AMP Converted from Intracellularly Transported Adenosine Upregulates p53 Expression to Induce Malignant Pleural Mesothelioma Cell Apoptosis.

Background/Aims: The present study investigated adenosine-induced apoptosis in human malignant pleural mesothelioma cells. Methods: MTT assay, TUNEL staining, flow cytometry using propidium iodide and annexin V-FITC, real-time RT-PCR, Western blotting, and assay of caspase-3, -8, and -9 activities were carried out using malignant pleural mesothelioma cell lines such as NCI-H28, NCI-H2052, NCI-H2452, and MST0-211H cells, and p53 or A₃ adenosine receptor was knocked-down by transfecting each siRNA into cells. Results: Adenosine induced apoptosis in all the malignant pleural mesothelioma cells used here, independently of caspase activation. The adenosine effect was prevented by the adenosine transporter inhibitor dipyridamole, the adenosine kinase inhibitor ABT-702, or the AA₃ adenosine receptor inhibitor MRS1191. Adenosine upregulated expression of the p53 mRNA and protein, that is abolished by ABT-702, but not by knocking-down A₃ adenosine receptor Adenosine-induced apoptosis in NCI-H28 cells was significantly inhibited by knocking-down p53 and in part by knocking-down A₃ adenosine receptor Conclusion: The results of the present study show that AMP converted from intracellularly transported adenosine upregulates p53 expression to induce caspase-independent apoptosis in malignant pleural mesothelioma cells and that A₃ adenosine receptor also participates partially in the apoptosis by the different mechanism. [ABSTRACT FROM AUTHOR]