BREFELDIN-A INHIBITS THE ANTIVIRAL ACTION OF INTERFERON AGAINST ENCEPHALOMYOCARDITIS VIRUS

Brefeldin A (BFA), a unique fungal metabolite of a 13-membered lactone ring, exhibits various biological actions, including antitumor, antif ungal and antiviral activities. In the present study, mouse L(B) cells were treated with various concentrations of interferon (IFN) and/or B FA overnight and infected with encephalomyocarditis virus (EMCV) after removal of IFN and BFA. Doses of BFA which neither inhibit the metabo lism of the cell nor the infectivity of EMCV, decreased the IFN-induce d antiviral activity against EMCV as demonstrated by virus titer from supernatants. Since 2-5A synthetase and double-stranded RNA (dsRNA)-de pendent protein kinase (PKR) have been suggested to be involved in the antiviral action of IFN against EMCV, their activities were investiga ted in L(B) cells after BFA treatment. Northern blot analysis and in s itu hybridization showed a decrease (2-3-fold) in the mRNA of 2'-5' ol igoadenylate (2-5A) synthetase after BFA treatment. BFA also inhibited the activity of 2-5A synthetase, 2-5A dependent RNase and phosphoryla tion of PKR in cellular extracts, indicating that BFA may be exerting its inhibitory effect both at the transcriptional and post-transcripti onal levels. This study reports a new biological action of BFA, demons trating that BFA antagonized the antiviral action of IFN by inhibiting IFN-induced enzymatic pathways. These studies also suggest that both 2-5A and PKR are important in the antiviral activity of IFN against EM CV.