scholarly journals l-Leucine availability regulates phosphatidylinositol 3-kinase, p70 S6 kinase and glycogen synthase kinase-3 activity in L6 muscle cells: evidence for the involvement of the mammalian target of rapamycin (mTOR) pathway in the l-leucine-induced up-regulation of System A amino acid transport

2000 ◽  
Vol 350 (2) ◽  
pp. 361 ◽  
Author(s):  
Karine PEYROLLIER ◽  
Eric HAJDUCH ◽  
Anne S. BLAIR ◽  
Russell HYDE ◽  
Harinder S. HUNDAL
Keyword(s):  
Amino Acid ◽  
Glycogen Synthase ◽  
Mammalian Target Of Rapamycin ◽  
Glycogen Synthase Kinase 3 ◽  
Acid Transport ◽  
Phosphatidylinositol 3 Kinase ◽  
S6 Kinase ◽  
P70 S6 Kinase ◽  
System A ◽  
L6 Muscle Cells

scholarly journals l-Leucine availability regulates phosphatidylinositol 3-kinase, p70 S6 kinase and glycogen synthase kinase-3 activity in L6 muscle cells: evidence for the involvement of the mammalian target of rapamycin (mTOR) pathway in the l-leucine-induced up-regulation of System A amino acid transport

2000 ◽  
Vol 350 (2) ◽  
pp. 361-368 ◽  
Author(s):  
Karine PEYROLLIER ◽  
Eric HAJDUCH ◽  
Anne S. BLAIR ◽  
Russell HYDE ◽  
Harinder S. HUNDAL
Keyword(s):  
Amino Acid ◽  
Glycogen Synthase ◽  
Mammalian Target Of Rapamycin ◽  
Muscle Cells ◽  
Glycogen Synthase Kinase 3 ◽  
Phosphatidylinositol 3 Kinase ◽  
S6 Kinase ◽  
P70 S6 Kinase ◽  
System A ◽  
L6 Muscle Cells

Amino acid availability is known to regulate diverse cell processes including the activation of p70 S6 kinase, initiation factors involved in mRNA translation, gene expression and cellular amino acid uptake. Essential amino acids, in particular the branched-chain amino acids (e.g. leucine), have been shown to be the dominant players in mediating these effects, although the precise nature by which they regulate these processes remain poorly understood. In this study we have investigated the mechanisms involved in the leucine-induced modulation of p70 S6 kinase and addressed whether this kinase participates in the up-regulation of the System A amino acid transporter in L6 muscle cells. Incubation of muscle cells that had been amino acid-deprived for 1h with L-leucine (2mM) led to a rapid (> 2-fold) activation of p70 S6 kinase, which was suppressed by both wortmannin and rapamycin. Consistent with this finding, addition of leucine caused a rapid (≈ 5-fold) but transient stimulation of phosphatidylinositol 3-kinase (PI3K). PI3K activation was inhibited by wortmannin and was not dependent upon insulin receptor substrate-1 activation. Unlike stimulation by insulin, activation of neither protein kinase B nor p42/p44 mitogen-activated protein kinase accompanied the leucine-induced stimulation of PI3K. However, the leucine-induced activation of PI3K and p70 S6 kinase did result in the concomitant inactivation of glycogen synthase kinase-3 (GSK-3). Leucine enhanced System A transport by ≈ 50%. We have shown previously that this stimulation is protein-synthesis-dependent and in the current study we show that it was blocked by both wortmannin and rapamycin. Our findings indicate that PI3K and the mammalian target of rapamycin are components of a nutrient signalling pathway that regulates the activation of p70 S6 kinase and induction of System A in L6 cells. The activation of this pathway by leucine is also responsible for the inactivation of GSK-3, and this is likely to have important regulatory implications for translation initiation.

scholarly journals The inhibition of glycogen synthase kinase-3 by insulin or insulin-like growth factor 1 in the rat skeletal muscle cell line L6 is blocked by wortmannin, but not by rapamycin: evidence that wortmannin blocks activation of the mitogen-activated protein kinase pathway in L6 cells between Ras and Raf

1994 ◽  
Vol 303 (1) ◽  
pp. 21-26 ◽  
Author(s):  
D A E Cross ◽  
D R Alessi ◽  
J R Vandenheede ◽  
H E McDowell ◽  
H S Hundal ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Map Kinase ◽  
Protein Phosphatase ◽  
Glycogen Synthase ◽  
Glycogen Synthase Kinase 3 ◽  
Rat Skeletal Muscle ◽  
S6 Kinase ◽  
P70 S6 Kinase ◽  
Skeletal Muscle Cell Line ◽  
Stimulation Of

Glycogen synthase kinase-3 (GSK3) is inactivated in vitro by p70 S6 kinase or MAP kinase-activated protein kinase-1 beta (MAPKAP kinase-1 beta; also known as Rsk-2). Here we show that GSK3 isoforms are inhibited by 40% within minutes after stimulation of the rat skeletal-muscle cell line L6 with insulin-like growth factor-1 (IGF-1) or insulin. GSK3 was similarly inhibited in rabbit skeletal muscle after an intravenous injection of insulin. Inhibition resulted from increased phosphorylation of GSK3, probably at a serine/threonine residue(s), because it was reversed by incubation with protein phosphatase-2A. Rapamycin blocked the activation of p70 S6 kinase by IGF-1 in L6 cells, but had no effect on the inhibition of GSK3 or the activation of MAPKAP kinase-1 beta. In contrast, wortmannin, a potent inhibitor of PtdIns 3-kinase, prevented the inactivation of GSK3 and the activation of MAPKAP kinase-1 beta and p70 S6 kinase by IGF-1 or insulin. Wortmannin also blocked the activation of p74raf-1. MAP kinase kinase and p42 MAP kinase, but not the formation of GTP-Ras by IGF-1. The results suggest that the stimulation of glycogen synthase by insulin/IGF-1 in skeletal muscle involves the MAP-KAP kinase-1-catalysed inhibition of GSK3, as well as the previously described activation of the glycogen-associated form of protein phosphatase-1.

scholarly journals The mechanism by which epidermal growth factor inhibits glycogen synthase kinase 3 in A431 cells

1994 ◽  
Vol 303 (1) ◽  
pp. 27-31 ◽  
Author(s):  
Y Saito ◽  
J R Vandenheede ◽  
P Cohen
Keyword(s):  
Growth Factor ◽  
Epidermal Growth Factor ◽  
Glycogen Synthase ◽  
Glycogen Synthase Kinase ◽  
Glycogen Synthase Kinase 3 ◽  
A431 Cells ◽  
S6 Kinase ◽  
P70 S6 Kinase ◽  
Epidermal Growth

Glycogen synthase kinase 3 (GSK3) was inhibited by 50% within 5 min when A431 cells were stimulated with epidermal growth factor (EGF). The inhibition was unaffected by rapamycin at concentrations which blocked the activation of p70 S6 kinase, and reversed by incubation with protein phosphatase-1. EGF stimulation of A431 cells inhibited GSK3 alpha and GSK3 beta to a similar extent, and inhibition was accompanied by phosphorylation of the tryptic peptides containing the serine residues phosphorylated in vitro by p70 S6 kinase or MAP kinase-activated protein (MAPKAP) kinase-1 beta (also termed Rsk-2). These results demonstrate that EGF inhibits GSK3 by inducing phosphorylation of a serine residue and that GSK3 is not phosphorylated in vivo by either p70 S6 kinase or protein kinase C.

In vivo regulation of protein-serine kinases by insulin in skeletal muscle of fructose-hypertensive rats

1999 ◽  
Vol 277 (2) ◽  
pp. E299-E307 ◽  
Author(s):  
Sanjay Bhanot ◽  
Baljinder S. Salh ◽  
Subodh Verma ◽  
John H. McNeill ◽  
Steven L. Pelech
Keyword(s):  
Skeletal Muscle ◽  
Glycogen Synthase ◽  
Insulin Injection ◽  
Glycogen Synthase Kinase 3 ◽  
Phosphatidylinositol 3 Kinase ◽  
S6 Kinase ◽  
Serine Kinases ◽  
Gsk 3Β

The effects of tail-vein insulin injection (2 U/kg) on the regulation of protein-serine kinases in hindlimb skeletal muscle were investigated in hyperinsulinemic hypertensive fructose-fed (FF) animals that had been fasted overnight. Basal protein kinase B (PKB) activity was elevated about twofold in FF rats and was not further stimulated by insulin. Phosphatidylinositol 3-kinase (PI3K), which lies upstream of PKB, was increased ∼3.5-fold within 2–5 min by insulin in control rats. Basal and insulin-activated PI3K activities were further enhanced up to 2-fold and 1.3-fold, respectively, in FF rats. The 70-kDa S6 kinase (S6K) was stimulated about twofold by insulin in control rats. Both basal and insulin-stimulated S6K activity was further enhanced up to 1.5-fold and 3.5-fold, respectively, in FF rats. In control rats, insulin caused a 40–50% reduction of the phosphotransferase activity of the β-isoform of glycogen synthase kinase 3 (GSK-3β), which is a PKB target in vitro. Basal GSK-3β activity was decreased by ∼40% in FF rats and remained unchanged after insulin treatment. In summary, 1) the PI3K → PKB → S6K pathway was upregulated under basal conditions, and 2) insulin stimulation of PI3K and S6K activities was enhanced, but both PKB and GSK-3 were refractory to the effects of insulin in FF rats.

scholarly journals Placental Glucose and Amino Acid Transport in Calorie-Restricted Wild-Type and Glut3 Null Heterozygous Mice

Endocrinology ◽  
2012 ◽  
Vol 153 (8) ◽  
pp. 3995-4007 ◽  
Author(s):  
Amit Ganguly ◽  
Laura Collis ◽  
Sherin U. Devaskar
Keyword(s):  
Amino Acid ◽  
Family Member ◽  
Glucose Transport ◽  
Amino Acid Transport ◽  
Mammalian Target Of Rapamycin ◽  
Acid Transport ◽  
Wild Type ◽  
System A ◽  
Leucine Transport

Calorie restriction (CR) decreased placenta and fetal weights in wild-type (wt) and glucose transporter (Glut) 3 heterozygous null (glut3+/−) mice. Because placental nutrient transport is a primary energy determinant of placentofetal growth, we examined key transport systems. Maternal CR reduced intra- and transplacental glucose and leucine transport but enhanced system A amino acid transport in wt mice. These transport perturbations were accompanied by reduced placental Glut3 and leucine amino acid transporter (LAT) family member 2, no change in Glut1 and LAT family member 1, but increased sodium coupled neutral amino acid transporter (SNAT) and SNAT2 expression. We also noted decreased total and active phosphorylated forms of mammalian target of rapamycin, which is the intracellular nutrient sensor, the downstream total P70S6 kinase, and pS6 ribosomal protein with no change in total and phosphorylated 4E-binding protein 1. To determine the role of placental Glut3 in mediating CR-induced placental transport changes, we next investigated the effect of gestational CR in glut3+/− mice. In glut3+/− mice, a key role of placental Glut3 in mediating transplacental and intraplacental glucose transport was established. In addition, reduced Glut3 results in a compensatory increase of leucine and system A transplacental transport. On the other hand, diminished Glut3-mediated intraplacental glucose transport reduced leucine transport and mammalian target of rapamycin and preserved LAT and enhancing SNAT. CR in glut3+/− mice further reduced transplacental glucose transport and enhanced system A amino acid transport, although the increased leucine transport was lost. In addition, increased Glut3 was seen and preserved Glut1, LAT, and SNAT. These placental changes collectively protect survival of wt and glut3+/− fetuses against maternal CR-imposed reduction of macromolecular nutrients.

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