Critical Role of Constitutive Type I Interferon Response in Bronchial Epithelial Cell to Influenza Infection

Innate antiviral responses in bronchial epithelial cells (BECs) provide the first line of defense against respiratory viral infection and the effectiveness of this response is critically dependent on the type I interferons (IFNs). However the importance of the antiviral responses in BECs during influenza infection is not well understood. We profiled the innate immune response to infection with H3N2 and H5N1 virus using Calu-3 cells and primary BECs to model proximal airway cells. The susceptibility of BECs to influenza infection was not solely dependent on the sialic acid-bearing glycoprotein, and antiviral responses that occurred after viral endocytosis was more important in limiting viral replication. The early antiviral response and apoptosis correlated with the ability to limit viral replication. Both viruses reduced RIG-I associated antiviral responses and subsequent induction of IFN-β. However it was found that there was constitutive release of IFN-β by BECs and this was critical in inducing late antiviral signaling via type I IFN receptors, and was crucial in limiting viral infection. This study characterizes anti-influenza virus responses in airway epithelial cells and shows that constitutive IFN-β release plays a more important role in initiating protective late IFN-stimulated responses during human influenza infection in bronchial epithelial cells

Regulation of a disintegrin and metalloprotease-33 expression by transforming growth factor-?

The asthma susceptibility gene, ADAM33, is selectively expressed in mesenchymal cells and the activity of soluble ADAM33 has been linked to angiogenesis and airway remodeling. TGF-? is a profibrogenic growth factor whose expression is increased in asthma and recent studies show that it enhances shedding of soluble ADAM33. In this study, we hypothesized that TGF-? also affects ADAM33 expression in bronchial fibroblasts in asthma. Primary fibroblasts were grown from bronchial biopsies from normal and asthmatic donors and treated with TGF-?(2) to induce myofibroblast differentiation. ADAM33 expression was assessed using quantitative RT-PCR and Western blotting. To examine the mechanisms whereby TGF-?(2) affected ADAM33 expression, quantitative methylation-sensitive PCR, chromatin immunoprecipitation and nuclear accessibility assays were conducted on the ADAM33 promoter. We found that TGF-?(2) caused a time- and concentration-dependent reduction in ADAM33 mRNA expression in normal and asthmatic fibroblasts, affecting levels of splice variants similarly. TGF-?(2) also induced ADAM33 protein turnover and appearance of a cell associated C-terminal fragment. TGF-?(2) down-regulated ADAM33 mRNA expression by causing chromatin condensation around the ADAM33 promoter with deacetylation of histone H3, demethylation of H3 on lysine-4, and hypermethylation of H3 on lysine-9. However, the methylation status of the ADAM33 promoter did not change. Together these data suggest that TGF-?(2) suppresses expression of ADAM33 mRNA in normal or asthmatic fibroblasts. This occurs by altering chromatin structure, rather than by gene silencing through DNA methylation as in epithelial cells. This may provide a mechanism to finely regulate levels of ADAM33 expression in fibroblasts and may self-limit TGF-?(2)-induced ectodomain shedding of ADAM33