Nature Cell Biology4, 658 - 665 (2002)
Published online: 12 August 2002; | doi:10.1038/ncb840
Akt regulates growth by directly phosphorylating Tsc2
Christopher J. Potter, Laura G. Pedraza
& Tian Xu
Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, Boyer Center for Molecular Medicine, 295 Congress Avenue, New Haven, CT 06536-0812, USA
The direct mechanism by which the serine/threonine kinase Akt (also known as protein kinase B (PKB)) regulates cell growth is unknown. Here, we report that Drosophila melanogaster Akt/PKB stimulates growth by phosphorylating the tuberous sclerosis complex 2 (Tsc2) tumour suppressor and inhibiting formation of a Tsc1−Tsc2 complex. We show that Akt/PKB directly phosphorylates Drosophila Tsc2 in vitro at the conserved residues, Ser 924 and Thr 1518. Mutation of these sites renders Tsc2 insensitive to Akt/PKB signalling, increasing the stability of the Tsc1−Tsc2 complex within the cell. Stimulating Akt/PKB signalling in vivo markedly increases cell growth/size, disrupts the Tsc1−Tsc2 complex and disturbs the distinct subcellular localization of Tsc1 and Tsc2. Furthermore, all Akt/PKB growth signals are blocked by expression of a Tsc2 mutant lacking Akt phosphorylation sites. Thus, Tsc2 seems to be the critical target of Akt in mediating growth signals for the insulin signalling pathway.
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