Tumor and Stem Cell Biology YB-1 Bridges Neural Stem Cells and Brain Tumor–Initiating Cells via Its Roles in Differentiation and Cell Growth Abbas Fotovati 1 , Samah Abu-Ali 1 , Pei-Shan Wang 1 , Loic P. Deleyrolle 2 , Cathy Lee 1 , Joanna Triscott 1 , James Y. Chen 1 , Sonia Franciosi 1 , Yasuhiro Nakamura 3 , Yasuo Sugita 4 , Takeshi Uchiumi 5 , Michihiko Kuwano 5 , Blair R. Leavitt 1 , Sheila K. Singh 6 , Alexa Jury 7 , Chris Jones 7 , Hiroaki Wakimoto 8 , Brent A. Reynolds 2 , Catherine J. Pallen 1 , and Sandra E. Dunn 1 Abstract The Y-box binding protein 1 (YB-1) is upregulated in many human malignancies including glioblastoma (GBM). It is also essential for normal brain development, suggesting that YB-1 is part of a neural stem cell (NSC) network. Here, we show that YB-1 was highly expressed in the subventricular zone (SVZ) of mouse fetal brain tissues but not in terminally differentiated primary astrocytes. Conversely, YB-1 knockout mice had reduced Sox-2, nestin, and musashi-1 expression in the SVZ. Although primary murine neurospheres were rich in YB-1, its expression was lost during glial differentiation. Glial tumors often express NSC markers and tend to loose the cellular control that governs differentiation; therefore, we addressed whether YB-1 served a similar role in cancer cells. YB-1, Sox-2, musashi-1, Bmi-1, and nestin are coordinately expressed in SF188 cells and 9/9 GBM patient- derived primary brain tumor–initiating cells (BTIC). Silencing YB-1 with siRNA attenuated the expression of these NSC markers, reduced neurosphere growth, and triggered differentiation via coordinate loss of GSK3-b. Furthermore, differentiation of BTIC with 1% serum or bone morphogenetic protein-4 suppressed YB-1 protein expression. Likewise, YB-1 expression was lost during differentiation of normal human NSCs. Consistent with these observations, YB-1 expression increased with tumor grade (n ¼ 49 cases). YB-1 was also coexpressed with Bmi-1 (Spearmans 0.80, P > 0.001) and Sox-2 (Spearmans 0.66, P > 0.001) based on the analysis of 282 cases of high-grade gliomas. These proteins were highly expressed in 10/15 (67%) of GBM patients that subsequently relapsed. In conclusion, YB-1 correlatively expresses with NSC markers where it functions to promote cell growth and inhibit differentiation. Cancer Res; 71(16); 5569–78. Ó2011 AACR. Introduction Glioblastoma (GBM), the most common primary brain tumor in adults, is usually associated with a 2-year survival rate of only 10% to 25% (1). In children, primary brain tumors are the second most common type of cancer, following leukemia, with an incidence of 3.8 per 100,000 person-years (2, 3). Like adults, children who suffer from GBM have a low chance of long-term survival, thus, a better molecular under- standing of these tumors may lead to new therapeutic targets. Y-box binding protein 1 (YB-1) is a transcription/translation factor involved in DNA repair (4) and multidrug resistance (5). Loss of YB-1 is embryonically lethal for mice where major developmental defects were reported in the brain (6, 7), yet the molecular mechanism underlying this is unknown. Although it is downregulated at postnatal life (8), it is highly expressed in cancer where its expression is associated with poor prognosis (4). YB-1 was highly expressed in gliomas when compared with surrounding normal brain tissues (9). We reported that YB-1 is essential for growth of adult and pediatric GBM cells by showing that silencing it with siRNA suppressed proliferation, invasion, and tumorigenesis (10). Furthermore, YB-1 conveyed resistance to temozolomide (10), a drug commonly used to treat GBM. Thus, YB-1 plays a role in normal and pathologic states of the brain. Whether these roles are related is not known. Poor responses to conventional therapeutic approaches and frequent relapses are serious challenges for patients with brain tumors. There are various factors contributing to this therapeutic resistance and relapse. One of the potential cul- prits is the presence of brain tumor–initiating cells (BTIC) also referred to repopulating cells which are multipotent, have the Authors' Affiliations: 1 University of British Columbia, Vancouver, British Columbia, Canada; 2 University of Florida, Gainesville, Florida; 3 St. Mary's Hospital and 4 Kurume University, Kurume; 5 Kyushu University, Fukuoka, Japan; 6 McMaster University, Hamilton, Ontario, Canada; 7 The Institute of Cancer Research, Royal Marsden Hospital, Surrey, England; and 8 Mas- sachusetts General Hospital, Boston, Massachusetts Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). Corresponding Authors: Sandra E. Dunn, University of British Columbia, Vancouver, BC V5Z 4H4 Canada. Phone: 604-875-2000; Fax: 604-875-3120; E-mail: sedunn@mail.ubc.ca or Abbas Fotovati, University of British Columbia, Vancouver, BC V5Z 4H4 Canada. E-mail: fotovati@hotmail.com doi: 10.1158/0008-5472.CAN-10-2805 Ó2011 American Association for Cancer Research. Cancer Research www.aacrjournals.org 5569 on April 13, 2017. © 2011 American Association for Cancer Research. cancerres.aacrjournals.org Downloaded from Published OnlineFirst July 5, 2011; DOI: 10.1158/0008-5472.CAN-10-2805