title: Expression of apolipoprotein C-III in McA-RH7777 cells enhances VLDL assembly and secretion under lipid-rich conditions.
abstract: Apolipoprotein (apo) C-III plays a regulatory role in VLDL lipolysis and clearance. In this study, we determined a potential intracellular role of apoC-III in hepatic VLDL assembly and secretion. Stable expression of recombinant apoC-III in McA-RH7777 cells resulted in increased secretion efficiency of VLDL-associated triacylglycerol (TAG) and apoB-100 in a gene-dosage-dependent manner. The stimulatory effect of apoC-III on TAG secretion was manifested only when cells were cultured under lipid-rich (i.e., media supplemented with exogenous oleate) but not lipid-poor conditions. The stimulated TAG secretion was accompanied by increased secretion of apoB-100 and apoB-48 as VLDL(1). Expression of apoC-III also increased mRNA and activity of microsomal triglyceride transfer protein (MTP). Pulse-chase experiments showed that apoC-III expression promoted VLDL(1) secretion even under conditions where the MTP activity was inhibited immediately after the formation of lipid-poor apoB-100 particles, suggesting an involvement of apoC-III in the second-step VLDL assembly process. Consistent with this notion, the newly synthesized apoC-III was predominantly associated with TAG within the microsomal lumen that resembled lipid precursors of VLDL. Introducing an Ala23-to-Thr mutation into apoC-III, a naturally occurring mutation originally identified in two Mayan Indian subjects with hypotriglyceridemia, abolished the ability of apoC-III to stimulate VLDL secretion from transfected cells. Thus, expression of apoC-III in McA-RH7777 cells enhances hepatic TAG-rich VLDL assembly and secretion under lipid-rich conditions.
authors.affiliation: Department of Biochemistry, Microbiology and Immunology, Department of Pathology and Laboratory Medicine, Ottawa Institute of Systems Biology, University of Ottawa Canada K1H 8M5.
authors.forename: Meenakshi
authors.initials: M
authors.lastname: Sundaram
authors.forename: Shumei
authors.initials: S
authors.lastname: Zhong
authors.forename: Maroun
authors.initials: M
authors.lastname: Bou Khalil
authors.forename: Philip H
authors.initials: PH
authors.lastname: Links
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhao
authors.forename: Jahangir
authors.initials: J
authors.lastname: Iqbal
authors.forename: M Mahmood
authors.initials: MM
authors.lastname: Hussain
authors.forename: Robin J
authors.initials: RJ
authors.lastname: Parks
authors.forename: Yuwei
authors.initials: Y
authors.lastname: Wang
authors.forename: Zemin
authors.initials: Z
authors.lastname: Yao
mesh_terms: D000818:Animals; D053299:Apolipoprotein B-100 / Q000378:metabolism*; D053283:Apolipoprotein B-48 / Q000378:metabolism*; D053305:Apolipoprotein C-III / Q000096:biosynthesis* / Q000235:genetics; D002352:Carrier Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D015243:Cholesterol, VLDL / Q000378:metabolism*; D018628:Gene Dosage; D055785:Gene Knockdown Techniques; D006801:Humans; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D014162:Transfection; D014280:Triglycerides / Q000378:metabolism*
chemical_list: D053299:Apolipoprotein B-100; D053283:Apolipoprotein B-48; D053305:Apolipoprotein C-III; D002352:Carrier Proteins; D015243:Cholesterol, VLDL; D034741:RNA, Small Interfering; D014280:Triglycerides; C106092:microsomal triglyceride transfer protein