Interleukin (IL)-1beta 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-1beta. Coincubation with
IL-4 or
IL-13 dose-dependently inhibited IL-1beta-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-1beta and
phorbol 12-myristate 13-acetate (PMA) with a reporter containing the proximal promoter (-627 to +35). This excludes sequences further upstream from a major regulatory role in
GM-CSF promoter activation by IL-1beta 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-1beta 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.