Tumorigenic and Antiproliferative Properties of the TALE-Transcription Factors MEIS2D and MEIS2A in Neuroblastoma

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-homeodomain 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 antagonistic functions. Specifically, expression of was low in aggressive stage 4 neuroblastoma but high in spontaneously regressing stage 4S neuroblastoma. Moderate elevation of expression reduced proliferation of -amplified human neuroblastoma cells, induced neuronal differentiation and impaired the ability of these cells to form tumors in mice. In contrast, silencing or upregulation enhanced the aggressiveness of the tumor phenotype. Mechanistically, MEIS2A uncoupled a negative feedback loop that restricts accumulation of cellular retinoic acid, an effective agent in neuroblastoma treatment. Overall, our results illuminate the basis for spontaneous regression in neuroblastoma and identify an MEIS2A-specific signaling network as a potential therapeutic target in this common pediatric malignancy. 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. .

MEIS transcription factors in development and disease

“…Likewise, in the mouse embryonic hindbrain and in neuroblastoma cell lines, expression of the Aldh1a2 gene encoding the RA-producing enzyme RALDH2 is under direct, positive regulation by MEIS2, while transcription of Cyp26a1, which encodes a RA-degrading enzyme, is decreased (Fig. 5C) (Groß et al, 2018;Vitobello et al, 2011). Given that RA is a wellestablished inducer of cell cycle exit and cellular differentiation in the nervous and hematopoietic systems, MEIS proteins can trigger irreversible differentiation processes by generating a local RA-source within a proliferating tissue or cell mass (Collins, 2002;Janesick et al, 2015).…”

“…However, a significant positive correlation exists between high MEIS2 expression and favorable disease outcome according to publicly available mRNA-expression profiles of samples from thousands of individuals with neuroblastoma. This correlation indicates that a purely oncogenic role for MEIS genes in neuroblastoma is unlikely (Groß et al, 2018). An initial explanation for these discrepancies came from analyzing alternative splicing of exon 12 and the resulting isoforms, MEIS2A and MEIS2D (Fig.…”

“…Among these are various HDcontaining proteins, including all HD-bearing members of the PAX protein family, as well as OTX2, DLX1 and DLX2, the pancreas-specific protein PDX1, or engrailed (en) in D. melanogaster (Agoston and Schulte, 2009;Agoston et al, 2012Agoston et al, , 2014Heine et al, 2008;Kobayashi, 2003;Liu et al, 2001;Schulte, 2014;Swift et al, 1998). MEIS also cooperates with members of more distant transcription factor families, such as the T-box family member EOMES, basic helix-loop-helix (bHLH) proteins such as MAX, Ets transcription factors like ELF1, zinc-finger transcription factors like KLF4 or teashirt (TSH), GATA-transcription factors, NF-Y, and nuclear receptors like the androgen receptor (AR) in prostate cancer or the ecdysone receptor (EcR) in D. melanogaster (Bessa et al, 2002;Bjerke et al, 2011;Cui et al, 2014;Groß et al, 2018;Jolma et al, 2015;Knoepfler et al, 1999;Ladam et al, 2018;Neto et al, 2017). In addition, MEIS can interact with several other nuclear proteins, including epigenetic regulators, with the nuclear enzyme poly-ADP polymerase 1 (PARP1/ARTD1), and even some structural proteins of the cell nucleus (Choe et al, 2009(Choe et al, , 2014Groß et al, 2018;Hau et al, 2017).…”

“…4A). Although alternative splicing and tissue-specific expression of the MEIS2a-d variants were recognized when the gene was first cloned (Oulad-Abdelghani et al, 1997), different functions for individual MEIS2 isoforms have only recently been established in the context of cancer (discussed in more detail below; Groß et al, 2018). Given that the MEIS1 and MEIS3 genes share the same exon-intron structure, it is plausible to assume that variants with similarly divergent biological activities also exist for other MEIS genes (Geerts et al, 2005).…”

“…It has been shown in neuroblastoma that expression of the MEIS2A isoform induces proliferation arrest and neuronal differentiation, whereas expression of the MEIS2D isoform or MEIS2A knockdown increases the aggressiveness of already highly malignant neuroblastoma cells and tumors. The differential roles for MEIS2A and MEIS2D in neuroblastoma cells most probably stem from their C-terminal domains, which can assemble largely non-overlapping interactomes, allowing them to recruit different proteins to the regulatory regions of target genes (Groß et al, 2018).…”