UC San Diego

This study investigates the regulation of de Novo purine nucleotide synthesis by two pentose phosphate enzymes mediated by Akt, a kinase which may be affected by amino acid availability. HeLa cells starved of lysine for three hours show up to a 66% decrease in de Novo purine synthesis rates compared to control levels. A 40% reduction in PRPP availability after lysine starvation, the product of non-oxidative PPP and precursor substrate to the first committed step in de Novo synthesis, most likely contributes to this overall reduction in purine synthesis. Akt activation, as well as lysine return for one hour, almost completely restores de Novo synthesis rates to control levels. TKT and TAL, enzymes unique to the PPP, show enzyme activity levels 57% and 49% of control levels during lysine starvation respectively, but can be restored to control levels upon Akt activation or lysine return. Cells expressing vectors of kinase-dead, dominant negative Akt fail to restore enzyme activity levels to control levels after lysine return. This strongly suggests that lysine starvation-induced reduction in Akt activity mediates TKT and TAL activity levels, thereby regulating de Novo purine nucleotide synthesis