Phosphatidylinositol 3-Kinase Is Required for Rhinovirus-induced Airway Epithelial Cell Interleukin-8 Expression

Abstract

Rhinovirus (RV) is a common cause of asthma exacerbations. The signaling mechanisms regulating RV-induced airway epithelial cell responses have not been well studied. We examined the role of phosphatidylinositol (PI) 3-kinase in RV-induced interleukin (IL)-8 expression. Infection of 16HBE14o؊ human bronchial epithelial cells with RV39 induced rapid activation of PI 3-kinase and phosphorylation of Akt, a downstream effector of PI 3-kinase. RV39 also colocalized with cit-Akt-PH, a citrogen-tagged fluorescent fusion protein encoding the pleckstrin homology domain of Akt, indicating that 3-phosphorylated PI accumulates at the site of RV infection. Inhibition of PI 3-kinase and Akt attenuated RV39-induced NF-B transactivation and IL-8 expression. Inhibition of PI 3-kinase also blocked internalization of labeled RV39 into 16HBE14o؊ cells, suggesting that the requirement of PI 3-kinase for RV39-induced IL-8 expression, at least in part, relates to its role in viral endocytosis. Rhinovirus (RV)2 is a single-stranded RNA virus from the Picornaviridae family responsible for the majority of common colds. Viral infections trigger the majority of asthma exacerbations (1, 2), and RV accounts for 60% of virus-induced exacerbations (1). RV is also an important trigger of chronic obstructive pulmonary disease (COPD) exacerbations (3, 4). The precise mechanisms by which RV induces asthma or COPD exacerbations are unknown, but numerous studies suggest a role for IL-8, a CXC chemokine with the neutrophil-attractant Glu-Leu-Arg (ELR) motif. IL-8 and neutrophils are found in the nasal secretions and sputum of patients with RV-induced asthma exacerbations (5-9). Further, the number of neutrophils correlates with the level of IL-8 (7, 9). RV induces IL-8 expression in cultured airway epithelial cells (10 -12). Increased neutrophil and IL-8 levels are a feature of asthma (13,14) and COPD exacerbations (15-17). Together, these data suggest that RV may stimulate asthma exacerbations by inducing bronchial epithelial cell production of IL-8, leading to a neutrophilic inflammatory response.The human RVs include more than 100 serotypes that are divided into two groups based on their cellular receptors. Intercellular adhesion molecule (ICAM)-1 is the airway epithelial cell receptor for major subgroup RVs (e.g. RV14, RV16, and RV39), whereas the low density lipoprotein receptor functions as the receptor for minor subgroup RVs (e.g. RV1B and RV2). Thus, antibodies to ICAM-1 inhibit major subgroup RV infection of epithelial cells (18).ICAM-1 is a type I transmembrane glycoprotein belonging to the immunoglobulin superfamily. In endothelial cells, ICAM-1 cross-linking increases phosphorylation and activation of pp60 Src (19,20) and pp125 focal adhesion kinase (21). The p85 regulatory subunit of class 1A PI 3-kinase serves as a substrate for both Src (22) and focal adhesion kinase (23, 24), suggesting that ICAM-1 ligation by RV could also activate PI 3-kinase. Other viruses with different membrane receptors also activate PI 3-kinase. Adenovirus atta...

Contribution of Bronchial Fibroblasts to the Antiviral Response in Asthma

“…Previous studies have shown that RV-39 (a major group virus)-induced IL-8 expression in epithelial cells occurred by ICAM binding and activation of PI3K (17,22). In our studies, we also found that inhibition of PI3K down-regulated both IL-8 and IL-6 mRNA induced by RV1b.…”

“…Previous studies have shown that IL-8 gene expression in BECs infected with RV-39 is independent of viral replication, being triggered by viral endocytosis and activation of PI3K (17). Pretreatment of bronchial fibroblasts with the PI3k inhibitor LY294002 for 1 h before infection inhibited expression of IL-8 or IL-6 induced by either RV1b or UV-irradiated RV1b (Table I).…”

Selective Transcriptional Down-Regulation of Human Rhinovirus-Induced Production of CXCL10 from Airway Epithelial Cells via the MEK1 Pathway

“…Despite this potential, our understanding of the signaling pathways regulating HRV-16-induced chemokine production remains limited. Recent studies, by us and others, have implicated the spleen tyrosine kinase, Syk, as well as PI3K and MAPK pathways in early, replication-independent viral signaling leading to production of CXCL8 (19,25,35). In contrast, few studies have focused on signaling involved in HRV-16-induced production of chemokines, such as CXCL10, that absolutely require rhinovirus replication for induction.…”

The relative balance of GM-CSF and TGF-β1 regulates lung epithelial barrier function

“…Cells were cultured for 5 days in DMEM ϩ 10% FBS before further experimental manipulation to allow the cells to form a model type I cell monolayer (28). Normal immortalized 16HBE14o-human bronchiolar epithelial cells (HBE cells) were acquired from M. Hershenson Laboratory (University of Michigan) (8,41). HBE cells were maintained on tissue culture plastic in DMEM ϩ 10% FBS and used at passages 10 -20.…”