ET-45KNOCKDOWN OF TNFSF13B INDUCES GLIOMA STEM CELL APOPTOSIS

Tumor Necrosis Factor (Ligand) Super Family member 13B (TNFSF13B; BAFF) is primarily produced by myeloid lineage cells, activated T cells and dendritic cells, and up-regulates anti-apoptotic Bcl-2 family proteins. Approximately 20% of glioblastoma overexpress TNFSF13B, which may account for treatment resistance. A Kaplan-Meier curve from a query of The Cancer Genome Atlas (TCGA) showed that glioblastoma patients with increased expression (EXP > 2) of TNFSF13B have a significantly shorter overall survival (P = 0.025). By immunoblotting, TNFSF13B expression was differentially expressed in a panel of glioma stem cells (GSCs). GFP-tagged TNFSF13B shRNA lentivirus was used to knock down TNFSF13B in multiple cell lines. Erlotinib or lapatinib inhibited cell viability to a greater extent in shTNFSF13B cells compared to scramble control. After 1 µM erlotinib treatment for 3 days, cell viability was suppressed by 34% in shTNFSF13B GSC11 cells compared to scramble control cells. Lapatinib (0.1 µM for 3 days) reduced cell viability by 40% in shTNFSF13B GSC11 cells compared to controls. Apoptosis, assessed by Annexin V-based flow cytometry, revealed a 30% increase in Annexin V staining after erlotinib treatment (1 µM for 3 days) in shTNFSF13B GSC11 cells compared with controls. The level of anti-apopototic proteins BCL-XL and Bid markedly decreased which was concomitant with an increase in cleaved caspase 9 in shTNFSF13B cells treated with EGFR inhibitors. Using an apoptosis protein array, we observed that anti-apoptotic proteins Bcl-2, survivin, claspin and HIF-1α significantly decreased in shTNFSF13B cells compared with scramble cells after treatment of 1 µM erlotinib. Ongoing in vivo studies are validating the impact of targeting TNFSF13B in a glioma xenograft model. Our studies identified TNFSF13B as a potentially important mediator of glioma stem cell survival in vitro and suggest that TNFSF13B may be a potential therapeutic target to enhance the efficacy of anti-EGFR therapy.