Functional analysis of the missense APOC3 mutation Ala23Thr associated with human hypotriglyceridemia

J Lipid Res. 2010 Jun;51(6):1524-34. doi: 10.1194/jlr.M005108. Epub 2010 Jan 23.


We have shown that expression of apolipoprotein (apo) C-III promotes VLDL secretion from transfected McA-RH7777 cells under lipid-rich conditions. To determine structural elements within apoC-III that confer to this function, we contrasted wild-type apoC-III with a mutant Ala23Thr originally identified in hypotriglyceridemia subjects. Although synthesis of [(3)H]glycerol-labeled TAG was comparable between cells expressing wild-type apoC-III (C3wt cells) or Ala23Thr mutant (C3AT cells), secretion of [(3)H]TAG from C3AT cells was markedly decreased. The lowered [(3)H]TAG secretion was associated with an inability of C3AT cells to assemble VLDL(1). Moreover, [(3)H]TAG within the microsomal lumen in C3AT cells was 60% higher than that in C3wt cells, yet the activity of microsomal triglyceride-transfer protein in C3AT cells was not elevated. The accumulated [(3)H]TAG in C3AT microsomal lumen was mainly associated with lumenal IDL/LDL-like lipoproteins. Phenotypically, this [(3)H]TAG fractionation profiling resembled what was observed in cells treated with brefeldin A, which at low dose specifically blocked the second-step VLDL(1) maturation. Furthermore, lumenal [(35)S]Ala23Thr protein accumulated in IDL/LDL fractions and was absent in VLDL fractions in C3AT cells. These results suggest that the presence of Ala23Thr protein in lumenal IDL/LDL particles might prevent effective fusion between lipid droplets and VLDL precursors. Thus, the current study reveals an important structural element residing within the N-terminal region of apoC-III that governs the second step VLDL(1) maturation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alanine / genetics
  • Apolipoproteins C / chemistry
  • Apolipoproteins C / genetics*
  • Apolipoproteins C / metabolism*
  • Brefeldin A / pharmacology
  • Carrier Proteins / metabolism
  • Cell Line
  • Gene Expression Regulation
  • Humans
  • Lipid Metabolism Disorders / genetics*
  • Lipoproteins, IDL / metabolism
  • Lipoproteins, LDL / metabolism
  • Lipoproteins, VLDL / metabolism
  • Microsomes / metabolism
  • Models, Molecular
  • Mutation, Missense*
  • Protein Binding / drug effects
  • Protein Structure, Secondary
  • Threonine / genetics
  • Triglycerides / metabolism*


  • Apolipoproteins C
  • Carrier Proteins
  • Lipoproteins, IDL
  • Lipoproteins, LDL
  • Lipoproteins, VLDL
  • Triglycerides
  • microsomal triglyceride transfer protein
  • Brefeldin A
  • Threonine
  • Alanine