title: Intracellularly transported adenosine induces apoptosis in HuH-7 human hepatoma cells by downregulating c-FLIP expression causing caspase-3/-8 activation.
abstract: Extracellular adenosine induced apoptosis of HuH-7 cells, a Fas-deficient human hepatoma cell line. The adenosine action was inhibited by dipyridamole, an adenosine transporter inhibitor, or 5'-amino-5'-deoxyadenosine, an inhibitor of adenosine kinase to convert from adenosine to AMP, but it was not affected by inhibitors for adenosine A(1), A(2a), A(2b), and A(3) adenosine receptors. Adenosine activated caspase-3 and -8, but not caspase-9, in HuH-7 cells, and the activation was abolished by dipyridamole. In the real-time RT-PCR and Western blot analysis, extracellular adenosine downregulated mRNA and protein levels for c-FLIP, and the effect was suppressed by dipyridamole. Furthermore, overexpression of c-FLIP short in HuH-7 cells inhibited adenosine-induced caspase-8 activity. Taken together, these results suggest that intracellularly transported adenosine, perhaps converted AMP as the ensuing event, activates caspase-8 and the downstream effector caspase caspase-3 by neutralizing caspase-8 inhibition due to c-FLIP as a consequence of decreased c-FLIP expression, leading to apoptosis. This extends our understanding of adenosine-induced molecular apoptotic pathways.
authors.affiliation: Department of Physiology, Hyogo College of Medicine, Nishinomiya, Japan.
authors.forename: Dongqin
authors.initials: D
authors.lastname: Yang
authors.forename: Takahiro
authors.initials: T
authors.lastname: Yaguchi
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Yamamoto
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Nishizaki
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D017209:Apoptosis / Q000502:physiology*; D001692:Biological Transport / Q000502:physiology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000473:pathology*; D053148:Caspase 3 / Q000378:metabolism*; D053181:Caspase 8 / Q000378:metabolism*; D015536:Down-Regulation; D004789:Enzyme Activation; D015870:Gene Expression; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology; D014407:Tumor Cells, Cultured
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D053148:Caspase 3; D053181:Caspase 8; D000241:Adenosine