Role for RalA downstream of Rac1 in skeletal muscle insulin signalling

Takenaka, Nobuyuki; Sumi, Yukio; Matsuda, Keiko; Fujita, Junko; Hosooka, Tetsuya; Noguchi, Tetsuya; Aiba, Atsu; Satoh, Takaya

doi:10.1042/bj20150218

Cited by 22 publications

(40 citation statements)

References 36 publications

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“…Another downstream target of Rac1, RalA was recently discovered to act on glucose transport. Overexpression of a constitutively activated Rac1 mutant was found to activate RalA (38) and importantly, expression of a dominant-negative mutant of RalA significantly reduced GLUT4 translocation in response to insulin, and this effect persisted in muscle expressing a constitutively activated mutant of Rac1 (39). Those findings suggest that RalA may mediate the effects on GLUT4 downstream of Rac1.…”

Section: Discussionmentioning

confidence: 78%

Insulin-stimulated glucose uptake partly relies on p21-activated kinase (PAK)-2, but not PAK1, in mouse skeletal muscle

Møller

Jaurji

Kjøbsted

et al. 2019

Preprint

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Non-standard abbreviations24 2DG: 2-Deoxyglucose 25 AUC: Area under the curve 26 BCA: Bicinchoninic acid 27 BW: Body weight 28 dKO: Double knockout 29 EDL: Extensor digitorum longus 30 FM: Fat mass 31 GLUT4: Glucose transporter 4 32 GTT: Glucose tolerance test 33 HFD: High-fat diet 34 HOMA-IR: Homeostatic Model Assessment of Insulin Resistance 35 ITT: Insulin tolerance test 36 i.p.: Intraperitoneal 37 KO: Knockout 38 L6-GLUT4myc: Rat L6 skeletal muscle cells overexpressing myc-tagged GLUT4 39 LBM: Lean body mass 40 mKO: Muscle-specific knockout 41 NOX: NADPH oxidase 42 PAK: p21-activated kinase 43 PI3K: Phosphoinositide 3-kinase 44 RER: Respiratory exchange ratio 45 r.o.: Retro-orbital 46 VO 2 : Oxygen uptake 47 48Glucose transport into skeletal muscle is essential for maintaining whole-body glucose homeostasis 49 and accounts for the majority of glucose disposal in response to insulin. The group I p21-activated 50 kinase (PAK) isoforms PAK1 and PAK2 are in skeletal muscle activated in response to insulin and 51 evidence suggests that PAK1 is necessary for insulin-stimulated GLUT4 translocation. In 52 accordance, insulin-induced PAK1 and PAK2 signalling are impaired in insulin-resistant skeletal 53 muscle. However, the role of PAK1 and PAK2 in insulin-stimulated glucose uptake in mature 54 skeletal muscle has not been determined. The aim of the present investigation was to determine the 55 requirement for PAK1 and PAK2 in whole-body glucose homeostasis and insulin-stimulated 56 glucose uptake in skeletal muscle. Therefore, glucose uptake was measured in isolated skeletal 57 muscle incubated with a pharmacological inhibitor (IPA-3) of group I PAKs and in muscle from 58 whole-body PAK1 knockout (KO), muscle-specific PAK2 (m)KO and double whole-body PAK1 59 and muscle-specific PAK2 knockout mice. Whole-body respiratory exchange ratio, indicative of 60 substrate utilization, was largely unaffected by lack of PAK1 and/or PAK2. Whole-body glucose 61 tolerance was mildly impaired in PAK2 mKO, but not PAK1 KO mice. In contrast to a previous 62 study of GLUT4 translocation in PAK1 KO mice, PAK1 KO muscles displayed normal insulin-63 stimulated glucose uptake in vivo and in isolated muscle. On the contrary, glucose uptake was 64 slightly reduced in response to insulin in glycolytic extensor digitorum longus muscle lacking 65 PAK2. In conclusion, the current study demonstrates that group I PAKs are largely dispensable for 66 the regulation of whole-body glucose homeostasis and skeletal muscle glucose uptake. Thus, the 67 present study challenges that group I PAKs, and especially PAK1, are necessary regulators of 68 insulin-stimulated glucose uptake in skeletal muscle. 69 109Although such studies implicate group I PAKs, and in particular PAK1, in the regulation of glucose 110 homeostasis and GLUT4 translocation in skeletal muscle, the relative role of PAK1 and PAK2 in 111 insulin-stimulated glucose uptake remains to be identified in mature skeletal muscle. Therefore, we 112 performed a systematic series of pharmacologic a...

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Section: Discussionmentioning

confidence: 78%

Insulin-stimulated glucose uptake partly relies on p21-activated kinase (PAK)-2, but not PAK1, in mouse skeletal muscle

Møller

Jaurji

Kjøbsted

et al. 2019

Preprint

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“…Recently, considerable progress has been made in our laboratory in obtaining in vivo data for insulin signaling in mouse skeletal muscle. First, siRNA-mediated efficient knockdown of signaling molecules such as RalA in mouse skeletal muscle has been achieved [ 29 ]. Second, a novel technique to visualize the activation of small GTPases, such as Rac1 and RalA, in situ in skeletal muscle fibers has been developed [ 25 , 28 , 29 ].…”

Section: Discussionmentioning

confidence: 99%

“…We have not yet examined the effect of depletion of FLJ00068 on Rac1 activation and GLUT4 translocation in mouse skeletal muscle because FLJ00068 gene knockout mice are currently not available in our laboratory. However, our recent progress in siRNA-mediated knockdown and in situ detection of the activation of small GTPases in mouse skeletal muscle [ 25 , 29 ] enabled us to test the involvement of FLJ00068 in Akt2-dependent activation of Rac1. In this study, we aim to provide in vivo evidence for the role of the GEF FLJ00068 in Akt2-dependent activation of Rac1 in mouse skeletal muscle.…”

Section: Introductionmentioning

confidence: 99%

Rac1 Activation Caused by Membrane Translocation of a Guanine Nucleotide Exchange Factor in Akt2-Mediated Insulin Signaling in Mouse Skeletal Muscle

2016

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Insulin-stimulated glucose uptake in skeletal muscle is mediated by the glucose transporter GLUT4, which is translocated to the plasma membrane following insulin stimulation. Several lines of evidence suggested that the protein kinase Akt2 plays a key role in this insulin action. The small GTPase Rac1 has also been implicated as a regulator of insulin-stimulated GLUT4 translocation, acting downstream of Akt2. However, the mechanisms whereby Akt2 regulates Rac1 activity remain obscure. The guanine nucleotide exchange factor FLJ00068 has been identified as a direct regulator of Rac1 in Akt2-mediated signaling, but its characterization was performed mostly in cultured myoblasts. Here, we provide in vivo evidence that FLJ00068 indeed acts downstream of Akt2 as a Rac1 regulator by using mouse skeletal muscle. Small interfering RNA knockdown of FLJ00068 markedly diminished GLUT4 translocation to the sarcolemma following insulin administration or ectopic expression of a constitutively activated mutant of either phosphoinositide 3-kinase or Akt2. Additionally, insulin and these constitutively activated mutants caused the activation of Rac1 as shown by immunofluorescent microscopy using a polypeptide probe specific to activated Rac1 in isolated gastrocnemius muscle fibers and frozen sections of gastrocnemius muscle. This Rac1 activation was also abrogated by FLJ00068 knockdown. Furthermore, we observed translocation of FLJ00068 to the cell periphery following insulin stimulation in cultured myoblasts. Localization of FLJ00068 in the plasma membrane in insulin-stimulated, but not unstimulated, myoblasts and mouse gastrocnemius muscle was further affirmed by subcellular fractionation and subsequent immunoblotting. Collectively, these results strongly support a critical role of FLJ00068 in Akt2-mediated Rac1 activation in mouse skeletal muscle insulin signaling.

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“…Ral-GAP␣1 (also called GRNL1) is the RGC2 highly expressed in skeletal muscle (17,70). Akt2-dependent phosphorylation of the catalytic subunit reduces Ral-GAP␣1 activity against the small GTPase RalA, favoring GTP-bound RalA and targeting of GLUT4 to CSM (16,17,70,112).…”

Section: Insulin Signaling and Glut4 Vesicle Traffickingmentioning

confidence: 99%

Mechanisms for greater insulin-stimulated glucose uptake in normal and insulin-resistant skeletal muscle after acute exercise

Cartee

2015

American Journal of Physiology-Endocrinology and Metabolism

107

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Enhanced skeletal muscle and whole body insulin sensitivity can persist for up to 24 -48 h after one exercise session. This review focuses on potential mechanisms for greater postexercise and insulinstimulated glucose uptake (ISGU) by muscle in individuals with normal or reduced insulin sensitivity. A model is proposed for the processes underlying this improvement; i.e., triggers initiate events that activate subsequent memory elements, which store information that is relayed to mediators, which translate memory into action by controlling an end effector that directly executes increased insulin-stimulated glucose transport. Several candidates are potential triggers or memory elements, but none have been conclusively verified. Regarding potential mediators in both normal and insulin-resistant individuals, elevated postexercise ISGU with a physiological insulin dose coincides with greater Akt substrate of 160 kDa (AS160) phosphorylation without improved proximal insulin signaling at steps from insulin receptor binding to Akt activity. Causality remains to be established between greater AS160 phosphorylation and improved ISGU. The end effector for normal individuals is increased GLUT4 translocation, but this remains untested for insulin-resistant individuals postexercise. Following exercise, insulin-resistant individuals can attain ISGU values similar to nonexercising healthy controls, but after a comparable exercise protocol performed by both groups, ISGU for the insulin-resistant group has been consistently reported to be below postexercise values for the healthy group. Further research is required to fully understand the mechanisms underlying the improved postexercise ISGU in individuals with normal or subnormal insulin sensitivity and to explain the disparity between these groups after similar exercise. insulin sensitivity; physical activity; glucose transporter 4; AMP-activated protein kinase; Akt substrate of 160 kDa Importance of Insulin-Stimulated Glucose Uptake by Skeletal MuscleUNDERSTANDING THE MECHANISMS regulating insulin-stimulated glucose uptake by skeletal muscle is important because 1) muscle accounts for most insulin-mediated glucose disposal (21) and 2) muscle insulin resistance is a key defect in the progression to type 2 diabetes mellitus (20,43,97). Even in nondiabetic individuals, insulin resistance increases the risk for atherogenesis, cardiovascular disease, hypertension, cognitive dysfunction, and some cancers (27,45,69).Insulin and exercise can independently increase glucose uptake secondary to redistribution of GLUT4 glucose transporters from the cell interior to cell surface membranes (CSM) (19,25,93). Elevated insulin-independent glucose uptake during exercise is mostly reversed by ϳ2-3 h postexercise, whereas enhanced muscle and whole body insulin sensitivity, detectable at ϳ1-4 h postexercise, can persist for up to 24 -48 h (1, 12, 13, 79, 88, 92, 124).Exercise capacity is related to muscle glycogen availability, and glycogen stores are diminished by vigorous exercise (59). Increase...

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Role for RalA downstream of Rac1 in skeletal muscle insulin signalling

Cited by 22 publications

References 36 publications

Insulin-stimulated glucose uptake partly relies on p21-activated kinase (PAK)-2, but not PAK1, in mouse skeletal muscle

Insulin-stimulated glucose uptake partly relies on p21-activated kinase (PAK)-2, but not PAK1, in mouse skeletal muscle

Rac1 Activation Caused by Membrane Translocation of a Guanine Nucleotide Exchange Factor in Akt2-Mediated Insulin Signaling in Mouse Skeletal Muscle

Mechanisms for greater insulin-stimulated glucose uptake in normal and insulin-resistant skeletal muscle after acute exercise

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