ApoA-IV is secreted on discrete HDL particles by the rat hepatoma cell line McA-RH7777 transfected with ApoA-IV cDNA.
In the present study, the synthesis and secretion of transfected apolipoprotein (apo) A-IV was investigated in rat hepatoma McA-RH7777, a cell line that does not express apoA-IV mRNA or protein. An expression plasmid that contained the rat apoA-IV cDNA was transfected into the cells; five stable transformants were selected that harbor different copy numbers of the apoA-IV construct and secrete different amounts of apoA-IV. Gel filtration column chromatography and density gradient ultracentrifugation, combined with gel electrophoresis and electron microscopy techniques, demonstrated that (1) the secreted apoA-IV associated mainly with high-density lipoproteins (HDLs) and only a trace amount of apoA-IV was associated with very-low-density lipoproteins; (2) overexpression of apoA-IV resulted in an increased number of disk-shaped structures (thickness, approximately 8.0 nm and diameter, approximately 22 nm); and (3) the electrophoretic mobilities of the apoA-IV-containing particles differed from those of apoA-I-containing HDL. Expression of apoA-IV exerted no discernible effect on the density distribution or the secretion efficiency of apoB-100. Additionally, secretion of apoB-100 and apoA-IV exhibited opposite responses to serum: apoB-100 secretion was stimulated eightfold after addition of serum, whereas apoA-IV secretion was inhibited by 40%. These results suggest that synthesis of apoA-IV may lead to the formation of a subclass of HDL with a different metabolic fate than that of lipoproteins containing either apoA-I or apoB.
Yao
Z
Z
Lipid and Lipoprotein Research Group, University of Alberta, Edmonton, Canada.
Lauer
S J
SJ
Sanan
D A
DA
Fazio
S
S
D000818:Animals; D001054:Apolipoproteins A / Q000235:genetics* / Q000378:metabolism*; D018076:DNA, Complementary; D004586:Electrophoresis; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000378:metabolism* / Q000648:ultrastructure; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D008854:Microscopy, Electron; D051381:Rats; D011994:Recombinant Proteins; D014162:Transfection; D014407:Tumor Cells, Cultured
D001054:Apolipoproteins A; D018076:DNA, Complementary; D008075:Lipoproteins, HDL; D011994:Recombinant Proteins; C022205:apolipoprotein A-IV