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

Marcus Matthias Schittenhelm, Bianca Walter, Vasileia Tsintari, Birgit Federmann, Mihada Bajrami Saipi, Figen Akmut, Barbara Illing, Ulrike Mau-Holzmann, Falko Fend, Charles Lopez, Kerstin Maria Kampa-Schittenhelm

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    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 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.

    Original languageEnglish (US)
    Pages (from-to)340-351
    Number of pages12
    JournalEBioMedicine
    Volume42
    DOIs
    StatePublished - Apr 1 2019

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    Keywords

    • Acute leukemia
    • Alternative splicing
    • ASPP2
    • Oncogenesis

    ASJC Scopus subject areas

    • Biochemistry, Genetics and Molecular Biology(all)

    Cite this

    Schittenhelm, M. M., Walter, B., Tsintari, V., Federmann, B., Bajrami Saipi, M., Akmut, F., Illing, B., Mau-Holzmann, U., Fend, F., Lopez, C., & Kampa-Schittenhelm, K. M. (2019). Alternative splicing of the tumor suppressor ASPP2 results in a stress-inducible, oncogenic isoform prevalent in acute leukemia. EBioMedicine, 42, 340-351. https://doi.org/10.1016/j.ebiom.2019.03.028