Studies of the extracellular ATP-adenosine pathway in human urinary tract epithelial cells.

Extracellular ATP may be metabolized to AMP and adenosine by the ectonucleotidases CD39 and CD73 and, in this study, we characterized the pathways for adenosine formation in human urinary tract epithelial cells. Bladder (RT4) and kidney (A498) epithelial cells were grown in cell culture and the expression of CD39 and CD73 was investigated by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. High-performance liquid chromatography was used to determine adenosine formation in cell medium. RT-PCR and immunohistochemistry revealed a high CD73 and a low CD39 expression in human urinary tract epithelial cells, whereas neutrophils had a higher CD39 than CD73 expression. Adenosine was produced when the cells were exposed to 5'-AMP (substrate for CD73), but not when exposed to 5'-ATP (substrate for CD39). A pronounced inhibition of 5'-AMP-induced adenosine formation by the CD73 inhibitor AMP-CP confirmed the involvement of CD73. Adenosine production from 5'-ATP was slightly increased (p < 0.05) when epithelial cells were cocultured with neutrophils. The data demonstrate that adenosine formation from extracellular ATP is negligible in urinary tract epithelial cells due to low CD39 expression in this cell type. However, the epithelial cells express CD73 and are able to convert extracellular AMP to adenosine.