Poster Presentation Advances in Neuroblastoma Research Congress 2016

PPM1D/Wip1, the candidate gene on 17q contributing to neuroblastoma development (#347)

Jelena Milosevic 1 , Susanne Fransson 2 , Diana Treis 1 , Malin Wickström 1 , Dali Zong 3 , Baldur Sveinbjörnsson 4 , Ninib Baryawno 1 , Santhilal Subhash 5 , Chandrasekhar Kanduri 5 , Kazuyasu Sakaguchi 6 , John Inge Johnsen 1 , Tommy Martinsson 2 , Per Kogner 1
  1. Women´s and Children´s Health, Karolinska Institutet, Stockholm, Sweden
  2. Department of Clinical Genetics, Institute of Biomedicine, University of Gothenburg, Sahlgrenska University Hospital, , Gothenburg, Sweden
  3. Center for Cancer Research, National Cancer Institute, Bethesda, USA
  4. Division of Immunology, University of Tromsö, Tromsö, Norway
  5. Department of Medical Genetics, Institute of Biomedicine, , The Sahlgrenska Academy, University of Gothenburg, , Gothenburg, Sweden
  6. Laboratory of Biological Chemistry, Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, Japan

Background: In neuroblastoma gain of 17q is the most powerful genetic predictor of adverse clinical outcome. 17q+ correlates with poor survival in our population-based material where we found aberrations of chromosome 17 in 85% of primary neuroblastomas, specifically, gain of PPM1D/Wip1 at 17q23. Wip1 is a serine/threonine phosphatase encoded by the gene PPM1D, described as a gatekeeper in the Mdm2-p53 regulatory loop involved in genetic stability, inflammation and a potential oncogene contributing to carcinogenesis.

Methods: Comparative genomic hybridization (CGH), immunostaining, mRNA arrays, qPCR, exome- and RNA-sequencing was used to examine PPM1D/Wip1 in neuroblastoma. Genetical and pharmacological inhibition was used to analyse the function of Wip1 in preclinical neuroblastoma models.

Results: CGH-array analysis detected PPM1D/Wip1 extra copies in all tumors and cell lines containing 17q-gain. Expression arrays and immunostaining showed high expression of Wip1 in neuroblastoma corresponding to poor survival. RNA-sequencing confirmed PPM1D-gain and revealed truncated isoforms with oncogenic potential. Exome-sequencing detected a mutation leading to constitutive PPM1D/Wip1 activation in an aggressive metastatic infant neuroblastoma. Wip1 knockdown experiments showed significant decrease of cell viability, proliferation and colony formation as well as substantial increase of DNA-damage response in neuroblastoma cells. Tumor xenograft development was significantly delayed showing median tumor development (0.10 mL) to be more than doubled (median 15 days, vs. 33 days, p<0.001) after Wip1 downregulation compared to scrambled controls. A novel Wip1 inhibitor was highly potent in cytotoxic/cytostatic effect in neuroblastoma cell lines (median IC50 0.8 mM). Furthermore, this Wip1 inhibitor significantly inhibited growth of established human neuroblastomas in nude mice after 12 days of treatment (P<0.01).

Conclusions: Our results show that PPM1D/Wip1 is oncogenic in neuroblastoma development activated due to chromosomal gain, alternative RNA-isoforms and/or DNA-mutation. PPM1D/Wip1 provides a novel therapeutic target in high-risk neuroblastoma.