cAMP/PKA enhances interleukin-1β-induced interleukin-6 synthesis through STAT3 in glial cells

We previously reported that interleukin (IL)-1 beta induces IL-6 synthesis via activation of the I kappa B/NF kappa B pathway, p38 mitogen-activated protein (MAP) kinase, stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), and signal transducer and activator of transcription (STAT)3, but not p44/p42 MAP kinase in rat glioma cell line, C6 cells and that cAMP enhances the IL-6 synthesis. However, the details behind enhancement of IL-IP-induced IL-6 synthesis by cAMP remain to be elucidated. In the present study, we investigated the exact mechanism of CAMP underlying the amplification of IL-1 beta-induced IL-6 synthesis in C6 cells. 8-Bromo cAMP significantly enhanced IL-1 beta-induced STAT3 phosphorylation without affecting phosphorylation of I kappa B, p38 MAP kinase or SAPK/JNK. In addition, we found that forskolin, a direct activator of adenylyl cydase, significantly enhanced IL-1 beta-induced STAT3 phosphorylation. Janus famil y of tyrosine kinase (JAK) inhibitor I markedly suppressed the amplification by 8-bromo cAMP of IL-1 beta-induced IL-6 release. IL-1 beta induced JAK2 phosphotylation, and FLLL32, a specific JAK2 inhibitor, significantly reduced IL-10-stimulated IL-6 release. 4-Cyano-3-methylisoquinoline, an inhibitor of protein ldnase A (PKA), significantly attenuated the enhancing effect of 8-bromo cAMP on IL-1 beta-induced STAT3 phosphorylation. 8-Bromo cAMP markedly induced JAK2 phosphorylation. PKA siRNA transfection reduced enhancement of IL-1 beta-induced IL-6 release by 8-bromo cAMP. In conclusion, our results strongly suggest that the adenylyl cyclase/cAMP/PKA pathway upregulates IL-1 beta-induced IL-6 synthesis through enhancement of the JAK2/STAT3 pathway in C6 glioma cells. (C) 2015 Elsevier Inc. All rights reserved.