Modeling Apoptotic Suppression in a Mouse Model of Brain Tumors

描述（申请人提供）：神经胶质瘤是最常见的原发性脑肿瘤，目前仍无法治愈。开发有效的治疗方法取决于更好地了解产生这些肿瘤的相关细胞程序。癌症研究中的一个新兴概念认为，如果没有伴随的细胞凋亡抑制，增殖细胞过程的激活不足以引起肿瘤进展。本研究计划的主要目的是研究抗凋亡基因在胶质瘤的发生、维持和发展中的作用。信号转导和转录激活因子（STAT）信号通路中的基因在胶质瘤中过度表达，该通路是与胶质瘤形成相关的多种细胞程序的中心枢纽，包括凋亡抑制。尤其是STAT3基因，与侵袭性间充质胶质瘤亚型相关。我们的假设是由STAT信号通路介导的凋亡抑制在胶质瘤不可避免的恶性进展中起着因果作用。我们将通过在体内表达STAT信号轴上的基因来验证这一假设，以阐明STAT通路激活对胶质瘤进展的影响。目前，大多数评估体内基因过表达的研究都是在免疫缺陷小鼠的异种移植模型上进行的，这些模型无法再现脑肿瘤的微环境。这些模型使用的是由完全恶性细胞植入形成的肿瘤，而不是由正常细胞中的转化事件产生的肿瘤，因此，对基因对肿瘤在其进化过程中必须克服的关键阶段的影响的分析变得模糊。为了研究抗凋亡基因如何影响肿瘤的发展，我们将采用一种使用RCAS/tv-a系统的体细胞转移方法。该模型允许在免疫能力小鼠中研究从其假定的起源细胞内源性肿瘤形成的基因表达。重要的是，该模型可用于研究免疫抑制对胶质瘤进展的影响，因为肿瘤诱导的免疫抑制是由STAT信号介导的。我们的初步研究表明STAT信号通路中的抗凋亡基因（包括Bcl-2和STAT3）促进肿瘤形成，降低生存率，促进免疫抑制肿瘤内巨噬细胞，并通过诱导坏死（高级别胶质瘤的标志）加速恶性进展。为了研究抗凋亡信号程序的影响并表征其功能，STAT信号轴上的基因将使用RCAS/tv-a系统进行表达。具体来说，我们将研究Bcl2 （Specific Aim 1）和STAT基因家族（Specific Aim 2）在肿瘤形成和进展中的作用。我们期望发现它们在神经胶质瘤恶性变性和促进肿瘤诱导的免疫抑制中的作用。最终，我们的结果将有助于确定神经胶质瘤的治疗靶点，该模型将用于测试针对这种致命疾病的新疗法。

DESCRIPTION (provided by applicant): Glioma, the most common primary brain tumor, remains incurable. Developing effective treatments depends on a better understanding of relevant cellular programs responsible for generating these tumors. An emerging concept in cancer research contends that activation of proliferative cellular processes is insufficient to cause tumor progression without concomitant suppression of apoptosis. The primary objective of this research proposal is to investigate the contribution of anti-apoptotic genes on the initiation, maintenance, and progression of glioma. Genes in the Signal Transducer and Activator of Transcription (STAT) signaling pathway are overexpressed in glioma and this pathway is a central hub of multiple cellular programs relevant to gliomagenesis including apoptotic suppression. The STAT3 gene, in particular, is associated with the aggressive mesenchymal subtype of glioma. Our hypothesis is that apoptotic suppression mediated by the STAT signaling pathway plays a causal role in the inexorable malignant progression of glioma. We will test this hypothesis by expressing genes in the STAT signaling axis in vivo to elucidate the effects of STAT pathway activation on glioma progression. Currently, most research evaluating gene overexpression in vivo is performed with xenograft models in immunodeficient mice that fail to recapitulate the microenvironment of brain tumors. These models use tumors formed by the implantation of fully malignant cells, rather than arising from a transformational event in a normal cell, thus obscuring analysis of the impact of a gene on the critical stages a tumor must overcome during its evolution. To study how anti-apoptotic genes affect tumor development we will employ a method of somatic cell transfer using the RCAS/tv-a system. This model permits the study of gene expression on endogenous tumor formation from its putative cell of origin in an immunocompetent mouse. Importantly, this model can be used to study the effect of immunosuppression on glioma progression as tumor-induced immunosuppression is mediated by STAT signaling. Our preliminary studies indicate that the anti-apoptotic genes in the STAT signaling pathway (including Bcl-2 and STAT3) enhance tumor formation, decrease survival, facilitate immunosuppressive intra-tumoral macrophages, and increase malignant progression by inducing necrosis - the hallmark of high-grade glioma. To investigate the impact of anti-apoptotic signaling programs and characterize their function, genes in the STAT signaling axis will be expressed using the RCAS/tv-a system. Specifically, we will investigate the roles of the Bcl2 (Specific Aim 1) and STAT gene families (Specific Aim 2) on tumor formation and progression. We expect to discover their contribution to the malignant degeneration of glioma and their promotion of tumor- induced immunosuppression. Ultimately, our results will help define therapeutic targets for glioma and the model will be used to test novel therapeutics against this deadly disease.