PROTEIN-KINASE-C REGULATES NUTRIENT-UPTAKE AND GROWTH IN HEPATOMA-CELLS

Background. Human hepatoma cells extract glutamine at rates severalfol d greater than normal hepatocytes through a high-affinity transporter encoded by the ATB(0) gene, which contains two putative phosphorylatio n sites for protein kinase C (PKC). The studies presented here were un dertaken to determine whether Sq stem B-0-mediated glutamine uptake re gulates hepatoma growth and whether PKC regulates the activity of this transporter. Methods. SK-Hep cells were treated with the PKC activato r phorbol 12-myristate 13-acetate (PMA) and the initial-rate transport of glutamine and other nutrients measured at specific times thereafte r. Growth rates were monitored during culture +/- PMA or an excess of system B-0 substrates relative to glutamine. Results. PMA treatment ex erted a rapid (half-life similar to 15 minutes) concentration-dependen t inhibition of glutamine uptake rates to 50% of control values via a posttranslational mechanism that decreased transporter maximum velocit y. This effect persisted after 24 hours and was abrogated by the PKC i nhibitor staurosporine. PMA also significantly decreased amino acid tr ansport System y(+) and System L, activities but not System A. Chronic treatment with PMA (PKC depletion) inhibited SK-Hep growth, as did at tenuation of System B-0-mediated! glutamine uptake with other. B-0 sub strates. Conclusions, System B-0-mediated glutamine uptake regulates h epatoma cell growth, whereas PKC influences both processes.