The Fao cell. A tissue culture model for lipoprotein synthesis and secretion. II. Modulation by lipid depletion and supplementation.
We have shown that the Fao cell, a differentiated rat hepatoma line, is an excellent model for the study of the synthesis of lipoproteins (Scarino, M L & Howell, K E, Exp cell res 170 (1987) 1 [1]. Here we demonstrate that variation of the lipid composition of the growth medium significantly modulates the composition and quantity of particles formed. Three growth conditions were compared: normal, lipid-depleted, and lipid-supplemented. The synthesis of both the protein and lipid moieties of the lipoproteins was quantitated using the radioactive metabolic precursors [35S]methionine and [14C]acetate. The total secretion of the cells was collected and fractionated into four density classes equivalent to plasma lipoproteins and a bottom fraction equivalent to plasma proteins. Each density class was evaluated for the apoprotein distribution after separation by SDS-PAGE and for lipid distribution and composition after lipid extraction. ApoE accounts for approx. 15% of the total protein synthesized and is the major apoprotein. The amount synthesized remains relatively constant under all growth conditions. In contrast, the amount of apoB synthesis varies over 600-fold. In lipid-depleted conditions, only 0.01 times the normal amount was synthesized, while in lipid-supplemented conditions 6.2 times the normal amount was synthesized. ApoB was associated with the lighter fraction; therefore the modulation increased the quantity of low-density particles formed. A similar but far less pronounced variation of the heavier particles and the apoA-I concentration was obtained. Under lipid-depleted conditions, 0.75 times the normal amount was synthesized, while under lipid-supplemented conditions 2.6 times the normal quantity was synthesized.
D000085:Acetates / Q000378:metabolism; D000818:Animals; D002250:Carbon Radioisotopes; D002460:Cell Line; D003470:Culture Media; D007457:Iodine Radioisotopes; D008055:Lipids; D008074:Lipoproteins / Q000096:biosynthesis / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D008715:Methionine / Q000378:metabolism; D008854:Microscopy, Electron; D051381:Rats; D011919:Rats, Inbred Strains; D013462:Sulfur Radioisotopes
D000085:Acetates; D002250:Carbon Radioisotopes; D003470:Culture Media; D007457:Iodine Radioisotopes; D008055:Lipids; D008074:Lipoproteins; D013462:Sulfur Radioisotopes; D008715:Methionine