IL-6/6R signaling is closely associated with tumor growth and poor prognosis. Although there is evidence that interleukin-6 receptor (IL-6R)-mediated signaling promotes the growth and malignancy of cancer, the role of IL-6R in cancer stem cells (CSCs) is poorly defined. This study investigated the role of IL-6R in the proliferation of CSCs. Sphere-forming cells were isolated from the H460 non-small cell lung cancer (NSCLC) cell line and identified as CSCs using confocal microscopy, RT-PCR and WST-1 assay. The H460 spheres demonstrated the typical characteristics of CSCs, including CD133 expression, upregulation of Nanog, self-renewal, and drug resistance to methotrexate (MTX) and fluorouracil (5-FU). The release of IL-6R and its ligand, IL-6, were quantitatively determined and compared between CSCs and non-CSCs. The concentration of soluble IL-6R (sIL-6R) was remarkably high in CSCs compared to that in non-CSCs. Furthermore, significant upregulation of the IL-6R gene was also observed in the CSCs. The growth of CSCs was significantly inhibited by transfection with IL-6R small-interfering RNA (siRNA), as well as with the IL-6R monoclonal antibody (mAb). In addition, blocking both IL-6R and IL-6 using siRNA or mAbs intensified the inhibition of CSC proliferation. These findings indicate that IL-6R is present in CSCs and has an important role in the proliferation of CSCs in the H460 lung cancer cell line. Therefore, we suggest that IL-6R is both a viable target for the development of CSC-directed lung cancer therapeutics and a potential CSC marker in NSCLC.

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