MODULATION OF CELLULAR PROLIFERATION ALTERS GLUTAMINE TRANSPORT AND METABOLISM IN HUMAN HEPATOMA-CELLS

Objective The authors determined the effects of growth inhibition on g lutamine transport and metabolism in human hepatoma cells. Summary Bac kground Data Hepatoma cells exhibit markedly higher (10- to 30-fold) g lutamine uptake than normal human hepatocytes, via a disparate transpo rter protein with a higher affinity for glutamine. Currently, little i s known about the effects of growth arrest on glutamine transport and metabolism in hepatoma cells. Methods The authors determined prolifera tion rates, glutamine transport, and glutaminase activities in the hum an hepatoma cell lines HepG2, Huh-7, and SK-Hep, both in the presence and absence of the chemotherapeutic agents novobiocin and sodium butyr ate. The transport activities for alanine, arginine, and leucine also were determined in both treated and untreated cells. Glutaminase activ ity was determined in normal human liver tissue and compared with that present in hepatoma cells. Results Glutaminase activities were simila r in all three cell lines studied, despite differences in proliferatio n rates, and were sixfold higher than the activity in normal human liv er. In contrast to normal hepatocytes, which expressed the liver-speci fic glutaminase, hepatomas expressed the kidney-type isoform. Sodium b utyrate (1 mmol/L) and novobiocin (0.1 mmol/L) inhibited cellular prol iferation and reduced both glutamine transport and glutaminase activit y by more than 50% after 48 hours in the faster-growing, less differen tiated SK-Hep cells. In contrast, the agents required 72 hours to atte nuate glutamine uptake by 30% and 50% in the slower-growing, more diff erentiated HepG2 and Huh-7 cell lines, respectively. Treatment of all three cell lines with novobiocin/butyrate also resulted in a 30% to 60 % attenuation of the transport of alanine, arginine, and leucine, and glutamine, indicating that inhibition of cellular proliferation simila rly affects disparate amino acid transporters. Conclusions Hepatocellu lar transformation is characterized by a marked increase in glutamine transport and metabolism. Inhibition of cellular proliferation attenua tes glutamine transport and metabolism.