Reduced activation of phosphatidylinositol-3 kinase and increased serine 636 phosphorylation of insulin receptor substrate-1 in primary culture of skeletal muscle cells from patients with type 2 diabetes.
To understand better the defects in the proximal steps of insulin signaling during type 2 diabetes, we used differentiated human skeletal muscle cells in primary culture. When compared with cells from control subjects, myotubes established from patients with type 2 diabetes presented the same defects as those previously evidenced in vivo in muscle biopsies, including defective stimulation of phosphatidylinositol (PI) 3-kinase activity, decreased association of PI 3-kinase with insulin receptor substrate (IRS)-1 and reduced IRS-1 tyrosine phosphorylation during insulin stimulation. In contrast to IRS-1, the signaling through IRS-2 was not altered. Investigating the causes of the reduced tyrosine phosphorylation of IRS-1, we found a more than twofold increase in the basal phosphorylation of IRS-1 on serine 636 in myotubes from patients with diabetes. Concomitantly, there was a higher basal mitogen-activated protein kinase (MAPK) activity in these cells, and inhibition of the MAPKs with PD98059 strongly reduced the level of serine 636 phosphorylation. These results suggest that IRS-1 phosphorylation on serine 636 might be involved in the reduced phosphorylation of IRS-1 on tyrosine and in the subsequent alteration of insulin-induced PI 3-kinase activation. Moreover, increased MAPK activity seems to play a role in the phosphorylation of IRS-1 on serine residue in human muscle cells.
Bouzakri
Karim
K
INSERM U449 and CRNHL, IFR 62, R. Laennec Medical Faculty, F-69370 Lyon Cedex 08, France.
Roques
Marina
M
Gual
Philippe
P
Espinosa
Sophie
S
Guebre-Egziabher
Fitsum
F
Riou
Jean-Paul
JP
Laville
Martine
M
Le Marchand-Brustel
Yannick
Y
Tanti
Jean-François
JF
Vidal
Hubert
H
D001706:Biopsy; D002478:Cells, Cultured; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006593:Hexokinase / Q000235:genetics; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D020935:MAP Kinase Signaling System / Q000502:physiology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics*; D010750:Phosphoproteins / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D011972:Receptor, Insulin / Q000187:drug effects / Q000378:metabolism; D012016:Reference Values; D012694:Serine
C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D010768:Phosphoserine; D019000:Phosphotyrosine; D012694:Serine; D019869:Phosphatidylinositol 3-Kinases; D006593:Hexokinase; D011972:Receptor, Insulin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases