Modulation of Akt kinase activity by binding to Hsp90

Sato, Saori; Fujita, Naoya; Tsuruo, Takashi

doi:10.1073/pnas.170276797

Cited by 884 publications

(760 citation statements)

References 33 publications

Supporting

Mentioning

711

Contrasting

Unclassified

Order By: Relevance

“…To determine which of these two phenomena is occurring, we tried to inhibit the A-loop phosphatase in vivo. We used okadaic acid (OA) to inhibit the A-loop phosphatase as protein phosphatase 2A has been reported to be an Aloop phosphatase in mammalian cells (Andjelkovicé t al., 1996;Sato et al, 2000;Borgatti et al, 2003;Ugi et al, 2004;Kuo et al, 2008). Microinjection of OA into unstimulated oocytes induced A-loop phosphorylation in the absence of 1-MeAde (Figure 5a), as expected from the constitutive activity of PDK1 (Alessi et al, 1997a, b;Hiraoka et al, 2004).…”

Section: Tm Phosphorylation Has a Negative Role In A-loop Phosphorylasupporting

confidence: 59%

Turn motif phosphorylation negatively regulates activation loop phosphorylation in Akt

2011

View full text Add to dashboard Cite

Akt, also known as protein kinase B, has a central role in various signaling pathways that regulate cellular processes such as metabolism, proliferation and survival. On stimulation, phosphorylation of the activation loop (Aloop) and hydrophobic motif (HM) of Akt by the kinase phosphoinositide-dependent kinase 1 (PDK1) and the mammalian target of rapamycin complex 2 (mTORC2), respectively, results in Akt activation. A well-conserved threonine in the turn motif (TM) is also constitutively phosphorylated by mTORC2 and contributes to the stability of Akt. The role of TM phosphorylation in HM and A-loop phosphorylation has not been sufficiently evaluated. Using starfish oocytes as a model system, this study provides the first evidence that TM phosphorylation has a negative role in A-loop phosphorylation. In this system, the maturation-inducing hormone, 1-methyladenine, stimulates Akt to reinitiate meiosis through activation of cyclin B-Cdc2. The phosphorylation status of Akt was monitored via introduction of exogenous human Akt (hAkt) in starfish oocytes. TM and HM phosphorylation was inhibited by microinjection of an anti-starfish TOR antibody, but not by rapamycin treatment, suggesting that both phosphorylation events depend on TORC2, as reported in mammalian cells. A single or double alanine substitution at each of three phosphorylation residues revealed that TM phosphorylation renders Akt susceptible to dephosphorylation on the A-loop. When A-loop phosphatase was inhibited by okadaic acid (OA), TM phosphorylation still reduced Aloop phosphorylation, suggesting that the effect is caused at least partially through reduction of sensitivity to PDK1. Negative regulation by TM phosphorylation was also observed in constitutively active Akt and was functionally reflected in meiosis resumption. By contrast, HM phosphorylation enhanced A-loop phosphorylation and achieved full activation of Akt via a mechanism at least partially independent of TM phosphorylation. These observations provide new insight into the mechanism controlling Akt phosphorylation in the cell.

show abstract

Section: Tm Phosphorylation Has a Negative Role In A-loop Phosphorylasupporting

confidence: 59%

Turn motif phosphorylation negatively regulates activation loop phosphorylation in Akt

2011

View full text Add to dashboard Cite

show abstract

“…Other proteins also interact with Akt and upregulate its activity (Pekarsky et al, 2000;Sato et al, 2000;Jahn et al, 2002). Binding of Snail1 requires the PH domain of Akt, similarly to other reported interactors (Sato et al, 2000;Jahn et al, 2002). It is possible that this interaction stabilizes the active Akt conformer, preventing the intramolecular association between the PH and the kinase domains (Calleja et al, 2007).…”

Section: Akt2 Interacts With Snail1mentioning

confidence: 67%

Akt2 interacts with Snail1 in the E-cadherin promoter

et al. 2011

View full text Add to dashboard Cite

Snail1 is a transcriptional factor essential for triggering epithelial-to-mesenchymal transition. Moreover, Snail1 promotes resistance to apoptosis, an effect associated to PTEN gene repression and Akt stimulation. In this article we demonstrate that Snail1 activates Akt at an additional level, as it directly binds to and activates this protein kinase. The interaction is observed in the nucleus and increases the intrinsic Akt activity. We determined that Akt2 is the isoform interacting with Snail1, an association that requires the pleckstrin homology domain in Akt2 and the C-terminal half in Snail1. Snail1 enhances the binding of Akt2 to the E-cadherin (CDH1) promoter and Akt2 interference prevents Snail1 repression of CDH1 gene. We also show that Snail1 binding increases Akt2 intrinsic activity on histone H3 and have identified Thr45 as a residue modified on this protein. Phosphorylation of Thr45 in histone H3 is sensitive to Snail1 and Akt2 cellular levels; moreover, Snail1 upregulates the binding of phosphoThr45 histone H3 to the CDH1 promoter. These results uncover an unexpected role of Akt2 in transcriptional control and point out to phosphorylation of Thr45 in histone H3 as a new epigenetic mark related to Snail1 and Akt2 action.

show abstract

“…Interestingly, the level of HSP90 protein was recently reported to be increased in muscle of patients with type 2 diabetes [35]. Such an increase in HSP90 might antagonise the down-regulation of functional insulin receptors mediated by hyperinsulinaemia, and, as suggested by recent studies, preserve insulin signalling through Akt [36,37]. Thus, increased levels of HSP90 in Arg1174Gln carriers could contribute to an increase in the relative amount of fully functional (wt/wt) insulin receptors, and hence the preservation of insulin action.…”

Section: Discussionmentioning

confidence: 90%

Partial rescue of in vivo insulin signalling in skeletal muscle by impaired insulin clearance in heterozygous carriers of a mutation in the insulin receptor gene

et al. 2006

View full text Add to dashboard Cite

Aims/hypothesis Recently we reported the coexistence of postprandial hypoglycaemia and moderate insulin resistance in heterozygous carriers of the Arg1174Gln mutation in the insulin receptor gene (INSR). Controlled studies of in vivo insulin signalling in humans with mutant INSR are unavailable, and therefore the cellular mechanisms underlying insulin resistance in Arg1174Gln carriers remain to be clarified. Subjects, materials and methods We studied glucose metabolism and insulin signalling in skeletal muscle from six Arg1174Gln carriers and matched control subjects during a euglycaemic-hyperinsulinaemic clamp.Results Impaired clearance of exogenous insulin caused four-fold higher clamp insulin levels in Arg1174Gln carriers compared with control subjects (p<0.05). In Arg1174Gln carriers insulin increased glucose disposal and non-oxidative glucose metabolism (p<0.05), but to a lower extent than in controls (p<0.05). Insulin increased Akt phosphorylation at Ser473 and Thr308, inhibited glycogen synthase kinase-3α activity, reduced phosphorylation of glycogen synthase at sites 3a+3b, and increased glycogen synthase activity in Arg1174Gln carriers (all p<0.05). In the insulin-stimulated state, Akt phosphorylation at Thr308 and glycogen synthase activity were reduced in Arg1174Gln carriers compared with controls (p<0.05), whereas glycogen synthase kinase-3α activity and phosphorylation of glycogen synthase at sites 3a+3b were similar in the two groups. Conclusions/interpretation In vivo insulin signalling in skeletal muscle of patients harbouring the Arg1174Gln mutation is surprisingly intact, with modest impairments in insulin-stimulated activity of Akt and glycogen synthase explaining the moderate degree of insulin resistance. Our data suggest that impaired insulin clearance in part rescues in vivo insulin signalling in muscle in these carriers of a mutant INSR, probably by increasing insulin action on the non-mutated insulin receptors.

show abstract

Modulation of Akt kinase activity by binding to Hsp90

Cited by 884 publications

References 33 publications

Turn motif phosphorylation negatively regulates activation loop phosphorylation in Akt

Turn motif phosphorylation negatively regulates activation loop phosphorylation in Akt

Akt2 interacts with Snail1 in the E-cadherin promoter

Partial rescue of in vivo insulin signalling in skeletal muscle by impaired insulin clearance in heterozygous carriers of a mutation in the insulin receptor gene

Contact Info

Product

Resources

About