An Interferon-induced Refractory State of L Cells: Role of the Nucleus and Cytoplasm

Abstract

SUMMARYPre-treatment of L cells with 750 units/ml of mouse interferon depressed the yield of interferon when the cells were treated with Newcastle disease virus (NDV). The refractory state persisted for more than 5 days. Nucleated fragments (karyoplasts) obtained by cytochalasin B-induced enucleation were made from such interferon pre-treated ceils; cells reconstituted from these karyoplasts produced less interferon in response to NDV than did ceils reconstituted from karyoplasts derived from untreated cells. The source of the enucleated cytoplasm (cytoplasts) used in the cellular reconstitutions did not affect the yields of interferon.Mammalian cells treated with a virus (e.g. Newcastle disease virus) or double-stranded RNA [e.g. poly(rI), poly(rC)] produce and secrete interferons, glycoproteins which interact with cells of the same or closely related species and produce in them an antiviral state (Lampson et al. I967; Field et al. I967; Vilcek & Kohase, I977). Production of interferon is dependent on cellular RNA and protein synthesis (Heller, 1963; Wagner, I964; Ho & Breinig, ~965; Youngner et al. 1965; Johnston & Burke, I973). Recently, reconstituted cells capable of interferon synthesis have been produced by means of cellular enucleation and reconstruction techniques (Burke & Veomett, I977). Such studies have confirmed previous conclusions by showing that the production of interferon is initially dependent upon the presence of a nucleus and that enucleated cells (cytoplasts) continue the synthesis of interferon if the cells were producing it prior to enucleation.Cells which have been treated with high concentrations of interferon produce relatively small amounts of interferon upon subsequent stimulation with an interferon inducer (Lockart, I963; Stewart et al. ~970. This property of interferon pre-treatment has been called 'blocking' (Colby, I977). The degree and duration of the inhibition of interferon synthesis is dependent upon the concentration of interferon used in the pre-treatment and the conditions of cell growth (Paucker & Boxaca, 1967). Although the factor(s) which causes the blocking reaction appears to co-purify with interferon (Golgher & Paucker, I973), the two activities -blocking and ability to induce the antiviral state -may be separable entities (e.g. Stringfellow, t976, ~977)-Little has been reported concerning the mechanism(s) which inhibit interferon synthesis in 'blocked' cells. For example, the antiviral state could be the factor responsible, with the inhibition of interferon synthesis resulting from the inability of the inducing virus to make the intracellular 'inducer' of interferon (Bausek & Merigan, I97o). Alternatively, there may be a block in the transcription of the interferon genes or translation of the interferon message or in some other step involved in interferon production.We have investigated the refractory state for interferon synthesis in cells 'blocked' by interferon pre-treatment, using cells reconstituted from nucleated fragments (karyoplasts) and enucleated fragmen...