Antimitogenic effects of interferon and (2′–5′)‐oligoadenylate in synchronized 3T3 fibroblasts

Abstract

Interferons are not only antiviral agents, but are also pleiotropic modifiers of cellular functions [ 1,2]. One aspect of IFN’s cellular activity, is its ability to inhibit normal and tumor cell proliferation [3]. In GO-arrested cells stimulated to grow by different mitogens, hormones or other positive growth-factors, IFN was reported to reduce the rate of cell entry into S-phase [4-71. In some cases, it also extended the S t G2 phases of the cell cycle [8,9]. Several observations have led us to propose that the (2’-S’)-oligoadenylate (oligo(A)) synthetase, which is induced in cells by IFN, is involved in the antimitogenic effects of IFN: First, (2’-5’)oligo(A) produces an antimitogenie effect when applied to intact lymphocytes stimulated by concanavalin A [lo]. Second, growthrelated variations in the synthesis and degradation of (2’~S’)-oligo(A) were demonstrated [ 11,121. Here, we have extended the study of the antimitogenic effect of dephosphorylated (2’-5’)ApApA to serum-stimulated Balb/c 3T3 fibroblasts. Using a series of chemically synthesized derivatives of this oligonucleotide, we show that inhibition of DNA synthesis takes place only if the (2’-5’)-oligo(A) is at least 3 nucleotides long and has a free hydroxyl-group at the 5’-position. We show that the antimitogenic action results from a decrease in the rate of cell entry into S-phase. Finally, we present evidence that the antimitogenic activity of (2’-5’)ApApA is mediated by ribonuclease F (RNase F) activation [ 13,141 and a decrease in protein synthesis during the Cl phase of the cell cycle. 2. Materials and methods