Cigarette smoke and its component acrolein augment IL-8/CXCL8 mRNA stability via p38 MAPK/MK2 signaling in human pulmonary cells

Abstract

Interleukin-8 (IL-8/CXCL8) is an important neutrophil chemoattractant known to be elevated in the airways of cigarette smokers and in patients with chronic obstructive pulmonary disease (COPD). We examined the acute effect of aqueous cigarette smoke extract (CSE) on IL-8 expression in primary human pulmonary cells, in particular in normal human bronchial smooth muscle cells (HBSMCs). IL-8 mRNA levels increased upon CSE exposure in a concentration- and time-dependent manner, and such an effect was accompanied by IL-8 secretion. CSE-evoked elevation of IL-8 mRNA was mimicked by its component acrolein. Both CSE and acrolein induced p38 mitogen-activated protein kinase (MAPK) phosphorylation, accompanied by the phosphorylation of MAPK-activated kinase 2 (MK2), a known downstream substrate of the p38 MAPK, both in HBSMCs and in human airway epithelial cells. Furthermore, pharmacological inhibition of p38 MAPK or MK2 strongly accelerated the decay of IL-8 mRNA levels upon stimulation with CSE or acrolein and subsequent blockade of mRNA neosynthesis with actinomycin D in pulmonary structural cells (HBSMCs and airways epithelial cells) as well as in human alveolar macrophages. Conversely, pharmacological inhibition of ERK1/2 signaling inhibited CSE-induced steady-state levels of IL-8 mRNA without affecting mRNA stability, thus suggesting inhibition at the transcriptional level. In sum, p38 MAPK/MK2 signaling is an important posttranscriptional mechanism underlying upregulation of IL-8 mRNA levels elicited by CSE and acrolein. Given the pivotal role of IL-8 in neutrophil chemotaxis and activation, our results shed light on the mechanisms through which cigarette smoke can initiate inflammation in the lung.

Effects of cigarette smoke on Toll-like receptor (TLR) activation of chronic obstructive pulmonary disease (COPD) macrophages

“…These drugs also reduce CXCL8 mRNA stabilization in CSE-exposed alveolar macrophages [15]. We would therefore expect p38 MAPK inhibitors to also reduce CXCL8 production from COPD alveolar macrophages exposed to CSE and then LPS.…”

“…As described previously [15], cell pellets were lysed in Trizol (Invitrogen, Paisley, UK) for RNA extraction and PCR analysis for CXCL8, TNF-α, TLR-2, TLR-4 and TLR-5. Total RNA was purified from cell lysates using the RNeasy Mini Kit (Qiagen, Crawley, UK), according to the manufacturer's instructions.…”

Kinases as Novel Therapeutic Targets in Asthma and Chronic Obstructive Pulmonary Disease

“…MK2 appears to play a role in prolonging NF-kB activation in Th2 cells and therefore amplifies allergic inflammation (Gorska et al, 2007). MK2 is also important in mediating the increased release of CXCL8 in response to cigarette smoke in human airway smooth muscle cells (Moretto et al, 2012). However, ATPcompetitive MK2 inhibitors have poor selectivity and low solubility (Schlapbach and Huppertz, 2009).…”

Interrelated role of cigarette smoking, oxidative stress, and immune response in COPD and corresponding treatments

“…Research has concluded that IL-6 induces lung inflammatory processes by way of Stat3 and promotes emphysema through the upregulation of alveolar cell apoptosis independent of Stat3 in emphysema and COPD, thereby suggesting that IL-6 trans-signaling and Stat3 hyperactivation may provide potential disease biomarkers and therapeutic targets (106). Additionally, a recent study has provided evidence for the initiation of the p38 MAPK and MAPKactivated kinase-2 (MK2) phosphorylation pathways by the CS-induced translation of IL-8 mRNA in bronchial smooth muscle cells (BSMC) (85). This being said, because IL-8 is a chemoattractant, it is suggested that CS may directly recruit neutrophils and propagate inflammation in BSMC by this mechanism.…”