Poly(inosinic acid)-poly(cytidylic acid) inhibition of DNA synthesis in synchronized HeLa cells

Viral double-stranded RNA, cytokines, and the flu

The symptoms of the flu, such as fever, drowsiness, and malaise, are the sole means by which this common clinical syndrome is defined. The syndrome is usually the first clinical manifestation of both acute bacterial and viral infections. In the case of acute bacterial infections, several proinflammatory cytokines induced by bacterial products have been implicated as the causative agents of the flu syndrome. Viruses induce similar cytokines to bacteria, plus substantial amounts of interferon-alpha (IFN-alpha), although the direct association of these cytokines with the viral flu syndrome is less clear. Furthermore, the viral inducer(s) of cytokines has not been defined. The best candidate cytokine inducer associated with a majority of viral infections is virus-associated double-stranded RNA (dsRNA). This review examines the essential physical properties of toxic dsRNA, the cytokines induced by it, its viral and cellular sources, evidence for its presence in infected cells, its quantities in normal and infected cells, its cytotoxic mechanisms, and its cell-penetration properties. Toxic effects of viruses and dsRNA are compared. Energetics and extraction artifact issues are also discussed. Whereas most research on dsRNA toxicity has employed synthetic dsRNA, studies with virus-associated dsRNA are featured when available. Finally, a model for how viral dsRNA might initiate systemic disease is presented.

Mitogenic effect of double-stranded RNA in human fibroblasts: role of autogenous interferon

The synthetic double-stranded RNA polyinosinate-polycytidylate [poly(I).poly(C)] was mitogenic in cultures of human foreskin fibroblasts, as demonstrated by a stimulation of 3H-thymidine incorporation and an increase in cell density. Poly(I).poly(C) is a potent inducer of interferon (IFN)-beta in human fibroblasts. Single-stranded poly(l) or poly(C) were not mitogenic in human fibroblasts and did not stimulate IFN production. Antiserum to interferon (IFN)-beta, added to poly(I).poly(C)-stimulated cultures in order to neutralize endogenously generated IFN, markedly amplified the mitogenic action. Under similar experimental conditions, antiserum to IFN-beta did not enhance the mitogenic action of epidermal growth factor (EGF). Dexamethasone enhanced the mitogenic action of poly(I).poly(C) in a manner similar to antiserum against IFN-beta. This effect of dexamethasone correlated with its marked inhibitory action on poly(I).poly(C)-stimulated IFN production. Together with the results of other related studies, these findings support the notion of an evolutionary link between the generation of a mitogenic signal and IFN induction. In addition, these results support the concept that autocrine secretion of IFN-beta can exert negative feedback control of cell proliferation.

Mitogenesis in normal human fibroblasts by polyinosinic . polycytidylic acid and other synthetic acidic polymers: enhancement of action by glucocorticoids

The ability of specific synthetic polyelectrolytes to act as mitogens for quiescent normal human fibroblasts in cultures is described. Of several acidic polymers tested, polyinosinic acid .polycytidylic acid (poly I.poly C) and dextran sulfate were the most effective in stimulating 3H]thymidine incorporation (2-to 10-fold). The concentration for a half-maximal effect (ED50) was 0.4 microgram/ml (0.8 nM) for poly I.poly C, and 1.7 microgram/ml (3.4 nM) for dextran sulfate. Single-stranded polyinosinic acid or polycytidylic acid had no effect. The time course of stimulation of DNA synthesis by these acidic polymers was similar to that for naturally occurring mitogens such as epidermal growth factor, beginning at about 18 hours and reaching a maximum rate 26 to 30 hours after the addition of polymer. Glucocorticoids that have an 11-beta hydroxyl group (e.g., dexamethasone) had no effect on DNA synthesis alone, but enhanced several-fold the mitogenic activity of poly I.poly C or dextran sulfate; the ED50 for dexamethasone was 0.75 ng/ml (1.9 nM). Glucocorticoids with an 11-keto group were inactive in this respect. The labeling index following treatment of cultures with poly I.poly C and dexamethasone was 14%, compared with a labeling index of 25% following stimulation by fetal calf serum. The extent of stimulation of DNA synthesis by poly I.poly C and dexamethasone was comparable to that induced by epidermal growth factor. It appears that both the poly I.poly C and dexamethasone are required for only a short period of time (approximately 3 hours) in order to produce maximal stimulation of DNA synthesis 30 hours later.

Effect of an interferon inducer, 9-methylstreptimidone, on Candida albicans infection in mice

The protective effect of an interferon inducer with a low molecular weight, 9-methylstreptimidone (9-MS), against Candida albicans infection in mice was investigated. The antibiotic was effective only when given prophylactically. When administered in such a manner, the growth of C. albicans in the kidneys and brain was inhibited at the initial stage of infection. The growth of C. albicans was not inhibited by the antibiotic in vitro, and no antifungal effect was obtained in a preparation containing induced interferon. These results suggest that the antifungal action of 9-methylstreptimidone in mice might be manifested not by direct antifungal activity but rather by a host-mediated activity that excludes interferon-inducing capability.