Original Article

Evidence that microsomal triglyceride transfer protein is limiting in the production of apolipoprotein B-containing lipoproteins in hepatic cells

Correspondence to: Haris Jamil.

The microsomal triglyceride transfer protein (MTP) is a heterodimeric lipid transfer protein that is required for the assembly and secretion of apolipoprotein B (apoB)-containing lipoproteins. A key unresolved question is whether the MTP-mediated step is rate limiting. To address this, a unique experimental strategy was used that allowed the in situ modulation and measurement of MTP triglyceride transfer activity. In order to accomplish this, an irreversible photoaffinity inhibitor, BMS-192951, was designed and synthesized. When incubated with purified MTP and irradiated with UV light at 360 nm, BMS -192951 inhibits triglyceride transfer by covalently binding to the protein. HepG2 cells were treated with either increasing concentrations of BMS-192951 (0–15 µM) with 5 min of ultraviolet irradiation, or 3.0 µM BMS-192951 with various lengths (0–15 min) of ultraviolet irradiation. Microsomal extracts were prepared exhaustively dialyzed to remove unbound inhibitor, and assayed for MTP-mediated triglyceride transfer activity. BMS -192951 was shown to reduce MTP activity in both a dose- and UV exposure time-dependent fashion. Measurement of apoB concentration in the media showed that apoB secretion was reduced in proportion to the in situ inhibition of MTP activity, while no change was observed in apoA-I secretion. Experiments performed in McArdle RH-7777 rat hepatoma cells and primary rat hepatocytes gave nearly identical results; the decrease in apoB secretion was proportional to the decrease in MTP activity.

These results indicate that MTP-mediated lipid transfer is limiting in the assembly and secretion of apoB -containing lipoproteins in hepatic cells under the conditions tested.—Jamil, H., C-H. Chu, J. K. Dickson, Jr., Y. Chen, M. Yan, S. A. Biller, R. E. Gregg, J. R. Wetterau, and D. A. Gordon. Evidence that microsomal triglyceride transfer protein is limiting in the production of apolipoprotein B -containing lipoproteins in hepatic cells. J. Lipid Res. 1998. 39: 1448–1454.

Supplementary key words: lipid transfer protein, protein disulfide isomerase, photoaffinity, benzophenone, HepG2 cells, McArdle RH-7777 cells, cholesteryl ester, phosphatidylcholine

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				S. K. Dougan, P. Rava, M. M. Hussain, and R. S. Blumberg MTP regulated by an alternate promoter is essential for NKT cell development J. Exp. Med., March 19, 2007; 204(3): 533 - 545. [Abstract] [Full Text] [PDF]

				A. M. Domitrovich, D. J. Felmlee, and A. Siddiqui Hepatitis C Virus Nonstructural Proteins Inhibit Apolipoprotein B100 Secretion J. Biol. Chem., December 2, 2005; 280(48): 39802 - 39808. [Abstract] [Full Text] [PDF]

				A. Nebel, P. J. P. Croucher, R. Stiegeler, S. Nikolaus, M. Krawczak, and S. Schreiber No association between microsomal triglyceride transfer protein (MTP) haplotype and longevity in humans PNAS, May 31, 2005; 102(22): 7906 - 7909. [Abstract] [Full Text] [PDF]

				G. F. Lewis, K. Uffelman, M. Naples, L. Szeto, M. Haidari, and K. Adeli Intestinal Lipoprotein Overproduction, a Newly Recognized Component of Insulin Resistance, Is Ameliorated by the Insulin Sensitizer Rosiglitazone: Studies in the Fructose-Fed Syrian Golden Hamster Endocrinology, January 1, 2005; 146(1): 247 - 255. [Abstract] [Full Text] [PDF]

				B. J. Geesaman, E. Benson, S. J. Brewster, L. M. Kunkel, H. Blanche, G. Thomas, T. T. Perls, M. J. Daly, and A. A. Puca Haplotype-based identification of a microsomal transfer protein marker associated with the human lifespan PNAS, November 25, 2003; 100(24): 14115 - 14120. [Abstract] [Full Text] [PDF]

				S. Kang, N. J. Spann, T. Y. Hui, and R. A. Davis ARP-1/COUP-TF II Determines Hepatoma Phenotype by Acting as Both a Transcriptional Repressor of Microsomal Triglyceride Transfer Protein and an Inducer of CYP7A1 J. Biol. Chem., August 15, 2003; 278(33): 30478 - 30486. [Abstract] [Full Text] [PDF]

				J. Bjorkegren, A. Beigneux, M. O. Bergo, J. J. Maher, and S. G. Young Blocking the Secretion of Hepatic Very Low Density Lipoproteins Renders the Liver More Susceptible to Toxin-induced Injury J. Biol. Chem., February 8, 2002; 277(7): 5476 - 5483. [Abstract] [Full Text] [PDF]

				J. A. Sellers and G. S. Shelness Lipoprotein assembly capacity of the mammary tumor-derived cell line C127 is due to the expression of functional microsomal triglyceride transfer protein J. Lipid Res., November 1, 2001; 42(11): 1897 - 1904. [Abstract] [Full Text] [PDF]

				J. P. Segrest, M. K. Jones, H. De Loof, and N. Dashti Structure of apolipoprotein B-100 in low density lipoproteins J. Lipid Res., September 1, 2001; 42(9): 1346 - 1367. [Abstract] [Full Text] [PDF]

				R. A. Davis and T. Y. Hui 2000 George Lyman Duff Memorial Lecture : Atherosclerosis Is a Liver Disease of the Heart Arterioscler. Thromb. Vasc. Biol., June 1, 2001; 21(6): 887 - 898. [Abstract] [Full Text] [PDF]

				Z. Li, Y. Kako, L. Pang, M. W. Freeman, J. M. Glick, X. Wang, and I. J. Goldberg Effects of overexpression of the amino-terminal fragment of apolipoprotein B on apolipoprotein B and lipoprotein production J. Lipid Res., December 1, 2000; 41(12): 1912 - 1920. [Abstract] [Full Text]

				G. F. Watts, F. M. Riches, S. E. Humphries, P. J. Talmud, and F. M. van Bockxmeer Genotypic associations of the hepatic secretion of VLDL apolipoprotein B-100 in obesity J. Lipid Res., March 1, 2000; 41(3): 481 - 488. [Abstract] [Full Text]

				U. J.F. Tietge, A. Bakillah, C. Maugeais, K. Tsukamoto, M. Hussain, and D. J. Rader Hepatic overexpression of microsomal triglyceride transfer protein (MTP) results in increased in vivo secretion of VLDL triglycerides and apolipoprotein B J. Lipid Res., November 1, 1999; 40(11): 2134 - 2139. [Abstract] [Full Text]

				A.-M. Hebbachi, A.-M. Brown, and G. F. Gibbons Suppression of cytosolic triacylglycerol recruitment for very low density lipoprotein assembly by inactivation of microsomal triglyceride transfer protein results in a delayed removal of apoB-48 and apoB-100 from microsomal and Golgi membranes of primary rat hepatocytes J. Lipid Res., October 1, 1999; 40(10): 1758 - 1768. [Abstract] [Full Text]

				E. Nicodeme, F. Benoist, R. McLeod, Z. Yao, J. Scott, C. C. Shoulders, and T. Grand-Perret Identification of Domains in Apolipoprotein B100 That Confer a High Requirement for the Microsomal Triglyceride Transfer Protein J. Biol. Chem., January 22, 1999; 274(4): 1986 - 1993. [Abstract] [Full Text] [PDF]

				D. K. Spady, M. N. Willard, and R. S. Meidell Role of Acyl-Coenzyme A:Cholesterol Acyltransferase-1 in the Control of Hepatic Very Low Density Lipoprotein Secretion and Low Density Lipoprotein Receptor Expression in the Mouse and Hamster J. Biol. Chem., August 25, 2000; 275(35): 27005 - 27012. [Abstract] [Full Text] [PDF]

				E. A. Fisher, M. Pan, X. Chen, X. Wu, H. Wang, H. Jamil, J. D. Sparks, and K. J. Williams The Triple Threat to Nascent Apolipoprotein B. EVIDENCE FOR MULTIPLE, DISTINCT DEGRADATIVE PATHWAYS J. Biol. Chem., July 20, 2001; 276(30): 27855 - 27863. [Abstract] [Full Text] [PDF]