A non-canonical role for EZH2 in rRNA methtlation

背景：越来越多的证据表明，失调的表观遗传修饰在 癌症的发生、发展和转移。表观遗传调控包括组蛋白修饰、DNA 甲基化和去甲基化，通过microRNA和长非编码RNA(LncRNAs)进行调节，以及 RNA甲基化和编辑。RNA甲基化发生在所有信使RNA(MRNA)、转移RNA(TRNA)上 和核糖体RNA(RRNA)。与最近在理解mRNA甲基化方面的进展相比， RRNA甲基化的作用还没有得到充分的研究。 表观遗传修饰物Polycomb组蛋白EZH2，一种众所周知的致癌性组蛋白赖氨酸 H3K27甲基化的甲基转移酶是多梳抑制复合体2(PRC2)的关键成分，是 在癌症中表达上调，是侵袭性癌症的生物标志物。我们的初步数据显示，EZH2直接 与唯一的rRNA 2‘-O-核糖甲基转移酶FBL相互作用，调节rRNA 2‘-O-甲基化水平。敲除EZH2改变FBL介导的IRES驱动的新生多肽合成 蛋白质翻译启动，以及其他核糖体功能。重要的是，我们的数据显示FBL被上调 在PCa、EZH2高FBLHigh PCA患者中，与其他患者相比，临床结果更差。 目标/假设：我们的总体假设是EZH2在PCA中扮演双重角色，一个典型的角色 作为组蛋白甲基转移酶，通过直接与FBL相互作用而发挥非典型作用，然后 调节rRNA甲基化和核糖体功能。此外，该新颖的EZH2函数是 不依赖于PRC2复合体及其赖氨酸甲基转移酶活性。EZH2基因的过表达 和FBL一起将促进PCA的进展。 基于我们的初步数据，我们提出了以下具体目标来检验我们的假设。 具体目的1：研究EZH2如何调控box C/D snoRNP的组装。 特定目标2：表征EZH2在rRNA甲基化和蛋白质中的非规范功能 通过其与FBL的体外相互作用合成。 具体目的3：研究EZH2-FBL的相互作用及EZH2的S新功能。 影响：这项工作将剖析EZH2如何通过其经典的 作为H3K27甲基转移酶发挥作用，并通过FBL在rRNA甲基化中发挥非规范功能。

Background: Mounting evidence suggests that dysregulated epigenetic modifications play a crucial role in cancer initiation, progression, and metastasis. Epigenetic regulations include histone modifications, DNA methylation and demethylation, regulations through microRNA and long non-coding RNAs (lncRNAs), and RNA methylation and editing. RNA methylation occurs on all messenger RNA (mRNA), transfer RNA (tRNA) and ribosome RNA (rRNA). Compared to the recent advances in understanding mRNA methylation, the function of rRNA methylation is understudied. The epigenetic modifier Polycomb group protein EZH2, a well-known oncogenic histone lysine methyltransferase for H3K27 methylation and a key component of Polycomb Repressive Complex 2 (PRC2), is upregulated in cancer and is a biomarker of aggressive cancers. Our preliminary data show that EZH2 directly interacts with FBL (Fibrillarin), the only characterized rRNA 2’-O-ribose methyltransferase, and regulates rRNA 2’-O-methylation levels. Knocking down EZH2 alters FBL-mediated nascent peptide synthesis, IRES-driven protein translation initiation, and other ribosomal functions. Importantly, our data reveal that FBL is upregulated in PCa, and EZH2highFBLhigh PCa patients had worse clinic outcomes compared to other patients. Objective/Hypothesis: Our overall hypotheses are that EZH2 plays dual roles in PCa, a canonical role as histone methyltransferase and a non-canonical role by directly interacting with FBL and then regulating rRNA methylation and ribosomal functions. Further, this novel EZH2 function is independent of the PRC2 complex and its lysine methyltransferase activity. Overexpression of EZH2 and FBL together will promote PCa progression. Based on our preliminary data, we propose the following specific aims to test our hypotheses. Specific Aim 1: To investigate how EZH2 regulates the assembly of box C/D snoRNP. Specific Aim 2: To characterize the non-canonical functions of EZH2 in rRNA methylation and protein synthesis through its interaction with FBL in vitro. Specific Aim 3: To examine the EZH2-FBL interaction and EZH2’s novel functions in vivo. Impact: This work will dissect how EZH2 performs its dual role in cancer progression through its canonical function as a H3K27 methyltransferase and a non-canonical function in rRNA methylation via FBL.