Molecular Regulation of Granulocyte Macrophage Colony-Stimulating Factor in Human Lung Epithelial Cells by Interleukin (IL)-1 b , IL-4, and IL-13 Involves Both Transcriptional and Post-Transcriptional Mechanisms

Interleukin (IL)-1 b stimulates the release of granulocyte macrophage colony-stimulating factor (GM-CSF) from lung epithelial cells. To investigate the molecular mechanisms underlying GM-CSF regulation, we studied GM-CSF production, messenger RNA (mRNA) expression levels, and GM-CSF promoter activity in A549 human alveolar carcinoma cells stimulated with IL-1 b . Coincubation with IL-4 or IL-13 dose-dependently inhibited IL-1 b –induced GM-CSF release. Time-course studies of intracellular and extracellular protein release and mRNA expression indicated tight coupling of protein and mRNA synthesis within 6 h after stimulation. IL-4 and IL-13 both inhibited expression of GM-CSF mRNA and protein by 2 h after stimulation. Stable transfection of A549 cells, with GM-CSF promoter/ enhancer constructs containing up to 3.3 kb upstream of the transcription start site, revealed maximal activation by IL-1 b and phorbol 12-myristate 13-acetate (PMA) with a reporter containing the proximal promoter ( 2 627 to 1 35). This excludes sequences further upstream from a major regulatory role in GM-CSF promoter activation by IL-1 b or PMA in these cells. IL-4 and IL-13 downregulated promoter activation but had no effect on GM-CSF mRNA half-life. However, IL-1 b activation of all constructs was far less pronounced than in Jurkat T cells, suggesting a requirement for additional mechanisms, possibly post-transcriptional, to potentiate the observed transcriptional induction.