IL-32γ suppresses lung cancer stem cell growth via inhibition of ITGAV-mediated STAT5 pathway

The cancer stem cells (CSCs) are thought to be responsible for cancer initiation, recurrence, and metastasis via a multifactorial process. IL-32γ has been known to inhibit several tumor developments. However, the role of IL-32γ in CSCs is unknown. The role of IL-32γ on tumor development was assessed in IL-32γ transgenic (Tg) mice allograft and xenograft model. In the in vitro assay, we analyzed CSC growth and apoptosis in cells with IL-32γ overexpression by cell viability assay and tumor-sphere formation assay. In addition, expression of cell proliferation, apoptosis markers, and signaling molecules was determined by western blot analysis. IL-32γ suppressed CD133+ CSC-induced allograft model in IL-32γ Tg mice and xenograft model. Tumor-sphere formation and cell viability assay revealed a greater inhibition of CSC proliferation and antineoplastic activity of IL-32γ in CD133+ CSCs as compared with normal cancer cells. The inhibitory effects of IL-32γ on tumor development were associated with inhibition of the STAT5 pathway. In addition, inhibition of STAT5 increased cleavage of caspase-3, but suppressed CD133 expression and colony formation. Web-based gene network analysis showed that IL-32 is correlated with ITGAV, an integrin gene. Our result revealed that knockdown of ITGAV by siRNA inhibited the phosphorylation of STAT5. Moreover, we identified that ITGAV overexpression reversed the effect of IL-32γ on phosphorylation of STAT5 and the expression of CD133. Our results demonstrate that IL-32γ negatively regulates CD133+ CSC proliferation and tumor development and suggest that IL-32γ has great potential for use in the treatment of cancer progression.