The insulin- and growth factor-stimulated protein kinases protein kinase B (PKB)/Akt and p70 S6 ribosomal kinase (S6K) are crucial regulators of cell growth. Recent advances, supported by work in this issue of Nature Cell Biology, have indicated that the tumour suppressor tuberous sclerosis complex-2 (TSC2) functions as an antagonist of S6K activation, an inhibition that is relieved by PKB-mediated phosphorylation of TSC2. In contrast to some previous models, these findings indicate that PKB functions upstream of S6K.
- Edward J. McManus
- Dario R. Alessi
