Abstract 3305: Trim3, the human homolog of Drosophila brat, regulates asymmetric division in glioblastoma stem cells

Abstract Glioblastoma (GBM) is the most common and malignant primary brain tumor. The recently described stem cell component of malignant gliomas is biologically critical, yet mechanisms that underlie its regulation are not understood. Mutations in Drosophila Brain tumor (brat) result in a massively enlarged fly brain that consists of a neuroblast cell population with neoplastic growth properties that has lost the ability to divide asymmetrically. Brat has been shown to promote asymmetric cell division and direct neural differentiation at least partially through its translational suppression of Myc. Here we investigated the role of brat homologs for their regulation of glioma behavior, especially as related to asymmetric division of glioma stem cells. We found that the human brat homolog, Trim3, is highly expressed in normal brain and that a substantial subset of GBMs (25-30%) show loss of heterozygosity (LOH) of chromosome 11p15.5, the site of Trim3. Trim3 expression was markedly reduced in human GBM cell lines compared to human astrocytes and reduced in human GBMs specimens compared to normal brain, consistent with results from mining existing gene expression data sets (oncomine). Since Drosophila brat is critical to neural differentiation and regulates Myc, we explored whether human Trim3 might regulate glioma stem cell properties by its regulation of Myc. We found that the forced expression of Trim3 in human GBM cell lines led to reduced Myc protein expression. This inverse relationship between Trim3 and Myc also held true in GBM samples. We used a lentiviral system to stably express Trim3 in GBM cell lines and neurospheres and found that Trim3 expression reduced glioma proliferation and colony formation in vitro and also led to smaller and less frequent neuropheres. In vivo, Trim3 suppressed tumor growth in an orthotopic xenograft model and led to prolonged survival. Trim3 expression was associated with reduced expression of nestin and CD133 by GBM neurosphere cultures, suggesting that its loss may enrich the stem cell compartment. Moreover, Trim3 expression by neurosphere stem cells favored a pattern of asymmetric cell division in GBM. Thus, Trim3 appears to direct asymmetric cell division in glioma stem cells and its loss is associated with stem cell enrichment and greater biologic potential. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3305. doi:10.1158/1538-7445.AM2011-3305