PPP2R2A tumor suppression haploinsufficiency in prostate cancer

PPP 2 R2 A基因编码PP 2A的B调节亚基B55α，该亚基被发现是半合子缺失的 在前列腺癌、卵巢癌和腔型B乳腺癌中的发生率较高。PP 2A是Ser/Thr磷酸酶， 由三聚体全酶的集合组成，其底物特异性和生物学功能， 由调节B亚基决定。至少有十四个已知的基因编码不同的B亚基 属于四个不相关的基因家族。众所周知，PP 2A是一种重要的肿瘤抑制因子， 功能，其抑制是多种人类正常上皮细胞转化所需的， 成纤维细胞与确定的癌基因组和失活的肿瘤抑制基因合作， 所涉及的全酶还没有被很好地理解。来自TCGA等的数据显示PPP 2 R2 A缺失 在大多数前列腺肿瘤中（>50%半合子/~7%纯合子丢失）。重要的是，PPP 2 R2 A 半合子丢失与其mRNA表达降低相关。此外，PCa患者表现出减少 无病生存与此改变。虽然这导致PPP 2 R2 A是一种肿瘤， 抑制子，没有数据支持该基因缺失导致PCa。我们发现， B55α在PCa细胞系中的异位表达，其天然表达水平低于正常前列腺 上皮细胞和其他PCa细胞系，导致显著的毒性。这种毒性与有丝分裂停滞有关， 整倍性、细胞死亡和有效的肿瘤生长抑制。我们的初步研究还显示 PCa和DU 145 3D类器官中的生长抑制和结构缺陷， B55α。此外，用吩噻嗪处理PC 3细胞，其结合并激活PP 2A，模拟细胞周期 在B55α重建中观察到的效应。我们假设PPP 2 R2 A半合子缺失和/或其他 减少PrEC中B55α表达的改变促进转化和致瘤性， B55α/PP 2A活性具有治疗潜力。为了验证这一假设，我们提出了两个目标：（1）。以确定 前列腺上皮细胞（PrECs）中B55α缺失/下调的转化潜力和致瘤性 和PCa细胞系以及B55α表达重建对其分化、生长能力的影响 和/或在作为3D类器官生长时侵入。（二）.为了确定B55α在3D中的生长抑制功能， 类器官与其有丝分裂功能和/或存活/分化改变的结果有关 途径以及是否可以用PP 2A激活药物靶向。这项工作的顺利完成将有助于 多项研究的可行性，旨在了解（a）癌基因/肿瘤抑制基因的协同作用， 小鼠中前列腺肿瘤的发展及其在人肿瘤中的相关性;（B）信号传导机制和 鉴定关键的靶底物;重要的是，（c）设计治疗性上调这种靶底物的策略， 肿瘤细胞中的全酶。由于PPP 2 R2 A改变在前列腺肿瘤中发生的频率很高， 拟议的研究将为开发新型PP 2A奠定分子和生物学框架 这些药物可能有助于治疗大量PPP 2 R2 A半合子缺失的前列腺癌患者。

The PPP2R2A gene encodes B55α, a B regulatory subunit of PP2A, which is found hemizygously deleted at high frequency in prostate, ovarian and luminal B breast cancer. PP2A is a Ser/Thr phosphatase that consists of a collection of trimeric holoenzymes whose substrate specificity, and thus biological function, is determined by the regulatory B subunit. There are at least fourteen known genes encoding different B subunits belonging to four unrelated gene families. While it is well known that PP2A plays a key tumor suppressor function, which inhibition is required for transformation of a variety of human normal epithelial cells and fibroblasts in cooperation with defined sets of oncogenes and inactivated tumor suppressor genes, the actual holoenzymes implicated are not well understood. Data from TCGA and others shows that PPP2R2A is deleted in the majority of prostate tumors (>50% hemizygous/~7% homozygous loss). Importantly, PPP2R2A hemizygous loss correlates with its reduced mRNA expression. Moreover, PCa patients present reduced disease free survival with this alteration. While this has led to the suggestion that PPP2R2A is a tumor suppressor, there is not data supporting that loss of this gene contributes to PCa. We have found that limited ectopic expression of B55α in PCa cell lines, which naturally express lower levels than normal prostate epithelial cells and other PCa cell lines, results in dramatic toxicity. This toxicity is linked to mitotic arrest, euploidy, cell death, and potent tumor growth inhibition in SCID mice. Our preliminary studies also show growth inhibition and architecture defects in PCa and DU145 3D organoids following inducible upregulation of B55α. Moreover, treatment of PC3 cells with phenothiazines, which bind and activate PP2A, mimic cell cycle effects seen with B55α reconstitution. We hypothesize that PPP2R2A hemizygous deletion and/or other alterations that reduce B55α expression in PrECs promote transformation and tumorigenicity and restoring B55α/PP2A activity has therapeutic potential. To test this hypothesis we propose two aims: (1). To determine the transforming potential and tumorigenicity of B55α loss/downregulation in Prostate Epithelial Cells (PrECs) and PCa cell lines and the effect of reconstitution of B55α expression in their ability to differentiate, grow and/or invade when grown as 3D organoids. (2). To determine if the growth suppressor function of B55α in 3D organoids is associated with its mitotic functions and/or the result of alterations in survival/differentiation pathways and if it can be targeted with PP2A activating drugs. Successful completion of this work will support the feasibility of multiple studies aimed at understanding (a) oncogene/tumor suppressor gene cooperativity in prostate tumor development in mice, and its correlation in human tumors; (b) signaling mechanisms and identification of key target substrates; and importantly, (c) devising strategies to therapeutically upregulate this holoenzyme in tumor cells. Because PPP2R2A alterations occur at high frequency in prostate tumors, the proposed studies will lay the molecular and biological framework for the development of novel classes of PP2A drugs that could potentially help treat the large pool of PCa patients with hemizygous deletions on PPP2R2A.