EFFECTS OF THE S-ADENOSYLMETHIONINE DECARBOXYLASE INHIBITOR, -4-AMINO-2-BUTENYL]METHYLAMINO)-5'-DEOXYADENOSINE, ON CELL-GROWTH AND POLYAMINE METABOLISM AND TRANSPORT IN CHINESE-HAMSTER OVARY CELL-CULTURES

The regulation of polyamine transport and the roles of polyamine trans port and synthesis in cell growth were investigated using cultured Chi nese hamster ovary (CHO) cells and CHOMG cells which are mutants lacki ng polyamine-transport activity. Metabolically stable methylated polya mine analogues were used to measure polyamine accumulation, and the ir reversible S-adenosyl-L-methionine decarboxylase inhibitor, )-4-amino- 2-butenyl]methylamino}-5'-deoxyadenosine (AbeAdo), was used to inhibit synthesis. Exposure to AbeAdo led to a dose-dependent decrease in gro wth for both cell lines, although CHOMG cells were more sensitive. Int racellular putrescine levels were greatly increased in AbeAdo-treated CHO cells and to a lesser extent in CHOMG cells, whereas intracellular spermidine and spermine levels were substantially reduced in both. Tr eatment with AbeAdo increased putrescine content in the culture medium to a much greater extent in CHOMG cultures indicating that a portion of the excess putrescine synthesized in response to AbeAdo treatment i s excreted, but that CHO cells salvage this putrescine whereas is lost to CHOMG cells which cannot take up polyamines. AbeAdo treatment incr eased polyamine transport into CHO cells despite high intracellular pu trescine, suggesting that spermidine and/or spermine, and not putresci ne, and the major factors regulating transport activity. The accumulat ion of either 1-methylspermidine or 1,12-dimethylspermine was signific antly increased by AbeAdo treatment. Accumulation was increased even f urther when protein synthesis was blocked by cycloheximide, indicating that a short-lived protein is involved in the regulation of polyamine uptake. In the presence of cycloheximide and AbeAdo or alpha-difluoro methylornithine, methylated polyamine derivatives accumulated to very high levels leading to cell death. these results show that the polyami ne-transport system plays an important role in retaining intracellular polyamines and that down-regulation of the transport system in respon se to increased intracellular polyamine content is necessary to preven t accumulation of toxic levels of polyamines.