SPECIFIC DEPLETION OF SPERMIDINE AND SPERMINE IN HTC CELLS TREATED WITH INHIBITORS OF AMINOPROPYLTRANSFERASES

The effects of a potent spermidine synthase inhibitor, trans-4-methylc yclohexylamine (4MCHA), and a spermine synthase inhibitor, N-(3-aminop ropyl)cyclohexylamine (APCHA), on polyamine biosynthesis and cell grow th have been studied in rat hepatoma cells (HTC cells) in culture, Tre atment of HTC cells with 4MCHA or APCHA caused a marked decrease of sp ermidine or spermine with a compensatory increase of putrescine and sp ermine or spermidine, respectively, in a dose-dependent manner, sugges ting specific and potent inhibition of each target enzyme, When 250 mu M 4MCHA or APCHA was administered to the cells for 8 days, spermidine was decreased to 2% of control culture or spermine below 1%, respecti vely, while total polyamine (sum of putrescine, spermidine, and spermi ne) remained almost unchanged during the culture, There were no signif icant changes in the growth rate during treatment with the inhibitors at 250 mu M concentration, The results suggest that in the growth of H TC cells, putrescine and spermine can be substituted for most of the f raction of cellular spermidine, and spermidine for most of the fractio n of cellular spermine, Of five enzymatic activities involved in polya mine biosynthesis and interconversion, S-adenosylmethionine decarboxyl ase activity increased 8-fold with 250 mu M 4MCHA, and 3-fold with 250 mu M APCHA during the treatment, This increase was partially due to t he increase of half-life of the enzyme, Separate roles for spermidine and spermine in the biosynthesis of the enzyme protein were also sugge sted,