Effects of retinoic acid versus dimethyl sulfoxide on Friend erythroleukemia cell growth. I. Cell proliferation, RNA content, and protein content.

The effect of all-trans-retinoic acid (RA), an oxidative product of vitamin A, on cell growth, cell cycle kinetics, RNA content, and protein content of exponentially growing Friend erythroleukemia (FL) cells was determined and compared with the results obtained with dimethyl sulfoxide [(DMSO) CAS: 67-68-5; methyl sulfoxide], an inducer of differentiation, and alpha-difluoromethylornithine (DFMO), a potent inhibitor of ornithine decarboxylase (EC 4.1.1.17) activity. Growth inhibition of FL cells was observed only during continuous treatment with RA. While RA did not prevent growth to a high cell density, if cultures were maintained in exponential growth, cell number was reduced by 37, 67.4, and 72.2% after 6-day exposure to 10(-7), 10(-6), and 10(-5) M RA, respectively. In comparison, 280 mM (2%) DMSO and 5 mM DFMO inhibited growth over the same time course by 92 and 97.3%, respectively. DMSO resulted in an early, transient (18-24 hr) accumulation of cells in G1 phase followed by a later (5 day), irreversible accumulation of G1 cells. RA required several cell generations (48-72 hr) before a dose-dependent G1 accumulation was observed. Two populations of RA-treated FL cells could be identified: one with an intermediate RNA content (T-cells) similar to near-plateau-phase control cultures and the other with low RNA content (Q-cells) similar to that observed for DMSO-differentiated (D) cells. The kinetics of the decrease in RNA content of Q-cells paralleled those of D-cells in DMSO-treated cultures; the proportion of Q- versus T-cells in RA-treated cultures was dependent on both concentration and length of exposure. DFMO treatment did not give rise to low-RNA-containing Q-cells. Protein content of RA-treated cells was also diminished and approached that observed for hemoglobin-containing D-cells. FL cells were recoverable from long-term (greater than 5 days) treatment with RA, though 2-3 days were required for reestablishment of exponentially growing cultures; apparently only moderate RNA-containing T-cells repopulated the culture. Neither RA nor DFMO treatment gave rise to benzedine-positive, hemoglobin-containing cells as compared to DMSO that induced differentiation in these cultures.