Molecular mechanisms of A3 adenosine receptor-induced G1 cell cycle arrest and apoptosis in androgen-dependent and independent prostate cancer cell lines: involvement of intrinsic pathway

Purpose A3 adenosine receptor has shown several physiological and pathological activities, including cell proliferation and apoptosis in various cancer cell lines. This study is designed to investigate molecular mechanism and apoptotic pathway of A3 adenosine receptor in DU-145, PC3 and LNcap-FGC10 human prostate cancer cells. Methods The expression level of A3 adenosine receptor was examined using real-time RT-PCR. cAMP concentration was also measured. MTT viability, cell counting and BrdU incorporation tests were used to study the cell proliferation effect of IB-MECA. Cell cycle analysis, Annexin V-FITC staining, Hoechst 33258 staining, mitochondrial membrane potential (Delta Psi M), caspase-3 activity, Bcl-2 and Bax protein expression were used to detect apoptosis. Result A3 adenosine receptors mRNAs were detected at different levels. IB-MECA inhibited forskolin-stimulated cAMP. IB-MECA at (1 mu M) suppressed cell proliferation and induced G1 cell cycle arrest. Indeed, IB-MECA down-regulated the expression of CDK4, cyclin D1 and up-regulated p53 expression. IB-MECA at (10-100 mu M) induced apoptosis. The activity of caspase-3 was also increased. Expression of Bcl-2 was decreased in response to IB-MECA, while the expression of Bax protein was increased. The results showed a significant loss of Delta Psi M, in a dose-dependent manner. Conclusion This study introduces a possible mechanism through A3 adenosine receptor activation. IB-MECA inhibited prostate cancer cells proliferation and induced G1 cell cycle arrest through p53, Cdk4/cyclinD1 pathway. Apoptosis determined by characteristic morphological changes and increased in sub-G1 population. Loss of MMP, activation of caspase-3 and down-regulation of Bcl2 expression indicated mitochondrial signaling pathway that involved in the apoptosis.