Requirement for Akt (protein kinase B) in insulin-induced activation of glycogen synthase and phosphorylation of 4E-BP1 (PHAS-1).
The roles of Akt (protein kinase B) and the atypical lambda isoform of protein kinase C (PKClambda), both of which act downstream of phosphoinositide 3-kinase, in the activation of glycogen synthase and phosphorylation of 4E-BP1 (PHAS-1) in response to insulin were investigated. A mutant Akt (Akt-AA) in which the phosphorylation sites targeted by growth factors are replaced by alanine was shown to inhibit insulin-induced activation of both Akt and glycogen synthase in L6 myotubes. Expression of a mutant Akt in which Lys179 in the kinase domain was replaced by aspartate also inhibited insulin-induced activation of glycogen synthase but had no effect on insulin activation of endogenous Akt. A kinase-defective mutant of PKClambda (lambdaDeltaNKD), which prevents insulin-induced activation of PKClambda, did not affect the activation of glycogen synthase by insulin. Insulin-induced phosphorylation of 4E-BP1 was inhibited by Akt-AA in Chinese hamster ovary cells. However, lambdaDeltaNKD had no effect on 4E-BP1 phosphorylation induced by insulin. These data suggest that Akt, but not PKClambda, is required for insulin activation of glycogen synthase and for insulin-induced phosphorylation of 4E-BP1.
Second Department of Internal Medicine, Kobe University School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
M
M
Takata
W
W
Ogawa
T
T
Kitamura
Y
Y
Hino
S
S
Kuroda
K
K
Kotani
A
A
Klip
A C
AC
Gingras
N
N
Sonenberg
M
M
Kasuga
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002352:Carrier Proteins; D002460:Cell Line; D006224:Cricetinae; D004789:Enzyme Activation; D006006:Glycogen Synthase / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D009154:Mutation; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt
D002352:Carrier Proteins; D007328:Insulin; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D006006:Glycogen Synthase; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt