The Regulation of Fatty Acid Biosynthesis in Human Skin Fibroblasts

Fatty acid biosynthesis has been studied using primary cultures of human skin fibroblasts. Acetyl coenzyme A carboxylase activity of cells incubated in medium containing 15% fetal calf serum was 0.17 ± 0.01 nmole of malonyl coenzyme A formed per mg of protein per min whereas in cells incubated for 2 to 3 days in a medium with 15% lipid-deficient fetal calf serum acetyl-CoA carboxylase activity increased to a level of 0.29 ± 0.02 nmole of malonyl-CoA formed per mg of protein per min. Equivalence point determinations using an antibody against acetyl-CoA carboxylase indicate that the increase in enzyme activity results from increased enzyme content in the cells rather than from activation of preformed enzyme. The effect of lipid-deficient medium on acetyl-CoA carboxylase activity was reversed by the addition of normal fetal calf serum or by the addition of any of a number of different albumin-bound free fatty acids to the lipid-deficient medium. When cells originally incubated in medium containing normal fetal calf serum were switched to medium containing lipid-deficient fetal calf serum, an 8-fold increase in the rate of acetate incorporation into lipid was observed in the first 7 hours, whereas cells switched from lipid-deficient to normal serum-containing medium or medium supplemented with free fatty acids showed an almost immediate decrease in the rate of acetate incorporation. The changes in acetate incorporation occurred before any change in enzyme activity was seen, indicating that two types of control are exerted on fatty acid biosynthesis in these cells.