Regulation of GLUT4 biogenesis in muscle: evidence for involvement of AMPK and Ca2+

2002 ◽  
Vol 282 (5) ◽  
pp. E1008-E1013 ◽  
Author(s):  
Edward O. Ojuka ◽  
Terry E. Jones ◽  
Lorraine A. Nolte ◽  
May Chen ◽  
Brian R. Wamhoff ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Culture Medium ◽  
Mitochondrial Enzymes ◽  
L6 Myotubes ◽  
Glut4 Expression ◽  
Dependent Protein ◽  
Amp Activated Protein Kinase ◽  
L6 Myocytes ◽  
Enhancer Factor

There is evidence suggesting that adaptive increases in GLUT4 and mitochondria in skeletal muscle occur in parallel. It has been reported that raising cytosolic Ca2+ in myocytes induces increases in mitochondrial enzymes. In this study, we tested the hypothesis that an increase in cytosolic Ca2+ induces an increase in GLUT4. We found that raising cytosolic Ca2+ by exposing L6 myotubes to 5 mM caffeine for 3 h/day for 5 days induced increases in GLUT4 protein and in myocyte enhancer factor (MEF)2A and MEF2D, which are transcription factors involved in regulating GLUT4 expression. The caffeine-induced increases in GLUT4 and MEF2A and MEF2D were partially blocked by dantrolene, an inhibitor of sarcoplasmic reticulum Ca2+ release, and completely blocked by KN93, an inhibitor of Ca2+-calmodulin-dependent protein kinase (CAMK). Caffeine also induced increases in MEF2A, MEF2D, and GLUT4 in rat epitrochlearis muscles incubated with caffeine in culture medium. 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR), which activates AMP-activated protein kinase (AMPK), also induced approximately twofold increases in GLUT4, MEF2A, and MEF2D in L6 myocytes. Our results provide evidence that increases in cytosolic Ca2+and activation of AMPK, both of which occur in exercising muscle, increase GLUT4 protein in myocytes and skeletal muscle. The data suggest that this effect of Ca2+ is mediated by activation of CAMK and indicate that MEF2A and MEF2D are involved in this adaptive response.

Regulation of muscle GLUT4 enhancer factor and myocyte enhancer factor 2 by AMP-activated protein kinase

2005 ◽  
Vol 289 (6) ◽  
pp. E1071-E1076 ◽  
Author(s):  
Burton F. Holmes ◽  
David P. Sparling ◽  
Ann Louise Olson ◽  
William W. Winder ◽  
G. Lynis Dohm
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Glucose Transporter ◽  
Myocyte Enhancer Factor 2 ◽  
Consensus Sequences ◽  
Glut4 Expression ◽  
Myocyte Enhancer Factor ◽  
Amp Activated Protein Kinase ◽  
Enhancer Factor

As the primary glucose transporter in skeletal muscle, GLUT4 is an important factor in the regulation of blood glucose. We previously reported that stimulation of AMP-activated protein kinase (AMPK) with 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) increased GLUT4 expression in muscle. GLUT4 enhancer factor (GEF) and myocyte enhancer factor 2 (MEF2) have been shown to be important for normal GLUT4 expression because deletion or truncation of the consensus sequences on the promoter causes depressed GLUT4 mRNA expression. This led to the current study to investigate possible roles for GEF and MEF2 in mediating the activation of GLUT4 gene transcription in response to AMPK. Here we show that, although AMPK does not appear to phosphorylate MEF2A, AMPK directly phosphorylates the GEF protein in vitro. MEF2 and GEF are activated in response to AMPK as we observed translocation of both to the nucleus after AICAR treatment. Nuclear MEF2 protein content was increased after 2 h, and GEF protein was increased in the nucleus 1 and 2 h post-AICAR treatment. Last, GEF and MEF2 increase in binding to the GLUT4 promoter within 2 h after AICAR treatment. Thus we conclude that GEF and MEF2 mediate the AMPK-induced increase in transcription of skeletal muscle GLUT4. AMPK can phosphorylate GEF and in response to AICAR, GEF, and MEF2 translocate to the nucleus and have increased binding to the GLUT4 promoter.

Muscle cell depolarization induces a gain in surface GLUT4 via reduced endocytosis independently of AMPK

2006 ◽  
Vol 290 (6) ◽  
pp. E1276-E1286 ◽  
Author(s):  
Nadeeja Wijesekara ◽  
Amanda Tung ◽  
Farah Thong ◽  
Amira Klip
Keyword(s):  
Protein Kinase ◽  
Energy Demand ◽  
Actin Polymerization ◽  
Membrane Depolarization ◽  
Akt Activation ◽  
L6 Myotubes ◽  
Dependent Protein ◽  
Cell Depolarization ◽  
Elevated Surface ◽  
Amp Activated Protein Kinase

Contracting skeletal muscle increases glucose uptake to sustain energy demand. This is achieved through a gain in GLUT4 at the membrane, but the traffic mechanisms and regulatory signals involved are unknown. Muscle contraction is elicited by membrane depolarization followed by a rise in cytosolic Ca2+ and actomyosin activation, drawing on ATP stores. It is unknown whether one or more of these events triggers the rise in surface GLUT4. Here, we investigate the effect of membrane depolarization on GLUT4 cycling using GLUT4 myc-expressing L6 myotubes devoid of sarcomeres and thus unable to contract. K+-induced membrane depolarization elevated surface GLUT4 myc, and this effect was additive to that of insulin, was not prevented by inhibiting phosphatidylinositol 3-kinase (PI3K) or actin polymerization, and did not involve Akt activation. Instead, depolarization elevated cytosolic Ca2+, and the surface GLUT4 myc elevation was prevented by dantrolene (an inhibitor of Ca2+ release from sarcoplasmic reticulum) and by extracellular Ca2+ chelation. Ca2+-calmodulin-dependent protein kinase-II (CaMKII) was not phosphorylated after 10 min of K+ depolarization, and the CaMK inhibitor KN62 did not prevent the gain in surface GLUT4 myc. Interestingly, although 5′-AMP-activated protein kinase (AMPK) was phosphorylated upon depolarization, lowering AMPKα via siRNA did not alter the surface GLUT4 myc gain. Conversely, the latter response was abolished by the PKC inhibitors bisindolylmaleimide I and calphostin C. Unlike insulin, K+ depolarization caused only a small increase in GLUT4 myc exocytosis and a major reduction in its endocytosis. We propose that K+ depolarization reduces GLUT4 internalization through signals and mechanisms distinct from those engaged by insulin. Such a pathway(s) is largely independent of PI3K, Akt, AMPK, and CaMKII but may involve PKC.

Skeletal Muscle Glucose Uptake During Exercise: How is it Regulated?

Physiology ◽  
2005 ◽  
Vol 20 (4) ◽  
pp. 260-270 ◽  
Author(s):  
Adam J. Rose ◽  
Erik A. Richter
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Glucose Uptake ◽  
Intracellular Signaling ◽  
Surface Membrane ◽  
Capillary Perfusion ◽  
Subsequent Increase ◽  
Dependent Protein ◽  
Skeletal Muscle Glucose Uptake ◽  
Amp Activated Protein Kinase

The increase in skeletal muscle glucose uptake during exercise results from a coordinated increase in rates of glucose delivery (higher capillary perfusion), surface membrane glucose transport, and intracellular substrate flux through glycolysis. The mechanism behind the movement of GLUT4 to surface membranes and the subsequent increase in transport by muscle contractions is largely unresolved, but it is likely to occur through intracellular signaling involving Ca2+-calmodulin-dependent protein kinase, 5′-AMP-activated protein kinase, and possibly protein kinase C.

scholarly journals Activation of protein kinase B β and γ isoforms by insulin in vivo and by 3-phosphoinositide-dependent protein kinase-1 in vitro: comparison with protein kinase B α

1998 ◽  
Vol 331 (1) ◽  
pp. 299-308 ◽  
Author(s):  
Kay S. WALKER ◽  
Maria DEAK ◽  
Andrew PATERSON ◽  
Kevin HUDSON ◽  
Philip COHEN ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Protein Kinase B ◽  
Rat Hepatocytes ◽  
Dependent Protein Kinase ◽  
L6 Myotubes ◽  
Dependent Protein ◽  
Stimulation Of

The regulatory and catalytic properties of the three mammalian isoforms of protein kinase B (PKB) have been compared. All three isoforms (PKBα, PKBβ and PKBγ) were phosphorylated at similar rates and activated to similar extents by 3-phosphoinositide-dependent protein kinase-1 (PDK1). Phosphorylation and activation of each enzyme required the presence of PtdIns(3,4,5)P3 or PtdIns(3,4)P2, as well as PDK1. The activation of PKBβ and PKBγ by PDK1 was accompanied by the phosphorylation of the residues equivalent to Thr308 in PKBα, namely Thr309 (PKBβ) and Thr305 (PKBγ). PKBγ which had been activated by PDK1 possessed a substrate specificity identical with that of PKBα and PKBβ towards a range of peptides. The activation of PKBγ and its phosphorylation at Thr305 was triggered by insulin-like growth factor-1 in 293 cells. Stimulation of rat adipocytes or rat hepatocytes with insulin induced the activation of PKBα and PKBβ with similar kinetics. After stimulation of adipocytes, the activity of PKBβ was twice that of PKBα, but in hepatocytes PKBα activity was four-fold higher than PKBβ. Insulin induced the activation of PKBα in rat skeletal muscle in vivo, with little activation of PKBβ. Insulin did not induce PKBγ activity in adipocytes, hepatocytes or skeletal muscle, but PKBγ was the major isoform activated by insulin in rat L6 myotubes (a skeletal-muscle cell line).

Leucine modulates contraction- and insulin-stimulated glucose transport and upstream signaling events in rat skeletal muscle

2010 ◽  
Vol 108 (2) ◽  
pp. 274-282 ◽  
Author(s):  
Nobumasa Iwanaka ◽  
Tatsuro Egawa ◽  
Nozomi Satoubu ◽  
Kouhei Karaike ◽  
Xiao Ma ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Glucose Transport ◽  
Mammalian Target Of Rapamycin ◽  
Α Subunit ◽  
Ampk Phosphorylation ◽  
Dependent Protein ◽  
Opposing Effects ◽  
Amp Activated Protein Kinase

Leucine has profound effects on glucose metabolism in muscle; however, the effects of leucine on glucose transport in muscle have not been well documented. We investigated the effects of leucine on contraction- and insulin-stimulated glucose transport in isolated rat epitrochlearis muscle in vitro. In the absence of insulin, tetanic contraction increased 3- O-methyl-d-glucose (3-MG) transport and Thr172 phosphorylation of the catalytic α-subunit of 5′-AMP-activated protein kinase (AMPK), a signaling intermediary leading to insulin-independent glucose transport. Leucine (2 mM, 30 min) significantly enhanced contraction-stimulated 3-MG transport and AMPK phosphorylation, accompanied by increased phosphorylation of p70 S6 kinase (p70S6K) Thr389. The stimulatory effects of leucine on 3-MG transport and AMPK phosphorylation were canceled by STO-609 blockade of Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) or rapamycin blockade of p70S6K. On the other hand, leucine blunted insulin-stimulated 3-MG transport and reduced insulin-stimulated Akt Thr473 phosphorylation. Leucine increased insulin-stimulated p70S6K Thr389 phosphorylation and enhanced the inhibitory phosphorylation of the insulin receptor substrate 1 (IRS1) Ser636/639. Furthermore, the effects of leucine on insulin-stimulated 3-MG transport and IRS phosphorylation were abolished by rapamycin. These results indicate that leucine activates contraction-stimulated glucose transport and inhibits insulin-stimulated glucose transport in skeletal muscle by activating mammalian target of rapamycin (mTOR)/p70S6K signaling. Enhanced increases in contraction-stimulated AMPK Thr172 phosphorylation and insulin-stimulated IRS1 Ser636/639 phosphorylation might be responsible for these opposing effects of leucine, respectively.

Activation of AMP-activated protein kinase increases mitochondrial enzymes in skeletal muscle

2000 ◽  
Vol 88 (6) ◽  
pp. 2219-2226 ◽  
Author(s):  
W. W. Winder ◽  
B. F. Holmes ◽  
D. S. Rubink ◽  
E. B. Jensen ◽  
M. Chen ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Muscle Contraction ◽  
Citrate Synthase ◽  
Aminolevulinic Acid ◽  
Chemical Activation ◽  
Quadriceps Muscle ◽  
Mitochondrial Enzymes ◽  
Glut 4 ◽  
Amp Activated Protein Kinase

Muscle contraction causes an increase in activity of 5′-AMP-activated protein kinase (AMPK). This study was designed to determine whether chronic chemical activation of AMPK will increase mitochondrial enzymes, GLUT-4, and hexokinase in different types of skeletal muscle of resting rats. In acute studies, rats were subcutaneously injected with either 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR; 1 mg/g body wt) in 0.9% NaCl or with 0.9% NaCl alone and were then anesthetized for collection and freezing of tissues. AMPK activity increased in the superficial, white region of the quadriceps and in soleus muscles but not in the deep, red region of the quadriceps muscle. Acetyl-CoA carboxylase (ACC) activity, a target for AMPK, decreased in all three muscle types in response to AICAR injection but was lowest in the white quadriceps. In rats given daily, 1 mg/g body wt, subcutaneous injections of AICAR for 4 wk, activities of citrate synthase, succinate dehydrogenase, and malate dehydrogenase were increased in white quadriceps and soleus but not in red quadriceps. Cytochrome c and δ-aminolevulinic acid synthase levels were increased in white, but not red, quadriceps. Carnitine palmitoyl-transferase and hydroxy-acyl-CoA dehydrogenase were not significantly increased. Hexokinase was markedly increased in all three muscles, and GLUT-4 was increased in red and white quadriceps. These results suggest that chronic AMPK activation may mediate the effects of muscle contraction on some, but not all, biochemical adaptations of muscle to endurance exercise training.

Reduced glycogen availability is associated with increased AMPKα2 activity, nuclear AMPKα2 protein abundance, and GLUT4 mRNA expression in contracting human skeletal muscle

2006 ◽  
Vol 31 (3) ◽  
pp. 302-312 ◽  
Author(s):  
Gregory R Steinberg ◽  
Matthew J Watt ◽  
Sean L McGee ◽  
Stanley Chan ◽  
Mark Hargreaves ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Mrna Expression ◽  
Muscle Glycogen ◽  
Glucose Transporter ◽  
Nuclear Translocation ◽  
Glut4 Expression ◽  
Human Myotubes ◽  
Exercise Muscle ◽  
Amp Activated Protein Kinase

Glycogen availability can influence glucose transporter 4 (GLUT4) expression in skeletal muscle through unknown mechanisms. The multisubstrate enzyme AMP-activated protein kinase (AMPK) has also been shown to play an important role in the regulation of GLUT4 expression in skeletal muscle. During contraction, AMPK α2 translocates to the nucleus and the activity of this AMPK isoform is enhanced when skeletal muscle glycogen is low. In this study, we investigated if decreased pre-exercise muscle glycogen levels and increased AMPK α2 activity reduced the association of AMPK with glycogen and increased AMPK α2 translocation to the nucleus and GLUT4 mRNA expression following exercise. Seven males performed 60 min of exercise at ~70% VO2 peak on 2 occasions: either with normal (control) or low (LG) carbohydrate pre-exercise muscle glycogen content. Muscle samples were obtained by needle biopsy before and after exercise. Low muscle glycogen was associated with elevated AMPK α2 activity and acetyl-CoA carboxylase β phosphorylation, increased translocation of AMPK α2 to the nucleus, and increased GLUT4 mRNA. Transfection of primary human myotubes with a constitutively active AMPK adenovirus also stimulated GLUT4 mRNA, providing direct evidence of a role of AMPK in regulating GLUT4 expression. We suggest that increased activation of AMPK α2 under conditions of low muscle glycogen enhances AMPK α2 nuclear translocation and increases GLUT4 mRNA expression in response to exercise in human skeletal muscle.Key words: exercise, subcellular localization, glycogen binding domain, AMP-activated protein kinase.

The role of CaMKII in regulating GLUT4 expression in skeletal muscle

2012 ◽  
Vol 303 (3) ◽  
pp. E322-E331 ◽  
Author(s):  
Edward O. Ojuka ◽  
Veeraj Goyaram ◽  
James A. H. Smith
Keyword(s):  
Gene Expression ◽  
Skeletal Muscle ◽  
Contractile Activity ◽  
Pharmacological Agents ◽  
Calcium Dependent ◽  
Binding Domains ◽  
Glut4 Expression ◽  
Dependent Protein ◽  
Glut4 Gene Expression ◽  
Enhancer Factor

Contractile activity during physical exercise induces an increase in GLUT4 expression in skeletal muscle, helping to improve glucose transport capacity and insulin sensitivity. An important mechanism by which exercise upregulates GLUT4 is through the activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) in response to elevated levels of cytosolic Ca2+ during muscle contraction. This review discusses the mechanism by which Ca2+ activates CaMKII, explains research techniques currently used to alter CaMK activity in cells, and highlights various exercise models and pharmacological agents that have been used to provide evidence that CaMKII plays an important role in regulating GLUT4 expression. With regard to transcriptional mechanisms, the key research studies that identified myocyte enhancer factor 2 (MEF2) and GLUT4 enhancer factor as the major transcription factors regulating glut4 gene expression, together with their binding domains, are underlined. Experimental evidence showing that CaMK activation induces hyperacetylation of histones in the vicinity of the MEF2 domain and increases MEF2 binding to its cis element to influence MEF2-dependent Glut4 gene expression are also given along with data suggesting that p300 might be involved in acetylating histones on the Glut4 gene. Finally, an appraisal of the roles of other calcium- and non-calcium-dependent mechanisms, including the major HDAC kinases in GLUT4 expression, is also given.

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