Submitted on December 21, 2007
Revised on July 9, 2008
Accepted on July 11, 2008
Stimulation of ecto-5'nucleotidase in human umbilical vein endothelial cells by lipopolysaccharide
Rachel W.S. Li1, Ricky Y.K. Man2, Paul M Vanhoutte3, and George P.H. Leung1*
1 The University of Hong Kong
2 University of Hong Kong
3 Li Ka Shing Faculty of Medicine, The University of Hong Kong
* To whom correspondence should be addressed. E-mail: gphleung{at}hkucc.hku.hk.
The involvement of ecto-5' nucleotidase (E-5'Nu) in the elevation of extracellular adenosine during inflammation is unclear. In the present study, the effect of lipopolysaccharide (LPS), an inflammation inducer, was investigated on E-5'Nu in human umbilical vein endothelial cells (HUVECs). E-5'Nu activity was enhanced after a 24 hour exposure to LPS. This effect was dose-dependent, with an EC50 of 1.66 ng/ml. At 10 µM, the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 abolished the LPS-induced E-5'Nu activity. However, at 10 µM, the NF-
B inhibitor ammonium pyrrolidine dithiocarbamate had no effect. LPS up-regulated the protein expression but not the messenger RNA expression of E-5'Nu. Inhibition of E-5'Nu by 100 µM 
,
-methylene adenosine-5'-diphosphate increased the LPS-induced inflammation, suggesting that E-5'Nu plays a significant role in reducing inflammation probably through the generation of adenosine. In conclusion, the experiments indicate that LPS up-regulates E-5'Nu activity in HUVECs, through a PI3K-dependent-increase in the abundance of E-5'Nu on cell membranes. Since adenosine is an anti-inflammatory molecule, E-5'Nu up-regulation may be crucial in protecting endothelial cells against inflammatory damage.
