Interferon affects both G₁ and S+G₂ in cells stimulated from quiescence to growth

Abstract

THE interferons were originally described as proteins, produced by cells in response to virus infection, which could induce viral resistance in cells of the same species¹. It is becoming clear that these proteins have other important biological activities² and can inhibit cell division in both normal and malignant cells^3–5. Although the phenomenon of growth inhibition by interferon is well established, data analysis of the effect in terms of the cell cycle is limited and not completely consistent. Killander et al.6 and Matarese and Rossi⁷, using asynchronously growing cultures of L1210 and Friend leukaemia cells respectively, have found that interferon-treated cells are delayed in both G₁ and G₂, and we have recently observed a similar effect of interferon on asynchronously growing MCF-7 cells⁸. Sokawa et al. have reported, however, that the only parameter affected in interferon-treated quiescent BALB/c 3T3 cells after serum stimulation, is their rate of entry into S (ref. 9). It is possible that the effect of interferon on the cell cycle of asynchronous transformed cells is different, in terms of cell cycle parameters, from its effect on quiescent untransformed cells. In an attempt to clarify this point, we have examined in detail the effect of interferon on the passage of serum-stimulated cells through the cell cycle, using BALB/c 3T3 and Swiss 3T3K cells, and a strain of human embryo lung diploid fibroblasts, HEL 27. In contrast to Sokawa et al., we have found that both G₁ and S+G₂ are extended by interferon treatment of all three cell types studied.