5′-N-ethylcarboxamide induces IL-6 expression via MAPKs and NF-κB activation through Akt, Ca²⁺/PKC, cAMP signaling pathways in mouse embryonic stem cells

Many studies suggest that adenosine modulates cell responses in a wide array of tissues through potent and selective regulation of cytokine production. This study examined the effects of adenosine on interleukin (IL)-6 expression and its related signal pathways in mouse embryonic stem (ES) cells. In this study, the adenosine analogue 5′-N-ethylcarboxamide (NECA) increased IL-6 protein expression level. Mouse ES cells expressed the A₁, A _2A, A_2B, and A₃ adenosine receptors (ARs), whose expression levels were increased by NECA and NECA-induced increase of IL-6 mRNA expression or secretion level was inhibited by the non-specific AR inhibitor, caffeine. NECA increased Akt and protein kinase C (PKC) phosphorylation, intracellular Ca²⁺ and cyclic adenosine monophosphate (cAMP) levels, which were blocked by caffeine. On the other hand, NECA-induced IL-6 secretion was partially inhibited by Akt inhibitor, bisindolylmaleimide I (PKC inhibitor), SQ 22536 (adenylate cyclate inhibitor) and completely blocked by the 3 inhibitor combination treatment. In addition, NECA increased mitogen activated protein kinase' (MAPK) phosphorylation, which were partially inhibited by the Akt inhibitor, bisindolylmaleimide I, and SQ 22536 and completely blocked by the 3 inhibitor combination treatment. NECA-induced increases of IL-6 protein expression and secretion levels were inhibited by MAPK inhibition. NECA-induced increase of nuclear factor (NF)-κB phosphorylation was inhibited by MAPK inhibitors. NECA also increased cAMP response element-binding protein (CREB) phosphorylation, which was blocked by MAPK or NF-κB inhibitors. Indeed, NECA-induced increase of IL-6 protein expression and secretion was blocked by NF-κB inhibitors. In conclusion, NECA stimulated IL-6 expression via MAPK and NF-κB activation through Akt, Ca²⁺/PKC, and cAMP signaling pathways in mouse ES cells.