Role of ribosomal proteins in regulating c-Myc

描述（由申请人提供）：我们的长期目标是了解核糖体蛋白在核糖体生物发生过程中调节c-Myc活性和预防c-Myc诱导的癌症形成中的作用。在这个提议中，我们将剖析L11-c-Myc自动调节反馈回路及其在抑制细胞转化中的意义。c-Myc通过增强RNA聚合酶I、II和III介导的核糖体生物合成来促进细胞生长。c-Myc的过度表达和异常的核糖体生物合成导致细胞生长失调并促进肿瘤发生。高水平的c-Myc与约80%的各种人类癌症相关。因此，c-Myc必须在细胞中受到严格控制。最近，我们已经确定了核糖体蛋白L11，一个组成部分的大亚基的核糖体，作为一个可能的反馈调节c-Myc。L11由c-Myc转录诱导。但是，L11的过表达抑制c-Myc依赖的反式激活和细胞增殖。L11直接结合到c-Myc的反式激活结构域（transactivational domain，C-Myc）内的Myc box II（MBII）基序，并通过该转录激活因子募集到c-Myc靶启动子，从而抑制c-Myc共激活因子之一TRRAP（其也结合到MBII）与这些启动子处的c-Myc的缔合。此外，通过siRNA敲低内源性L11增加了c-Myc mRNA和蛋白水平以及其活性。最后，L11对于内源性c-Myc水平的后期降低和其活性响应于血清刺激的后期抑制至关重要。鉴于这些令人兴奋的发现，我假设L11可能作为一个自动调节反馈抑制剂的c-Myc，发挥生理作用，负调控c-Myc增强细胞增殖和肿瘤发生。因此，我们将通过解决三个具体目标来系统地研究这个以前未经检验的假设：（1）。剖析L11抑制c-Myc依赖性转录的分子机制;（2）.阐明L11如何调节c-Myc蛋白和mRNA水平;（3）.确定L11-c-Myc抑制性反馈调节在细胞和动物模型系统中的生理意义。这些研究将为核糖体生物发生过程中c-Myc的调控提供新的分子见解，并揭示L11在预防c-Myc诱导的肿瘤发生中的潜在作用。此外，这些研究将为开发抑制c-Myc的抗肿瘤药物提供重要信息，因此可能用于治疗含有高水平活性c-Myc的癌症。公共卫生相关性：我提出的研究将为c-Myc癌蛋白在从头蛋白产生过程中的调节提供新的分子见解，并揭示核糖体蛋白L11在预防c-Myc诱导的癌症形成中的潜在作用，因为c-Myc在80%以上的人类癌症中高度表达。此外，这些研究将为开发抑制c-Myc的抗肿瘤药物提供重要信息，因此可能用于治疗含有高水平活性c-Myc的癌症。

DESCRIPTION (provided by applicant): Our long-term goal is to understand the roles of ribosomal proteins in regulating c-Myc activity during ribosomal biogenesis and in preventing c-Myc-induced cancer formation. In this proposal, we will dissect the L11-c-Myc auto-regulatory feedback loop and its implication in repressing cell transformation. c-Myc promotes cell growth by enhancing ribosomal biogenesis mediated by RNA polymerases I, II and III. Overexpression of c-Myc and aberrant ribosomal biogenesis lead to deregulated cell growth and contribute to tumorigenesis. High levels of c-Myc associate with ~80% of various human cancers. Thus, c-Myc must be tightly controlled in cells. Recently, we have identified ribosomal protein L11, a component of the large subunit of the ribosome, as a likely feedback regulator of c-Myc. L11 is transcriptionally induced by c-Myc. But, overexpression of L11 inhibits c-Myc-dependent transactivation and cell proliferation. L11 directly binds to the Myc box II (MBII) motif within the transactivational domain (TAD) of c-Myc and is recruited to c-Myc target promoters by this transcriptional activator, consequently inhibiting the association of one of the c-Myc coactivators, TRRAP, which also binds to MBII, with c-Myc at these promoters. Furthermore, knockdown of endogenous L11 by siRNA increases c-Myc mRNA and protein levels as well as its activity. Finally, L11 is crucial for the later stage reduction of endogenous c-Myc levels and the late phase inhibition of its activity in response to serum stimulation. In light of these exciting findings, I hypothesize that L11 may act as an auto-regulatory feedback inhibitor of c-Myc, playing a physiological role in negatively regulating c-Myc-enhanced cell proliferation and tumorigenesis. Hence, we will systematically investigate this previously untested hypothesis by addressing three specific aims: (1). Dissect molecular mechanisms underlying L11 inhibition of c-Myc-dependent transcription; (2). Elucidate how L11 regulates c-Myc protein and mRNA levels; (3). Determine the physiological significance of L11-c-Myc inhibitory feedback regulation in cell and animal model systems. These studies will offer new molecular insight into the regulation of c-Myc during ribosomal biogenesis and reveal a potential role of L11 in preventing c-Myc-induced tumorigenesis. Also, these studies will provide important information for developing anti-tumor drugs that inhibit c-Myc and thus are likely useful for treating cancers harboring high levels of active c-Myc. PUBLIC HEALTH RELEVANCE: My proposed studies will offer new molecular insight into the regulation of the c-Myc oncoprotein during de novo protein production, and reveal a potential role of the ribosomal protein L11 in preventing c-Myc-induced cancer formation, as c-Myc is highly expressed in more than 80% of human cancers. Also, these studies will provide important information for developing anti-tumor drugs that inhibit c-Myc and thus are likely useful for treating cancers harboring high levels of active c-Myc.