Mechanism of inhibition of insulin-stimulated glucose transport by 4-bromocrotonic acid in 3T3-L1 adipocytes.
We have demonstrated previously that 4-bromocrotonic acid (Br-C4) inhibited insulin-stimulated glucose transport by interfering with GLUT4 translocation. In the present study, we further examined the underlying mechanism involved. Since insulin-induced insulin receptor substrate-1-associated phosphatidylinositol (PI) 3-kinase activity was not altered by Br-C4, we determined and found insulin activation of protein kinase B (PKB) and protein kinase Clambda (PKClambda) were both inhibited. However, time-course studies showed that only the inhibition of PKB activation correlated with the inhibition of insulin-stimulated glucose transport. In concert, insulin-stimulated Ser(473/474) phosphorylation on PKB(alpha/beta) were similarly decreased by Br-C4. The finding that okadaic acid-stimulated glucose transport and PKClambda activity were both inhibited by Br-C4 suggested that the effect of Br-C4 on Ser(473/474) phosphorylation was not mediated by protein phosphatase 2A. Moreover, whereas Br-C4 nearly abolished insulin-stimulated integrin-linked kinase (ILK) activity, it only inhibited insulin-stimulated PKB activity by 20%, implying that ILK was not the major kinase for Ser(473/474) phosphorylation. Taken together, these results support the notion that PKB is involved in insulin-stimulated glucose transport. In addition, Br-C4 seems to inhibit insulin-stimulated glucose transport via inhibiting insulin activation of PKB, probably by interfering with insulin activation of an upstream kinase responsible for the phosphorylation of Ser(473/474) residue.
Chai
Shin-Pei
SP
Institute of Biochemistry, National Yang-Ming University, Taipei, Taiwan, ROC.
Fong
Jim C
JC
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D003437:Crotonates / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D007476:Ionophores / Q000494:pharmacology; D007527:Isoenzymes; D051379:Mice; D019319:Okadaic Acid / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D064546:Protein Kinase C beta; D051571:Protein Kinase C-alpha; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D014443:Tyrosine / Q000378:metabolism; D000099293:Protein Kinase C-lambda; D000099221:Protein Kinase C zeta; D000099200:Scaffold Protein ILK
D003437:Crotonates; D005947:Glucose; D007004:Hypoglycemic Agents; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D007476:Ionophores; D007527:Isoenzymes; D019319:Okadaic Acid; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011493:Protein Kinase C; D064546:Protein Kinase C beta; D051571:Protein Kinase C-alpha; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D014443:Tyrosine; D000099293:Protein Kinase C-lambda; D000099221:Protein Kinase C zeta; D000099200:Scaffold Protein ILK; C526295:Irs1 protein, mouse; C034444:4-bromocrotonic acid; C496630:Prkca protein, mouse