EFFECTS OF L-VALINE ON GROWTH AND POLYAMINE METABOLISM IN HUMAN COLON-CARCINOMA CELLS

HT-29 cells, originating from a human colon carcinoma, can proliferate in standard culture conditions with an absolute requirement for polya mines. The major precursor provided in the culture medium for polyamin e biosynthesis is L-arginine. L-Arginine conversion to L-ornithine by arginase is followed by stepwise conversion of this latter amino acid to putrescine, spermidine and spermine. The aim of the present work wa s to document the consequences of a total inhibition of L-arginine flu x through arginase, resulting in a decreased L-ornithine availability, on HT-29 cell proliferation and polyamine metabolism, L-Valine, a kno wn arginase inhibitor, when used at a high concentration, i.e., 100 mM , inhibits L-arginine flux through arginase almost totally. The additi on in the culture medium of 100 mM L-valine or 50 mM NaCl used to mimi c the L-valine induced increase in medium osmolality both reduced equa lly cellular growth. Cell viability, protein synthesis or oxidative me tabolism measured in isolated cells were unaffected by the L-valine tr eatment, suggesting that decreased proliferation was not associated wi th an acute toxic effect of this aminoacid, but was rather due to the increase in the medium osmolality. L-Valine treated cells displayed an altered polyamine metabolism when compared with control cells grown i n the absence of the amino acid, After 4 days of treatment with 100 mM L-valine, L-ornithine flux through ornithine decarboxylase was signif icantly higher as well as putrescine and spermidine cellular uptakes i n treated cells. However, the changes in polyamine metabolism led to s imilar polyamine cell contents in untreated and L-valine treated cells . In conclusion, we propose that the observed alterations of polyamine metabolism may reflect an adaptative response of HT-29 cells to the p resence of L-valine which contribute together with the low amount of L -ornithine present in the culture medium to polyamine homeostasis. (C) 1998 Elsevier Science B.V.