EFFECT OF OROTIC-ACID ON TGF-BETA-1-INDUCED GROWTH-INHIBITION OF L1210 LEUKEMIC-CELLS

Transforming growth factor-beta 1 (TGF-beta 1) exerted growth-inhibito ry effect on L1210 leukemic cell line, manifested by the decrease in v iable and increase in dead cells, The cell death evoked by TGF-beta 1 was both necrotic and apoptotic, quantified by the trypan blue exclusi on method and apoptotic index, respectively. The induction of programm ed cell death by TGF-beta 1 was confirmed by gel electrophoresis of DN A, where the characteristic 'DNA ladder' resulting from the internucle osomal DNA cleavage was visualized. The enhancement of cell mortality by TGF-beta 1 was associated with the inhibition of ornithine decarbox ylase (ODC) expression (measured by the reverse transcriptase-polymera se chain reaction method) and impaired activity of this key enzyme in polyamine synthesis, Orotic acid (OA) - a known tumor promoter - stimu lated proliferation of L1210 leukemic cells and diminished the necroti c effect of TGF-beta 1, but it did not change the extent of apoptosis evoked by TGF-beta 1. OA increased the expression of ODC and diminishe d depressional influence of TGF-beta 1 on transcription and activity o f ODC in leukemic cells. In conclusion: OA is a bioactive compound sti mulating the growth of leukemic cells and diminishing the growth-inhib itory effect of TGF-beta 1. ODC gene is probably one of the targets fo r both OA and TGF-beta 1 influences in L1210 leukemic cells.