Mechanism of Antiviral Action of Interferon: Analysis Using 2-5A Synthetase Producing Cells

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To clarify the function of 2-5A synthetase, we constructed a mouse cell producing human 2-5A synthetase. The expression plasmid having human 2-5A synthetase cDNA ligated immediately down stream of SV40 promoter was cotransfected with neo gene into mouse L929 cells. Of G418 resistant cells selected, three strains expressing the human 2-5A synthetase cdna were obtained, which were designated as LAS0, LAS3 and LAS4. When challenged with VSV or EMCV, the virus multiplications were 1/100 - 1/1000 lower than L929 cells. On the other hand, the growth of VSV in LAS3 was almost the same as in L929 cells, but that of EMCV in LAS3 was about 1/1000 lowere than in L929 cells. Furthermore the doubling time of the cell growth became slower in LAS0, LAS3 and LAS4 cells than in L929 cells, and it was correlated with the level of 2-5A synthetase. Thus, 2-5A synthetase is responsible independently of other enzymes induced by IFN for the suppression of virus growth and cell growth.When serum-starved HeLaS3 cells were stimulated by the addition of FCS, PDGF, EGF or insulin, 2-5A synthetase was induced. Addition of anti-IFN- monoclonal antibody inhibited both the expression of 2-5A synthetase gene and the production of the enzyme, suggesting that autocrine IFN- was involved in 2-5A synthetase induction. Inhibition of 2-5A synthetase induction by anti-IFN- antibody enhanced the second, but not the first cycle of DNA synthesis. These results suggested that in HeLa cells after stimulation with growth factors the IFN/2-5A synthetase system played a role in cell growth negative regulatory mechanisms.