MEK–ERK Inhibition Corrects the Defect in VLDL Assembly in HepG2 Cells: Potential Role of ERK in VLDL-ApoB100 Particle Assembly

• Published in: Arteriosclerosis, thrombosis, and vascular biology Vol. 27; no. 1; pp. 211 - 218
• Main Authors: Tsai, Julie, Qiu, Wei, Kohen-Avramoglu, Rita, Adeli, Khosrow
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Heart Association, Inc 01.01.2007; Hagerstown, MD Lippincott
• Subjects: Animals; Apolipoprotein B-100 - metabolism; Associated diseases and complications; Atherosclerosis (general aspects, experimental research); Biological and medical sciences; Blood and lymphatic vessels; Blood vessels and receptors; Butadienes - pharmacology; Cardiology. Vascular system; Cell Line, Tumor; Cricetinae; Diabetes. Impaired glucose tolerance; Diacylglycerol O-Acyltransferase - genetics; Diacylglycerol O-Acyltransferase - metabolism; Diseases of the peripheral vessels. Diseases of the vena cava. Miscellaneous; Dose-Response Relationship, Drug; Endocrine pancreas. Apud cells (diseases); Endocrinopathies; Enzyme Inhibitors - pharmacology; Extracellular Signal-Regulated MAP Kinases - antagonists & inhibitors; Extracellular Signal-Regulated MAP Kinases - drug effects; Extracellular Signal-Regulated MAP Kinases - genetics; Extracellular Signal-Regulated MAP Kinases - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation - drug effects; Gene Expression Regulation - physiology; Hepatoblastoma - metabolism; Hepatoblastoma - pathology; Hepatocytes - cytology; Hepatocytes - drug effects; Hepatocytes - metabolism; Humans; Lipoproteins, VLDL - metabolism; Liver Neoplasms - metabolism; Liver Neoplasms - pathology; MAP Kinase Kinase 1 - antagonists & inhibitors; MAP Kinase Kinase 1 - drug effects; MAP Kinase Kinase 1 - genetics; MAP Kinase Kinase 1 - metabolism; MAP Kinase Kinase 2 - antagonists & inhibitors; MAP Kinase Kinase 2 - drug effects; MAP Kinase Kinase 2 - genetics; MAP Kinase Kinase 2 - metabolism; Medical sciences; Mesocricetus; Nitriles - pharmacology; Oleic Acid - pharmacology; Particle Size; Rats; RNA, Messenger - genetics; RNA, Messenger - metabolism; Signal Transduction - drug effects; Signal Transduction - physiology; Triglycerides - metabolism; Vertebrates: cardiovascular system; Vascular disease; Particle; MEK-ERK; Extracellular signal-regulated protein kinase; Enzyme; VLDL; Atherosclerosis; apolipoprotein B100; HepG2; Cardiovascular disease; Apolipoprotein
• ISSN: 1079-5642; 1524-4636
• DOI: 10.1161/01.ATV.0000249861.80471.96

OBJECTIVE—Hepatic VLDL assembly is defective in HepG2 cells, resulting in the secretion of immature triglyceride-poor LDL-sized apoB particles. We investigated the mechanisms underlying defective VLDL assembly in HepG2 and have obtained evidence implicating the MEK–ERK pathway. METHODS AND RESULTS—HepG2 cells exhibited considerably higher levels of the ERK1/2 mass and activity compared with primary hepatocytes. Inhibition of ERK1/2 using the MEK1/MEK2 inhibitor, U0126 (but not the inactive analogue) led to a significant increase in apoB secretion. In the presence of oleic acid, ERK1/2 inhibition caused a major shift in the lipoprotein distribution with a majority of particles secreted as VLDL, an effect independent of insulin. In contrast, overexpression of constitutively active MEK1 decreased apoB and large VLDL secretion. MEK1/2 inhibition significantly increased both cellular and microsomal TG mass, and mRNA levels for DGAT-1 and DGAT-2. In contrast to ERK, modulation of the PI3-K pathway or inhibition of the p38 MAP kinase, had no effect on lipoprotein density profile. Modulation of the MEK–ERK pathway in primary hamster hepatocytes led to changes in apoB secretion and altered the density profile of apoB-containing lipoproteins. CONCLUSION—Inhibition of the overactive ras-MEK–ERK pathway in HepG2 cells can correct the defect in VLDL assembly leading to the secretion of large, VLDL-sized particles, similar to primary hepatocytes, implicating the MEK–ERK cascade in VLDL assembly in the HepG2 model. Modulation of this pathway in primary hepatocytes also regulates apoB secretion and appears to alter the formation of VLDL-1 sized particles.