Cellular Predisposition to Retinoblastoma Tumorigenesis

描述(申请人提供)：癌症可能是由于信号蛋白的“正常”表达，使特定类型的细胞对特定的致癌突变敏感。然而，细胞类型特定的信号通路易患特定癌症的方式还知之甚少。视网膜母细胞瘤是解决这一问题的合适模型，因为在RB1基因失活的情况下，起源于视网膜母细胞瘤的细胞特别容易启动肿瘤的发生。因此，该项目旨在识别和表征特定的信号，使视网膜母细胞瘤起源的细胞对Rb功能的丧失敏感。初步研究证实视锥细胞光受体前体细胞(CPS)是视网膜母细胞瘤的候选细胞来源，并表明人CPS在视网膜细胞中是独一无二的，因为它们显著表达MDM2癌蛋白和甲状腺激素受体亚型TR？2，这在Rb缺陷性小鼠垂体肿瘤的前体中也是显著的。他们还揭示了MDM2和tr？2对于视网膜母细胞瘤细胞的增殖和存活是必不可少的，mdm2是抑制致癌应激反应所必需的，而tr？2是维持另一种对Rb缺陷肿瘤的发展至关重要的蛋白质--F-box蛋白Skp2的表达所必需的。为了确定这些CP特征是否是视网膜母细胞瘤发生的基础，目标1将定义视锥回路在原发人类CP对Rb耗竭的反应中的作用。目的2将通过检测Rb基因缺陷的小鼠CP中MDM2的异位表达(无论是来自锥体靶向转基因还是来自完整的人MDM2基因)来扩展这些体外研究，以确定是否在体内解除了对CP增殖的调控并引发了CP源性视网膜母细胞瘤。目的3明确TR2在视网膜母细胞瘤细胞增殖和存活中的作用，并特异性地评价TR2是否需要促进Skp2的表达，以及是否通过拮抗相关的TR1亚型而起作用。目的4将评估在体内是否与其对人视网膜母细胞瘤细胞的作用类似，在体内促进Rb缺陷的小鼠垂体肿瘤的发展，并将确定引起这些肿瘤的异常增殖的Rb缺陷细胞中tr？2缺失的细胞效应。总之，这些研究将评估“正常”的CP回路是否使锥体前体对RB1失活的致癌效应敏感。这些研究可能会产生超越视网膜母细胞瘤的影响，通过定义与Rb缺失共同协作的细胞类型特定特征，使Rb缺陷癌症的发展成为可能。 公共卫生相关性：这些研究将确定使正常细胞对特定致癌基因突变的影响敏感的信号特征。在某种程度上，这还没有在其他癌症中广泛实现，这项研究将有助于建立一个重要的、新的范式来研究人类肿瘤发生。通过这些研究确定的细胞类型特异性特征可能为癌症治疗提供新的靶点。

DESCRIPTION (provided by applicant): Cancers may arise due to the "normal" expression of signaling proteins that sensitize specific cell types to specific oncogenic mutations. However, the means by which cell type-specific signaling pathways predispose to particular cancers is poorly understood. Retinoblastoma is a suitable model with which to address this issue, as the retinoblastoma cell of origin is exceptionally predisposed to initiate tumorigenesis in the event that the RB1 gene is inactive. Accordingly, this project aims to identify and characterize specific signals that sensitize the retinoblastoma cell of origin to the loss of Rb function. Preliminary Studies identified cone photoreceptor precursors (CPs) as a candidate retinoblastoma cell of origin and showed that human CPs are unique among retinal cells in that they prominently express the MDM2 oncoprotein and a thyroid hormone receptor isoform, TR?2, that is also prominent in the precursors to Rb- deficient mouse pituitary tumors. They also revealed that MDM2 and TR?2 are essential for retinoblastoma cell proliferation and survival, that MDM2 is needed to suppress the oncogenic stress response, and that TR?2 is needed to sustain the expression of yet another protein that is essential to the development of Rb-deficient tumors, the F-box protein Skp2. To determine whether these CP features underlie retinoblastoma tumorigenesis, Aim 1 will define the roles of the cone circuitry in the response of primary human CPs to Rb depletion. Aim 2 will extend these in vitro studies by examining whether ectopic MDM2 expression in Rb- deficient mouse CPs - either from a cone-targeted transgene or from an intact human MDM2 locus - deregulates CP proliferation and elicits CP-derived retinoblastomas in vivo. Aim 3 seeks to define the role of TR?2 in retinoblastoma cell proliferation and survival, and will specifically evaluate whether TR?2 is needed to promote Skp2 expression and acts by antagonizing the related TR?1 isoform. Aim 4 will evaluate whether TR?2 contributes to the development of Rb-deficient mouse pituitary tumors in vivo, similar to its effects on human retinoblastoma cells in vitro, and will define the cellular effects of TR?2 loss in the abnormally proliferating Rb-deficient cells that give rise to these tumors. Together, these studies will evaluate whether "normal" CP circuitry sensitizes cone precursors to the oncogenic effects of RB1 inactivation. The studies are likely to have an impact extending beyond retinoblastoma, by defining cell type-specific features that commonly collaborate with Rb loss to enable the development of Rb-deficient cancers. PUBLIC HEALTH RELEVANCE: These studies will identify signaling features that sensitize normal cells to the effects of specific oncogenic mutations. To the extent that this has not been widely achieved in other cancers, the research will help to establish an important and novel paradigm for investigating human tumorigenesis. The cell type-specific features that are identified through these studies could provide novel targets for cancer therapy.