β2 adrenergic receptor activation stimulates pro-inflammatory cytokine production in macrophages via PKA- and NF-κB-independent mechanisms

Activation of the 1 2 adrenergic receptor (beta(2)AR) located on macrophages has been reported to possess anti-inflammatory properties, inhibiting nuclear factor kappa B (NF-kappa B) activation and cytokine production induced by pro-inflammatory stimuli. Here, we show that activation of the beta(2)AR in the absence of pro-inflammatory stimuli produced up to an 80- and 8-fold increase in IL-1 beta and IL-6 transcripts, respectively, in the RAW 264.7 murine macrophage cell line. This increase in mRNA expression was accompanied by a significant increase in IL-1 beta and IL-6 protein production. Pretreatment of RAW cells with pharmacological inhibitors of protein kinase A (PKA) or NF-kappa B pathway failed to block this cytokine increase. Instead, the beta(2)AR-mediated increase in cytokines required activation of both the B-raf-ERK1/2 and p38 pathways. Treatment of RAW cells with the exchange protein directly activated by cAMP (EPAC) agonist also resulted in the up-regulation of IL- I and IL-6 transcripts. Examination of the main transcription factors downstream of the ERK1/2 and p38 signaling revealed that beta(2)AR activation resulted in the stimulation of CRE-, but not C/ EBP beta-, ETS-, or NF-kappa B-dependent transcription. Western blot analysis further showed that among the transcription factors which recognize the CRE-binding site, ATF-1 and ATF-2 but not CREB proteins were phosphorylated in an ERK1/2- and p38-dependent manner. Collectively, these results demonstrate that beta(2)ARs possess pro-inflammatory properties and that their activation leads to IL-1 beta and IL-6 production through ERK1/2- and p38-dependent activation of ATF-1 and ATF-2 transcription factors. (c) 2006 Published by Elsevier Inc.