Adenosine induces apoptosis in SBC-3 human lung cancer cells through A(3) adenosine receptor-dependent AMID upregulation.

BACKGROUND/AIMS We have shown that A(3) adenosine receptor mediates apoptosis in human lung cancer cells such as A549 cells, an epithelial adenocarcinoma cell line, and Lu-65 cells, a giant cell cancer cell line, via each different signaling pathway. AMID, a pro-apoptotic protein, induces caspase-independent apoptosis by accumulating in the nucleus. The present study investigated AMID-dependent apoptosis through A(3) adenosine receptor in SBC-3 cells, a human small cell lung cancer cell line. METHODS MTT assay, TUNEL staining, flow cytometry using propidium iodide and annexin V-FITC, and Western blotting were carried out in SBC-3 cells transfected with and without the siRNA to silence the A(3) adenosine receptor-targeted gene or the AMID-targeted gene. RESULTS Adenosine induced SBC-3 cell apoptosis in a concentration (0.01-10 mM) and treatment time (24-72 h)-dependent manner, and a similar effect was obtained with the A(3) adenosine receptor agonist 2-Cl-IB-MECA. Adenosine-induced SBC-3 cell death was inhibited by the A(3) adenosine receptor inhibitor MRS1191, knocking-down A(3) adenosine receptor, or knocking-down AMID. Adenosine upregulated expression of the AMID mRNA and protein in SBC-3 cells, that is suppressed by knocking-down A(3) adenosine receptor. In addition, adenosine increased nuclear AMID localization in concert with decreased cytosolic AMID localization. CONCLUSION The results of the present study show that adenosine induces SBC-3 cell apoptosis by upregulating AMID expression and promoting AMID translocation into the nucleus via A(3) adenosine receptor.