Reactive oxygen species mediate oxidized low-density lipoprotein-induced endothelin-1 gene expression via extracellular signal-regulated kinase in vascular endothelial cells

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Abstract

Background

Oxidized low-density lipoprotein (oxLDL) promotes expression and secretion of endothelin-1 (ET-1), however, the precise mechanism involved is unclear. This study was designed to identify the regulatory mechanism of oxLDL-induced ET-1 expression in endothelial cells.

Methods

ET-1 mRNA expression, secretion and promoter activity were evaluated by reverse transcriptase-PCR (RT-PCR), enzyme immunometric and luciferase assays, respectively.

Results

oxLDL (35 μg/ml) significantly enhanced reactive oxygen species (ROS), mRNA expression, secretion and promoter activity of ET-1 in human umbilical vein endothelial cells (HUVECs), all of which were nullified by the antioxidant N-acetyl cysteine (NAC). oxLDL stimulated the extracellular signal-regulated kinase (ERK) phosphorylation in HUVECs, which was blocked by NAC and the mitogen-activated protein/extracellular signal-regulated kinase (MEK) inhibitor PD98059. NAC and PD98059 stopped oxLDL-elicited increase in mRNA expression, secretion and promoter activity of ET-1. Fusion plasmids with decreasing length of 5′-flanking sequence of ET-1 from −566 bpLuc to −250 bpLuc displayed increased luciferase activity after 24 h of oxLDL treatment. Interestingly, fusion plasmid from −233 and −185 bpLuc significantly reduced the luciferase activity in control and oxLDL-treated HUVECs. In addition, transfection of the reporter construct −250Luc, which contains a 2 bp mutation at activator protein-1 site, abolished both basal and oxLDL-stimulated ET-1 promoter activities.

Conclusion

Collectively, our data favor the notion that oxLDL stimulates ERK phosphorylation via ROS accumulation, which in turn stimulates vascular endothelial transcriptional factor activator protein-1 and ET-1 expression as well as secretion.

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