A(3) adenosine receptor mediates apoptosis in 5637 human bladder cancer cells by G(q) protein/PKC-dependent AIF upregulation.

BACKGROUND/AIMS A(3) adenosine receptor mediates apoptosis in a variety of cancer cells via diverse signaling pathways. The present study was conducted to assess A(3) adenosine receptor-mediated apoptosis in human bladder cancer cell lines and to understand the underlying mechanism. METHODS Human bladder cancer cell lines such as 253J, 5637, KK-47, TCCSUP, T24, and UMUC-3 cells were cultured. The siRNA to silence the A(3) adenosine receptor-targeted gene was constructed and transfected into cells. MTT assay, TUNEL staining, Western blotting, and real-time RT-PCR were carried out. RESULTS For all the investigated cell types adenosine induced apoptosis in a concentration (0.01-10 mM)- and treatment time (24-48 h)-dependent manner. Adenosine-induced 5637 cell death was significantly inhibited by the A(3) adenosine receptor inhibitor MRS1191 or knocking-down A(3) adenosine receptor, and the A(3) adenosine receptor agonist 2-Cl-IB-MECA mimicked the adenosine effect. The adenosine effect was prevented by GF109203X, an inhibitor of protein kinase C (PKC), but it was not affected by forskolin, an activator of adenylate cyclase. Adenosine-induced 5637 cell death, alternatively, was not inhibited by the pan-caspase inhibitor Z-VAD. Adenosine upregulated expression of apoptosis-inducing factor (AIF), that is suppressed by knocking-down A(3) adenosine receptor, and accumulated AIF in the nucleus. CONCLUSION The results of the present study show that adenosine induces 5637 cell apoptosis by upregulating AIF expression via an A(3) adenosine receptor-mediated G(q) protein/PKC pathway.