Inhibition of the differentiation of 3T3-L1 cells by interferon-beta and difluoromethyl ornithine.

Both mouse interferon-beta (MuIFN-beta) and the inhibitor of ornithine decarboxylase (ODC), alpha-difluoromethyl ornithine (DFMO), inhibited the differentiation of mouse 3T3-L1 fibroblasts into adipocytes in a dose-dependent manner. DFMO and MuIFN-beta added together to cultures that were induced to differentiate produced an additive anti-differentiation effect. In contrast to this additive cellular effect, DFMO reduced the antiviral activity of MuIFN-beta in both undifferentiated and differentiated cells; DFMO alone had no detectable effect on replication of encephalomyocarditis virus. Putrescine, the product of ornithine decarboxylation, when added to 3T3-L1 cultures (i) enhanced differentiation, (ii) reversed completely the inhibition of differentiation by DFMO, but (iii) had little effect on the antidifferentiation effect of MuIFN-beta. Polyamine content changed four-fold or less in cultures treated with 0.5 mM DFMO and less than two-fold in cultures treated with 100 IU/ml MuIFN-beta for seven days. Thus, it appears not only that MuIFN-beta and DFMO inhibit differentiation of 3T3-L1 cells by different mechanisms but also that the antiviral action of IFN does not involve the regulation of polyamine metabolism by ornithine decarboxylase.