Intervention in Genotoxic StressInduced Senescence by Cordycepin Through Activation of eIF2 and Suppression of Sp1

In this study, we show that cordycepin (3-deoxyadenosine), a major nucleoside isolated from Cordyceps species, attenuates genotoxic stressinduced senescence. Etoposide- or doxorubicin-treated cells exhibited senescent morphology, growth arrest, and positive staining for senescence-associated -galactosidase. The induction of the senescent phenotype was inhibited by the treatment of cordycepin. This suppression was correlated with blunted activation of the p16(INK4a) and p21(WAF1/CIP1) gene promoters, as well as a decreased level of p21 (WAF1/CIP1) mRNA. Other adenosine-related substances including ATP, ADP, and adenosine did not mimic the suppressive effect of cordycepin. The antisenescence effect of cordycepin was mediated by activation of eukaryotic translation initiation factor 2 (eIF2) because (1) cordycepin induced phosphorylation of eIF2, (2) selective activation of eIF2 mimicked the suppressive effect of cordycepin on senescence, and (3) functional knockdown of eIF2 reversed the effect of cordycepin. Unexpectedly, induction of p53 by etoposide was not inhibited by cordycepin, whereas (1) expression of Sp1 (required for the induction of p21(WAF1/CIP1) and activation of p16(INK4a) by genotoxic stress) was attenuated by cordycepin, (2) DNA binding activity of Sp1 was also inhibited, and (3) selective inhibition of Sp1 reproduced the suppressive effect of cordycepin on senescence. These results suggest that cordycepin interferes with senescence signaling via activation of eIF2 and suppression of Sp1 without affecting the level of p53.