LIVER FATTY-ACID-BINDING PROTEIN EXPRESSION IN TRANSFECTED FIBROBLASTS STIMULATES FATTY-ACID UPTAKE AND METABOLISM

The role of cytosolic liver fatty acid binding protein (L-FABP) in fat ty acid uptake and metabolism was examined using cultured L-cell fibro blasts transfected with the cDNA encoding for L-FABP. [H-3]oleic acid was used to determine the effects of intracellular esterification on f atty acid uptake and to determine esterified fatty acid localization t o specific lipid classes. cis-Parinaric acid, a poorly esterified fatt y acid, was used to determine uptake in the absence of any appreciable esterification. High-expression L-cells had a 80% and 50% greater ini tial uptake rate for both [H-3]oleic acid and cis-parinaric acid, resp ectively compared to low-expression L-cells. Maximal uptake of [H-3]ol eic acid did not plateau because of intracellular esterification. In h igh-expressing cells, maximal cis-parinaric acid uptake rapidly platea ued at a level 34% higher than in low-expression cells. After 1 min of incubation, the majority of cellular [H-3]oleic acid was unesterified , with the bulk of the esterified portion preferentially localized to phospholipids. After 5 and 30 min, cells expressing L-FABP esterified a significantly greater amount of [H-3]oleic acid into both the neutra l lipid and phospholipid fractions than did low-expression cells. L-FA BP expression also selectively stimulated [H-3]oleic acid incorporatio n into choline glycerophospholipids. Thus, L-FABP expression not only stimulated fatty acid uptake at all time points, but also stimulated i ntracellular esterification into specific lipid pools. These results s how in detail for the first time using an intact cell culture system t hat L-FABP expression not only stimulated fatty acid uptake, but also increased intracellular esterification of exogenously supplied fatty a cids.