Expression of apolipoprotein C-III in McA-RH7777 cells enhances VLDL assembly and secretion under lipid-rich conditions.
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.
Sundaram
Meenakshi
M
Department of Biochemistry, Microbiology and Immunology, Department of Pathology and Laboratory Medicine, Ottawa Institute of Systems Biology, University of Ottawa Canada K1H 8M5.
Zhong
Shumei
S
Bou Khalil
Maroun
M
Links
Philip H
PH
Zhao
Yang
Y
Iqbal
Jahangir
J
Hussain
M Mahmood
MM
Parks
Robin J
RJ
Wang
Yuwei
Y
Yao
Zemin
Z
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*
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