Alternative splicing of the tumor suppressor ASPP2 results in a stress-inducible, oncogenic isoform prevalent in acute leukemia

Abstract

Background 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. Methods 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 . Findings 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. Interpretation 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 ASPP2 κ 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.

Systematic Analysis of Alternative Splicing Landscape in Pancreatic Adenocarcinoma Reveals Regulatory Network Associated with Tumorigenesis and Immune Response

“…Accumulating evidence implicates aberrant AS events as the hallmarks of carcinogenesis, including tumor growth, angiogenesis, immune evasion, and metastasis [ 13 – 15 ]. AS promotes tumor progression not only by activating oncogene isoforms such as VEGFA but also through facilitating the degradation of suppressor genes such as TP53 [ 16 , 17 ]. AS events are also accurate predictive markers for various cancer types, including breast, lung, colorectal, and liver [ 18 – 21 ].…”

A genomic-clinicopathologic Nomogram for the preoperative prediction of lymph node metastasis in gastric cancer

“…Protein phosphatase 3 regulatory factor subunit 1 (PPP3R1) is a member of β-regulatory subunit family of calcineurin that codes for apoptosis-stimulating protein of p53 (ASPP) in the p53 integrin family [ 55 ]. The ASPP enhances P53-mediated apoptosis by binding to the P53 core domain [ 56 ]. However, the specific molecular mechanisms of the differentially expressed genes in the pathways have not been established.…”

Targeting of Post-Transcriptional Regulation as Treatment Strategy in Acute Leukemia

“…Apoptosis-stimulating Protein of TP53-2 (ASPP2) is a tumor suppressor enhancing TP53-mediated apoptosis. It has been found that a splice variant ASPP2κ is overexpressed in AML and displays anti-apoptotic function, therefore supporting proliferation of the cells [54].…”