PKB/AKT: functional insights from genetic models

Scheid, Michael P.; Woodgett, James R.

doi:10.1038/35096067

Cited by 568 publications

(448 citation statements)

References 91 publications

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“…Furthermore, exendin-4 treatment was also able to reduce the effects of cytokines on apoptosis in cells infected with constitutively-active PKB, although the protective effects of exendin-4 were not observed in all Adv-CA cells, possibly due to the extremely high levels of activated PKB already present. Nonetheless, in agreement with the finding of an important role for PKB in GLP-1 signalling, it has been shown that inhibition of PI3-K, the upstream regulator of PKB activity [23], decreases the IGF-1-mediated protection of beta cells against cytokines [41,42]. IGF-1 is a known regulator of PI3-K/PKB, whereas the mechanisms that link the G protein-coupled GLP-1 receptor to cell survival pathways are not well understood.…”

Section: Discussionsupporting

confidence: 83%

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Glucagon-like peptide-1 protects beta cells from cytokine-induced apoptosis and necrosis: role of protein kinase B

et al. 2005

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Aims/hypothesis: The gut hormone glucagonlike peptide-1 (GLP-1) decreases beta cell apoptosis in a protein kinase B (PKB)-dependent fashion, and increases islet cell mass and function in vivo. In contrast, cytokines induce beta cell apoptosis, leading to decreased islet mass and type 1 diabetes. In the present study we used rat INS-1E beta cells and primary rat islet cells to examine the potential role of PKB as a mediator of the effect of GLP-1 on cytokine-induced apoptosis. Methods: Cell viability was determined by MTTassay, and apoptosis and necrosis by Hoechst 33342-propidium iodide staining. Immunoblot analysis was used to detect changes in protein expression, including active (phosphorylated) and total PKB, phosphorylated and total glycogen synthase kinase-3β, activated caspase-3 and inducible nitric oxide synthase. Reactive oxygen species were determined by 1,7-dichlorofluorescein (DCF) analysis, and mutant forms of PKB were introduced into cells using adenoviral vectors. Results: Incubation of INS-1E cells with cytokines (IL-1β, TNF-α and interferon-γ; 10-50 ng/ml) for 18 h significantly decreased cell viability (by 44%, p<0.001), cell proliferation (by 80%, p<0.001), and activation of PKB (by 67%, p<0.001). Pre-treatment with exendin-4 (10 −7 mol/l), a long-acting GLP-1 receptor agonist, partially protected the cells against cytokine-induced toxicity (p<0.01) in association with a reduction in cytokine-induced inhibition of PKB phosphorylation (p<0.05). Exendin-4 pre-treatment did not change cell proliferation. Cytokine treatment increased apoptosis (by 156%, p<0.05) and necrosis (from undetectable to 2.6% of cells). These increases were both reduced by pre-treatment with exendin-4 (p<0.05-0.01). Furthermore, cytokine-induced apoptosis and necrosis were significantly increased in cells infected with kinase-dead PKB (p<0.05), and the protective effect of exendin-4 on both parameters was fully abolished in these cells. Similar changes were observed in primary islet cells. In parallel with these changes, exendin-4 decreased the cytokine-induced activation of caspase-3 (by 46%, p<0.05), and decreased levels of inducible nitric oxide synthase (by 71%, p<0.05) and reactive oxygen species (by 27%, p< 0.05). Conclusions/interpretation: The results of our study indicate that GLP-1 plays a protective role against cytokineinduced apoptosis and necrosis in beta cells through a PKB-dependent signalling pathway.

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Section: Discussionsupporting

confidence: 83%

“…In mammals, three closely related isoforms of PKB are encoded by distinct genetic loci: PKBα/Akt1, PKBβ/Akt2 and PKBγ/Akt3 [23]. The pancreatic beta cell contains high levels of PKBα [24], and the targeted overexpression of PKBα in vivo enhances beta cell mass and function through effects on cell number and cell size [25,26].…”

Section: Introductionmentioning

confidence: 99%

Glucagon-like peptide-1 protects beta cells from cytokine-induced apoptosis and necrosis: role of protein kinase B

et al. 2005

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“…These results once again lend support to the growing appreciation that apoptosis and inflammation are not mutually exclusive but may be linked. In addition, the Akt phosphorylated on serine 473, which is the first step toward its membrane association and full activation [48,49], was significantly increased by fB deficiency, which may have contributed to the reduction in apoptosis observed in these studies. Furthermore, MRL/lpr mice had significantly greater quantities of p-PTEN (serine 380) than fB -/-MRL/lpr mice.…”

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confidence: 74%

Absence of functional alternative complement pathway alleviates lupus cerebritis

et al. 2007

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The complement inhibitor, Crry, which blocks both the classical and alternative pathways, alleviates CNS disease in the lupus model, MRL/MpJ-Tnfrsf6lpr (MRL/lpr) mice. To understand the role of the alternative pathway, we studied mice deficient in a key alternative pathway protein, complement factor B (fB). Immune deposits (IgG and C3) were reduced in the brains of MRL/lpr fB-deficient (fB -/-MRL/lpr) compared to fBsufficient (MRL/lpr) mice, indicating reduced complement activation. Reduced neutrophil infiltration (22% of MRL/lpr mice) and apoptosis (caspase-3 activity was reduced to 33% of MRL/lpr mice) in these mice indicates that the absence of the alternative pathway was neuroprotective. Furthermore, expression of phospho (p)-Akt (0.16 AE 0.02 vs. 0.35 AE 0.13, p <0.03) was increased, while expression of p-PTEN (0.40 AE 0.06 vs. 0.11 AE 0.07, p <0.05) was decreased in fB -/-MRL/lpr mice compared to their MRL/lpr counterparts. The expression of fibronectin, laminin and collagen IV was significantly decreased in fB -/-MRL/lpr mice compared to MRL/lpr mice, indicating that in the lupus setting, tissue integrity was maintained in the absence of the alternative pathway. Absence of fB reduced behavioral alterations in MRL/lpr mice. Our results suggest that in lupus, the alternative pathway may be the key mechanism through which complement activation occurs in brain, and therefore it might serve as a therapeutic target for lupus cerebritis. IntroductionSystemic lupus erythematosus (SLE) is an autoimmune disease, with central nervous system (CNS) involvement occurring in 20-70% of patients. Complement activation is believed to play a key role in the pathogenesis of SLE [1]. The relevance of complement in lupus cerebritis is supported by enhanced C3 and C4 index values in the cerebrospinal fluid of patients [2] and increased levels of the anaphylatoxins, C3a and C5a, which correlate with the CNS flares [3]. This is also true in experimental lupus cerebritis, and is supported by our recent studies, in which systemic inhibition of the C3/C5 convertases reduced pathological alterations in the CNS of the lupus mouse model, MRL/MpJ-Tnfrsf6lpr (MRL/lpr) mice [4,5]. Complement can be activated through classical, alternative and lectin pathways. Complement factor B (fB) is a key protein required for the activation of the alternative pathway [6] and is increased in circulation and in tissues of lupus mice [7][8][9]. In addition, fB solubilizes immune complexes, inhibits proliferation, acts as a B cell growth factor and activates monocytes 15]. Mice with targeted deletion of the fB gene (fB -/-) were protected from lupus nephritis and ischemiareperfusion injury [7,16]. However, the role of fB in the pathogenesis of lupus cerebritis has not been defined. Bb, one of the split products of fB, can induce apoptosis [17], which is a key feature in the brains of MRL/lpr mice [5,18]. Apoptosis can also be induced by several other factors such as nitric oxide (NO), edema, and the extracellular matrix (ECM) proteins through integrin si...

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“…PKB is a serine-threonine kinase that is activated by phosphatidylinositol-3-kinase (PI3-K) in response to insulin, as well as to various growth factors [21,22,23]. The three different isoforms of PKB (α, β and γ) are widely expressed in mammalian cells, including the pancreatic beta cells, which contain high levels of PKBα [24,25].…”

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confidence: 99%

“…The three different isoforms of PKB (α, β and γ) are widely expressed in mammalian cells, including the pancreatic beta cells, which contain high levels of PKBα [24,25]. Although it is well established that PKB mediates some of the metabolic actions of insulin in peripheral tissues [22,26], activation of PKB also results in the phosphorylation of various downstream protein targets that affect proliferation, cell cycle entry and intracellular apoptotic pathways [21,22,23]. These pleiotropic actions of PKB result in increased cell numbers as well as enhanced cell survival.…”

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confidence: 99%

Glucagon-like peptide-1 regulates proliferation and apoptosis via activation of protein kinase B in pancreatic INS-1 beta cells

et al. 2004

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Aims/hypothesis. The incretin hormone glucagon-like peptide-1 augments islet cell mass in vivo by increasing proliferation and decreasing apoptosis of the beta cells. However, the signalling pathways that mediate these effects are mostly unknown. Using a clonal rat pancreatic beta cell line (INS-1), we examined the role of protein kinase B in mediating beta-cell growth and survival stimulated by glucagon-like peptide-1. Methods. Immunoblot analysis was used to detect active (phospho-) and total protein kinase B. Proliferation was assessed using 3 H-thymidine incorporation, while apoptosis was quantitated using 4′-6-diamidino-2-phenylindole staining and APO percentage apoptosis assay. Kinase-dead and wild-type protein kinase B was introduced into cells using adenoviral vectors. Results. Glucagon-like peptide-1 rapidly activated protein kinase B in INS-1 cells (by 2.7±0.7-fold, p<0.05). This effect was completely abrogated by inhibition, with wortmannin, of the upstream activator of protein kinase B, phosphatidylinositol-3-kinase. Glucagon-like peptide-1 also stimulated INS-1 cell proliferation in a dose-dependent manner (by 1.8±0.5-fold at 10 −7 mol/l, p<0.01), and inhibited staurosporine-induced apoptosis (by 69±12%, p<0.05). Both of these effects were also prevented by wortmannin treatment. Ablation of protein kinase B by adenovirus-mediated overexpression of the kinase-dead form of protein kinase Bα prevented protein kinase B phosphorylation and completely abrogated both cellular proliferation (p<0.05) and protection from drug-induced cellular death (p<0.01) induced by glucagon-like peptide-1. Conclusions/interpretation. These results identify protein kinase B as an essential mediator linking the glucagon-like peptide-1 signal to the intracellular machinery that modulates beta-cell growth and survival. [Diabetologia (2004) 47:478-487]

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PKB/AKT: functional insights from genetic models

Cited by 568 publications

References 91 publications

Glucagon-like peptide-1 protects beta cells from cytokine-induced apoptosis and necrosis: role of protein kinase B

Glucagon-like peptide-1 protects beta cells from cytokine-induced apoptosis and necrosis: role of protein kinase B

Absence of functional alternative complement pathway alleviates lupus cerebritis

Glucagon-like peptide-1 regulates proliferation and apoptosis via activation of protein kinase B in pancreatic INS-1 beta cells

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