Stimulation of endothelial ecto 5′-nucleotidase by lipopolysaccharides via phosphatidylinositol-3 pathway

Abstract

Inflammation of endothelium is associated with atherosclerosis. It is known that adenosine possesses anti-inflammatory function and its level is increased at the sites of inflammation. The mechanism underlying the increased adenosine level is not fully understood. Therefore, we studied the effect of inflammation on endothelial ecto-5’nucleotidase (ecto-5’Nu), an enzyme which metabolizes extracellular adenosine monophosphate into adenosine. Lipopolysaccharide (LPS) was used to induce inflammation of human umbilical vein endothelial cells (HUVEC). Biochemical assay revealed that the ecto-5’Nu activity in HUVEC was stimulated by LPS after 24 hr treatment. RT-PCR showed that mRNA expression of ecto-5’Nu was not changed but western blot showed that its protein expression was increased by LPS. In addition, LY294-002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, reduced the LPS-stimulated ecto-5’Nu activity but ammonium pyrrolidine dithiocarbamate (APDC), a NF-êB inhibitor, had no effect. The stimulation of ecto-5’Nu by LPS was unaltered when HUVEC was incubated in 25 mM glucose, a condition which mimics the hyperglycemia of diabetes. In conclusion, it is suggested that the increased extracellular adenosine level during inflammation may be related to increased translational regulation of ecto-5’Nu through a PI3K signaling pathway and this mechanism may not be affected in diabetes.