Microsomal Triglyceride Transfer Protein Activity is Not Required for the Initiation of Apolipoprotein B-containing Lipoprotein Assembly in Mca-rh7777 Cells.
From: Department of Medicine, University of Alabama at Birmingham Medical Center, Birmingham, Alabama 35294, USA. ndashti@uab.edu
The Journal of biological chemistry
- Publish Date: Sep 2007
- ISSN: 0021-9258
- Volume: 282
- Issue: 39
- Pages: 28597-608
- Medium: Print
- Language: English
- Citation (JAMA): Dashti Nassrin, Manchekar Medha, Liu Yanwen, et al. Microsomal Triglyceride Transfer Protein Activity is Not Required for the Initiation of Apolipoprotein B-containing Lipoprotein Assembly in Mca-rh7777 Cells.. J. Biol. Chem. Sep 2007;282:28597-608
Abstract
We previously demonstrated that the N-terminal 1000 amino acid residues of human apolipoprotein (apo) B (designated apoB:1000) are competent to fold into a three-sided lipovitellin-like lipid binding cavity to form the apoB “lipid pocket” without a structural requirement for microsomal triglyceride transfer protein (MTP). Our results established that this primordial apoB-containing particle is phospholipid-rich (Manchekar, M., Richardson, P. E., Forte, T. M., Datta, G., Segrest, J. P., and Dashti, N. (2004) J. Biol. Chem. 279, 39757-39766). In this study we have investigated the putative functional role of MTP in the initial lipidation of apoB:1000 in stable transformants of McA-RH7777 cells. Inhibition of MTP lipid transfer activity by 0.1 microm BMS-197636 and 5, 10, and 20 microm of BMS-200150 had no detectable effect on the synthesis, lipidation, and secretion of apoB:1000-containing particles. Under identical experimental conditions, the synthesis, lipidation, and secretion of endogenous apoB100-containing particles in HepG2 and parental untransfected McA-RH7777 cells were inhibited by 86-94%. BMS-200150 at 40 microm nearly abolished the secretion of endogenous apoB100-containing particles in HepG2 and parental McA-RH cells but caused only 15-20% inhibition in the secretion of apoB: 1000-containing particles. This modest decrease was attributable to the nonspecific effect of a high concentration of this compound on hepatic protein synthesis, as reflected in a similar (20-25%) reduction in albumin secretion. Suppression of MTP gene expression in stable transformants of McA-RH7777 cells by micro-interfering RNA led to 60-70% decrease in MTP mRNA and protein levels, but it had no detectable effect on the secretion of apoB:1000. Our results provide a compelling argument that the initial addition of phospholipids to apoB:1000 and initiation of apoB-containing lipoprotein assembly occur independently of MTP lipid transfer activity.
Mesh Headings (Keywords): Albumins, Animals, Apolipoprotein B-100, Binding Sites, Carrier Proteins, Cell Line, Tumor, Dose-Response Relationship, Drug, Egg Proteins, Humans, Indoles, Isoindoles, Liver, Phospholipids, Piperidines, Protein Biosynthesis, RNA, Small Interfering, Rats
Check for Full Text / PubMed Unique Identifier (PMID): 17690102
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