Phosphorylation and Regulation of Akt/PKB by the Rictor-mTOR Complex

Abstract

Deregulation of Akt/protein kinase B (PKB) is implicated in the pathogenesis of cancer and diabetes. Akt/PKB activation requires the phosphorylation of Thr308 in the activation loop by the phosphoinositide-dependent kinase 1 (PDK1) and Ser473 within the carboxyl-terminal hydrophobic motif by an unknown kinase. We show that in Drosophila and human cells the target of rapamycin (TOR) kinase and its associated protein rictor are necessary for Ser473 phosphorylation and that a reduction in rictor or mammalian TOR (mTOR) expression inhibited an Akt/PKB effector. The rictor-mTOR complex directly phosphorylated Akt/PKB on Ser473 in vitro and facilitated Thr308 phosphorylation by PDK1. Rictor-mTOR may serve as a drug target in tumors that have lost the expression of PTEN, a tumor suppressor that opposes Akt/PKB activation.

Association of Factor V Secretion with Protein Kinase B Signaling in Platelets from Horses with Atypical Equine Thrombasthenia

“…Mammalian target of rapamycin (mTOR) phosphorylates AKT on S473, and was present at comparable levels in platelets from normal and affected horses at these time points. This also was observed for rictor, a component of mTOR complex 2 (mTORC2) which provides substrate specificity for AKT 14. Protein kinase Cα (PKCα), which is phosphorylated by mTORC2 at serine 657,15, 16 was present and phosphorylated identically in resting platelets from all horses and throughout the time course after activation with α‐thrombin (Fig 4B).…”

“…Normal levels of the mTORC2 components rictor and mTOR, as well as normal phosphorylation of the mTORC2 target serine 657 of PKCα after activation, provide evidence that this complex functions normally in AET platelets 15, 16. Although recent studies have shown that pharmacological inhibition of mTORC2 does not inhibit aggregation of washed platelets, the role of this complex in fibrinogen binding and α‐granule secretion remains undefined 14, 24. Glycogen synthase kinase (GSK‐3β) phosphorylation also occurs normally after the pharmacological inhibition of mTORC2.…”

Mitochondrial unfolded protein response gene Clpp is required to maintain ovarian follicular reserve during aging, for oocyte competence, and development of pre‐implantation embryos

“…Ovaries ( n  = 3 for each genotype) were collected from 3‐ and 6‐month‐old Clpp +/+ and Clpp −/− mice and western analysis was performed to assess the expression of p‐S6 and p‐AKT473 proteins, as downstream mediators of mTORC1 and mTORC2 activation (Sarbassov, Guertin, Ali & Sabatini, 2005). There was no significant difference in p‐S6 or p‐AKT473 expression at 3 months between Clpp −/− and Clpp +/+ mice ovaries (Figure 6a–b), while both p‐S6 (1 ± 0.30 vs. 3.29 ± 0.56, p  <   0.01) and p‐AKT473 (1 ± 0.40 vs. 2.452 ± 0.57 p  <   0.05) protein expressions were significantly increased in Clpp −/− mice ovaries at 6 months (Figure 6c–d).…”

SopB activates the Akt-YAP pathway to promote Salmonella survival within B cells

“…Both inhibitors blocked the phosphorylation of YAP in B cells infected with Salmonella WT (Figure 1(c,d). To strengthen the role of Akt in YAP phosphorylation during Salmonella infection of B cells, we generated a conditional knockout mouse for the Rictor gene, which is part of the mTORC2 complex responsible for phosphorylating Akt at serine 473 [38]. (Figure S3).…”