Adenosine-induced caspase-3 activation by tuning Bcl-X sub(L)/DIABLO/IAP expression in HuH-7 human hepatoma cells

• Published in: Cell biology and toxicology 2010-08, Vol.26 (4), p.319-330
• Main Authors: Yang, Dongqin, Yaguchi, Takahiro, Nakano, Takashi, Nishizaki, Tomoyuki
• Format: Article
• Language: English
• ISSN: 0742-2091; 1573-6822
• DOI: 10.1007/s10565-009-9145-7

Extracellular adenosine disrupted mitochondrial membrane potentials in HuH-7 cells, a Fas-deficient human hepatoma cell line, and the effect was inhibited by the adenosine transporter inhibitor dipyridamole or by overexpressing Bcl-X sub(L). Adenosine downregulated the expression of mRNAs and proteins for Bcl-X sub(L) and inhibitor of apoptosis protein 2 (IAP2) to directly inhibit caspase-3, -7, and -9, but it otherwise upregulated the expression of mRNA and protein for DIABLO, an inhibitor of IAPs. Those adenosine effects were attenuated by dipyridamole. Caspase-3 and -8 were implicated in adenosine-induced HuH-7 cell death, and adenosine actually activated caspase-3 without caspase-9 activation. The caspase-3 activation was inhibited by overexpressing Bcl-X sub(L) or IAP2. Taken together, the results of the present study indicate that intracellularly transported adenosine activates caspase-3 by neutralizing caspase-3 inhibition due to IAP as a result of decreased IAP2 expression and reduced IAP activity in response to increased DIABLO expression and perhaps DIABLO release from damaged mitochondria, in addition to caspase-8 activation. This represents further insight into adenosine-induced HuH-7 cell apoptotic pathway.