Abstract
Interleukin-24 (IL-24) displays cancer-specific apoptosis-inducing properties in a broad spectrum of human tumors without harmful effects on normal cells. The human IL-24 protein is secreted as a glycosylated protein and functions as a pro-Th1 cytokine and a potent antiangiogenic molecule. However, the function of secreted recombinant human IL-24 (srhIL-24) protein in esophageal squamous cell carcinoma (ESCC) cells has not been studied. In the present study, we prepared a stable site-specific-integrated cell line, Flp-InTMCHO/IL-24 (FCHO/IL-24), which secreted rhIL-24 at a higher level than three random-integrated cell lines. In vitro, we identified that the purified srhIL-24 inhibited proliferation and induced the apoptosis of ESCC Eca-109 cells and activated STAT3, which was related with the IL-20 receptors. In vivo, the tumorigenicity of Eca-109 cells was significantly inhibited by s.c. injection of FCHO/IL-24 cells. Decreased tumor microvessel density and an increased number of TUNEL-positive tumor cells were associated with tumor growth inhibition, indicating the presence of antiangiogenic activity and induction of apoptotic activity. In summary, the present study demonstrated that srhIL-24 induced growth inhibition and apoptosis in ESCC Eca-109 cells in vitro and in vivo, which may be mediated by the receptor pathway.