Abstract
Expression of apolipoprotein C-III in McA-RH7777 cells enhances VLDL assembly and secretion under lipid-rich conditions
Highlights
IntroductionApolipoprotein (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
Apolipoprotein C-III plays a regulatory role in VLDL lipolysis and clearance
Transient transfection of apoC-III into McA-RH7777 cells, a rat hepatoma cell line that does not express endogenous apoC-III, resulted in increased secretion of [3H]glycerollabeled TAG compared with CMV5 vector transfected controls under lipid-rich conditions (Fig. 1A)
Summary
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. 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. Expression of apoC-III in McA-RH7777 cells enhances hepatic TAG-rich VLDL assembly and secretion under lipid-rich conditions.—Sundaram, M., S. The positive correlation between apoC-III and plasma TAG is mainly attributable to the roles of apoC-III in i) inhibiting lipolytic activity of LPL [10, 11], and ii) attenuating the binding of TAG-rich lipoproteins to heparin sulfate proteoglycans [12] and LDL receptor [13] and preventing uptake
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