Adenosine rescues glioma cells from cytokine-induced death by interfering with the signaling network involved in nitric oxide production

Abstract

We investigated the influence of adenosine on inducible nitric oxide (NO) synthase (iNOS)-dependent NO synthesis and viability of cytokine-treated C6 rat glioma cells. Adenosine significantly inhibited interferon-gamma (IFN-gamma)+interleukin-1beta (IL-1beta)-induced synthesis of iNOS mRNA/protein and subsequent production of NO in C6 cells. The uptake of adenosine into glioma cells was not required for the suppression of iNOS induction, as confirmed by the inability of the adenosine transport blocker nitrobenzylthyoinosine to block the observed effect. Adenosine also blocked the IFN-gamma+IL-1beta-triggered expression of mRNA for the proinflammatory cytokine TNF-alpha, while it significantly enhanced the accumulation of cyclooxygenase-2 (COX-2) mRNA in glioma cells. However, blockade of TNF-alpha action and COX-2 activity with anti-TNF-alpha antibodies and indomethacin, respectively, revealed that modulation of TNF-alpha and COX-2 was not involved in adenosine-mediated iNOS suppression. Adenosine significantly inhibited cytokine-induced activation of mitogen-activated protein kinase (MAPK) family members p38 MAPK, p42/44 MAPK and c-Jun N-terminal kinase (JNK) in C6 cells. The levels of transcription factors IRF-1 and c-Fos, as well as the phosphorylation of c-Jun were also reduced in adenosine-treated C6 cells, while the activation of NF-kappaB was enhanced via increased phosphorylation of its inhibitory unit IkappaB. Importantly, adenosine-mediated suppression of NO release rescued glioma cells from NO-dependent cytokine cytotoxicity. These data suggest a possible role for adenosine-mediated inhibition of glial NO synthesis in regulation of the inflammatory CNS damage and brain cancer progression.