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Molecular mechanisms of lipopolysaccharide induced ICAM-1 expression in A549 cells
C R Fakler1, B Wu, H W McMicken
1Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA. cfakler@neo.bcm.tmc.edu
Objective And Design:
Lung intercellular adhesion molecule-1 (ICAM-1) expression is increased by LPS or hyperoxia on type II cells in vivo. The goals of the present study were to determine the mechanisms of ICAM-1 expression in a lung alveolar epithelial cell line (A549) exposed to lipopolysaccharide (LPS).
Materials:
A549 cells, a transformed human cell line with characteristics of alveolar epithelial cells, were used.
Treatment:
Cells were exposed to LPS, TNF-alpha, IL-1beta, or media alone for up to 12 h.
Methods:
Northern blot analyses were done to determine mRNA expression of ICAM-1 after exposures. Protein binding to NF-kappaB sequences were determined by gel mobility shift assays and super-shift analysis.
Results:
ICAM-1 mRNA expression was induced in A549 cells with exposure to LPS for 1 to 4 h, and was diminished to baseline at 8 h, and the inductions were independent of TNF-alpha and IL-1beta expression. Nuclear protein extracts from LPS-exposed cells bound to a NF-kappaB sequence and the timing of increased binding correlated closely with ICAM-1 mRNA induction. Super-shift studies indicated that p65 was involved in the binding to the NF-kappaB sequence and p50 was not.
Conclusion:
LPS inducibility of ICAM-1 mRNA in A549 cells is independent of TNF- and IL-1 in A549 cells, and the similar time course of mRNA induction and NF-kappaB activation suggest the induction of ICAM-1 is mediated, in part, by NF-kappaB.