Serine Phosphorylation by mTORC1 Promotes IRS-1 Degradation through SCFβ-TRCP E3 Ubiquitin Ligase

Yoneyama, Yoshimasa; Inamitsu, Tomomi; Chida, Kazuhiro; Iemura, Shun‐ichiro; Natsume, Tohru; Maeda, Tatsuya; Hakuno, Fumihiko; Takahashi, Shinichiro

doi:10.1016/j.isci.2018.06.006

Cited by 69 publications

(63 citation statements)

References 55 publications

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“…In recent years, it has also been suggested Handling Editor: E. Closs. that mTORc1 is able to phosphorylate upstream targets of the insulin signalling pathway in muscle, leading to inhibition of the pathway, and in turn impaired translocation of the GLUT4 glucose transporter to the plasma membrane (Yoneyama et al 2018). Thus, it has been proposed that a potential mechanism by which obesity-induced increases in blood BCAA concentrations could lead to the development of insulin resistance is through the chronic activation of mTORc1 suppressing insulin signalling in skeletal muscle.…”

Section: Introductionmentioning

confidence: 99%

Leucine and mTORc1 act independently to regulate 2-deoxyglucose uptake in L6 myotubes

et al. 2020

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Chronic mTORc1 hyperactivation via obesity-induced hyperleucinaemia has been implicated in the development of insulin resistance, yet the direct impact of leucine on insulin-stimulated glucose uptake in muscle cells remains unclear. To address this, differentiated L6 myotubes were subjected to various compounds designed to either inhibit mTORc1 activity (rapamycin), blunt leucine intracellular import (BCH), or activate mTORc1 signalling (3BDO), prior to the determination of the uptake of the glucose analogue, 2-deoxyglucose (2-DG), in response to 1 mM insulin. In separate experiments, L6 myotubes were subject to various media concentrations of leucine (0-0.8 mM) for 24 h before 2-DG uptake in response to insulin was assessed. Both rapamycin and BCH blunted 2-DG uptake, irrespective of insulin administration, and this occurred in parallel with a decline in mTOR, 4E-BP1, and p70S6K phosphorylation status, but little effect on AKT phosphorylation. In contrast, reducing leucine media concentrations suppressed 2-DG uptake, both under insulin-and non-insulin-stimulated conditions, but did not alter the phosphorylation state of AKT-mTORc1 components examined. Unexpectedly, 3BDO failed to stimulate mTORc1 signalling, but, nonetheless, caused a significant increase in 2-DG uptake under non-insulin-stimulated conditions. Both leucine and mTORc1 influence glucose uptake in muscle cells independent of insulin administration, and this likely occurs via distinct but overlapping mechanisms.

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Section: Introductionmentioning

confidence: 99%

Leucine and mTORc1 act independently to regulate 2-deoxyglucose uptake in L6 myotubes

et al. 2020

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“…In this paper, we present the precise mechanism of IGF-I-induced IRS-1 protein degradation. The downstream kinase mTORC1 phosphorylates the serine residue of IRS-1 at amino acid 422; this phosphorylation recruits ubiquitin ligase, resulting in IRS-1 degradation (19). Given our data, we envisage a possible scenario: since the IRS-1 protein level is dynamically changed in response to IGF stimulation and varies in each cell, cells with higher IRS-1 levels are eliminated under physiological conditions.…”

Section: Discussionmentioning

confidence: 84%

“…Because protein degradation of IRS-1 is induced by the activation of the downstream IGF signal kinase mTORC1 (16)(17)(18)(19), it is possible that the level of GFP-fused IRS-1 also degraded and the GFP signal diminished in response to IGF signal activation. To exclude this possibility, we generated stable cell lines expressing both mycIRS-1 and GFP independently (L6-mycIRS-1-GFP).…”

Section: Cells Overexpressing Irs-1 Were Selectively Excluded When Thmentioning

confidence: 99%

Myoblasts With Higher IRS-1 Levels Are Eliminated From the Normal Cell Layer During Differentiation

et al. 2020

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Insulin receptor substrate (IRS)-1 is a major substrate of insulin-like growth factor (IGF)-I receptors. It is well-known that IGF-I and II play essential roles in myogenesis progression. Herein, we report an unexpected phenomenon that IRS-1-overexpressing L6 myoblasts are eliminated from normal cell layers at the beginning of differentiation. Initially, the IRS protein level and apoptosis were examined during myogenic differentiation in L6 myoblasts. We found that the IRS-1 protein level decreased, whereas active caspase 3 increased around 1 day after induction of differentiation. The addition of a pan-caspase inhibitor, Z-VAD-FMK, inhibited differentiation-induced suppression of the IRS-1 protein level. Apoptosis was not enhanced in L6 myoblasts stably expressing high levels of IRS-1 (L6-IRS-1). However, when L6-IRS-1 was cultured with control cells (L6-mock), we observed that L6-IRS-1 was eliminated from the cell layer. We have recently reported that, in L6-IRS-1, internalization of the IGF-I receptor was delayed and IGF signal activation was sustained for a longer period than in L6-mock. When cells stably expressing IRS-1 3YA mutant, which could not maintain the IGF signals, were cultured with normal cells, elimination from the cell layer was not detected. These data suggested that the high level of IRS-1 in myoblasts induces elimination from the cell layer due to abnormal sustainment of IGF-I receptor activation.

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“…Insulin and insulin-like growth factors (IGFs), IGF-I and IGF-II, are mainly involved in muscle hypertrophy and play pivotal roles in growth, differentiation, survival, and various aspects of metabolism in a wide range of mammalian tissues [ 4 , 23 – 25 ]. Modulation of IGF-1 signaling is required for the downregulation of IRS-1 phosphorylation, and the P3K/AKT/mTOR signaling pathway activates IRS-1 degradation [ 33 ]. Activated AKT, in turn, phosphorylates and activates a second kinase, mTOR [ 4 , 16 , 33 , 34 ].…”

Section: Discussionmentioning

confidence: 99%

“…Modulation of IGF-1 signaling is required for the downregulation of IRS-1 phosphorylation, and the P3K/AKT/mTOR signaling pathway activates IRS-1 degradation [ 33 ]. Activated AKT, in turn, phosphorylates and activates a second kinase, mTOR [ 4 , 16 , 33 , 34 ]. In disagreement with previous reports [ 13 ], our data showed that ALA induced IRS-1 phosphorylation and subsequent stimulation of the PI3K/AKT pathway, resulting in activation of the p70S6 pathway in skeletal muscle of OLETF rats.…”

Section: Discussionmentioning

confidence: 99%

Alpha-lipoic acid preserves skeletal muscle mass in type 2 diabetic OLETF rats

et al. 2018

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BackgroundIncreased oxidative stress and impaired antioxidant defense are important mechanisms in the pathogenesis of diabetic myopathy. Alpha-lipoic acid (ALA) has been indicated as a weight-loss treatment in rodents and humans, but studies are limited. In the present study, we aimed to determine the influence of ALA, a potent biological antioxidant, on metabolic and growth processes in diabetic rat skeletal muscle.MethodsMale 25-week-old type 2 diabetic rats (OLETF) were randomly divided into two groups, a control group (OLETF-C) and an ALA-treated group (OLETF-ALA) supplemented with 100 mg/kg ALA for 8 weeks. Age-matched, healthy, nondiabetic LETO (LETO-C) rats were used as controls.ResultsAt 32 weeks of age, body weight was decreased by 6.8%, and the areas under the curve of IP-GTT, fasting glucose, and insulin were less in OLETF-ALA rats compared with OLETF-C rats. ALA significantly preserved muscle mass and enhanced muscle fiber cross-sectional area and fiber frequency percentage in the skeletal muscle of OLETF rats. Although the activation of myoD, myogenin, and myostatin in gastrocnemius muscle was significantly inhibited in OLETF-ALA rats relative to OLETF-C rats, there were no differences in the expression levels of muscle atrogin-1 and MuRF1 between the two groups. ALA treatment significantly increased the levels of phosphorylated 5′-AMPK, SIRT1, and PGC-1α, as well as the levels of phosphorylated AKT, mTOR, and p70S6 kinase in OLETF-ALA rats compared with OLETF-C rats. In contrast, the levels of phosphorylated p38 MAPK, IRS-1, and FOXO1 were decreased in OLETF-ALA rats compared with OLETF-C rats.ConclusionsALA treatment preserved mass in the gastrocnemius muscles of OLETF rats. ALA significantly upregulated the AMPK/SIRT1/PGC-1α and AKT/mTOR/p70S6K signaling pathways in OLETF rat skeletal muscle. Therefore, ALA may be a potential therapeutic intervention for skeletal muscle loss in animal models of insulin resistance.

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Serine Phosphorylation by mTORC1 Promotes IRS-1 Degradation through SCFβ-TRCP E3 Ubiquitin Ligase

Cited by 69 publications

References 55 publications

Leucine and mTORc1 act independently to regulate 2-deoxyglucose uptake in L6 myotubes

Leucine and mTORc1 act independently to regulate 2-deoxyglucose uptake in L6 myotubes

Myoblasts With Higher IRS-1 Levels Are Eliminated From the Normal Cell Layer During Differentiation

Alpha-lipoic acid preserves skeletal muscle mass in type 2 diabetic OLETF rats

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