PROJECT 4: Interrogating PP2A Signaling in Human Cancers

国际癌症基因组表征工作已经确定了几种蛋白磷酸酶2A（PP 2A） 亚基在人类癌症中以比最初预期更高的频率反复突变或缺失。 这一观察结果并不令人惊讶，因为PP 2A是人类细胞中主要的丝氨酸-苏氨酸磷酸酶家族， 在控制细胞信号传导和体内平衡方面广泛重要， 被证明是肿瘤抑制基因。然而，理解PP 2A的进展受到以下因素的干扰： 这种酶至少有80种不同的异构体。转化的相互作用研究 由DNA肿瘤病毒和宿主细胞蛋白质编码的蛋白质已经确定了许多机制， 有助于自发性癌症的发生。特别地，SV 40早期区蛋白结合 与包括视网膜母细胞瘤（RB）和p53在内的几种肿瘤抑制基因产物相关。研究 与PP 2A相互作用的SV 40小t抗原（SV 40 ST）和PyST都使我们开始了解 PP 2A的特定形式有助于肿瘤抑制。我们之前已经证明，抑制 特定的PP 2A亚基表型模仿SV 40 ST诱导的细胞转化，并且这些相同的PP 2A亚基表型模仿SV 40 ST诱导的细胞转化， 亚基是人类癌症中的肿瘤抑制基因。使用新开发的基因组规模工具，我们有 系统地鉴定了有助于细胞转化的特定PP 2A亚基，并表明， 这些亚基的丢失扰乱了细胞转化所必需的三条途径（WNT、MYC、AKT）。 尽管这些研究已经推进了我们对SV 40 ST如何干扰PP 2A的理解， 有助于转化，我们缺乏对分子连接的详细分子理解 PP 2A和细胞转化所必需的途径之间的关系。我们建议整合创新的基因 和蛋白质组学技术来鉴定肿瘤抑制因子PP 2A干扰的底物和途径 亚单位。在最近的工作中，我们发现STRiatin相互作用磷酸酶和激酶（STRIAK） 复合物不仅结合ST-PP 2A复合物，而且也是通过改变 PP 2A功能。我们假设ST或肿瘤抑制因子PP 2A亚单位的突变， PP 2A全酶复合物不仅通过置换肿瘤抑制因子B亚基，而且通过调节 PP 2A与STRIPAK复合物在病毒和非病毒病因癌症中的相互作用。在这个项目中，我们 将使用生物化学，遗传学和细胞生物学方法来了解PP 2A-STRIPAK相互作用 诱导细胞转化不仅可以增强我们对这个肿瘤抑制因子家族的机制理解 而且还将为帮助编程恶性状态的途径提供新的见解。另外这些 研究将为治疗上针对这些途径的策略提供基础。

International cancer genome characterization efforts have identified several protein phosphatase 2A (PP2A) subunits as recurrently mutated or deleted in human cancers at a higher frequency than originally anticipated. This observation is not surprising since PP2A, the major serine-threonine phosphatase family in human cells, is broadly important in controlling cell signaling and homeostasis and particular PP2A subunits have been shown to act as tumor suppressor genes. However, progress in understanding PP2A has been confounded by the fact that the enzyme exists in at least 80 different isoforms. The study of the interactions of transforming proteins encoded by DNA tumor viruses and host cell proteins has identified many mechanisms that also contribute to the genesis of spontaneously arising cancers. In particular, the SV40 Early Region proteins bind to and inactivate several tumor suppressor gene products including retinoblastoma (RB) and p53. Studies of both SV40 small t antigen (SV40ST) and PyST, which interact with PP2A, have allowed us to begin to see how particular forms of PP2A contribute to tumor suppression. We have previously shown that suppressing particular PP2A subunits phenocopies cell transformation induced by SV40 ST and that these same PP2A subunits are tumor suppressor genes in human cancers. Using newly developed genome scale tools, we have systematically identified the specific PP2A subunits that contribute to cell transformation and have shown that loss of these subunits perturbs three pathways essential for cell transformation (WNT, MYC, AKT). Although these studies have advanced our understanding of how perturbation of PP2A by SV40ST contributes to transformation, we lack a detailed molecular understanding of the molecular connections between PP2A and the pathways essential for cell transformation. We propose to integrate innovative genetic and proteomic technologies to identify substrates and pathways perturbed by tumor suppressor PP2A subunits. In recent work we have found that the STRiatin Interacting Phosphatase And Kinase (STRIPAK) complex not only binds ST-PP2A complexes but is also required for cell transformation induced by altering PP2A function. We hypothesize that ST, or mutations in tumor suppressor PP2A subunits, reprogram the PP2A holoenzyme complex not only by displacing tumor suppressor B subunits but also by modulating the interaction of PP2A with the STRIPAK complex in cancers of both viral and non-viral etiology. In this Project we will use biochemical, genetic and cell biological approaches to understand how PP2A-STRIPAK interactions induce cell transformation to not only enhance our mechanistic understanding of this tumor suppressor family but will also provide new insights into the pathways that help program the malignant state. In addition, these studies will provide a foundation for strategies to target these pathways therapeutically.