Institution: | a Department of Animal Physiology, Faculty of Veterinary Medicine, Warsaw Agricultural University, Nowoursynowska 166, 02-787, Warsaw, Poland b Department of Gastroenterology, Medical Center for Postgraduate Education, Warsaw, Poland c Department of Plant Genetics and Breeding in Horticulture, Faculty of Horticulture, Warsaw Agricultural University, Warsaw, Poland d Department of Pathology, Faculty of Veterinary Medicine, Warsaw Agricultural University, Warsaw, Poland |
Abstract: | Previous studies have shown that growth suppression and apoptosis of leukemic cells exposed to TGF-β1 is associated with the inhibition of ornithine decarboxylase (ODC) — the key enzyme of polyamine pathway. The aim of the present study was to evaluate the influence of 12-O-tetradecanoylphorbol 13-acetate (TPA) — a potent ODC inducer on antiproliferative and apoptotic effects of TGF-β1 in L1210 leukemic cells. Cells were incubated in 2%FCS/RPMI1640 medium, supplemented with TGF-β1 (2 ng/ml), TPA (100 ng/ml) or -difluoromethyl-ornithine (DFMO) (5 mM). Cell proliferation, apoptosis and necrosis were evaluated using methyl-3H] thymidine, electron microscopy, electrophoresis of DNA and trypan blue exclusion. Expression and activity of ODC were determinated by RT-PCR and measurement of 14CO2 release from L-1-14C ornithine, respectively. TGF-β1 inhibited proliferation and induced apoptotic and necrotic cell death in L1210 leukemic cells. The above effects were associated with the inhibition of ODC expression and activity, measured 2 and 4 hr after TGF-β1 administration, respectively. The presence of DFMO, an irreversible inhibitor of ODC, led to apoptotic fragmentation of DNA, similar to that observed in TGF-β1-treated cultures. Administration of TPA simultaneously with TGF-β1 significantly reduced antiproliferative, apoptotic and necrotic effects of TGF-β1, and prevented its inhibitory action on ODC expression and activity. It is concluded that: down-regulation of ODC expression may be one of the early events associated with TGF-β1-evoked suppression of growth and apoptosis; ODC is involved in the mechanism of protective action of TPA on TGF-β1-related growth inhibition of L1210 leukemic cells. |