Differential Regulation of Epithelial-Derived C-C Chemokine Expression by IL-4 and the Glucocorticoid Budesonide

Airway epithelial cells are a rich source of eosinophil-selective C-C chemokines. We investigated whether cytokines and the topical glucocorticoid budesonide differentially regulate RANTES, monocyte chemoattractant protein-4 (MCP-4), and eotaxin mRNA and protein expression in the human bronchial epithelial cell line BEAS-2B and in primary human bronchial epithelial cells by Northern blot analysis and ELISAs. Eotaxin and MCP-4 mRNA expression induced by TNF-α alone or in combination with IFN-γ was near-maximal after 1 h, peaked at 4 and 8 h, respectively, remained unchanged up to 24 h, and was protein synthesis independent. In contrast, RANTES mRNA was detectable only after 2 h and slowly increased to a peak at 24 h, and was protein synthesis dependent. Induction of eotaxin and MCP-4 mRNA showed a 10- to 100-fold greater sensitivity to TNF-α compared with RANTES mRNA. IL-4 and IFN-γ had selective effects on chemokine expression; IL-4 selectively up-regulated the expression of eotaxin and MCP-4 and potentiated TNF-α-induced eotaxin, while IFN-γ markedly potentiated only the TNF-α-induced expression of RANTES. Although budesonide inhibited the expression of chemokine mRNA to a variable extent, it effectively inhibited production of eotaxin and RANTES protein. Budesonide inhibited both RANTES- and eotaxin promoter-driven reporter gene activity. Budesonide also selectively accelerated the decay of eotaxin and MCP-4 mRNA. These results point to IL-4 as a possible mediator by which Th2 cells may induce selective production of C-C chemokines from epithelium and indicate that glucocorticoid inhibit chemokine expression through multiple mechanisms of action.

Negative Feedback Between Prostaglandin and α- and β-Chemokine Synthesis in Human Microglial Cells and Astrocytes

The understanding of immune surveillance and inflammation regulation in cerebral tissue is essential in the therapy of neuroimmunological disorders. We demonstrate here that primary human glial cells were able to produce α- and β-chemokines (IL-8 > growth related protein α (GROα) ≫ RANTES > microphage inflammatory protein (MIP)-1α and MIP-1β) in parallel to PGs (PGE2 and PGF2α) after proinflammatory cytokine stimulation: TNF-α + IL-1β induced all except RANTES, which was induced by TNF-α + IFN-γ. Purified cultures of astrocytes and microglia were also induced by the same combination of cytokines, to produce all these mediators except MIP-1α and MIP-1β, which were produced predominantly by astrocytes. The inhibition of PG production by indomethacin led to a 37–60% increase in RANTES, MIP-1α, and MIP-1β but not in GROα and IL-8 secretion. In contrast, inhibition of IL-8 and GRO activities using neutralizing Abs resulted in a specific 6-fold increase in PGE2 but not in PGF2α production by stimulated microglial cells and astrocytes, whereas Abs to β-chemokines had no effect. Thus, the production of PGs in human glial cells down-regulates their β-chemokine secretion, whereas α-chemokine production in these cells controls PG secretion level. These data suggest that under inflammatory conditions, the intraparenchymal production of PGs could control chemotactic gradient of β-chemokines for an appropriate effector cell recruitment or activation. Conversely, the elevated intracerebral α-chemokine levels could reduce PG secretion, preventing the exacerbation of inflammation and neurotoxicity.

The Heat Shock Response Inhibits RANTES Gene Expression in Cultured Human Lung Epithelium

The chemokine RANTES is thought to be involved in the pathophysiology of inflammation-associated acute lung injury. Although much is known regarding signals that induce RANTES gene expression, relatively few data exist regarding signals that inhibit RANTES gene expression. The heat shock response, a highly conserved cellular defense mechanism, has been demonstrated to inhibit a variety of lung proinflammatory responses. We tested the hypothesis that induction of the heat shock response inhibits RANTES gene expression. Treatment of A549 cells with TNF-α induced RANTES gene expression in a concentration-dependent manner. Induction of the heat shock response inhibited subsequent TNF-α-mediated RANTES mRNA expression and secretion of immunoreactive RANTES. Transient transfection assays involving a RANTES promoter-luciferase reporter plasmid demonstrated that the heat shock response inhibited TNF-α-mediated activation of the RANTES promoter. Inhibition of NF-κB nuclear translocation with isohelenin inhibited TNF-α-mediated RANTES mRNA expression, indicating that RANTES gene expression is NF-κB dependent in A549 cells. Induction of the heat shock response inhibited degradation of the NF-κB inhibitory protein, I-κBα but did not significantly inhibit phosphorylation of I-κBα. We conclude that the heat shock response inhibits RANTES gene expression by a mechanism involving inhibition of NF-κB nuclear translocation and subsequent inhibition of RANTES promoter activation. The mechanism by which the heat shock response inhibits NF-κB nuclear translocation involves stabilization of I-κBα, without significantly affecting phosphorylation of I-κBα.

Respiratory Syncytial Virus-Induced RANTES Production from Human Bronchial Epithelial Cells Is Dependent on Nuclear Factor-κB Nuclear Binding and Is Inhibited by Adenovirus-Mediated Expression of Inhibitor of κBα

Respiratory syncytial virus (RSV) infection is an important cause of lower respiratory tract illness, the severity of which may be partly due to cellular recruitment. RSV infection activates chemokine secretion from airway epithelial cells by largely unknown mechanisms. We investigated the regulation of RSV-induced activation of the chemokine RANTES in the bronchial epithelial cell line BEAS-2B and primary normal human tracheobronchial epithelial cultures. RANTES protein and mRNA were detected at 24 h and up until 72 h from cultures of BEAS-2B infected with replicating virus, but not with UV-inactivated RSV. RSV infection of BEAS-2B or normal human tracheobronchial epithelial cells stimulated NF-κB translocation to the nucleus and binding to the RANTES-specific κB-binding sequences within 2 h, with levels peaking at 24 h. Supershift assays indicated that binding was due to p50/p65 heterodimers. BEAS-2B cells were transfected with a replication-deficient adenoviral vector, expressing a mutated, nondegradable form of IκBα. IκBα overexpression specifically blocked NF-κB translocation and inhibited mRNA accumulation and secretion of RANTES induced by RSV or TNF-α plus IFN-γ. Adenoviral transfection did not interfere with RSV replication or significantly induce apoptosis. Further, a control adenovirus, expressing the β-galactosidase gene, did not alter cellular functions. Thus, NF-κB nuclear translocation is a critical step in RSV induction of RANTES secretion. Elucidating the mechanisms of cellular activation by RSV and targeting specific areas may lead to novel therapeutic approaches in the treatment of RSV.