Endothelial Cell-Derived IL-6 Induces Bcl-2 in Oral Cancer Stem Cells

Cancer stem cells are resistant to chemotherapy and capable of generating new tumors. Targeted disruption of the perivascular niche is an emerging strategy to eliminate cancer stem cells and prevent tumor recurrence. Previous studies have shown that interleukin (IL)-6 is upregulated in head and neck squamous cell carcinomas (HNSCC), and that IL-6 enhances stemness in several cancer models. However, the effect of IL-6 on the survival of head and neck cancer stem cells (HNCSC) is unknown. Objective: The goal of this study is to determine the effect of endothelial cell-secreted IL-6 on the expression of the pro-survival protein Bcl-2 in HNCSC. Methods: Stem cells were sorted from a head and neck tumor cell line (UM-SCC-74B) by flow cytometry using ALDH and CD44 (putative markers of HNCSC). 4x10^4/well ALDH+CD44+ or ALDH-CD44- cells were seeded in 6-well ultra-low attachment plates. These cells were treated for 24 hours with one of the following conditions: 1) Conditioned medium (CM) from primary human dermal microvascular endothelial cells (HDMEC) containing neutralizing anti-IL-6 antibody; 2) CM from HDMEC containing isotype-matched non-specific IgG; 3) Endothelial basal medium (EBM) containing neutralizing anti-IL-6 antibody; or 4) EBM containing isotype-matched non-specific IgG. Bcl-2 expression was analyzed by Western Blot and RT-PCR. Results: We observed that endothelial cell CM induced Bcl-2 expression in ALDH+CD44+ cells, but not in ALDH-CD44- cells. Notably, blockade of IL-6 abrogated the induction of Bcl-2 by endothelial cell CM. Conclusion: These data demonstrate that a potent pro-survival protein (Bcl-2) is upregulated in head and neck cancer stem cells in response to endothelial cell-derived IL-6. These results suggest that targeted disruption of IL-6-mediated crosstalk among cells of the perivascular niche might constitute a therapeutic target for HNSCC. Supported by University of Michigan Student Research Program and AADR Fellowship (DV); and by P50-CA97248, R01-DE15948, R21-DE19279 from the NIH (JEN).