Sirt2 deacetylase is a novel AKT binding partner critical for AKT activation by insulin.
AKT/PKB kinases transmit insulin and growth factor signals downstream of phosphatidylinositol 3-kinase (PI3K). AKT activation involves phosphorylation at two residues, Thr(308) and Ser(473), mediated by PDK1 and the mammalian target of rapamycin complex 2 (mTORC2), respectively. Impaired AKT activation is a key factor in metabolic disorders involving insulin resistance, whereas hyperactivation of AKT is linked to cancer pathogenesis. Here, we identify the cytoplasmic NAD(+)-dependent deacetylase, Sirt2, as a novel AKT interactor, required for optimal AKT activation. Pharmacological inhibition or genetic down-regulation of Sirt2 diminished AKT activation in insulin and growth factor-responsive cells, whereas Sirt2 overexpression enhanced the activation of AKT and its downstream targets. AKT was prebound with Sirt2 in serum or glucose-deprived cells, and the complex dissociated following insulin treatment. The binding was mediated by the pleckstrin homology and the kinase domains of AKT and was dependent on AMP-activated kinase. This regulation involved a novel AMP-activated kinase-dependent Sirt2 phosphorylation at Thr(101). In cells with constitutive PI3K activation, we found that AKT also associated with a nuclear sirtuin, Sirt1; however, inhibition of PI3K resulted in dissociation from Sirt1 and increased association with Sirt2. Sirt1 and Sirt2 inhibitors additively inhibited the constitutive AKT activity in these cells. Our results suggest potential usefulness of Sirt1 and Sirt2 inhibitors in the treatment of cancer cells with up-regulated PI3K activity and of Sirt2 activators in the treatment of insulin-resistant metabolic disorders.
From the Cancer Institute and Department of Biochemistry, University of Mississippi Medical Center, Jackson, Mississippi 39216.
Gopalakrishnan
G
Ramakrishnan
Gantulga
G
Davaakhuu
Ludmila
L
Kaplun
Wen-Cheng
WC
Chung
Ajay
A
Rana
Azeddine
A
Atfi
Lucio
L
Miele
Guri
G
Tzivion
D041721:3T3-L1 Cells; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004789:Enzyme Activation / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D041681:NIH 3T3 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000502:physiology; D011485:Protein Binding; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D056564:Sirtuin 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D056565:Sirtuin 2 / Q000235:genetics / Q000378:metabolism*
D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D056564:Sirtuin 1; D056565:Sirtuin 2; C447939:SIRT1 protein, human; C474199:SIRT2 protein, human; C470545:Sirt1 protein, mouse; C418743:Sirt2 protein, mouse
AMP-activated Kinase (AMPK); Akt; Insulin; Phosphorylation; Sirtuins