Secretion of atherogenic risk factor apolipoprotein B-100 is increased by a potential mechanism of JNK/PKC-mediated insulin resistance in liver cells.
Apolipoprotein B-100 (ApoB) is the main protein of the atherogenic lipoproteins and plasma ApoB levels reflect the total numbers of atherogenic lipoproteins. Induction of insulin resistance was accompanied by a considerable rise in the production of hepatic very low density lipoprotein (VLDL) containing ApoB and triglyceride. Increased plasma levels of ApoB and triglyceride in VLDL are common characteristics of the dyslipidemia associated with insulin resistance and type 2 diabetes mellitus. Thus, we investigate whether phorbol 12-myristate-13-acetate (PMA)-induced insulin resistance affects the increase of ApoB secretion. PMA increased ApoB secretion and transcriptional level of microsomal triglyceride transfer protein (MTP). PMA treatment also resulted in increase of insulin receptor substrate 1 (IRS1) serine312 (Ser312) and serine1101 (Ser1101) phosphorylation and induction of IRS1 degradation. Additionally, PMA induced activation of c-jun N-terminal kinase (JNK) and protein kinase C (PKC) isoforms (alpha, betaI, delta, zeta, theta), and reduced AKT8 virus oncogene cellular homolog (AKT) activation in a time dependent manner. PMA-induced ApoB secretion, MTP promoter activities, and IRS1 degradation was significantly decreased by treatment of JNK and PKCs inhibitors. Orthovanadate, a potent tyrosine phosphatase inhibitor, increased tyrosine phosphorylation of IRS1 and decreased ApoB secretion of Chang liver cells although PMA was co-treated. From the results, it was concluded that PMA-induced insulin resistance, through induction of serine phosphorylation of IRS1 mediated by activated JNK and PKCs, increases ApoB secretion in Chang liver cells.
Jin
Un-Ho
UH
Molecular and Cellular Glycobiology Unit, Department of Biological Sciences, SungKyunKwan University, 300 Chunchun-Dong, Suwon, Kyunggi-Do 440-746, Korea.
Kang
Yun-Jeong
YJ
Chang
Young-Chae
YC
Kim
Cheorl-Ho
CH
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D053299:Apolipoprotein B-100 / Q000187:drug effects / Q000378:metabolism*; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance / Q000502:physiology*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008079:Lipoproteins, VLDL / Q000187:drug effects / Q000378:metabolism; D024821:Metabolic Syndrome / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012307:Risk Factors; D012694:Serine / Q000737:chemistry; D013755:Tetradecanoylphorbol Acetate / Q000378:metabolism / Q000494:pharmacology; D014638:Vanadates / Q000737:chemistry / Q000494:pharmacology
D048868:Adaptor Proteins, Signal Transducing; D053299:Apolipoprotein B-100; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D008079:Lipoproteins, VLDL; C106092:microsomal triglyceride transfer protein; D014638:Vanadates; D012694:Serine; D017346:Protein Serine-Threonine Kinases; D011493:Protein Kinase C; D048031:JNK Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate