢性缺失是否促进体内肿瘤发生？2)miR-34在p53通路中的生理作用是什么？3)哪些p53靶点与miR-34强烈合作？为了回答这些问题，本申请提出利用我们实验室先前产生的miR-34家族的组成型和条件性敲除小鼠。miR-34功能的完全基因失活与哺乳动物的生存能力相容，这为在生理背景下测试这些miRNA的肿瘤抑制特性提供了独特的机会。初步结果显示，miR-34缺陷小鼠和细胞中的p53依赖性功能是完整的，这表明该miRNA家族在p53通路中的功能可能是冗余的或高度环境特异性的。因此，在本申请的第一个目的中提出的实验集中于两种人类癌症的小鼠模型，其中已经描述了miR-34损失，而在第二个目的下的实验试图揭示miR-34和其他p53靶标之间的冗余。详细了解miR-34家族成员在正常和病理过程中的功能，不仅是探索其肿瘤抑制特性的关键一步，也是开发新的抗癌策略的关键一步。

DESCRIPTION (provided by applicant): MicroRNAs (miRNAs) are small, non-coding RNAs that act as post-transcriptional regulators. MicroRNA deregulation is a common feature of human cancers, and numerous miRNAs have oncogenic or tumor suppressive properties. The miR-34 family (miR-34a, miR-34b and miR-34c) has garnered much attention because it is directly regulated by p53 and can induce cell cycle arrest and apoptosis in vitro. Importantly, its inactivation has been observed in a number of human cancers. Despite the growing body of evidence suggesting its role as a tumor suppressor, most, if not all, previous studies on miR-34 have been done in vitro or using non-physiologic expression levels of miR-34, which are prone to artifactual results. Hence, its exact functions, mechanism and functionally relevant targets in vivo are still largely unknown. These gaps of knowledge prevent its exploitation for therapeutic intervention. The objective of this application is to investigate the physiologic and tumor suppressive properties of the miR-34 family. The central hypothesis is that members of the miR-34 family are important modulators of the p53 response, and are bona fide tumor suppressors. The proposal aims to answer the following questions: 1) Does chronic loss of miR-34 expression promote tumorigenesis in vivo? 2) What is the physiologic role of miR-34 in the p53 pathway? 3) Which p53 targets strongly cooperate with miR-34? To answer these questions, this application proposes to take advantage of constitutive and conditional knockout mice for the miR-34 family previously generated in our laboratory. Complete genetic inactivation of miR-34 function is compatible with viability in mammals, providing a unique opportunity to test the tumor suppressive properties of these miRNAs in a physiologic context. Initial results show that p53-dependent functions in miR-34-deficient mice and cells are intact, suggesting the functions of this miRNA family in the p53 pathway are likely redundant or highly context-specific. Thus, the experiments proposed in the first Aim of this application focus on two mouse models of human cancers wherein miR-34 loss has been described, while experiments under the second Aim seek to uncover redundancies between miR-34 and other p53 targets. The detailed understanding functions of members of the miR-34 family in normal and pathological processes that will emerge from the proposed study is a critical step towards not only exploring their tumor suppressive properties, but also developing novel anticancer strategies.