Okadaic acid inhibits insulin-induced glucose transport in fetal brown adipocytes in an Akt-independent and protein kinase C zeta-dependent manner.
In the present study we have investigated the effect of increased serine/threonine phosphorylation of insulin receptor substrates-1 and -2 (IRS-1 and IRS-2) by okadaic acid pretreatment on brown adipocyte insulin signalling leading to glucose transport, an important metabolic effect of insulin in brown adipose tissue. Okadaic acid pretreatment before insulin stimulation decreased IRS-1 and IRS-2 tyrosine phosphorylation in parallel to a decrease in their sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobility. IRS-1/IRS-2-associated p85alpha and phosphatidylinositol (PI) 3-kinase enzymatic activity were partly reduced in brown adipocytes pretreated with okadaic acid upon stimulation with insulin. Furthermore, insulin-induced glucose uptake was totally abolished by the inhibitor in parallel with a total inhibition of insulin-induced protein kinase C (PKC) zeta activity. However, activation of Akt/PKB or p70 S6 kinase (p70(s6k)) by insulin remained unaltered. Our results suggest that downstream of PI 3-kinase, insulin signalling diverges into at least two independent pathways through Akt/PKB and PKC zeta, the PKC zeta pathway contributing to glucose transport induced by insulin in fetal brown adipocytes.
Valverde
A M
AM
Departamento de Bioquímica y Biología Molecular, Centro Mixto CSIC/UCM, Facultad de Farmacia, Universidad Complutense, 28040, Madrid, Spain.
Lorenzo
M
M
Navarro
P
P
Mur
C
C
Benito
M
M
D002001:Adipose Tissue, Brown / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005333:Fetus; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017208:Rats, Wistar; D011972:Receptor, Insulin / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D000099221:Protein Kinase C zeta
D004791:Enzyme Inhibitors; D005947:Glucose; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D019319:Okadaic Acid; D010750:Phosphoproteins; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D019893:Ribosomal Protein S6 Kinases; D000099221:Protein Kinase C zeta; C526292:IRS1 protein, human; C526297:IRS2 protein, human; C526296:Irs1 protein, rat; C526299:Irs2 protein, rat; C494918:AKT1 protein, human; C494920:Akt1 protein, rat