β2-Adrenoceptor Activation Stimulates IL-6 Production via PKA, ERK1/2, Src, and Beta-Arrestin2 Signaling Pathways in Human Bronchial Epithelia

Objective beta(2)-Adrenoceptor agonists are widely used to treat asthma because of their bronchial-dilation effects. We previously reported that isoprenaline, via the apical and basolateral beta(2)-adrenoceptor, induced Cl- secretion by activating cyclic AMP (cAMP)-dependent pathways in human bronchial epithelia. Despite these results, whether and how the beta(2)-adrenoceptor-mediated cAMP-dependent pathway contributes to pro-inflammatory cytokine release in human bronchial epithelia remains poorly understood. Methods We investigated beta(2)-adrenoceptor-mediated signaling pathways involved in the production of two pro-inflammatory cytokines, interleukin (IL)-6 and IL-8, in 16HBE14o-human bronchial epithelia. The effects of isoprenaline or formoterol were assessed in the presence of protein kinase A (PKA), exchange protein directly activated by cAMP (EPAC), Src, and extracellular signal-regulated protein kinase (ERK)1/2 inhibitors. The involvement of beta-arrestin2 was examined using siRNA knockdown. Results Isoprenaline and formoterol (both beta(2) agonists) induced IL-6, but not IL-8, release, which could be inhibited by ICI 118,551 (beta(2) antagonist). The PKA-specific inhibitor, H89, partially inhibited IL-6 release. Another intracellular cAMP receptor, EPAC, was not involved in IL-6 release. Isoprenaline-mediated IL-6 secretion was attenuated by dasatinib, a Src inhibitor, and PD98059, an ERK1/2 inhibitor. Isoprenaline treatment also led to ERK1/2 phosphorylation. In addition, knockdown of beta-arrestin2 by siRNA specifically suppressed cytokine release when a high concentration of isoprenaline (1 mM) was used. Conclusion Our results suggest that activation of the beta(2)-adrenoceptor in 16HBE14o-cells stimulated the PKA/Src/ERK1/2 and/or beta-arrestin2 signaling pathways, leading to IL-6 release. Therefore, our data reveal that beta(2)-adrenoceptor signaling plays a role in the immune regulation of human airway epithelia.

Automated summary

The activation of beta(2)-adrenoceptors in human bronchial epithelial cells stimulates specific signaling pathways, leading to the release of pro-inflammatory cytokine IL-6, but not IL-8. The pathways involving PKA/Src/ERK1/2 and beta-arrestin2 play essential roles in this process.