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Microsomal triglyceride transfer protein (MTP) regulation in HepG2 cells: insulin negatively regulates MTP gene expression. 1995

M C Lin, and D Gordon, and J R Wetterau
Department of Metabolic Diseases, Bristol-Myers Squibb, Princeton, NJ 08543-4000, USA.

The microsomal triglyceride transfer protein (MTP) is a heterodimeric lipid transfer protein that is required for the assembly and secretion of apoB-containing lipoproteins. In this study, four factors that modulate lipid and lipoprotein metabolism were tested for their ability to regulate MTP levels in HepG2 cells. Of the factors tested, only insulin (> or = 10(-9) M), and high concentrations of glucose (> 30 mM) were found to decrease MTP large subunit mRNA levels. Oleate and glucagon had no effect on MTP mRNA levels. The insulin effect was dose- and time-dependent and was mediated through the insulin receptor. In addition, insulin also decreased protein disulfide isomerase (the small subunit of MTP) mRNA levels, although to a lesser extent. Due to the slow turnover rate of MTP (t1/2 = 4.4 days), short-term insulin treatment (24 h) did not change MTP activity levels, indicating that the regulation of MTP mRNA levels by insulin is unrelated to insulin's acute inhibition of apoB secretion in HepG2 cells. In summary, MTP mRNA levels are acutely regulated by insulin in HepG2 cells; however, sustained changes in MTP mRNA levels would be required to affect MTP protein levels.

UI MeSH Term Description Entries
D007328 Insulin A 51-amino acid pancreatic hormone that plays a major role in the regulation of glucose metabolism, directly by suppressing endogenous glucose production (GLYCOGENOLYSIS; GLUCONEOGENESIS) and indirectly by suppressing GLUCAGON secretion and LIPOLYSIS. Native insulin is a globular protein comprised of a zinc-coordinated hexamer. Each insulin monomer containing two chains, A (21 residues) and B (30 residues), linked by two disulfide bonds. Insulin is used as a drug to control insulin-dependent diabetes mellitus (DIABETES MELLITUS, TYPE 1). Iletin,Insulin A Chain,Insulin B Chain,Insulin, Regular,Novolin,Sodium Insulin,Soluble Insulin,Chain, Insulin B,Insulin, Sodium,Insulin, Soluble,Regular Insulin
D007535 Isomerases A class of enzymes that catalyze geometric or structural changes within a molecule to form a single product. The reactions do not involve a net change in the concentrations of compounds other than the substrate and the product.(from Dorland, 28th ed) EC 5. Isomerase
D010446 Peptide Fragments Partial proteins formed by partial hydrolysis of complete proteins or generated through PROTEIN ENGINEERING techniques. Peptide Fragment,Fragment, Peptide,Fragments, Peptide
D002352 Carrier Proteins Proteins that bind or transport specific substances in the blood, within the cell, or across cell membranes. Binding Proteins,Carrier Protein,Transport Protein,Transport Proteins,Binding Protein,Protein, Carrier,Proteins, Carrier
D003864 Depression, Chemical The decrease in a measurable parameter of a PHYSIOLOGICAL PROCESS, including cellular, microbial, and plant; immunological, cardiovascular, respiratory, reproductive, urinary, digestive, neural, musculoskeletal, ocular, and skin physiological processes; or METABOLIC PROCESS, including enzymatic and other pharmacological processes, by a drug or other chemical. Chemical Depression,Chemical Depressions,Depressions, Chemical
D005947 Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Dextrose,Anhydrous Dextrose,D-Glucose,Glucose Monohydrate,Glucose, (DL)-Isomer,Glucose, (alpha-D)-Isomer,Glucose, (beta-D)-Isomer,D Glucose,Dextrose, Anhydrous,Monohydrate, Glucose
D006023 Glycoproteins Conjugated protein-carbohydrate compounds including MUCINS; mucoid, and AMYLOID glycoproteins. C-Glycosylated Proteins,Glycosylated Protein,Glycosylated Proteins,N-Glycosylated Proteins,O-Glycosylated Proteins,Glycoprotein,Neoglycoproteins,Protein, Glycosylated,Proteins, C-Glycosylated,Proteins, Glycosylated,Proteins, N-Glycosylated,Proteins, O-Glycosylated
D006207 Half-Life The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacologic, physiologic, or radiologic activity. Halflife,Half Life,Half-Lifes,Halflifes
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D012333 RNA, Messenger RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm. Messenger RNA,Messenger RNA, Polyadenylated,Poly(A) Tail,Poly(A)+ RNA,Poly(A)+ mRNA,RNA, Messenger, Polyadenylated,RNA, Polyadenylated,mRNA,mRNA, Non-Polyadenylated,mRNA, Polyadenylated,Non-Polyadenylated mRNA,Poly(A) RNA,Polyadenylated mRNA,Non Polyadenylated mRNA,Polyadenylated Messenger RNA,Polyadenylated RNA,RNA, Polyadenylated Messenger,mRNA, Non Polyadenylated

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