Department of Oncology, Hematology, Rheumatology, Immunology and Pulmology, University Hospital Tübingen, Germany.
Institute of General and Molecular Pathology and Pathological Anatomy, University Hospital Tübingen, Germany.
EBioMedicine. 2019 Apr;42:340-351. doi: 10.1016/j.ebiom.2019.03.028. Epub 2019 Apr 2.
Apoptosis-stimulating Protein of TP53-2 (ASPP2) is a tumor suppressor enhancing TP53-mediated apoptosis via binding to the TP53 core domain. TP53 mutations found in cancers disrupt ASPP2 binding, arguing for an important role of ASPP2 in TP53-mediated tumor suppression. We now identify an oncogenic splicing variant, ASPP2κ, with high prevalence in acute leukemia.
An mRNA screen to detect ASPP2 splicing variants was performed and ASPP2κ was validated using isoform-specific PCR approaches. Translation into a genuine protein isoform was evaluated after establishing epitope-specific antibodies. For functional studies cell models with forced expression of ASPP2κ or isoform-specific ASPP2κ-interference were created to evaluate proliferative, apoptotic and oncogenic characteristics of ASPP2κ.
Exon skipping generates a premature stop codon, leading to a truncated C-terminus, omitting the TP53-binding sites. ASPP2κ translates into a dominant-negative protein variant impairing TP53-dependent induction of apoptosis. ASPP2κ is expressed in CD34+ leukemic progenitor cells and functional studies argue for a role in early oncogenesis, resulting in perturbed proliferation and impaired induction of apoptosis, mitotic failure and chromosomal instability (CIN) - similar to TP53 mutations. Importantly, as expression of ASPP2κ is stress-inducible it defines a novel class of dynamic oncogenes not represented by genomic mutations.
Our data demonstrates that ASPP2κ plays a distinctive role as an antiapoptotic regulator of the TP53 checkpoint, rendering cells to a more aggressive phenotype as evidenced by proliferation and apoptosis rates - and ASPP2κ expression results in acquisition of genomic mutations, a first initiating step in leukemogenesis. We provide proof-of-concept to establish ASPP2κ as a clinically relevant biomarker and a target for molecule-defined therapy. FUND: Unrestricted grant support from the Wilhelm Sander Foundation for Cancer Research, the IZKF Program of the Medical Faculty Tübingen, the Brigitte Schlieben-Lange Program and the Margarete von Wrangell Program of the State Ministry Baden-Wuerttemberg for Science, Research and Arts and the Athene Program of the excellence initiative of the Eberhard-Karls University, Tübingen.
肿瘤抑制因子 TP53 凋亡刺激蛋白 2（ASPP2）可通过与 TP53 核心结构域结合来增强 TP53 介导的细胞凋亡。在癌症中发现的 TP53 突变会破坏 ASPP2 的结合，这表明 ASPP2 在 TP53 介导的肿瘤抑制中起着重要作用。我们现在发现了一种癌基因剪接变异体 ASPP2κ，它在急性白血病中具有较高的发生率。
进行了检测 ASPP2 剪接变异体的 mRNA 筛选，并使用同工型特异性 PCR 方法验证了 ASPP2κ。建立了表位特异性抗体后，评估了其翻译为真正的蛋白同工型的情况。为了进行功能研究，创建了强制表达 ASPP2κ 或同工型特异性 ASPP2κ 干扰的细胞模型，以评估 ASPP2κ 的增殖、凋亡和致癌特征。
外显子跳跃导致提前出现终止密码子，导致 C 末端截短，缺失 TP53 结合位点。ASPP2κ 翻译为显性负性蛋白变异体，削弱了 TP53 依赖性凋亡的诱导。ASPP2κ 在 CD34+白血病祖细胞中表达，功能研究表明其在早期致癌作用中发挥作用，导致增殖失调和凋亡诱导受损、有丝分裂失败和染色体不稳定（CIN）-类似于 TP53 突变。重要的是，由于 ASPP2κ 的表达是应激诱导的，它定义了一类新的动态癌基因，而不是由基因组突变代表的。
我们的数据表明，ASPP2κ 作为 TP53 检查点的抗凋亡调节剂发挥着独特的作用，使细胞呈现出更具侵袭性的表型，这表现在增殖和凋亡率上-ASPP2κ 的表达导致基因组突变的获得，这是白血病发生的第一个起始步骤。我们提供了概念验证，将 ASPP2κ 确立为一种具有临床相关性的生物标志物和分子定义治疗的靶点。
Wilhelm Sander 癌症研究基金会的无限制资助、图宾根大学医学系的 IZKF 计划、Brigitte Schlieben-Lange 计划和巴登-符腾堡州州立科学、研究和艺术部的 Margarete von Wrangell 计划以及图宾根大学卓越倡议的 Athene 计划。
