Sox10 Has a Broad Expression Pattern in Gliomas and Enhances Platelet-Derived Growth Factor-B–Induced Gliomagenesis Maria Ferletta, Lene Uhrbom, Tommie Olofsson, Fredrik Ponte´n, and Bengt Westermark Department of Genetics and Pathology, Rudbeck Laboratory, Uppsala, Sweden Abstract without any known intermediate stages of the tumor, whereas In a previously published insertional mutagenesis screen secondary glioblastoma arises by progression from a lower for candidate brain tumor genes in the mouse using a grade to a higher tumor grade. Common genetic alterations in Moloney mouse leukemia virus encodingplatelet-derived primary glioblastoma are amplification of EGFR and MDM2 growth factor (PDGF)-B, the Sox10 gene was tagged in and deletions of the INK4A gene (1, 2). During the progression five independent tumors. The proviral integrations of secondary glioblastoma, mutations accumulate over time suggest an enhancer effect on Sox10. All Moloney murine and more than 65% of the tumors have mutations in TRP53. leukemia virus/PDGFB tumors had a high protein Overexpression of the platelet-derived growth factor receptor-a expression of Sox10 independently of malignant grade (PDGFRA) and PDGFA are characteristic for secondary glio- or tumor type. To investigate the role of Sox10 in blastoma (3). Constitutive expression of growth factors and gliomagenesis, we used the RCAS/tv-a mouse model in their receptors has been shown to be necessary for the develop- which the expression of retroviral-encoded genes can be ment of brain tumors resulting in autocrine stimulation and directed to glial progenitor cells (Ntv-a mice). Both Ntv-a increased activity of downstream pathways (4). Inactivation transgenic mice, wild-type, and Ntv-a p19Arf null mice of the tumor suppressor gene phosphatase and tensin homo- were injected with RCAS-SOX10 alone or in combination logue (PTEN; refs. 5, 6) is another common trait of glio- with RCAS-PDGFB. Infection with RCAS-SOX10 alone blastoma. PTEN signals through Akt and many glioblastomas did not induce any gliomas. Combined infection of have an increased activity of Akt (7). RCAS-SOX10 and RCAS-PDGFB in wild-type Ntv-a mice To better understand the role of PDGF in gliomagenesis, we yielded a tumor frequency of 12%, and in Ntv-a ArfÀ/À have generated a mouse glioma model in which a Moloney mice the tumor frequency was 30%. This indicates that murine leukemia virus (MMLV)/PDGFB–containing retrovirus Sox10 alone is not sufficient to induce gliomagenesis but (MMLV/PDGFB) together with a replication-competent helper acts synergistically with PDGFB in glioma development. virus was injected into newborn mouse brains, which resulted All induced tumors displayed characteristics of in malignant brain tumors (8). All tumors grew invasively and PNET-like structures and oligodendroglioma. The tumors diffusely, and most of them had areas of necrosis and had a strongand widely distributed expression of angiogenesis. The tumors stained positively for nestin, Sox10 and PDGFR-A. We investigated the expression suggesting that they had evolved from an immature neuroglial of Sox10 in other human tumors and in a number of progenitor cell (8). We have postulated that the tumors gliomas. The Sox10 expression was restricted to gliomas developed through an autocrine PDGF receptor activation in and melanomas. All glioma types expressed Sox10, combination with insertional mutagenesis through proviral and tumors of low-grade glioma had a much broader integrations. A number of common proviral integration sites distribution of Sox10 compared with high-grade gliomas. were identified, targeting candidate tumor-causing genes (9). (Mol Cancer Res 2007;5(9):891–7) One of the tagged genes was Sox10. Sox10 is a transcription factor and belongs to the Sox superfamily, which all contain a Introduction DNA binding motif known as the high-mobility group domain. Glioblastoma is the most common and malignant primary During development, Sox10 first appears in the developing brain tumor in the adult, with a mean survival time after neural crest and is expressed during the formation of the diagnosis of 1 year. Primary glioblastoma develops de novo peripheral nervous system (10). In central nervous system, Sox10 was first found on glial progenitor cells but later also detected in oligodendrocytes in the adult brain (11). Sox10 Received 3/6/07; revised 5/7/07; accepted 5/31/07. precedes the expression of PDGFR-a in oligodendrocyte Grant support: The Swedish Cancer Society and the Swedish Children’s Cancer precursors, but once the PDGFR-a is expressed, they are Foundation. Sox10 null The costs of publication of this article were defrayed in part by the payment of found in the same cells (12). Homozygous mice die page charges. This article must therefore be hereby marked advertisement in before or at birth. The entire peripheral nervous system is accordance with 18 U.S.C. Section 1734 solely to indicate this fact. defective and motor neurons are absent (13). The levels of Requests for reprints: Maria Ferletta, Department of Genetics and Pathology, Uppsala University, Rudbeck Laboratory C11, Dag Hammarskjoldsv 20, S-751 PDGFR-a are reduced, suggesting that Sox10 influences the 85 Uppsala, Sweden. Phone: 46-18-611-1174; Fax: 46-18-55-89-31. E-mail: expression of PDGFR-a (12). In human, mutations in the [email protected] SOX10 Copyright D 2007 American Association for Cancer Research. gene have been linked to Waardenburg-Shah syndrome doi:10.1158/1541-7786.MCR-07-0113 type IV, which is characterized by depigmentation of hair and Mol Cancer Res 2007;5(9). September 2007 891 Downloaded from mcr.aacrjournals.org on September 29, 2021. © 2007 American Association for Cancer Research. 892 Ferletta et al. FIGURE 1. Schematic illustration of proviral integrations upstream of Sox10. Five proviral integrations were tagged upstream of the transcriptional start site of Sox10 in five different tumors. Arrows illustrate the position and the transcriptional orientation of the proviral genome. Data were adapted from the Ensembl Mouse Genome Browser and exact positions of the integrations can be found in the Retrovirus Tagged Cancer Gene Database (http:// RTCGD.ncifcrf.gov/). skin, and Hirschsprung’s disease (megacolon; ref. 14). PDGFB–induced tumors (9). The proviral integration sites Mutations in SOX10 in combination with Waardenburg-Shah were at both transcriptional orientations and located upstream syndrome type IV have also been associated with severe of Sox10 within an area of 60 kb (Fig. 1). The upstream dysmyelination syndromes (PCWH; ref. 14). Further, Sox10 is localization of the proviral insertions suggests an enhancer expressed in, and during the development of, melanocytes, effect on Sox10. which also are derived from the neural crest. During The brain tumors induced by the MMLV/PDGFB viruses melanocyte specification, Sox10 is responsible for activating were of different malignancy grades and could be divided the melanocyte transcription regulator Mitf, which controls into glioblastoma-like, oligodendroglioma-like, and PNET-like melanocyte survival and differentiation (15, 16). (primitive neuroectodermal tumor) tumors. When analyzing the In the present investigation, we have studied the role of MMLV/PDGFB tumors for Sox10 expression, we found that all Sox10 in human and mouse gliomas. For studies in the mouse, analyzed tumors had a high protein expression of Sox10, we used the RCAS/tv-a model (replication-competent avian independent of the tumor type. The protein was expressed also leukemia virus splice acceptor/avian leukemia virus receptor) in in tumors without integrations in Sox10 (Fig. 2). In addition, which the expression of retrovirus-encoded genes can be real-time PCR analysis has previously shown that Sox10 is directed either to glial progenitor cells (Ntv-a mice; mice strongly up-regulated in both early and late MMLV/PDGFB– expressing the tv-a receptor behind the nestin promoter) or induced tumors (17). astrocytes (Gtv-a mice; mice expressing tv-a by the glial fibrillary acidic protein promoter). We have found that Sox10 Sox10 Enhances PDGF-Induced Gliomagenesis has a broad distribution in different types of gliomas in both To investigate the role of Sox10 in gliomagenesis, we used human and mouse tumors. Sox10 was not able to initiate the RCAS/tv-a mouse model. Cells infected with RCAS virus tumorigenesis by itself, but in combination with an RCAS virus containing SOX10 (RCAS-SOX10) were injected intracerebral- expressing PDGFB, the tumor incidence was increased. ly in newborn mice. Both Ntv-a transgenic mice, wild-type (wt), and Ntv-a p19Arf null mice were injected with RCAS- Results SOX10 alone or in combination with RCAS-PDGFB (Table 1). Sox10 Is Highly Expressed in PDGFB-Induced Mouse Infection with RCAS-SOX10 alone did not induce any gliomas, Gliomas neither in Ntv-a wt nor in Ntv-a ArfÀ/À mice. Injections with In our previous screen for candidate glioma genes in the RCAS-PDGFB together with an empty RCAS vector (RCAS-X) mouse, Sox10 wastaggedinfiveindependentMMLV/ gave rise to 3 tumors from 37 injected mice in the Ntv-a ArfÀ/À FIGURE 2. Sox10 expression in PDGFB-induced tumors. Immunohistochemical staining of Sox10 in mouse gliomas induced with MMLV/PDGFB. A. A representative PNET-like tumor. B. A glioblastoma-like tumor. C. A PNET-like tumor in which one of the Sox10 integrations was identified. Mol Cancer Res 2007;5(9). September 2007 Downloaded from mcr.aacrjournals.org on September 29, 2021. © 2007 American Association for Cancer Research. Sox10 in Gliomagenesis 893 Table 1. Tumor Incidence in Mice Injected with Different All the tumors grew invasively and had vessel formation. The RCAS Virus in Different Combinations tumor cells were relatively small and displayed perineuronal satellitosis (Fig. 3A). All tumors showed a strong and widely Genotype RCAS No. No. Incidence P a Mice Tumors (%) distributed expression of Sox10 and PDGFR- (Fig. 3B and C). Only scattered cells in the tumors were positive for the Ntv-a wt SOX10 28 0 0 astrocytic marker GFAP (Fig.