| Abstract: | Of the three biological polyamines, putrescine (Put), spermidine (Spd), and spermine (Spm), the relevance of Spm to cell proliferation has yet to be defined because of our general inability to deplete it selectively in intact cells. In the present study, Spm depletion was accomplished by treating cultured L1210 cells for 96 hr with alpha-difluoromethylornithine (DFMO) and an analog of Spd such as aminopropylcadaverine, N4-methylSpd, N4-ethylSpd, or homoSpd. DFMO, a specific inhibitor of ornithine decarboxylase, halts continued polyamine biosynthesis and the Spd analog serves as a functional substitute for Spd. Thus, while the Spd analog fulfills the role(s) of Spd in cell proliferation, Spm becomes steadily depleted. In cells treated with DFMO plus the analog, aminopropylcadaverine, Spm pools decline steadily and growth inhibition occus after 48 hr (when Spm pools decline to 60% of control). By 96 hr, Spm is approximately 15% of control and growth is less than 30%. Prevention studies with exogenous polyamines confirm a causal relationship between Spm depletion and growth inhibition. The critical levels of polyamines for cell proliferation to take place were found to be 30% of control for Spd and 60% for Spm. The use of DFMO plus a Spd analog is proposed as a system for studying the cellular consequences of Spm depletion. Spd depletion can be achieved for comparison purposes by treating cells with DFMO alone. |
