Genetic drivers of metastatic dissemination in sonic hedgehog medulloblastoma.

Noah C Jenkins,Michael D Taylor,Walavan Sivakumar,Carolyn A Pedone,Daniel W Fults,Xiaochong Wu,Ricky R Kalra,Adrian Dubuc

doi:10.1186/s40478-014-0085-y

Abstract

Leptomeningeal dissemination (LMD), the metastatic spread of tumor cells via the cerebrospinal fluid to the brain and spinal cord, is an ominous prognostic sign for patients with the pediatric brain tumor medulloblastoma. The need to reduce the risk of LMD has driven the development of aggressive treatment regimens, which cause disabling neurotoxic side effects in long-term survivors. Transposon-mediated mutagenesis studies in mice have revealed numerous candidate metastasis genes. Understanding how these genes drive LMD will require functional assessment using in vivo and cell culture models of medulloblastoma. We analyzed two genes that were sites of frequent transposon insertion and highly expressed in human medulloblastomas: Arnt (aryl hydrocarbon receptor nuclear translocator) and Gdi2 (GDP dissociation inhibitor 2). Here we show that ectopic expression of Arnt and Gdi2 promoted LMD in mice bearing Sonic hedgehog (Shh)-induced medulloblastomas. We overexpressed Arnt and Gdi2 in a human medulloblastoma cell line (DAOY) and an immortalized, nontransformed cell line derived from mouse granule neuron precursors (SHH-NPD) and quantified migration, invasiveness, and anchorage-independent growth, cell traits that are associated with metastatic competence in carcinomas. In SHH-NPD cells. Arnt and Gdi2 stimulated all three traits. In DAOY cells, Arnt had the same effects, but Gdi2 stimulated invasiveness only. These results support a mechanism whereby Arnt and Gdi2 cause cells to detach from the primary tumor mass by increasing cell motility and invasiveness. By conferring to tumor cells the ability to proliferate without surface attachment, Arnt and Gdi2 favor the formation of stable colonies of cells capable of seeding the leptomeninges.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-014-0085-y) contains supplementary material, which is available to authorized users.

Highlights

An important goal in designing therapies for patients with the malignant brain tumor medulloblastoma is to reduce the risk of metastasis
Sleeping Beauty transposon mutagenesis identifies Arnt and Gdi2 as common insertion site genes in metastatic medulloblastomas Arnt and Gdi2 emerged as candidate leptomeningeal dissemination (LMD)-inducing genes from a study in which SB transposon mobilization in Math1+ granule neuron precursor cells (GNPs) in Patched+/− mice caused the typically localized, Sonic hedgehog (Shh)-driven medulloblastomas to disseminate widely throughout the spinal leptomeninges [19]
We show here that ectopic expression of Arnt and Gdi2, which were identified in an unbiased genetic screen for metastasis genes using SB transposon mutagenesis, promotes LMD in Shh-induced medulloblastomas in mice

Summary

Introduction

An important goal in designing therapies for patients with the malignant brain tumor medulloblastoma is to reduce the risk of metastasis. A defining characteristic of metastasis in medulloblastoma is leptomeningeal dissemination (LMD), the spread of tumor cells via the cerebrospinal fluid (CSF) to the leptomeningeal spaces of the brain and spinal cord. The need to minimize metastasis risk is critical because survival times are very low once LMD has occurred. Guided by this principle, pediatric oncologists have designed multimodality treatments, which combine surgery, chemotherapy, and craniospinal radiation [1,2]. Pediatric oncologists have designed multimodality treatments, which combine surgery, chemotherapy, and craniospinal radiation [1,2] Hope for prolonging disease-free survival and eliminating treatment-related neurotoxicity rests on developing therapies that target the molecular mediators of LMD, our knowledge of which is limited

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Conclusion