Induction of an interferon‐γ Stat3 response in nerve cells by pre‐treatment with gp130 cytokines

Many cytokines mediate their effects through Jak/STAT signaling pathways providing many opportunities for cross‐talk between different cytokines. We examined the interaction between two cytokine families, gp130‐related cytokines and interferon‐γ (IFN‐γ), which are coexpressed in the nervous system during acute trauma and pathological conditions. Typical nerve cells show an IFN‐γ response that is restricted to activating STAT1, with minor activation of STAT3. IFN‐γ elicited a pronounced STAT3 response in cells pre‐treated for 5–7 h with ciliary neurotrophic factor (CNTF), leukemia inhibitory factor or interleukin‐6. CNTF or interleukin‐6 induced an IFN‐γ STAT3 response in a variety of cells including SH‐SY5Y human neuroblastoma, HMN‐1 murine motor neuron hybrid cells, rat sympathetic neurons and human hepatoma HepG2 cells. The enhancement was measured as an increase in tyrosine phosphorylated STAT3, in STAT3‐DNA binding and in STAT‐luciferase reporter gene activity. The enhanced STAT3 response was not due to an increase in overall STAT3 levels but was dependent upon ongoing protein synthesis. The induction by CNTF was inhibited by the protein kinase C inhibitor, BIM, and the MAPK‐kinase inhibitor, U0126. Further, H‐35 hepatoma cells expressing gp130 receptor chimeras lacking either the SHP‐2 docking site or the Box 3 STAT binding sites failed to enhance the IFN‐γ STAT3 response. These results provide evidence for an interaction between gp130 and IFN‐γ cytokines that can significantly alter the final cellular response to IFN‐γ.