Effect of dexamethasone, 2-bromopalmitate and clofibrate on L-FABP mediated hepatoma proliferation

Cytosolic liver fatty acid binding protein (L-FABP) is involved in many intracellular functions including cellular mitogenesis. We investigated the role of L-FABP and the plasma membrane liver fatty acid binding proteins (L-FABP(pm)) in the modulation of hepatoma growth and proliferation, hypothesizing that agents that affect either the content of, or ligand binding to, L-FABP would affect hepatocellular mitogenesis. L-FABP expressing 1548-rat hepatoma cells were treated with 0.5 microM dexamethasone or 500 microM clofibrate for 4 days to downregulate and upregulate L-FABP expression, respectively. The competitive inhibitor 2-bromopalmitate (BrPA, 600 microM) was used to inhibit ligand binding to L-FABP. The peripherally present plasma membrane fatty acid transporter was inactivated by treating cells with 1:50 rabbit antisera (FABP-Ab) raised against L-FABP. Western blot analysis was used to monitor L-FABP levels while [(3)H]-thymidine incorporation and growth curves were used to monitor hepatocellular proliferation. [(3)H]-Palmitate clearance studies were performed using monolayer cultures. Palmitate clearance in dexamethasone-, BrPA- and FABP-Ab-treated cells was significantly reduced when compared with control (P < 0.05), while clofibrate treatment moderately increased the rate. [(3)H]-Thymidine incorporation by dexamethasone- and BrPA-treated cells was significantly lower than control (P < 0.05), suggesting that hepatocellular proliferation was inhibited. Clofibrate treatment did not statistically affect growth rate. Lowering L-FABP using dexamethasone or interfering with its activity using BrPA significantly affected hepatocellular proliferation. This may be due to the non-availability of long-chain fatty acids or other intracellular mediators that are transported by L-FABP to the nucleus.