CCAAT/enhancer-binding protein and activator protein-1 transcription factors regulate the expression of interleukin-8 through the mitogen-activated protein kinase pathways in response to mechanical stretch of human airway smooth muscle cells

Here we investigated the mechanisms by which mechanical stretch regulates the production of IL-8 in primary human airway smooth muscle cells (HASMC). Bronchial HASMC were subjected to cyclic mechanical stretch (12%, 1 Hz) using the computer-controlled Flex-cell Strain system. Mechanical stretch increased IL-8 mRNA expression and protein production. Cyclic stretch of HASMC also increased the kinase activities of ERK1/2, JNK1, p38, and the DNA binding activities of AP-1 and C/EBP transcription factors with little effect on NF-kappaB. The inhibition of AP-1 and C/EBP transcriptional activities blocked the production of IL-8 in culture supernatants. Furthermore, the inhibition of ERK1/2 and p38 but not JNK1 caused a significant downregulation in the expression and production of IL-8 in response to cyclic stretch. Although protein tyrosine kinases were required for the activation of both ERK1/2 and p38 kinase, stretch-activated channels, small GTPase proteins, and extracellular Ca2+ influx were required only for the activation of p38 kinase whereas phosphoinositide 3-kinase was needed for ERK1/2 activation. In addition, the phosphorylation of ERK1/2 was essential for the activation of AP-1 whereas p38 MAP kinase was needed for the activation of C/EBP. Our data demonstrate that the cyclic stretch of HASMC causes the increased production of IL-8 by activating the AP-1 and C/EBP transcription factors through the activation of ERK1/2 and p38 kinase signaling pathways.