TLR9 and glioma: Moreover, in glioma cells, insulin-like growth factor 1 (IGF-1) could induce TLR9 expression through hypoxia-induced factor 1 alpha signaling, which further leads to secretion of cytokines IL-1β, IL-6, IL-8, and CXCR4 (a chemokine receptor that plays an important role in cell migration) [128].