Ž . Biochimica et Biophysica Acta 1379 1998 151–160 Effects of L-valine on growth and polyamine metabolism in human colon carcinoma cells Mohamed Selamnia, Veronique Robert, Camille Mayeur, Pierre-Henri Duee, ´ ´ Franc ¸ois Blachier ) Laboratoire de Nutrition et de Securite Alimentaire, bat. 230, Institut National de la Recherche Agronomique, ´ ´ ˆ 78352 Jouy-en-Josas cedex, France Received 13 June 1997; revised 18 July 1997; accepted 21 July 1997 Abstract HT-29 cells, originating from a human colon carcinoma, can proliferate in standard culture conditions with an absolute requirement for polyamines. The major precursor provided in the culture medium for polyamine 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 was to document the consequences of a total inhibition of L-arginine flux through arginase, resulting in a decreased L-ornithine availability, on HT-29 cell proliferation and polyamine metabolism. L-Valine, a known arginase inhibitor, when used at a high concentration, i.e., 100 mM, inhibits L-arginine flux through arginase almost totally. The addition in the culture medium of 100 mM L-valine or 50 mM NaCl used to mimic the L-valine induced increase in medium osmolality both reduced equally cellular growth. Cell viability, protein synthesis or oxidative metabolism measured in isolated cells were unaffected by the L-valine treatment, suggesting that decreased proliferation was not associated with 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 in the absence of the amino acid. After 4 days of treatment with 100 mM L-valine, L-ornithine flux through ornithine decarboxylase was significantly higher as well as putrescine and spermidine cellular uptakes in treated cells. However, the changes in polyamine metabolism led to similar 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 presence of L-valine which contribute together with the low amount of L-ornithine present in the culture medium to polyamine homeostasis. q 1998 Elsevier Science B.V. 1. Introduction Tumoral intestinal cell lines, although malignant and originating from colon, have provided a useful tool for the study of proliferation and differentiation w x yrq of intestinal cells 1,2 . Among them, HT-29 Glc ) Corresponding author. Fax: q33-1-34652311. cells originating from a human colon carcinoma, can spontaneously differentiate after confluency in ente- rocyte-like cells equipped with a typical brush border membrane, and expressing enzymes associated with wx this structure such as dipeptidyl peptidase IV 3. These cells are able to convert L-arginine into L- wx ornithine and polyamines 4 which have been demonstrated to be strictly necessary for optimal cell wx wx growth 5 and for cellular differentiation 6 . Posi- 0304-4165r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0304-4165 97 00095-0