201. Expression of apolipoprotein C-III in McA-RH7777 cells enhances VLDL assembly and secretion under lipid-rich conditions[S]
- Author
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Meenakshi Sundaram, Shumei Zhong, Maroun Bou Khalil, Philip H. Links, Yang Zhao, Jahangir Iqbal, M. Mahmood Hussain, Robin J. Parks, Yuwei Wang, and Zemin Yao
- Subjects
triacylglycerol ,hypotriglyceridemia ,hypertriglyceridemia ,microsomal triglyceride transfer protein ,hepatocyte ,Biochemistry ,QD415-436 - 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 VLDL1. Expression of apoC-III also increased mRNA and activity of microsomal triglyceride transfer protein (MTP). Pulse-chase experiments showed that apoC-III expression promoted VLDL1 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.
- Published
- 2010
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