Metabolic characteristics of a human hepatoma cell line stably transfectedwith hormone-sensitive lipase

Clones of HepG2 cells were selected that stably express the cDNA for hormon e-sensitive lipase (HSL). When cells were cultured in the presence of label led extracellular oleate, accumulation of labelled fatty acid as cellular t riacylglycerol (TAG) was significantly lower in the transfectants compared with the wild-type cells. There was no change in the net rate of phospholip id (PL) synthesis. Culture of cells containing isotopically prelabelled TAG resulted in a greater net loss of TAG from the transfected cells than from the wild-type cells. The excess loss of labelled TAG was primarily due to an increased TAG fatty acid oxidation. Free fatty acid release into the med ium was not increased in the transfectants, nor was the very low rate of li poprotein lipid secretion. Also, there was no increased net trafficking of fatty acids from TAG into PLs. Changes in the H-3:C-14 ratio of TAG prelabe lled with [H-3]glycerol and [C-14]oleate suggested that none of excess TAG fatty acid released in the transfected cells underwent intracellular re-est erification to TAG prior to oxidation. The results suggest that fatty acids mobilized by HSL are directed immediately into the oxidative pathway and a re not available for biosynthetic processes. It appears likely, therefore, that intracellular TAG-derived fatty acids which enter the oxidative pathwa y exist in a different compartment from those that are directed towards syn thesis.