Abstract 4944: Identification of B-cell lymphoma 6 as a novel therapeutic target in glioblastoma

Abstract

Abstract Background Glioblastoma multiforme (GBM) is one of the most aggressive cancers in humans. Identification and characterization of the GBM-promoting factors is imperative for the development of novel and effective clinical interventions. We recently discovered that the expression of B-cell lymphoma 6 (BCL6), a gene involved in the development of B cell lymphoma, is up-regulated in GBM. This study aims to explore the functional implications of BCL6 in this disease. Methods We analysed the transcriptional level of BCL6 in primary glioma samples, and screened the protein expression in a panel of human GBM cell lines as well as primary GBM explants. cDNA microarray analysis was conducted to identify the potential downstream targets of BCL6 in GBM. Small-interfering RNA (siRNA), small hairpin RNA (shRNA), and CRISPR-mediated gene silencing strategies were applied to examine the biological function of BCL6. Finally, inhibitors targeting BCL6 were tested in glioma cells. Results In silico analysis revealed elevated BCL6 mRNA levels in both primary GBM samples and cell lines when compared with neural stem cell or non-tumor brain tissues. Western blot confirmed the prevalent expression of BCL6 in GBM cell lines as well as primary GBM explants. Functional studies showed that BCL6 played an important role in promoting cell growth. Depletion of endogenous BCL6 through siRNA, shRNA or CRISPR in GBM cells led to marked inhibition of cell proliferation both in vitro and in vivo. Transcriptome analysis showed that BCL6 is an important regulator of TP53 signaling pathway. Knockdown of BCL6 increased the expression of p53, p21CIP and p27KIP. CHIP-qPCR further confirmed that BCL6 interacted directly to the TP53 promoter and suppressed its expression. Moreover, BCL6 negatively regulated MEK-ERK activation in GBM cells. BCL6 depletion reduced the phosphorylation levels of both MEK1/2 and ERK1/2, but had little effect on AKT phosphorylation. Our further investigations uncovered that BCL6 modulated the expression of several key regulators of MEK-ERK pathway, such as SPRY1, SPRY2 and AXL. Finally, BCL6 inhibitor showed marked anti-proliferation activity in GBM cells, suggesting that targeting BCL6 may serve as a new strategy to treat GBM. Conclusion Our data suggest that BCL6 is involved in glioma tumorigenesis through regulating both the TP53 and MEK-ERK pathways, and that BCL6 is a potential therapeutic target for glioma treatment. Citation Format: Ye Chen, Liang Xu, Masaharu Hazawa, Anand M. Thippeswamy, Henry Yang, Markus Müschen, De-Chen Lin, Phillip Koeffler. Identification of B-cell lymphoma 6 as a novel therapeutic target in glioblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4944. doi:10.1158/1538-7445.AM2015-4944