Growth promotion of transfected hepatoma cells by liver fatty acid binding protein

Abstract

Former studies have linked hepatocyte growth with liver fatty acid binding protein (L-FABP) of rat liver cytosol. In search for the roles of L-FABP in hepatocytes, we previously stably transfected rat L-FABP sense and antisense cDNAs into rat hepatoma HTC cells that do not contain L-FABP RNA or protein, thereby providing a zero-background, homologous cell model of L-FABP-expression suitable for controlled studies of its intracellular functions in hepatocyte-derived cells. The present study demonstrates the abilities of L-FABP to promote DNA synthesis and cell growth, preserve cell morphology, extend survival, and act cooperatively with unsaturated fatty acids in the transfected hepatoma cells in the absence of serum. Following removal of serum, the three control L-FABP-nonexpressing cell lines increased in cell lines increased in cell number for 24 hr and thereafter declined, whereas the three L-FABP-expressing cell lines exhibited a 39% higher rate of DNA synthesis per cell at 24 hr and grew in cell number for 48 hr. As a result, at 72 hr there were 2.5-fold (avg.) as many L-FABP-expressing cells than L-FABP-nonexpressing cells. In addition, the L-FABP-expressing cells retained their original polygonal morphology at 48 hr, when in contrast most of the control nonexpressing cells were spherical in shape with membrane blebs. In an effort to identify the agonists that collaborate with L-FABP in the growth promotion and preservation of cell morphology, various free fatty acids were examined at 48 hr for their ability to eliminate the differences in behavior of the two cell types in the serum-free medium. The unsaturated fatty acids, oleic acid (18:1 omega 9), linoleic acid (18:2 omega 6), alpha-linolenic acid (18:3 omega 3), and arachidonic acid (20:4 omega 6), at 1 microM markedly elevated the level of DNA synthesis in the more depressed control L-FABP-nonexpressing cells and moderately raised it in the less depressed L-FABP-expressing cells. In accord, the control L-FABP-nonexpressing cells needed 10(-6)-10(-5) M linoleic acid to achieve the extent of DNA synthesis attained by the expressing cells in the absence of added fatty acid. At 10 microM linoleic acid, their levels of DNA synthesis were equal. In contrast, five saturated fatty acids had no detectable effect on DNA synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)