Interleukin 6 signaling maintains the stem-like properties of bladder cancer stem cells

Background: The relapse and metastasis of bladder cancer are due to its strong resistance to chemotherapeutic drugs after surgery as a result of the expansion and self-renewal of cancer stem cells (CSCs). However, the molecular mechanisms underlying the biology of bladder CSCs are unknown. This study aimed to investigate the role of interleukin 6 (IL6)/IL6 receptor (IL6R) in the stem-like characteristics of bladder CSCs. Methods: Enzyme-linked immunosorbent assay (ELISA) and real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) was performed to detect IL6 expression in the supernatant and cells of bladder CSCs, respectively. Following that, self-renewal, stem cell-associated gene expression, invasion, metastasis, and tumorigenicity were assessed by sphere-forming assay, qRT-PCR, invasion and transwell assays, and tumor-forming experiment in NOD/SCID mice, respectively. Finally, Western blot and qRT-PCR were employed to examine the IL6 signaling pathway in regulating the stem-like properties of bladder CSCs. Results: The spheres, originating from the bladder cancer cell lines RT4 and J82, possessed a higher expression of stem-associated genes. The expression levels of IL6 were elevated in the supernatant and cells of the bladder CSCs. IL6R was also up-regulated in the bladder CSCs. Recombinant IL6 promoted the stem-like properties of the bladder CSCs, including self-renewal, expression of stem-associated genes, invasion, migration, and tumorigenicity. Mechanistically, IL6 exerted its biological effects by binding to IL6R, which enhanced the phosphorylation of STAT3 and triggered its activation. Furthermore, these effects were alleviated by the FDA-approved drug tocilizumab. Conclusions: Our findings demonstrate that IL6/IL6R/STAT3 maintains the stem-like properties of bladder CSCs. Furthermore, IL6R may serve as a potential therapeutic target for CSCs in bladder cancer.