Zinc can influence ornithine decarboxylase activity in rat thymus cells

Abstract

The thymus of young rats contained a high basal activity of ornithine decarboxylase (ODC). Treatment with zinc sulphate caused a slight increase of thymic ODC activity within 6 hours and a more marked enhancement (three-fold) in the spleen 24 h after treatment. In spite of the high activity of thymic ODCin vivo, ODC was not detectable in primary cultures of rat thymocytes, but was early and largely induced after treatment with Concanavalin A (Con A). The presence of 0.1 mM zinc in the medium increased the response of ODC to Con A. This effect of zinc in mitogen activated thymocytes may be due to the stabilization of ODC, which was found to decay with a half life of 65 min after the block of protein synthesis with cycloheximide. On the contrary in absence of zinc the half life of the enzyme was 40 min, as in the rat thymus in vivo.Zinc alone, at 0.1 mM concentration, did not affect ODC activity in resting thymocytes during the early times, but the metal was able to cause an increase of the enzyme activity after 4-6 days of culture. Other heavy metals such as mercury, cadmium and copper provoked a late increase of ODC activity, but their action was evident only at dosages which were toxic for the cells.

Zinc is required for the expression of ornithine decarboxylase in a difluoromethylornithine-resistant cell line

“…Ornithine decarboxylase (ODC), the key enzyme in polyamine biosynthesis, is essential for cell proliferation and can be induced following growth stimuli [9,10]. It has been shown that ODC activity can be enhanced by Zn2+ supplementation in certain rat tissues or in cultured thymocytes [11,12]. In the present study we have investigated the effect of restricted Zn2+ availability on ODC induction and expression in L1210-DFMOr cells [13], an ODC-overproducing cell line which has been selected for resistance to the inhibitor difluoromethylornithine (DFMO).…”

“…Wild-type L1210 cells were utilized under the same experimental conditions. Thymocytes were isolated from rat thymus glands as previously described [12], diluted in RPMI 1640 medium as described above, but at a density of 107/ml and treated with 10 ,ug/ml concanavalin A for 4 h. DTPA (0.6 mM) and ZnSO4 (0.4 mM) were added 15 min before the mitogen. At the time indicated after treatment, cells were harvested and washed with PBS.…”