FIGURE 7.

Cordycepin activates AMPK. A, adenosine blocks cordycepin-mediated repression of protein synthesis. NIH3T3 cells were treated with cordycepin and/or adenosine for 2 h, and protein synthesis rates were measured by ³⁵S incorporation, corrected for total protein concentration. B, import and phosphorylation of cordycepin are required for inhibition of protein synthesis. Cells were treated with nitrobenzylthioinosine (NBTI, 10 μm) or iodotubericidin (ITu, 0.1 μm) for 15 min before treatment with cordycepin (200 μm) for 1 h. Protein synthesis rates were determined as before. C, cordycepin induces AMPK activation. Western blots are shown for AMPK β1 and its autophosphorylation site (Ser¹⁰⁸), acetyl-CoA carboxylase and its AMPK phosphorylation site (Ser⁷⁹) as well as for the proteins listed in the legend to Fig. 5. Treatment with cordycepin was for the indicated times and dose. D, protein synthesis in cells pretreated with Compound C or DMSO for 15 min prior to the addition of 200 μm cordycepin and incubation for 1 h. E, cells were treated as in D, and Western blotting was performed for the proteins indicated as described above.