Investigating Max as a tumor suppressor gene in small cell lung cancer and other neuroendocrine tumors

总结 MYC家族转录调节因子的表达失调是一个广泛的基因组学中的共同点。 小细胞肺癌（SCLC）是一种高度侵袭性的神经内分泌肿瘤， 这是美国癌症死亡率的主要原因之一。MYC家族蛋白特异性 与MAX异二聚化以结合基因组DNA并刺激广泛转录。令人惊奇的是， 最近的报道表明，MAX是通过在一个重要的亚群中缺失和截短突变而失活的。 SCLC和其他神经内分泌癌。矛盾的是，MAX可能作为一种肿瘤抑制剂，但仍然是 在小细胞肺癌中，MYC致癌性至关重要，这对我们理解这些肿瘤的病因有重要意义。 肿瘤，但尚未进行系统研究。这项建议是基于我们两个人的调查结果。 实验室，（i）肿瘤前SCLC（preSC）中的全基因组CRISPR失活筛选显示 MAX靶向sgRNA高度促进生长;和（ii）MAX的缺失显著加速SCLC 在本地小鼠模型中。这些结果首次提供了高度相关的生物系统， 阐明MAX的肿瘤抑制功能。 目的1：研究MAX基因缺失的小细胞肺癌的生物学特性，包括细胞增殖、细胞凋亡、细胞周期、细胞周期蛋白表达等。 和基因组稳定性。此外，我们将使用ChIP-Seq和RNA-Seq来确定 SCLC和MAX缺失的SCLC中的MYC/MYCL和MAX结合和靶基因表达。我们将在功能上 询问通过综合基因组分析鉴定的关键MAX靶基因的重要性。目标以 研究将包括已经确定的一个碳代谢的MAX依赖调节剂。Aim 2基于 假设MAX缺失不仅改变了MYC活性，而且破坏了更广泛的MYC-MAX， 激活子和抑制子的转录网络。我们将确定MYC/MYCL是否有MAX独立 在我们的SCLC模型和人SCLC细胞系中，研究网络成员是否具有致癌功能， 拮抗或协同MYC（如MXD/MNT、MLX和MondoA），影响SCLC 进展在目标3中，我们提出确定核心MAX调节基因和共同的途径， MAX的神经内分泌肿瘤抑制作用。这将需要我们的新基因的分子和遗传表征。 甲状腺髓样癌和嗜铬细胞瘤模型导致MAX损失（在Rb/p53 缺乏背景）和鉴定与MAX-无效SCLC共有的途径。这项研究将扩大 我们的研究范围，以揭示MAX如何抑制神经内分泌癌。我们预计， 研究将加深我们对MYC网络在驱动和抑制两方面的复杂作用的理解 肿瘤和识别新的肿瘤发生途径，可能有潜力作为治疗目标。

SUMMARY Dysregulated expression of the MYC family of transcriptional regulators is a common denominator in a wide spectrum of human cancers, including small cell lung carcinoma (SCLC), a highly aggressive neuroendocrine- type tumor that is among the leading causes of US cancer mortality. MYC family proteins specifically heterodimerize with MAX in order to bind genomic DNA and stimulate widespread transcription. Surprisingly, recent reports show that MAX is inactivated through deletions and truncating mutations in a significant subset of SCLC and other neuroendocrine cancers. The paradox that MAX may act as a tumor suppressor, but yet be crucial for MYC oncogenicity in SCLC, has important implications for our understanding of the etiology of these tumors but has not been systematically investigated. This proposal is based on the findings from our two laboratories that (i) a whole-genome CRISPR inactivation screen in pre-neoplastic SCLC (preSCs) revealed MAX-targeting sgRNAs to be highly growth promoting; and (ii) deletion of MAX dramatically accelerates SCLC in an autochthonous mouse model. These results provide, for the first time, highly relevant biological systems to elucidate MAX's tumor suppressor function. In Aim 1 we will characterize the biological properties of MAX-deleted SCLC including proliferation, apoptosis and genomic stability. Moreover, we will use ChIP-Seq and RNA-Seq to determine the genomic landscape of MYC/MYCL and MAX binding and target gene expression in SCLC and MAX-deleted SCLC. We will functionally interrogate the importance of key MAX target genes identified through integrative genomic analyses. Targets to be studied will include MAX-dependent regulators of one carbon metabolism already identified. Aim 2 is based on the hypothesis that MAX deletion not only alters MYC activity but disrupts the broader MYC- MAX transcriptional network of activators and repressors. We will determine if MYC/MYCL have MAX independent oncogenic functions in our SCLC models and in human SCLC cell lines, and examine whether network members that antagonize or cooperate with MYC (such as MXD/MNT, MLX, and MondoA), act to influence SCLC progression. In Aim 3 we propose to determine core MAX-regulated genes and pathways common to neuroendocrine tumor suppression by MAX. This will entail molecular and genetic characterization of our new models of thyroid medullary carcinomas and pheochromocytomas resulting from MAX loss (in an Rb/p53 deficient background) and identification of pathways shared with MAX-null SCLC. This research will extend the breadth of our studies to uncover how MAX suppresses neuroendocrine cancers. We anticipate that these studies will deepen our understanding of the complex role of the MYC network in both driving and suppressing neoplasia and identify novel tumorigenic pathways that may have the potential to serve as therapeutic targets.