Role of the mitochondrial RNA polymerase POLRMT in MYC function

描述（由申请人提供）：癌细胞表现出与其正常对应物显著的代谢差异。目前，有显着的乐观，癌细胞特有的代谢性状可能代表可行的治疗靶点。包括我们在内的多个研究小组的工作已经明确表明，MYC癌蛋白是人类癌细胞中发生的代谢重编程的中心调节因子。为了深入了解MYC在人类癌症中的作用，我们最近进行了无偏倚的表达谱筛选，以确定其转录与恶性转化密切相关的重要下游靶点。通过筛选，我们鉴定了POLRMT基因。POLRMT是编码单链RNA聚合酶分子mtRNAP的核基因，其负责从小的环状线粒体基因组（mtDNA）转录。(MYC以前已经证明可以调节三种主要的核RNA聚合酶分子。MYC诱导POLRMT/mtRNAP的功能研究表明，MYC通过控制POLRMT表达来调节线粒体内的所有转录。此外，由于mtRNAP转录mtDNA复制所需的RNA引物，MYC也调节细胞线粒体基因组含量。遗传拯救实验表明，这两种效应完全依赖于mtRNAP，而不是最近描述的核异构体编码的POLRMT，spRNAP-IV。MYC和POLRMT表达之间的联系已在多种人类癌细胞系中得到证实，并得到来自公共癌症基因表达数据集的证据的支持。MYC还调节原代人类细胞中的POLRMT表达。最重要的是，阻断MYC诱导POLRMT表达的能力导致严格依赖于活化MYC的存在的稳健的细胞凋亡。重新激活MYC的潜在凋亡潜力或“内在肿瘤抑制活性”的策略被广泛视为未来抗癌治疗的令人兴奋的机会。最后，MYC依赖性细胞凋亡，从阻断POLRMT诱导的结果似乎是由于一个独特的要求POLRMT/mtRNAP在表达的电子传递链和随后的影响嘧啶生物合成途径的嘧啶编码的组件。几十年来，靶向嘧啶生物合成已被公认为是一种成功的抗癌疗法，我们的数据表明，POLRMT/mtRNAP的诱导可能代表了干预该途径的新节点，特别是表达高水平MYC的人类癌症形式。本文提出的研究将检验这一假设，并提供一个详细的机制，我们已经确定的途径，沿着的基本，MYC依赖的生存功能，它提供给肿瘤细胞的理解。 公共卫生相关性：癌细胞相对于其正常对应物具有一组独特的代谢反应，并且许多当前的努力集中于利用这些差异用于抗癌治疗。我们已经确定了一种独特的线粒体酶，由MYC癌蛋白调节，对癌细胞的生存至关重要，并代表了MYC控制途径中的靶向节点。

DESCRIPTION (provided by applicant): Cancer cells exhibit profound metabolic differences from their normal counterpart. Currently, there is significant optimism that the metabolic traits unique to cancer cells may represent viable therapeutic targets. Work from a number of groups, ours included, has firmly implicated the MYC oncoprotein as a central regulator of the metabolic reprogramming that takes place in human cancer cells. To gain insight into MYC's role in human cancer, we recently performed an unbiased expression profiling screen to identify essential downstream targets whose transcription is tightly correlated with malignant transformation. Via the screen, we identified the POLRMT gene. POLRMT is a nuclear gene that encodes the single chain RNA polymerase molecule, mtRNAP that is responsible for transcription from the small, circular mitochondrial genome (mtDNA). (MYC had previously been shown to regulate the three major nuclear RNA polymerase molecules.) Functional studies of the induction of POLRMT/mtRNAP by MYC show that MYC regulates all transcription within the mitochondria via its control of POLRMT expression. Furthermore, because mtRNAP transcribes the RNA primers required for replication of the mtDNA, MYC regulates cellular mitochondrial genome content as well. Genetic rescue experiments show that both of these efects depends exclusively on mtRNAP and not on a recently described nuclear isoform encoded by POLRMT, spRNAP-IV. The link between MYC and POLRMT expression has been confirmed in a variety of human cancer cell lines and is supported by evidence from public cancer gene expression datasets. MYC also regulates POLRMT expression in primary human cells. Most importantly, blocking the ability of MYC to induce POLRMT expression results in robust apoptosis that strictly depends on the presence of activated MYC. Strategies that reactivate the latent apoptotic potential or "intrinsic tumor suppressor activity" of MYC are widely viewed as an exciting opportunity for future anti-cancer therapy. Finally, the MYC-dependent apoptosis that results from blocking POLRMT induction appears to result from a unique requirement for POLRMT/mtRNAP in the expression of mitochondrial-encoded components of the electron transport chain and subsequent effects on the pyrimidine biosynthesis pathway. Targeting pyrimidine biosynthesis has been recognized as a successful anti-cancer therapy for many decades and our data suggest that induction of POLRMT/mtRNAP may represent a novel node for intervention in this pathway, specifically in the forms of human cancer that express high levels of MYC. The studies proposed here will test this hypothesis and provide a detailed mechanistic understanding of the pathway we have identified, along with the essential, MYC-dependent survival function it provides to tumor cells. PUBLIC HEALTH RELEVANCE: Cancer cells have a unique set of metabolic reactions relative to their normal counterparts and many current efforts are focused on exploiting these differences for anti-cancer therapy. We have identified a unique mitochondrial enzyme regulated by the MYC oncoprotein that is essential for survival of cancer cells and which represents a targetable node in the pathway MYC controls.