JNK-AP-1 pathway involved in interleukin-1β-induced calcitonin gene-related peptide secretion in human type II alveolar epithelial cells

In a previous study, we found that calcitonin gene-related peptide (CGRP) could be induced by proinflammatory factor IL-1β in A549 human type II alveolar (AEII) epithelial cells. We investigated the mechanism of IL-1β-induced CGRP secretion and found that the PKC-p38 MAPK-NF-κB pathway was involved. In the present study, we found that IL-1β stimulation induced c-Jun N-terminal kinase (JNK) activity within 15 min in A549 cells. In investigating whether JNK was involved in IL-1β-induced CGRP secretion, the JNK II inhibitor SP600125 was used and it significantly attenuated IL-1β-induced CGRP secretion and c-Jun activity, which was elevated after IL-1β stimulation from mRNA to protein level. EMSA results showed the activation of activator protein 1 (AP-1) after 2-h IL-1β stimulation, and the JNK II inhibitor blocked c-Jun and AP-1 activity. Bioinformatic analysis showed five predicted AP-1 binding sites on the promoter of β-CGRP; deletion analysis identified an AP-1 consensus site at −643 bp relative to the initiation site, which mediates the β-CGRP gene transcription in response to IL-1β. These data suggest that besides the PKC-p38 MAPK-NF-κB pathway, the JNK-AP-1 pathway is involved in IL-1β-induced CGRP secretion in A549 human type II alveolar epithelial cells, and a 643-bp site upstream of the transcription start site on the promoter of β-CGRP is the AP-1 response element.