Molecular Cell Biology Tumorigenic and Antiproliferative Properties of the TALE-Transcription Factors MEIS2D and MEIS2A in Neuroblastoma Anja Groß 1 , Catrine Schulz 1 , Jasmine Kolb 1 , Jan Koster 2 , Sibylle Wehner 3 , Sebastian Czaplinski 1 , Abdulghani Khilan 1 , Hermann Rohrer 4 , Patrick N. Harter 1 , Thomas Klingebiel 3 , Julian D. Langer 5 , Dirk Geerts 6 , and Dorothea Schulte 1 Abstract Neuroblastoma is one of only a few human cancers that can spontaneously regress even after extensive dissemination, a poorly understood phenomenon that occurs in as many as 10% of patients. In this study, we identify the TALE-homeo- domain transcription factor MEIS2 as a key contributor to this phenomenon. We identified MEIS2 as a MYCN-independent factor in neuroblastoma and showed that in this setting the alternatively spliced isoforms MEIS2A and MEIS2D exert antag- onistic functions. Specifically, expression of MEIS2A was low in aggressive stage 4 neuroblastoma but high in spontaneously regressing stage 4S neuroblastoma. Moderate elevation of MEIS2A expression reduced proliferation of MYCN-amplified human neuroblastoma cells, induced neuronal differentiation and impaired the ability of these cells to form tumors in mice. In contrast, MEIS2A silencing or MEIS2D upregulation enhanced the aggressiveness of the tumor phenotype. Mecha- nistically, MEIS2A uncoupled a negative feedback loop that restricts accumulation of cellular retinoic acid, an effective agent in neuroblastoma treatment. Overall, our results illumi- nate the basis for spontaneous regression in neuroblastoma and identify an MEIS2A-specific signaling network as a poten- tial therapeutic target in this common pediatric malignancy. Significance: This study illuminates the basis for spontaneous regressions that can occur in a common pediatric tumor, with implications for the development of new treatment strategies. Cancer Res; 78(8); 1935–47. Ó2018 AACR. Introduction Alternative splicing, the combinatorial use of protein coding exons during the maturation of pre-mRNA to mRNA, facilitates expression of multiple mRNA isoforms from the same gene, thus greatly expanding the protein repertoire in a given cell. In humans, over 90% of multiexon genes are subject to alternative splicing, and the number of different splice isoforms synthesized from a single gene can vary between few and several thousands (1). Genome-wide transcriptome profiling of normal and diseased tissues revealed an unexpected high incidence of conditions involving altered mRNA splicing of disease-associated genes. In fact, defective splicing has been linked to all aspects of cancer biology, including tumor initiation and progression, metastasis and therapy resistance (2). In addition, alternative splicing is particularly prevalent in the mammalian nervous system, with emerging roles in nearly all aspects of neuronal development and function, and dysregulated splicing has been implicated in neu- rodegenerative pathologies, schizophrenia, and autism spectrum disorders (3, 4). Neuroblastoma is a pediatric solid tumor that arises from the sympathoadrenal lineage of the neural crest. Neuroblastoma accounts for about 15% of all childhood cancer deaths in the United States and Europe, making it the most frequent extracra- nial solid tumor in infants and young children (5). This neuro- endocrine malignancy displays diverse clinical spectrums, ranging from defined tumors removable by surgery (categorized as INSS stages st1 and st2) to highly metastasized disease (st3 and st4). Patients with st4 tumors frequently exhibit amplification of the MYCN protooncogene and have a poor survival probability, even under aggressive, multi-modal therapy (5, 6). In about 10% of patients, however, tumors and metastases regress spontaneously without any treatment. Such regressing tumors mostly occur in patients under one year of age at diagnosis and are recognized as the distinct tumor stage 4S. 4S tumors show low cell proliferation and contain large numbers of terminally differentiated neurons (7). The underlying cause of this spontaneous tumor regression is still unknown, although favorable expression of neurotrophin receptors, permissive epigenetic modification of differentiation- related genes and telomere shortening have been implicated (7). 1 Institute of Neurology (Edinger Institute), University Hospital Frankfurt, Goethe University, Frankfurt, Germany. 2 Department of Oncogenomics, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands. 3 Clinic for Pediatric and Adolescent Medicine, University Hospital Frankfurt, Goethe University, Frankfurt, Germany. 4 Institute for Clinical Neuroanatomy, University Hospital Frankfurt, Goethe University, Frankfurt, Germany. 5 Department of Molecular Membrane Biology, Max-Planck Institute for Biophysics, Frankfurt, Germany. 6 Department of Medical Biology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands. Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). Current address for J. Kolb: Dr. Ehrlich Pharma, D-88410 Bad Wurzach, Germany; and current address for A. Khilan: College of Science and Engineering, Hamad bin Khalifa University, Doha, Qatar. Corresponding Author: Dorothea Schulte, University Hospital Frankfurt, Hein- rich Hoffmann Street 7, 60528 Frankfurt, Germany. Phone: 49-69-6301-84159; Fax: 49-69-6301-84150; E-mail: dorothea.schulte@kgu.de doi: 10.1158/0008-5472.CAN-17-1860 Ó2018 American Association for Cancer Research. Cancer Research www.aacrjournals.org 1935 Downloaded from http://aacrjournals.org/cancerres/article-pdf/78/8/1935/2777492/1935.pdf by guest on 11 October 2023