Mechanism Of Apoptosis Induced By Ortho-topolin Riboside In The Human Hepatoma Cell Line SMMC-7721

The naturally occurring cytokinin,ortho-Topolin Riboside(oTR),has been recently reported to have a strong anticancer effect.However,the molecular mechanism has not been elucidated.From our research we found that oTR strongly inhibited the proliferation of SMMC-7721 cells inducing apoptosis.After oTR treatment,up-regulation of the protein levels of pro-apoptotic Bax and the down-regulation of the anti-apoptotic proteins,Bcl-2 and Bcl-xL was observed,leading to the loss of mitochondrial membrane potential,the release of cytochrome c from the mitochondria into the cytosol,the downstream activation of caspase-9 and caspase-3,as well as the cleavage of poly ADP-ribose-polymerase(PARP),the effect of apoptosis could be blocked by the pan-specific caspase inhibitor z-VAD-fmk and caspase-9-specific inhibitor z-LEHD-fmk.Moreover,oTR was shown to inhibit the activation of the extracellular signal-regulated kinase-1/2(ERK1/2)as well as the Akt pathway.These results suggest that oTR interferes with the mitogen-activated protein kinase(MAPK)and Akt pathways and induces the apoptosis of human SMMC-7721 cells through the activation of intrinsic mitochondria-mediated pathways.However,the apoptosis was completely prevented when cells were treated with A-134974,an inhibitor of adenosine kinase,it indicated that the intracellular phosphorylation of oTR is necessary for its cytotoxic effects to SMMC-7721 cells.